diff --git a/components/eamxx/src/control/atmosphere_driver.cpp b/components/eamxx/src/control/atmosphere_driver.cpp
index a5dacd856d7..4f2c0fc21b4 100644
--- a/components/eamxx/src/control/atmosphere_driver.cpp
+++ b/components/eamxx/src/control/atmosphere_driver.cpp
@@ -140,11 +140,10 @@ init_scorpio(const int atm_id)
   // Init scorpio right away, in case some class (atm procs, grids,...)
   // needs to source some data from NC files during construction,
   // before we start processing IC files.
-  EKAT_REQUIRE_MSG (!scorpio::is_eam_pio_subsystem_inited(),
+  EKAT_REQUIRE_MSG (!scorpio::is_subsystem_inited(),
       "Error! The PIO subsystem was alreday inited before the driver was constructed.\n"
       "       This is an unexpected behavior. Please, contact developers.\n");
-  MPI_Fint fcomm = MPI_Comm_c2f(m_atm_comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm,atm_id);
+  scorpio::init_subsystem(m_atm_comm,atm_id);
 
   // In CIME runs, gptl is already inited. In standalone runs, it might
   // not be, depending on what scorpio does.
@@ -713,7 +712,7 @@ void AtmosphereDriver::initialize_output_managers () {
     }
     om.set_logger(m_atm_logger);
     for (const auto& it : m_atm_process_group->get_restart_extra_data()) {
-      om.add_global(it.first,*it.second);
+      om.add_global(it.first,it.second);
     }
 
     // Store the "Output Control" pl of the model restart as the "Checkpoint Control" for all other output streams
@@ -909,7 +908,7 @@ void AtmosphereDriver::restart_model ()
   }
 
   // Restart the num steps counter in the atm time stamp
-  int nsteps = scorpio::get_attribute<int>(filename,"nsteps");
+  int nsteps = scorpio::get_attribute<int>(filename,"GLOBAL","nsteps");
   m_current_ts.set_num_steps(nsteps);
   m_run_t0.set_num_steps(nsteps);
 
@@ -917,18 +916,22 @@ void AtmosphereDriver::restart_model ()
     const auto& name = it.first;
           auto& any  = it.second;
 
-
-    auto data = scorpio::get_any_attribute(filename,name);
-    EKAT_REQUIRE_MSG (any->content().type()==data.content().type(),
-        "Error! Type mismatch for restart global attribute.\n"
-        " - file name: " + filename + "\n"
-        " - att  name: " + name + "\n"
-        " - expected type: " + any->content().type().name() + "\n"
-        " - actual type: " + data.content().type().name() + "\n"
-        "NOTE: the above names use type_info::name(), which returns an implementation defined string,\n"
-        "      with no guarantees. In particular, the string can be identical for several types,\n"
-        "      and/or change between invocations of the same program.\n");
-    *any = data;
+    if (any.isType<int>()) {
+      ekat::any_cast<int>(any) = scorpio::get_attribute<int>(filename,"GLOBAL",name);
+    } else if (any.isType<std::int64_t>()) {
+      ekat::any_cast<std::int64_t>(any) = scorpio::get_attribute<std::int64_t>(filename,"GLOBAL",name);
+    } else if (any.isType<float>()) {
+      ekat::any_cast<float>(any) = scorpio::get_attribute<float>(filename,"GLOBAL",name);
+    } else if (any.isType<double>()) {
+      ekat::any_cast<double>(any) = scorpio::get_attribute<double>(filename,"GLOBAL",name);
+    } else if (any.isType<std::string>()) {
+      ekat::any_cast<std::string>(any) = scorpio::get_attribute<std::string>(filename,"GLOBAL",name);
+    } else {
+      EKAT_ERROR_MSG (
+          "Error! Unrecognized/unsupported concrete type for restart extra data.\n"
+          " - extra data name  : " + name + "\n"
+          " - extra data typeid: " + any.content().type().name() + "\n");
+    }
   }
 
   m_atm_logger->info("  [EAMxx] restart_model ... done!");
@@ -1660,6 +1663,9 @@ void AtmosphereDriver::finalize ( /* inputs? */ ) {
     m_atm_process_group = nullptr;
   }
 
+  // Destroy iop
+  m_iop = nullptr;
+
   // Destroy the buffer manager
   m_memory_buffer = nullptr;
 
@@ -1681,9 +1687,10 @@ void AtmosphereDriver::finalize ( /* inputs? */ ) {
     finalize_gptl();
   }
 
-  // Finalize scorpio
-  if (scorpio::is_eam_pio_subsystem_inited()) {
-    scorpio::eam_pio_finalize();
+  // Finalize scorpio. Check, just in case we're calling finalize after
+  // an exception, thrown before the AD (and scorpio) was inited
+  if (scorpio::is_subsystem_inited()) {
+    scorpio::finalize_subsystem();
   }
 
   m_atm_logger->info("[EAMxx] Finalize ... done!");
diff --git a/components/eamxx/src/control/intensive_observation_period.cpp b/components/eamxx/src/control/intensive_observation_period.cpp
index a374c595102..ab01bfc7e3e 100644
--- a/components/eamxx/src/control/intensive_observation_period.cpp
+++ b/components/eamxx/src/control/intensive_observation_period.cpp
@@ -30,75 +30,6 @@ namespace ekat {
 namespace scream {
 namespace control {
 
-// Helper functions for reading data from .nc file to support
-// cases not currently supported in EAMxx scorpio interface.
-namespace {
-// Read the value of a dimensionless variable from file.
-template<typename T>
-void read_dimensionless_variable_from_file(const std::string& filename,
-                                           const std::string& varname,
-                                           T*                 value)
-{
-  EKAT_REQUIRE_MSG(scorpio::has_variable(filename,varname),
-                   "Error! IOP file does not have variable "+varname+".\n");
-
-  int ncid, varid, err1, err2;
-  bool was_open = scorpio::is_file_open_c2f(filename.c_str(),-1);
-  if (not was_open) {
-    scorpio::register_file(filename,scorpio::FileMode::Read);
-  }
-  ncid = scorpio::get_file_ncid_c2f (filename.c_str());
-  err1 = PIOc_inq_varid(ncid,varname.c_str(),&varid);
-  EKAT_REQUIRE_MSG(err1==PIO_NOERR,
-    "Error! Something went wrong while retrieving variable id.\n"
-    " - filename : " + filename + "\n"
-    " - varname  : " + varname + "\n"
-    " - pio error: " + std::to_string(err1) + "\n");
-
-  err2 = PIOc_get_var(ncid, varid, value);
-  EKAT_REQUIRE_MSG(err2==PIO_NOERR,
-    "Error! Something went wrong while retrieving variable.\n"
-    " - filename : " + filename + "\n"
-    " - varname  : " + varname + "\n"
-    " - pio error: " + std::to_string(err2) + "\n");
-
-  if (not was_open) {
-    scorpio::eam_pio_closefile(filename);
-  }
-}
-
-// Read variable with arbitrary number of dimensions from file.
-template<typename T>
-void read_variable_from_file(const std::string&              filename,
-                             const std::string&              varname,
-                             const std::string&              vartype,
-                             const std::vector<std::string>& dimnames,
-                             const int                       time_idx,
-                             T*                              data)
-{
-  EKAT_REQUIRE_MSG(scorpio::has_variable(filename,varname),
-                   "Error! IOP file does not have variable "+varname+".\n");
-
-  // Compute total size of data to read
-  int data_size = 1;
-  for (auto dim : dimnames) {
-    const auto dim_len = scorpio::get_dimlen(filename, dim);
-      data_size *= dim_len;
-  }
-
-  // Read into data
-  scorpio::register_file(filename, scorpio::FileMode::Read);
-  std::string io_decomp_tag = varname+","+filename;
-  scorpio::register_variable(filename, varname, varname, dimnames, vartype, io_decomp_tag);
-  std::vector<scorpio::offset_t> dof_offsets(data_size);
-  std::iota(dof_offsets.begin(), dof_offsets.end(), 0);
-  scorpio::set_dof(filename, varname, dof_offsets.size(), dof_offsets.data());
-  scorpio::set_decomp(filename);
-  scorpio::grid_read_data_array(filename, varname, time_idx, data, data_size);
-  scorpio::eam_pio_closefile(filename);
-}
-}
-
 IntensiveObservationPeriod::
 IntensiveObservationPeriod(const ekat::Comm& comm,
                            const ekat::ParameterList& params,
@@ -144,6 +75,13 @@ IntensiveObservationPeriod(const ekat::Comm& comm,
   initialize_iop_file(run_t0, model_nlevs);
 }
 
+IntensiveObservationPeriod::
+~IntensiveObservationPeriod ()
+{
+  const auto iop_file = m_params.get<std::string>("iop_file");
+  scorpio::release_file(iop_file);
+}
+
 void IntensiveObservationPeriod::
 initialize_iop_file(const util::TimeStamp& run_t0,
                     int model_nlevs)
@@ -153,6 +91,11 @@ initialize_iop_file(const util::TimeStamp& run_t0,
 
   const auto iop_file = m_params.get<std::string>("iop_file");
 
+  // All the scorpio::has_var call can open the file on the fly, but since there
+  // are a lot of those calls, for performance reasons we just open it now.
+  // All the calls to register_file made on-the-fly inside has_var will be no-op.
+  scorpio::register_file(iop_file,scorpio::FileMode::Read);
+
   // Lambda for allocating space and storing information for potential iop fields.
   // Inputs:
   //   - varnames:    Vector of possible variable names in the iop file.
@@ -173,7 +116,7 @@ initialize_iop_file(const util::TimeStamp& run_t0,
     bool has_var = false;
     std::string file_varname = "";
     for (auto varname : varnames) {
-      if (scorpio::has_variable(iop_file, varname)) {
+      if (scorpio::has_var(iop_file, varname)) {
         has_var = true;
         file_varname = varname;
         break;
@@ -183,7 +126,7 @@ initialize_iop_file(const util::TimeStamp& run_t0,
       // Store if iop file has a different varname than the iop field
       if (iop_varname != file_varname) m_iop_file_varnames.insert({iop_varname, file_varname});
       // Store if variable contains a surface value in iop file
-      if (scorpio::has_variable(iop_file, srf_varname)) {
+      if (scorpio::has_var(iop_file, srf_varname)) {
         m_iop_field_surface_varnames.insert({iop_varname, srf_varname});
       }
       // Store that the IOP variable is found in the IOP file
@@ -291,11 +234,12 @@ initialize_iop_file(const util::TimeStamp& run_t0,
   // Initialize time information
   int bdate;
   std::string bdate_name;
-  if      (scorpio::has_variable(iop_file, "bdate"))    bdate_name = "bdate";
-  else if (scorpio::has_variable(iop_file, "basedate")) bdate_name = "basedate";
-  else if (scorpio::has_variable(iop_file, "nbdate"))   bdate_name = "nbdate";
+  if      (scorpio::has_var(iop_file, "bdate"))    bdate_name = "bdate";
+  else if (scorpio::has_var(iop_file, "basedate")) bdate_name = "basedate";
+  else if (scorpio::has_var(iop_file, "nbdate"))   bdate_name = "nbdate";
   else EKAT_ERROR_MSG("Error! No valid name for bdate in "+iop_file+".\n");
-  read_dimensionless_variable_from_file<int>(iop_file, bdate_name, &bdate);
+
+  scorpio::read_var(iop_file, bdate_name, &bdate);
 
   int yr=bdate/10000;
   int mo=(bdate/100) - yr*100;
@@ -306,11 +250,15 @@ initialize_iop_file(const util::TimeStamp& run_t0,
   if      (scorpio::has_dim(iop_file, "time")) time_dimname = "time";
   else if (scorpio::has_dim(iop_file, "tsec")) time_dimname = "tsec";
   else EKAT_ERROR_MSG("Error! No valid dimension for tsec in "+iop_file+".\n");
+  
   const auto ntimes = scorpio::get_dimlen(iop_file, time_dimname);
-  m_time_info.iop_file_times_in_sec =
-    decltype(m_time_info.iop_file_times_in_sec)("iop_file_times", ntimes);
-  read_variable_from_file(iop_file, "tsec", "int", {time_dimname}, -1,
-                          m_time_info.iop_file_times_in_sec.data());
+  m_time_info.iop_file_times_in_sec = view_1d_host<int>("iop_file_times", ntimes);
+  scorpio::read_var(iop_file,"tsec",m_time_info.iop_file_times_in_sec.data());
+
+  // From now on, when we read vars, "time" must be treated as unlimited, to avoid issues
+  if (not scorpio::is_dim_unlimited(iop_file,time_dimname)) {
+    scorpio::pretend_dim_is_unlimited(iop_file,time_dimname);
+  }
 
   // Check that lat/lon from iop file match the targets in parameters. Note that
   // longitude may be negtive in the iop file, we convert to positive before checking.
@@ -318,8 +266,10 @@ initialize_iop_file(const util::TimeStamp& run_t0,
   const auto nlons = scorpio::get_dimlen(iop_file, "lon");
   EKAT_REQUIRE_MSG(nlats==1 and nlons==1, "Error! IOP data file requires a single lat/lon pair.\n");
   Real iop_file_lat, iop_file_lon;
-  read_variable_from_file(iop_file, "lat", "real", {"lat"}, -1, &iop_file_lat);
-  read_variable_from_file(iop_file, "lon", "real", {"lon"}, -1, &iop_file_lon);
+
+  scorpio::read_var(iop_file,"lat",&iop_file_lat);
+  scorpio::read_var(iop_file,"lon",&iop_file_lon);
+
   const Real rel_lat_err = std::fabs(iop_file_lat - m_params.get<Real>("target_latitude"))/
                              m_params.get<Real>("target_latitude");
   const Real rel_lon_err = std::fabs(std::fmod(iop_file_lon + 360.0, 360.0)-m_params.get<Real>("target_longitude"))/
@@ -332,7 +282,7 @@ initialize_iop_file(const util::TimeStamp& run_t0,
   // Store iop file pressure as helper field with dimension lev+1.
   // Load the first lev entries from iop file, the lev+1 entry will
   // be set when reading iop data.
-  EKAT_REQUIRE_MSG(scorpio::has_variable(iop_file, "lev"),
+  EKAT_REQUIRE_MSG(scorpio::has_var(iop_file, "lev"),
                     "Error! Using IOP file requires variable \"lev\".\n");
   const auto file_levs = scorpio::get_dimlen(iop_file, "lev");
   FieldIdentifier fid("iop_file_pressure",
@@ -343,7 +293,8 @@ initialize_iop_file(const util::TimeStamp& run_t0,
   iop_file_pressure.get_header().get_alloc_properties().request_allocation(Pack::n);
   iop_file_pressure.allocate_view();
   auto data = iop_file_pressure.get_view<Real*, Host>().data();
-  read_variable_from_file(iop_file, "lev", "real", {"lev"}, -1, data);
+  scorpio::read_var(iop_file,"lev",data);
+
   // Convert to pressure to millibar (file gives pressure in Pa)
   for (int ilev=0; ilev<file_levs; ++ilev) data[ilev] /= 100;
   iop_file_pressure.sync_to_dev();
@@ -589,7 +540,8 @@ read_iop_file_data (const util::TimeStamp& current_ts)
   if (has_level_data) {
     // Load surface pressure (Ps) from iop file
     auto ps_data = surface_pressure.get_view<Real, Host>().data();
-    read_variable_from_file(iop_file, "Ps", "real", {"lon","lat"}, iop_file_time_idx, ps_data);
+
+    scorpio::read_var(iop_file,"Ps",ps_data,iop_file_time_idx);
     surface_pressure.sync_to_dev();
 
     // Pre-process file pressures, store number of file levels
@@ -676,7 +628,7 @@ read_iop_file_data (const util::TimeStamp& current_ts)
     if (field.rank()==0) {
       // For scalar data, read iop file variable directly into field data
       auto data = field.get_view<Real, Host>().data();
-      read_variable_from_file(iop_file, file_varname, "real", {"lon","lat"}, iop_file_time_idx, data);
+      scorpio::read_var(iop_file,file_varname,data,iop_file_time_idx);
       field.sync_to_dev();
     } else if (field.rank()==1) {
       // Create temporary fields for reading iop file variables. We use
@@ -693,7 +645,7 @@ read_iop_file_data (const util::TimeStamp& current_ts)
 
       // Read data from iop file.
       std::vector<Real> data(file_levs);
-      read_variable_from_file(iop_file, file_varname, "real", {"lon","lat","lev"}, iop_file_time_idx, data.data());
+      scorpio::read_var(iop_file,file_varname,data.data(),iop_file_time_idx);
 
       // Copy first adjusted_file_levs-1 values to field
       auto iop_file_v_h = iop_file_field.get_view<Real*,Host>();
@@ -703,7 +655,7 @@ read_iop_file_data (const util::TimeStamp& current_ts)
       const auto has_srf = m_iop_field_surface_varnames.count(fname)>0;
       if (has_srf) {
         const auto srf_varname = m_iop_field_surface_varnames[fname];
-        read_variable_from_file(iop_file, srf_varname, "real", {"lon","lat"}, iop_file_time_idx, &iop_file_v_h(adjusted_file_levs-1));
+        scorpio::read_var(iop_file,srf_varname,&iop_file_v_h(adjusted_file_levs-1),iop_file_time_idx);
       } else {
         // No surface value exists, compute surface value
         const auto dx = iop_file_v_h(adjusted_file_levs-2) - iop_file_v_h(adjusted_file_levs-3);
@@ -754,7 +706,7 @@ read_iop_file_data (const util::TimeStamp& current_ts)
 			     KOKKOS_LAMBDA (const int ilev) {
 			       iop_field_v(ilev) = iop_file_v(0);
 			     });
-	Kokkos::parallel_for(Kokkos::RangePolicy<>(model_end-1, total_nlevs),
+        Kokkos::parallel_for(Kokkos::RangePolicy<>(model_end-1, total_nlevs),
 			     KOKKOS_LAMBDA (const int ilev) {
 			       iop_field_v(ilev) = iop_file_v(adjusted_file_levs-1);
 			     });
@@ -930,5 +882,3 @@ correct_temperature_and_water_vapor(const field_mgr_ptr field_mgr)
 
 } // namespace control
 } // namespace scream
-
-
diff --git a/components/eamxx/src/control/intensive_observation_period.hpp b/components/eamxx/src/control/intensive_observation_period.hpp
index 6c0b3640ffb..be3d389257b 100644
--- a/components/eamxx/src/control/intensive_observation_period.hpp
+++ b/components/eamxx/src/control/intensive_observation_period.hpp
@@ -55,7 +55,7 @@ class IntensiveObservationPeriod
                              const Field& hybm);
 
   // Default destructor
-  ~IntensiveObservationPeriod() = default;
+  ~IntensiveObservationPeriod();
 
   // Read data from IOP file and store internally.
   void read_iop_file_data(const util::TimeStamp& current_ts);
diff --git a/components/eamxx/src/diagnostics/tests/field_at_level_tests.cpp b/components/eamxx/src/diagnostics/tests/field_at_level_tests.cpp
index 44b4cd851b9..b7867c3ac72 100644
--- a/components/eamxx/src/diagnostics/tests/field_at_level_tests.cpp
+++ b/components/eamxx/src/diagnostics/tests/field_at_level_tests.cpp
@@ -74,7 +74,7 @@ TEST_CASE("field_at_level")
 
   using IPDF = std::uniform_int_distribution<int>;
   IPDF ipdf (1,nlevs-2);
-  for (const std::string& lev_loc : {"model_top", "model_bot", "rand"}) {
+  for (const std::string lev_loc : {"model_top", "model_bot", "rand"}) {
     int lev;
     std::string lev_str;
     if (lev_loc=="bot") {
diff --git a/components/eamxx/src/dynamics/homme/eamxx_homme_process_interface.cpp b/components/eamxx/src/dynamics/homme/eamxx_homme_process_interface.cpp
index b550348fa49..dfd116b0832 100644
--- a/components/eamxx/src/dynamics/homme/eamxx_homme_process_interface.cpp
+++ b/components/eamxx/src/dynamics/homme/eamxx_homme_process_interface.cpp
@@ -52,7 +52,8 @@ HommeDynamics::HommeDynamics (const ekat::Comm& comm, const ekat::ParameterList&
   // This class needs Homme's context, so register as a user
   HommeContextUser::singleton().add_user();
 
-  auto homme_nsteps = std::make_shared<ekat::any>(-1);
+  ekat::any homme_nsteps;
+  homme_nsteps.reset<int>(-1);
   m_restart_extra_data["homme_nsteps"] = homme_nsteps;
 
   if (!is_parallel_inited_f90()) {
@@ -516,7 +517,7 @@ void HommeDynamics::run_impl (const double dt)
 
     // Update nstep in the restart extra data, so it can be written to restart if needed.
     const auto& tl = c.get<Homme::TimeLevel>();
-    auto& nstep = ekat::any_cast<int>(*m_restart_extra_data["homme_nsteps"]);
+    auto& nstep = ekat::any_cast<int>(m_restart_extra_data["homme_nsteps"]);
     nstep = tl.nstep;
 
     // Post process Homme's output, to produce what the rest of Atm expects
@@ -955,7 +956,7 @@ void HommeDynamics::restart_homme_state () {
         auto& tl = c.get<Homme::TimeLevel>();
 
   // For BFB restarts, set nstep counter in Homme's TimeLevel to match the restarted value.
-  const auto& nstep = ekat::any_ptr_cast<int>(*m_restart_extra_data["homme_nsteps"]);
+  const auto& nstep = ekat::any_ptr_cast<int>(m_restart_extra_data["homme_nsteps"]);
   tl.nstep = *nstep;
   set_homme_param("num_steps",*nstep);
 
@@ -1135,7 +1136,7 @@ void HommeDynamics::initialize_homme_state () {
   const int n0  = tl.n0;
   const int n0_qdp  = tl.n0_qdp;
 
-  ekat::any_cast<int>(*m_restart_extra_data["homme_nsteps"]) = tl.nstep;
+  ekat::any_cast<int>(m_restart_extra_data["homme_nsteps"]) = tl.nstep;
 
   const auto phis_dyn_view = m_helper_fields.at("phis_dyn").get_view<const Real***>();
   const auto phi_int_view = m_helper_fields.at("phi_int_dyn").get_view<Pack*****>();
diff --git a/components/eamxx/src/dynamics/homme/homme_grids_manager.cpp b/components/eamxx/src/dynamics/homme/homme_grids_manager.cpp
index 55b236adee0..270f1ffbdda 100644
--- a/components/eamxx/src/dynamics/homme/homme_grids_manager.cpp
+++ b/components/eamxx/src/dynamics/homme/homme_grids_manager.cpp
@@ -155,21 +155,24 @@ void HommeGridsManager::build_dynamics_grid () {
   auto dg_dofs = dyn_grid->get_dofs_gids();
   auto cg_dofs = dyn_grid->get_cg_dofs_gids();
   auto elgpgp  = dyn_grid->get_lid_to_idx_map();
+  auto elgids  = dyn_grid->get_partitioned_dim_gids ();
   auto lat     = dyn_grid->create_geometry_data("lat",layout2d,rad);
   auto lon     = dyn_grid->create_geometry_data("lon",layout2d,rad);
 
   auto dg_dofs_h = dg_dofs.get_view<gid_type*,Host>();
   auto cg_dofs_h = cg_dofs.get_view<gid_type*,Host>();
   auto elgpgp_h  = elgpgp.get_view<int**,Host>();
+  auto elgids_h  = elgids.get_view<int*,Host>();
   auto lat_h     = lat.get_view<Real***,Host>();
   auto lon_h     = lon.get_view<Real***,Host>();
 
   // Get (ie,igp,jgp,gid) data for each dof
-  get_dyn_grid_data_f90 (dg_dofs_h.data(),cg_dofs_h.data(),elgpgp_h.data(), lat_h.data(), lon_h.data());
+  get_dyn_grid_data_f90 (dg_dofs_h.data(),cg_dofs_h.data(),elgpgp_h.data(),elgids_h.data(), lat_h.data(), lon_h.data());
 
   dg_dofs.sync_to_dev();
   cg_dofs.sync_to_dev();
   elgpgp.sync_to_dev();
+  elgids.sync_to_dev();
   lat.sync_to_dev();
   lon.sync_to_dev();
 
diff --git a/components/eamxx/src/dynamics/homme/interface/dyn_grid_mod.F90 b/components/eamxx/src/dynamics/homme/interface/dyn_grid_mod.F90
index 851659c7f12..cf8d955fe90 100644
--- a/components/eamxx/src/dynamics/homme/interface/dyn_grid_mod.F90
+++ b/components/eamxx/src/dynamics/homme/interface/dyn_grid_mod.F90
@@ -42,7 +42,7 @@ subroutine dyn_grid_init ()
 
   end subroutine dyn_grid_init
 
-  subroutine get_my_dyn_data (dg_gids, cg_gids, elgpgp, lat, lon)
+  subroutine get_my_dyn_data (dg_gids, cg_gids, elgpgp, elgids, lat, lon)
     use iso_c_binding,     only: c_int, c_double
     use dimensions_mod,    only: nelemd, np
     use homme_context_mod, only: elem, par
@@ -55,7 +55,7 @@ subroutine get_my_dyn_data (dg_gids, cg_gids, elgpgp, lat, lon)
     ! Inputs
     !
     real(kind=c_double), intent(out) :: lat (:,:,:), lon(:,:,:)
-    integer(kind=c_int), intent(out) :: cg_gids (:), dg_gids(:), elgpgp(:,:)
+    integer(kind=c_int), intent(out) :: cg_gids (:), dg_gids(:), elgpgp(:,:), elgids(:)
     !
     ! Local(s)
     !
@@ -80,6 +80,7 @@ subroutine get_my_dyn_data (dg_gids, cg_gids, elgpgp, lat, lon)
     call bndry_exchangeV(par,edge)
     do ie=1,nelemd
       call edgeVunpack_nlyr(edge,elem(ie)%desc,el_cg_gids(:,:,ie),1,0,1)
+      elgids(ie) = elem(ie)%GlobalId
       do ip=1,np
         do jp=1,np
           idof = (ie-1)*16+(jp-1)*4+ip
diff --git a/components/eamxx/src/dynamics/homme/interface/homme_grid_mod.F90 b/components/eamxx/src/dynamics/homme/interface/homme_grid_mod.F90
index 6f11024627f..28dfed502f8 100644
--- a/components/eamxx/src/dynamics/homme/interface/homme_grid_mod.F90
+++ b/components/eamxx/src/dynamics/homme/interface/homme_grid_mod.F90
@@ -105,18 +105,18 @@ end subroutine finalize_geometry_f90
   ! Note: dg_grid=.true. is to request dofs for a Discontinuous Galerkin grid,
   !       that is, corresponding edge dofs on bordering elems have different gids.
   !       If dg_grid=.false., the shared dofs have the same gid.
-  subroutine get_dyn_grid_data_f90 (dg_gids_ptr, cg_gids_ptr, elgpgp_ptr, lat_ptr, lon_ptr) bind(c)
+  subroutine get_dyn_grid_data_f90 (dg_gids_ptr, cg_gids_ptr, elgpgp_ptr, elgid_ptr, lat_ptr, lon_ptr) bind(c)
     use dimensions_mod,    only: nelemd, np
     use dyn_grid_mod,      only: get_my_dyn_data
     !
     ! Input(s)
     !
-    type (c_ptr), intent(in) :: dg_gids_ptr, cg_gids_ptr, elgpgp_ptr, lat_ptr, lon_ptr
+    type (c_ptr), intent(in) :: dg_gids_ptr, cg_gids_ptr, elgpgp_ptr, elgid_ptr, lat_ptr, lon_ptr
     !
     ! Local(s)
     !
     real(kind=c_double), pointer :: lat (:,:,:), lon(:,:,:)
-    integer(kind=c_int), pointer :: cg_gids (:), dg_gids(:), elgpgp(:,:)
+    integer(kind=c_int), pointer :: cg_gids (:), dg_gids(:), elgpgp(:,:), elgid(:)
 
     ! Sanity check
     call check_grids_inited(.true.)
@@ -124,10 +124,11 @@ subroutine get_dyn_grid_data_f90 (dg_gids_ptr, cg_gids_ptr, elgpgp_ptr, lat_ptr,
     call c_f_pointer (dg_gids_ptr, dg_gids, [nelemd*np*np])
     call c_f_pointer (cg_gids_ptr, cg_gids, [nelemd*np*np])
     call c_f_pointer (elgpgp_ptr,  elgpgp,  [3,nelemd*np*np])
+    call c_f_pointer (elgid_ptr,   elgid,   [nelemd])
     call c_f_pointer (lat_ptr,     lat,     [np,np,nelemd])
     call c_f_pointer (lon_ptr,     lon,     [np,np,nelemd])
 
-    call get_my_dyn_data (dg_gids, cg_gids, elgpgp, lat, lon)
+    call get_my_dyn_data (dg_gids, cg_gids, elgpgp, elgid, lat, lon)
   end subroutine get_dyn_grid_data_f90
 
   subroutine get_phys_grid_data_f90 (pg_type, gids_ptr, lat_ptr, lon_ptr, area_ptr) bind(c)
diff --git a/components/eamxx/src/dynamics/homme/interface/scream_homme_interface.hpp b/components/eamxx/src/dynamics/homme/interface/scream_homme_interface.hpp
index 8968fc49fb1..496472b54c0 100644
--- a/components/eamxx/src/dynamics/homme/interface/scream_homme_interface.hpp
+++ b/components/eamxx/src/dynamics/homme/interface/scream_homme_interface.hpp
@@ -65,6 +65,7 @@ int get_num_global_elems_f90 ();
 void get_dyn_grid_data_f90 (AbstractGrid::gid_type* const& dg_gids,
                             AbstractGrid::gid_type* const& cg_gids,
                             int* const& elgp,
+                            AbstractGrid::gid_type* const& elgids,
                             double* const& lat, double* const& lon);
 void get_phys_grid_data_f90 (const int& pg_type,
                              AbstractGrid::gid_type* const& gids,
diff --git a/components/eamxx/src/dynamics/homme/tests/dyn_grid_io.cpp b/components/eamxx/src/dynamics/homme/tests/dyn_grid_io.cpp
index bb09daa1c49..ec1e709c7cd 100644
--- a/components/eamxx/src/dynamics/homme/tests/dyn_grid_io.cpp
+++ b/components/eamxx/src/dynamics/homme/tests/dyn_grid_io.cpp
@@ -41,8 +41,7 @@ TEST_CASE("dyn_grid_io")
   ekat::Comm comm(MPI_COMM_WORLD);  // MPI communicator group used for I/O set as ekat object.
 
   // Initialize the pio_subsystem for this test:
-  MPI_Fint fcomm = MPI_Comm_c2f(comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm);
+  scorpio::init_subsystem(comm);
 
   // Init homme context
   if (!is_parallel_inited_f90()) {
@@ -179,7 +178,7 @@ TEST_CASE("dyn_grid_io")
   }
 
   // Cleanup everything
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
   Homme::Context::finalize_singleton();
   cleanup_test_f90();
 }
diff --git a/components/eamxx/src/physics/nudging/eamxx_nudging_process_interface.cpp b/components/eamxx/src/physics/nudging/eamxx_nudging_process_interface.cpp
index 40925c9edd1..832c030e97b 100644
--- a/components/eamxx/src/physics/nudging/eamxx_nudging_process_interface.cpp
+++ b/components/eamxx/src/physics/nudging/eamxx_nudging_process_interface.cpp
@@ -355,7 +355,7 @@ void Nudging::run_impl (const double dt)
     Real var_fill_value = constants::DefaultFillValue<Real>().value;
     // Query the helper field for the fill value, if not present use default
     if (f.get_header().has_extra_data("mask_value")) {
-      var_fill_value = f.get_header().get_extra_data<float>("mask_value");
+      var_fill_value = f.get_header().get_extra_data<Real>("mask_value");
     }
 
     const int ncols = fl.dim(0);
diff --git a/components/eamxx/src/physics/nudging/tests/create_map_file.cpp b/components/eamxx/src/physics/nudging/tests/create_map_file.cpp
index 1a83abb5f7b..d8a67d84b27 100644
--- a/components/eamxx/src/physics/nudging/tests/create_map_file.cpp
+++ b/components/eamxx/src/physics/nudging/tests/create_map_file.cpp
@@ -7,7 +7,7 @@ TEST_CASE("create_map_file")
   using namespace scream;
 
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   // Add a dof in the middle of two coarse dofs
   const int ngdofs_src = 12;
@@ -21,21 +21,15 @@ TEST_CASE("create_map_file")
 
   scorpio::register_file(filename, scorpio::FileMode::Write);
 
-  scorpio::register_dimension(filename, "n_a", "n_a", ngdofs_src, false);
-  scorpio::register_dimension(filename, "n_b", "n_b", ngdofs_tgt, false);
-  scorpio::register_dimension(filename, "n_s", "n_s", nnz,        false);
+  scorpio::define_dim(filename, "n_a", ngdofs_src);
+  scorpio::define_dim(filename, "n_b", ngdofs_tgt);
+  scorpio::define_dim(filename, "n_s", nnz);
 
-  scorpio::register_variable(filename, "col", "col", "1", {"n_s"}, "int",    "int",    "");
-  scorpio::register_variable(filename, "row", "row", "1", {"n_s"}, "int",    "int",    "");
-  scorpio::register_variable(filename, "S",   "S",   "1", {"n_s"}, "double", "double", "");
+  scorpio::define_var(filename, "col", {"n_s"}, "int");
+  scorpio::define_var(filename, "row", {"n_s"}, "int");
+  scorpio::define_var(filename, "S",   {"n_s"}, "double");
 
-  std::vector<scorpio::offset_t> dofs(nnz);
-  std::iota(dofs.begin(),dofs.end(),0);
-  scorpio::set_dof(filename,"col",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"row",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"S",  dofs.size(),dofs.data());
-
-  scorpio::eam_pio_enddef(filename);
+  scorpio::enddef(filename);
 
   std::vector<int> col(nnz), row(nnz);
   std::vector<double> S(nnz);
@@ -54,10 +48,10 @@ TEST_CASE("create_map_file")
       S[ngdofs_src+2*i+1] = 0.5;
   }
 
-  scorpio::grid_write_data_array(filename,"row",row.data(),nnz);
-  scorpio::grid_write_data_array(filename,"col",col.data(),nnz);
-  scorpio::grid_write_data_array(filename,"S",  S.data(),  nnz);
+  scorpio::write_var(filename,"row",row.data());
+  scorpio::write_var(filename,"col",col.data());
+  scorpio::write_var(filename,"S",  S.data());
 
-  scorpio::eam_pio_closefile(filename);
-  scorpio::eam_pio_finalize();
+  scorpio::release_file(filename);
+  scorpio::finalize_subsystem();
 }
diff --git a/components/eamxx/src/physics/nudging/tests/create_nudging_data.cpp b/components/eamxx/src/physics/nudging/tests/create_nudging_data.cpp
index f5c8e6b4bda..000322b2374 100644
--- a/components/eamxx/src/physics/nudging/tests/create_nudging_data.cpp
+++ b/components/eamxx/src/physics/nudging/tests/create_nudging_data.cpp
@@ -20,7 +20,7 @@ TEST_CASE("create_nudging_data") {
   const auto t0    = get_t0();
 
   // Initialize the pio_subsystem for this test:
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   // Create a grids manager
   const auto gm = create_gm(comm,ngcols,nlevs);
@@ -56,5 +56,5 @@ TEST_CASE("create_nudging_data") {
   om2->finalize();
   om3->finalize();
 
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
diff --git a/components/eamxx/src/physics/nudging/tests/nudging_tests.cpp b/components/eamxx/src/physics/nudging/tests/nudging_tests.cpp
index f5411205627..8870b4cce20 100644
--- a/components/eamxx/src/physics/nudging/tests/nudging_tests.cpp
+++ b/components/eamxx/src/physics/nudging/tests/nudging_tests.cpp
@@ -44,7 +44,7 @@ TEST_CASE("nudging_tests") {
   };
 
   // Init scorpio
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   // A refined grid, with one extra node in between each of the coarse ones
   const int ngcols_fine = 2*ngcols_data - 1;
@@ -462,5 +462,5 @@ TEST_CASE("nudging_tests") {
   }
 
   // Clean up scorpio
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
diff --git a/components/eamxx/src/physics/spa/spa_functions_impl.hpp b/components/eamxx/src/physics/spa/spa_functions_impl.hpp
index d9547953d1e..287f69a9889 100644
--- a/components/eamxx/src/physics/spa/spa_functions_impl.hpp
+++ b/components/eamxx/src/physics/spa/spa_functions_impl.hpp
@@ -83,7 +83,7 @@ create_horiz_remapper (
   const int ncols_data = scorpio::get_dimlen(spa_data_file,"ncol");
   const int nswbands   = scorpio::get_dimlen(spa_data_file,"swband");
   const int nlwbands   = scorpio::get_dimlen(spa_data_file,"lwband");
-  scorpio::eam_pio_closefile(spa_data_file);
+  scorpio::release_file(spa_data_file);
 
   // We could use model_grid directly if using same num levels,
   // but since shallow clones are cheap, we may as well do it (less lines of code)
diff --git a/components/eamxx/src/physics/spa/tests/spa_one_to_one_remap_test.cpp b/components/eamxx/src/physics/spa/tests/spa_one_to_one_remap_test.cpp
index 5579c3efa7e..71a7187ed38 100644
--- a/components/eamxx/src/physics/spa/tests/spa_one_to_one_remap_test.cpp
+++ b/components/eamxx/src/physics/spa/tests/spa_one_to_one_remap_test.cpp
@@ -25,7 +25,7 @@ TEST_CASE("spa_one_to_one_remap","spa")
 {
   // Set up the mpi communicator and init the pio subsystem
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   std::string spa_data_file = SCREAM_DATA_DIR "/init/spa_data_for_testing.nc";
 
@@ -107,7 +107,7 @@ TEST_CASE("spa_one_to_one_remap","spa")
 
   // All Done
   reader = nullptr;
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 } // run_property
 
 // Some helper functions for the require statements:
diff --git a/components/eamxx/src/physics/spa/tests/spa_read_data_from_file_test.cpp b/components/eamxx/src/physics/spa/tests/spa_read_data_from_file_test.cpp
index 4c6533b5870..059781f40d8 100644
--- a/components/eamxx/src/physics/spa/tests/spa_read_data_from_file_test.cpp
+++ b/components/eamxx/src/physics/spa/tests/spa_read_data_from_file_test.cpp
@@ -26,7 +26,7 @@ TEST_CASE("spa_read_data","spa")
 
   // Set up the mpi communicator and init the pio subsystem
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   std::string spa_data_file  = SCREAM_DATA_DIR "/init/spa_data_for_testing.nc";
   std::string spa_remap_file = SCREAM_DATA_DIR "/init/spa_data_for_testing.nc";
@@ -104,7 +104,7 @@ TEST_CASE("spa_read_data","spa")
 
   // Clean up
   reader = nullptr;
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 // Some helper functions for the require statements:
diff --git a/components/eamxx/src/share/atm_process/atmosphere_process.hpp b/components/eamxx/src/share/atm_process/atmosphere_process.hpp
index da8f7c09deb..071ef906a75 100644
--- a/components/eamxx/src/share/atm_process/atmosphere_process.hpp
+++ b/components/eamxx/src/share/atm_process/atmosphere_process.hpp
@@ -78,7 +78,6 @@ class AtmosphereProcess : public ekat::enable_shared_from_this<AtmosphereProcess
   using ci_string = ekat::CaseInsensitiveString;
   using logger_t  = ekat::logger::LoggerBase;
   using LogLevel  = ekat::logger::LogLevel;
-  using any_ptr_t = std::shared_ptr<ekat::any>;
 
   template<typename T>
   using strmap_t = std::map<std::string,T>;
@@ -268,8 +267,8 @@ class AtmosphereProcess : public ekat::enable_shared_from_this<AtmosphereProcess
   //  - these maps are: data_name -> ekat::any
   //  - the data_name is unique across the whole atm
   // The AD will take care of ensuring these are written/read to/from restart files.
-  const strmap_t<any_ptr_t>& get_restart_extra_data () const { return m_restart_extra_data; }
-        strmap_t<any_ptr_t>& get_restart_extra_data ()       { return m_restart_extra_data; }
+  const strmap_t<ekat::any>& get_restart_extra_data () const { return m_restart_extra_data; }
+        strmap_t<ekat::any>& get_restart_extra_data ()       { return m_restart_extra_data; }
 
   // Boolean that dictates whether or not the conservation checks are run for this process
   bool has_column_conservation_check () { return m_column_conservation_check_data.has_check; }
@@ -477,7 +476,7 @@ class AtmosphereProcess : public ekat::enable_shared_from_this<AtmosphereProcess
   std::shared_ptr<logger_t>  m_atm_logger;
 
   // Extra data needed for restart
-  strmap_t<any_ptr_t>  m_restart_extra_data;
+  strmap_t<ekat::any>  m_restart_extra_data;
 
   // Use at your own risk. Motivation: Free up device memory for a field that is
   // no longer used, such as a field read in the ICs used only to initialize
diff --git a/components/eamxx/src/share/field/field_impl.hpp b/components/eamxx/src/share/field/field_impl.hpp
index 1964622d005..f192d70bb68 100644
--- a/components/eamxx/src/share/field/field_impl.hpp
+++ b/components/eamxx/src/share/field/field_impl.hpp
@@ -465,10 +465,15 @@ update (const Field& x, const ST alpha, const ST beta)
   ST fill_val = constants::DefaultFillValue<ST>().value;
 
   if (x.get_header().has_extra_data("mask_value")) {
-    if (typeid(ST) == typeid(int)) {
+
+    if (dt==DataType::IntType) {
       fill_val = x.get_header().get_extra_data<int>("mask_value");
-    } else {
+    } else if (dt==DataType::FloatType) {
       fill_val = x.get_header().get_extra_data<float>("mask_value");
+    } else if (dt==DataType::DoubleType) {
+      fill_val = x.get_header().get_extra_data<double>("mask_value");
+    } else {
+      EKAT_ERROR_MSG ("Error! Unrecognized/unsupported field data type in Field::update.\n");
     }
   }
 
diff --git a/components/eamxx/src/share/grid/abstract_grid.cpp b/components/eamxx/src/share/grid/abstract_grid.cpp
index 3e6b9fd0a0c..0cc83822c23 100644
--- a/components/eamxx/src/share/grid/abstract_grid.cpp
+++ b/components/eamxx/src/share/grid/abstract_grid.cpp
@@ -223,6 +223,26 @@ get_global_max_dof_gid () const ->gid_type
   return m_global_max_dof_gid;
 }
 
+auto AbstractGrid::
+get_global_min_partitioned_dim_gid () const ->gid_type
+{
+  // Lazy calculation
+  if (m_global_min_partitioned_dim_gid==std::numeric_limits<gid_type>::max()) {
+    m_global_min_partitioned_dim_gid = field_min<gid_type>(m_partitioned_dim_gids,&get_comm());
+  }
+  return m_global_min_partitioned_dim_gid;
+}
+
+auto AbstractGrid::
+get_global_max_partitioned_dim_gid () const ->gid_type
+{
+  // Lazy calculation
+  if (m_global_max_partitioned_dim_gid==-std::numeric_limits<gid_type>::max()) {
+    m_global_max_partitioned_dim_gid = field_max<gid_type>(m_partitioned_dim_gids,&get_comm());
+  }
+  return m_global_max_partitioned_dim_gid;
+}
+
 Field
 AbstractGrid::get_dofs_gids () const {
   return m_dofs_gids.get_const();
@@ -233,6 +253,16 @@ AbstractGrid::get_dofs_gids () {
   return m_dofs_gids;
 }
 
+Field
+AbstractGrid::get_partitioned_dim_gids () {
+  return m_partitioned_dim_gids;
+}
+
+Field
+AbstractGrid::get_partitioned_dim_gids () const {
+  return m_partitioned_dim_gids.get_const();
+}
+
 Field
 AbstractGrid::get_lid_to_idx_map () const {
   return m_lid_to_idx.get_const();
@@ -521,8 +551,10 @@ void AbstractGrid::copy_data (const AbstractGrid& src, const bool shallow)
 {
   if (shallow) {
     m_dofs_gids = src.m_dofs_gids;
+    m_partitioned_dim_gids = src.m_partitioned_dim_gids;
   } else {
     m_dofs_gids = src.m_dofs_gids.clone();
+    m_partitioned_dim_gids = src.m_partitioned_dim_gids.clone();
   }
 
   if (shallow) {
diff --git a/components/eamxx/src/share/grid/abstract_grid.hpp b/components/eamxx/src/share/grid/abstract_grid.hpp
index 00abba1571a..2098fd49e94 100644
--- a/components/eamxx/src/share/grid/abstract_grid.hpp
+++ b/components/eamxx/src/share/grid/abstract_grid.hpp
@@ -112,11 +112,19 @@ class AbstractGrid : public ekat::enable_shared_from_this<AbstractGrid>
   gid_type get_num_global_dofs () const { return m_num_global_dofs; }
   gid_type get_global_min_dof_gid () const;
   gid_type get_global_max_dof_gid () const;
+  gid_type get_global_min_partitioned_dim_gid () const;
+  gid_type get_global_max_partitioned_dim_gid () const;
 
   // Get a Field storing 1d data (the dof gids)
   Field get_dofs_gids () const;
   Field get_dofs_gids ();
 
+  // Get Field storing the gids that this process owns along the partitioned dim
+  // NOTE: for some grids, this is the same as get_dofs_gids. The SEGrid is a counterexample:
+  //       the dofs are the GLL dofs, but the partitioned dim is the element dimension
+  Field get_partitioned_dim_gids ();
+  Field get_partitioned_dim_gids () const;
+
   // Get a Field storing 2d data, where (i,j) entry contains the j-th coordinate of
   // the i-th dof in the native dof layout. Const verison returns a read-only field
   Field get_lid_to_idx_map () const;
@@ -180,10 +188,8 @@ class AbstractGrid : public ekat::enable_shared_from_this<AbstractGrid>
   virtual bool check_valid_lid_to_idx () const { return true; }
 
   void reset_field_tag_name (const FieldTag t, const std::string& s) { m_special_tag_names[t] = s; }
-  std::string get_dim_name (const FieldLayout& lt, const int idim) const {
-    const auto t = lt.tag(idim);
-    return m_special_tag_names.count(t)==1 ? m_special_tag_names.at(t) : lt.names()[idim];
-  }
+  bool has_special_tag_name (const FieldTag t) const { return m_special_tag_names.count(t)==1; }
+  std::string get_special_tag_name (const FieldTag t) const { return m_special_tag_names.at(t); }
 
   // This member is used mostly by IO: if a field exists on multiple grids
   // with the same name, IO can use this as a suffix to diambiguate the fields in
@@ -203,7 +209,6 @@ class AbstractGrid : public ekat::enable_shared_from_this<AbstractGrid>
   //       since it calls get_2d_scalar_layout.
   void create_dof_fields (const int scalar2d_layout_rank);
 
-
   // The grid name and type
   GridType     m_type;
   std::string  m_name;
@@ -222,9 +227,15 @@ class AbstractGrid : public ekat::enable_shared_from_this<AbstractGrid>
   // The global ID of each dof
   Field     m_dofs_gids;
 
+  // The global ID of the owned entries of the partitioned dimension (if any)
+  Field     m_partitioned_dim_gids;
+
   // The max/min dof GID across all ranks. Mutable, to allow for lazy calculation
   mutable gid_type  m_global_min_dof_gid =  std::numeric_limits<gid_type>::max();
   mutable gid_type  m_global_max_dof_gid = -std::numeric_limits<gid_type>::max();
+  // Same as above, but for partitioned dim gids
+  mutable gid_type  m_global_min_partitioned_dim_gid =  std::numeric_limits<gid_type>::max();
+  mutable gid_type  m_global_max_partitioned_dim_gid = -std::numeric_limits<gid_type>::max();
 
   // The fcn is_unique is expensive, so we lazy init this at the first call.
   mutable bool m_is_unique;
diff --git a/components/eamxx/src/share/grid/mesh_free_grids_manager.cpp b/components/eamxx/src/share/grid/mesh_free_grids_manager.cpp
index d1525bfec02..e0f78e10cf0 100644
--- a/components/eamxx/src/share/grid/mesh_free_grids_manager.cpp
+++ b/components/eamxx/src/share/grid/mesh_free_grids_manager.cpp
@@ -70,10 +70,12 @@ build_se_grid (const std::string& name, ekat::ParameterList& params)
   se_grid->setSelfPointer(se_grid);
 
   // Set up the degrees of freedom.
-  auto dof_gids = se_grid->get_dofs_gids();
-  auto lid2idx  = se_grid->get_lid_to_idx_map();
+  auto dof_gids  = se_grid->get_dofs_gids();
+  auto elem_gids = se_grid->get_partitioned_dim_gids();
+  auto lid2idx   = se_grid->get_lid_to_idx_map();
 
   auto host_dofs    = dof_gids.template get_view<AbstractGrid::gid_type*,Host>();
+  auto host_elems   = elem_gids.template get_view<AbstractGrid::gid_type*,Host>();
   auto host_lid2idx = lid2idx.template get_view<int**,Host>();
 
   // Count unique local dofs. On all elems except the very last one (on rank N),
@@ -82,6 +84,7 @@ build_se_grid (const std::string& name, ekat::ParameterList& params)
   int offset = num_local_dofs*m_comm.rank();
 
   for (int ie = 0; ie < num_local_elems; ++ie) {
+    host_elems[ie] = ie + num_local_elems*m_comm.rank();
     for (int igp = 0; igp < num_gp; ++igp) {
       for (int jgp = 0; jgp < num_gp; ++jgp) {
         int idof = ie*num_gp*num_gp + igp*num_gp + jgp;
@@ -96,6 +99,7 @@ build_se_grid (const std::string& name, ekat::ParameterList& params)
 
   // Sync to device
   dof_gids.sync_to_dev();
+  elem_gids.sync_to_dev();
   lid2idx.sync_to_dev();
 
   se_grid->m_short_name = "se";
@@ -162,13 +166,13 @@ add_geo_data (const nonconstgrid_ptr_type& grid) const
     lev.sync_to_dev();
   } else if (geo_data_source=="IC_FILE"){
     const auto& filename = m_params.get<std::string>("ic_filename");
-    if (scorpio::has_variable(filename,"lat") &&
-        scorpio::has_variable(filename,"lon")) {
+    if (scorpio::has_var(filename,"lat") &&
+        scorpio::has_var(filename,"lon")) {
       load_lat_lon(grid,filename);
     }
 
-    if (scorpio::has_variable(filename,"hyam") &&
-        scorpio::has_variable(filename,"hybm")) {
+    if (scorpio::has_var(filename,"hyam") &&
+        scorpio::has_var(filename,"hybm")) {
       load_vertical_coordinates(grid,filename);
     }
   }
diff --git a/components/eamxx/src/share/grid/point_grid.cpp b/components/eamxx/src/share/grid/point_grid.cpp
index 8cf73e21f2a..7346020fa3e 100644
--- a/components/eamxx/src/share/grid/point_grid.cpp
+++ b/components/eamxx/src/share/grid/point_grid.cpp
@@ -15,6 +15,9 @@ PointGrid (const std::string& grid_name,
 {
   create_dof_fields (get_2d_scalar_layout().rank());
 
+  // The partitioned dim is the COL dim, which concide with the dofs
+  m_partitioned_dim_gids = m_dofs_gids;
+
   // The lid->idx map is the identity map.
   auto lid2idx = get_lid_to_idx_map();
   auto h_lid_to_idx = lid2idx.get_view<int**,Host>();
diff --git a/components/eamxx/src/share/grid/remap/horiz_interp_remapper_data.cpp b/components/eamxx/src/share/grid/remap/horiz_interp_remapper_data.cpp
index d44fc6aa2f0..b26501a499b 100644
--- a/components/eamxx/src/share/grid/remap/horiz_interp_remapper_data.cpp
+++ b/components/eamxx/src/share/grid/remap/horiz_interp_remapper_data.cpp
@@ -40,40 +40,19 @@ get_my_triplets (const std::string& map_file) const
   // 1. Load the map file chunking it evenly across all ranks
   scorpio::register_file(map_file,scorpio::FileMode::Read);
 
-  // 1.1 Create a "helper" grid, with as many dofs as the number
-  //     of triplets in the map file, and divided linearly across ranks
-  const int ngweights = scorpio::get_dimlen(map_file,"n_s");
-  int nlweights = ngweights / comm.size();
-  if (comm.rank() < (ngweights % comm.size())) {
-    nlweights += 1;
-  }
-
-  gid_type offset = nlweights;
-  comm.scan(&offset,1,MPI_SUM);
-  offset -= nlweights; // scan is inclusive, but we need exclusive
+  // Inform scorpio that we will provide "int" pointers for row/col indices
+  scorpio::change_var_dtype(map_file,"row","int");
+  scorpio::change_var_dtype(map_file,"col","int");
 
-  // Create a unique decomp tag, which ensures all refining remappers have
-  // their own decomposition
-  static int tag_counter = 0;
-  const std::string int_decomp_tag  = "RR::gmtg,int,grid-idx=" + std::to_string(tag_counter++);
-  const std::string real_decomp_tag = "RR::gmtg,real,grid-idx=" + std::to_string(tag_counter++);
+  // Decompose n_s dim linearly across ranks
+  scorpio::set_dim_decomp (map_file,"n_s");
+  int nlweights = scorpio::get_dimlen_local(map_file,"n_s");
 
-  // 1.2 Read a chunk of triplets col indices
+  // 1.1 Read a chunk of triplets col indices
   std::vector<gid_type> cols(nlweights);
   std::vector<gid_type> rows(nlweights);
   std::vector<Real>  S(nlweights);
 
-  scorpio::register_variable(map_file, "col", "col", {"n_s"}, "int",  int_decomp_tag);
-  scorpio::register_variable(map_file, "row", "row", {"n_s"}, "int",  int_decomp_tag);
-  scorpio::register_variable(map_file, "S",   "S",   {"n_s"}, "real", real_decomp_tag);
-
-  std::vector<scorpio::offset_t> dofs_offsets(nlweights);
-  std::iota(dofs_offsets.begin(),dofs_offsets.end(),offset);
-  scorpio::set_dof(map_file,"col",nlweights,dofs_offsets.data());
-  scorpio::set_dof(map_file,"row",nlweights,dofs_offsets.data());
-  scorpio::set_dof(map_file,"S"  ,nlweights,dofs_offsets.data());
-  scorpio::set_decomp(map_file);
-
   // Figure out if we are reading the right map, that is:
   //  - n_a or n_b matches the fine grid ncols
   //  - the map "direction" (fine->coarse or coarse->fine) matches m_type
@@ -95,13 +74,13 @@ get_my_triplets (const std::string& map_file) const
       " - fine grid ncols: " + std::to_string(ncols_fine) + "\n"
       " - remapper type: " + std::string(type==InterpType::Refine ? "refine" : "coarsen") + "\n");
 
-  scorpio::grid_read_data_array(map_file,"col",-1,cols.data(),nlweights);
-  scorpio::grid_read_data_array(map_file,"row",-1,rows.data(),nlweights);
-  scorpio::grid_read_data_array(map_file,"S"  ,-1,S.data(),nlweights);
+  scorpio::read_var(map_file,"col",cols.data());
+  scorpio::read_var(map_file,"row",rows.data());
+  scorpio::read_var(map_file,"S"  ,S.data());
 
-  scorpio::eam_pio_closefile(map_file);
+  scorpio::release_file(map_file);
 
-  // 1.3 Dofs in grid are likely 0-based, while row/col ids in map file
+  // 1.2 Dofs in grid are likely 0-based, while row/col ids in map file
   // are likely 1-based. To match dofs, we need to offset the row/cols
   // ids we just read in.
   int map_file_min_row = std::numeric_limits<int>::max();
diff --git a/components/eamxx/src/share/grid/remap/vertical_remapper.cpp b/components/eamxx/src/share/grid/remap/vertical_remapper.cpp
index 78d18e086a6..c899bef26dc 100644
--- a/components/eamxx/src/share/grid/remap/vertical_remapper.cpp
+++ b/components/eamxx/src/share/grid/remap/vertical_remapper.cpp
@@ -70,7 +70,7 @@ VerticalRemapper (const grid_ptr_type& src_grid,
 
   // Add tgt pressure levels to the tgt grid
   tgt_grid->set_geometry_data(m_remap_pres);
-  scorpio::eam_pio_closefile(map_file);
+  scorpio::release_file(map_file);
 }
 
 FieldLayout VerticalRemapper::
@@ -154,13 +154,7 @@ set_pressure_levels(const std::string& map_file)
 
   auto remap_pres_scal = m_remap_pres.get_view<Real*,Host>();
 
-  std::vector<scorpio::offset_t> dofs_offsets(m_num_remap_levs);
-  std::iota(dofs_offsets.begin(),dofs_offsets.end(),0);
-  const std::string decomp_tag = "VR::spl,nlev=" + std::to_string(m_num_remap_levs) + ",file-idx=" + std::to_string(file2idx[map_file]);
-  scorpio::register_variable(map_file, "p_levs", "p_levs", {"lev"}, "real", decomp_tag);
-  scorpio::set_dof(map_file,"p_levs",m_num_remap_levs,dofs_offsets.data());
-  scorpio::set_decomp(map_file);
-  scorpio::grid_read_data_array(map_file,"p_levs",-1,remap_pres_scal.data(),remap_pres_scal.size());
+  scorpio::read_var(map_file,"p_levs",remap_pres_scal.data());
 
   m_remap_pres.sync_to_dev();
 }
diff --git a/components/eamxx/src/share/grid/se_grid.cpp b/components/eamxx/src/share/grid/se_grid.cpp
index 741bdb4e640..284191a69da 100644
--- a/components/eamxx/src/share/grid/se_grid.cpp
+++ b/components/eamxx/src/share/grid/se_grid.cpp
@@ -1,6 +1,7 @@
 #include "share/grid/se_grid.hpp"
+#include "share/field/field_utils.hpp"
 
-#include "ekat/kokkos//ekat_subview_utils.hpp"
+#include <ekat/kokkos/ekat_subview_utils.hpp>
 
 namespace scream {
 
@@ -29,6 +30,9 @@ SEGrid (const std::string& grid_name,
   const auto units = ekat::units::Units::nondimensional();
   m_cg_dofs_gids = Field(FieldIdentifier("cg_gids",FieldLayout({CMP},{get_num_local_dofs()}),units,this->name(),DataType::IntType));
   m_cg_dofs_gids.allocate_view();
+
+  m_partitioned_dim_gids = Field(FieldIdentifier("el_gids",FieldLayout({EL},{m_num_local_elem}),units,this->name(),DataType::IntType));
+  m_partitioned_dim_gids.allocate_view();
 }
 
 FieldLayout
@@ -127,20 +131,6 @@ SEGrid::get_3d_tensor_layout (const bool midpoints,
   return fl.rename_dims(m_special_tag_names);
 }
 
-Field SEGrid::get_cg_dofs_gids ()
-{
-  EKAT_REQUIRE_MSG (m_cg_dofs_gids.is_allocated(),
-      "Error! CG dofs have not been created yet.\n");
-  return m_cg_dofs_gids;
-}
-
-Field SEGrid::get_cg_dofs_gids () const
-{
-  EKAT_REQUIRE_MSG (m_cg_dofs_gids.is_allocated(),
-      "Error! CG dofs have not been created yet.\n");
-  return m_cg_dofs_gids.get_const();
-}
-
 std::shared_ptr<AbstractGrid> SEGrid::clone (const std::string& clone_name, const bool shallow) const
 {
   auto grid = std::make_shared<SEGrid>(clone_name,m_num_local_elem,m_num_gp,get_num_vertical_levels(),get_comm());
diff --git a/components/eamxx/src/share/grid/se_grid.hpp b/components/eamxx/src/share/grid/se_grid.hpp
index 79274e96bca..87c86887fe3 100644
--- a/components/eamxx/src/share/grid/se_grid.hpp
+++ b/components/eamxx/src/share/grid/se_grid.hpp
@@ -43,8 +43,8 @@ class SEGrid : public AbstractGrid
   }
 
   // Retrieve list of the CG grid dofs. Const version returns a read-only field
-  Field get_cg_dofs_gids ();
-  Field get_cg_dofs_gids () const;
+  Field get_cg_dofs_gids ()       { return m_cg_dofs_gids;             }
+  Field get_cg_dofs_gids () const { return m_cg_dofs_gids.get_const(); }
 
   std::shared_ptr<AbstractGrid> clone (const std::string& clone_name,
                                        const bool shallow) const override;
@@ -59,6 +59,10 @@ class SEGrid : public AbstractGrid
   int       m_num_global_elem;
   int       m_num_gp;
 
+  // The max/min elem GID across all ranks. Mutable, to allow for lazy calculation
+  mutable gid_type  m_global_min_elem_gid =  std::numeric_limits<gid_type>::max();
+  mutable gid_type  m_global_max_elem_gid = -std::numeric_limits<gid_type>::max();
+
   // The dofs gids for a CG version of this grid
   Field m_cg_dofs_gids;
 };
diff --git a/components/eamxx/src/share/io/CMakeLists.txt b/components/eamxx/src/share/io/CMakeLists.txt
index 8866e294495..afb0ef888db 100644
--- a/components/eamxx/src/share/io/CMakeLists.txt
+++ b/components/eamxx/src/share/io/CMakeLists.txt
@@ -1,38 +1,65 @@
-set(SCREAM_SCORPIO_SRCS
-  scream_scorpio_interface.F90
+#########################################
+#       SCORPIO interface library       #
+#########################################
+
+# This small lib contains some interfaces to scorpio, which are formulated
+# in terms of names rather than IDs. Internally, we store a list of
+# small structs, holding handlers to PIO data and extra metadata, which
+# allows to perform sanity checks and print more helpful messages
+
+add_library(scream_scorpio_interface
+  scream_scorpio_types.cpp
   scream_scorpio_interface.cpp
-  scream_scorpio_interface_iso_c2f.F90
-  scream_output_manager.cpp
-  scorpio_input.cpp
-  scorpio_output.cpp
-  scream_io_utils.cpp
 )
-
-# Create io lib
-add_library(scream_io ${SCREAM_SCORPIO_SRCS})
-set_target_properties(scream_io PROPERTIES
-  Fortran_MODULE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/modules
+target_link_libraries(scream_scorpio_interface PUBLIC ekat)
+target_link_libraries(scream_scorpio_interface PRIVATE pioc)
+target_include_directories(scream_scorpio_interface PUBLIC
+  ${SCREAM_BIN_DIR}/src   # For scream_config.h
 )
-target_include_directories(scream_io PUBLIC ${CMAKE_CURRENT_BINARY_DIR}/modules)
 
 if (DEFINED ENV{ADIOS2_ROOT})
-  target_include_directories(scream_io PRIVATE $ENV{ADIOS2_ROOT}/include)
+  target_include_directories(scream_scorpio_interface PRIVATE $ENV{ADIOS2_ROOT}/include)
 endif ()
 
 if (SCORPIO_Fortran_INCLUDE_DIRS)
-  target_include_directories(scream_io PUBLIC ${SCORPIO_Fortran_INCLUDE_DIRS})
+  target_include_directories(scream_scorpio_interface PUBLIC ${SCORPIO_Fortran_INCLUDE_DIRS})
 endif ()
 
 if (SCORPIO_C_INCLUDE_DIRS)
-  target_include_directories(scream_io PUBLIC ${SCORPIO_C_INCLUDE_DIRS})
+  target_include_directories(scream_scorpio_interface PUBLIC ${SCORPIO_C_INCLUDE_DIRS})
 endif ()
 
-target_link_libraries(scream_io PUBLIC scream_share piof pioc)
-
 if (SCREAM_CIME_BUILD)
-  target_link_libraries(scream_io PUBLIC csm_share)
+  # Add interface to E3SM shr lib (to retrieve PIO subsystem info)
+  target_sources (scream_scorpio_interface PRIVATE
+    scream_shr_interface_c2f.F90
+  )
+  target_compile_definitions (scream_scorpio_interface PRIVATE SCREAM_CIME_BUILD)
+  set_target_properties(scream_scorpio_interface PROPERTIES
+    Fortran_MODULE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/modules
+  )
+  target_include_directories(scream_scorpio_interface PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/modules)
+  target_link_libraries(scream_scorpio_interface PUBLIC csm_share)
 endif()
 
+##################################
+#       EAMxx I/O library        #
+##################################
+
+# This library allows for a simple(r) interaction between EAMxx
+# data structures (such as grids, fields, remappers,...) and
+# the scorpio interface library
+
+# Create io lib
+add_library(scream_io
+  scream_output_manager.cpp
+  scorpio_input.cpp
+  scorpio_output.cpp
+  scream_io_utils.cpp
+)
+
+target_link_libraries(scream_io PUBLIC scream_share scream_scorpio_interface)
+
 if (NOT SCREAM_LIB_ONLY)
   add_subdirectory(tests)
 endif()
diff --git a/components/eamxx/src/share/io/scorpio_input.cpp b/components/eamxx/src/share/io/scorpio_input.cpp
index 0c04a612a02..e8a510130e0 100644
--- a/components/eamxx/src/share/io/scorpio_input.cpp
+++ b/components/eamxx/src/share/io/scorpio_input.cpp
@@ -220,7 +220,7 @@ void AtmosphereInput::read_variables (const int time_index)
 
     // Read the data
     auto v1d = m_host_views_1d.at(name);
-    scorpio::grid_read_data_array(m_filename,name,time_index,v1d.data(),v1d.size());
+    scorpio::read_var(m_filename,name,v1d.data(),time_index);
 
     // If we have a field manager, make sure the data is correctly
     // synced to both host and device views of the field.
@@ -335,7 +335,7 @@ void AtmosphereInput::read_variables (const int time_index)
 /* ---------------------------------------------------------- */
 void AtmosphereInput::finalize() 
 {
-  scorpio::eam_pio_closefile(m_filename);
+  scorpio::release_file(m_filename);
 
   m_field_mgr = nullptr;
   m_io_grid   = nullptr;
@@ -351,51 +351,60 @@ void AtmosphereInput::finalize()
 void AtmosphereInput::init_scorpio_structures() 
 {
   std::string iotype_str = m_params.get<std::string>("iotype", "default");
-  int iotype = scorpio::str2iotype(iotype_str);
+  auto iotype = scorpio::str2iotype(iotype_str);
 
   scorpio::register_file(m_filename,scorpio::Read,iotype);
 
-  // Register variables with netCDF file.
-  register_variables();
-  set_degrees_of_freedom();
-
-  // Finish the definition phase for this file.
-  scorpio::set_decomp  (m_filename); 
-}
-
-/* ---------------------------------------------------------- */
-void AtmosphereInput::register_variables()
-{
-  // Register each variable in IO stream with the SCORPIO interface.
-  // This allows SCORPIO to lookup vars in the nc file with the correct
-  // dof decomposition across different ranks.
+  // Some input files have the "time" dimension as non-unlimited. This messes up our
+  // scorpio interface. To avoid trouble, if a dim called 'time' is present we
+  // treat it as unlimited, even though it isn't.
+  if (scorpio::has_dim(m_filename,"time") and not scorpio::is_dim_unlimited(m_filename,"time")) {
+    scorpio::pretend_dim_is_unlimited(m_filename,"time");
+  }
 
-  // Cycle through all fields
-  const auto& fp_precision = "real";
+  // Check variables are in the input file
   for (auto const& name : m_fields_names) {
-    // Determine the IO-decomp and construct a vector of dimension ids for this variable:
     const auto& layout = m_layouts.at(name);
+
+    // Determine the IO-decomp and construct a vector of dimension ids for this variable:
     auto vec_of_dims   = get_vec_of_dims(layout);
-    auto io_decomp_tag = get_io_decomp(layout);
 
-    for (size_t  i=0; i<vec_of_dims.size(); ++i) {
-      auto partitioned = m_io_grid->get_partitioned_dim_tag()==layout.tags()[i];
-      auto dimlen = partitioned ? m_io_grid->get_partitioned_dim_global_size() : layout.dims()[i];
-      scorpio::register_dimension(m_filename, vec_of_dims[i], vec_of_dims[i], dimlen, partitioned);
+    // Check that the variable is in the file.
+    EKAT_REQUIRE_MSG (scorpio::has_var(m_filename,name),
+        "Error! Input file does not store a required variable.\n"
+        " - filename: " + m_filename + "\n"
+        " - varname : " + name + "\n");
+
+    const auto& var = scorpio::get_var(m_filename,name);
+    EKAT_REQUIRE_MSG (var.dim_names()==vec_of_dims,
+        "Error! Layout mismatch for input file variable.\n"
+        " - filename: " + m_filename + "\n"
+        " - varname : " + name + "\n"
+        " - expected dims : " + ekat::join(vec_of_dims,",") + "\n"
+        " - dims from file: " + ekat::join(var.dim_names(),",") + "\n");
+
+    // Check that all dims for this var match the ones on file
+    for (int i=0; i<layout.rank(); ++i) {
+      const int file_len  = scorpio::get_dimlen(m_filename,vec_of_dims[i]);
+      const bool partitioned = m_io_grid->get_partitioned_dim_tag()==layout.tag(i);
+      const int eamxx_len = partitioned ? m_io_grid->get_partitioned_dim_global_size()
+                                        : layout.dim(i);
+      EKAT_REQUIRE_MSG (eamxx_len==file_len,
+          "Error! Dimension mismatch for input file variable.\n"
+        " - filename : " + m_filename + "\n"
+        " - varname  : " + name + "\n"
+        " - var dims : " + ekat::join(vec_of_dims,",") + "\n"
+        " - dim name : " + vec_of_dims[i] + "\n"
+        " - expected extent : " + std::to_string(eamxx_len) + "\n"
+        " - extent from file: " + std::to_string(file_len) + "\n");
     }
 
-    // TODO: Reverse order of dimensions to match flip between C++ -> F90 -> PIO,
-    // may need to delete this line when switching to full C++/C implementation.
-    std::reverse(vec_of_dims.begin(),vec_of_dims.end());
-
-    // Register the variable
-    // TODO  Need to change dtype to allow for other variables. 
-    //  Currently the field_manager only stores Real variables so it is not an issue,
-    //  but in the future if non-Real variables are added we will want to accomodate that.
-    //TODO: Should be able to simply inquire from the netCDF the dimensions for each variable.
-    scorpio::register_variable(m_filename, name, name,
-                               vec_of_dims, fp_precision, io_decomp_tag);
+    // Ensure that we can read the var using Real data type
+    scorpio::change_var_dtype (m_filename,name,"real");
   }
+
+  // Set decompositions for the variables
+  set_decompositions();
 }
 
 /* ---------------------------------------------------------- */
@@ -408,121 +417,56 @@ AtmosphereInput::get_vec_of_dims(const FieldLayout& layout)
   std::vector<std::string> dims_names;
   dims_names.reserve(layout.rank());
   for (int i=0; i<layout.rank(); ++i) {
-    dims_names.push_back(m_io_grid->get_dim_name(layout,i));
-    if (dims_names.back()=="dim") {
-      dims_names.back() += std::to_string(layout.dim(i));
-    }
-  }
+    const auto t = layout.tag(i);
+    std::string n = m_io_grid->has_special_tag_name(t)
+                  ? m_io_grid->get_special_tag_name(t)
+                  : layout.names()[i];
 
-  return dims_names;
-}
+    // If t==CMP, and the name stored in the layout is the default ("dim"),
+    // we append also the extent, to allow different vector dims in the file
+    n += n=="dim" ? std::to_string(layout.dim(i)) : "";
 
-/* ---------------------------------------------------------- */
-std::string AtmosphereInput::
-get_io_decomp(const FieldLayout& layout)
-{
-  std::string decomp_tag = "dt=real,grid-idx=" + std::to_string(m_io_grid->get_unique_grid_id()) + ",layout=";
-
-  std::vector<int> range(layout.rank());
-  std::iota(range.begin(),range.end(),0);
-  auto tag_and_dim = [&](int i) {
-    return m_io_grid->get_dim_name(layout,i) +
-           std::to_string(layout.dim(i));
-  };
-
-  decomp_tag += ekat::join (range, tag_and_dim,"-");
+    dims_names.push_back(n);
+  }
 
-  return decomp_tag;
+  return dims_names;
 }
 
 /* ---------------------------------------------------------- */
-void AtmosphereInput::set_degrees_of_freedom()
-{
-  // For each field, tell PIO the offset of each DOF to be read.
-  // Here, offset is meant in the *global* array in the nc file.
-  for (auto const& name : m_fields_names) {
-    auto var_dof = get_var_dof_offsets(m_layouts.at(name));
-    scorpio::set_dof(m_filename,name,var_dof.size(),var_dof.data());
-  }
-} // set_degrees_of_freedom
-
-/* ---------------------------------------------------------- */
-std::vector<scorpio::offset_t>
-AtmosphereInput::get_var_dof_offsets(const FieldLayout& layout)
+void AtmosphereInput::set_decompositions()
 {
   using namespace ShortFieldTagsNames;
 
-  // Precompute this *before* the early return, since it involves collectives.
-  // If one rank owns zero cols, and returns prematurely, the others will be left waiting.
-  AbstractGrid::gid_type min_gid;
-  if (layout.has_tag(COL) or layout.has_tag(EL)) {
-    min_gid = m_io_grid->get_global_min_dof_gid();
-  }
-
-  // It may be that this MPI ranks owns no chunk of the field
-  if (layout.size()==0) {
-    return {};
-  }
+  // First, check if any of the vars is indeed partitioned
+  const auto decomp_tag  = m_io_grid->get_partitioned_dim_tag();
 
-  std::vector<scorpio::offset_t> var_dof(layout.size());
-
-  // Gather the offsets of the dofs of this variable w.r.t. the *global* array.
-  // Since we order the global array based on dof gid, and we *assume* (we actually
-  // check this during set_grid) that the grid global gids are in the interval
-  // [gid_0, gid_0+num_global_dofs), the offset is simply given by
-  // (dof_gid-gid_0)*column_size (for partitioned arrays).
-  // NOTE: a "dof" in the grid object is not the same as a "dof" in scorpio.
-  //       For a SEGrid 3d vector field with (MPI local) layout (nelem,2,np,np,nlev),
-  //       scorpio sees nelem*2*np*np*nlev dofs, while the SE grid sees nelem*np*np dofs.
-  //       All we need to do in this routine is to compute the offset of all the entries
-  //       of the MPI-local array w.r.t. the global array. So long as the offsets are in
-  //       the same order as the corresponding entry in the data to be read/written, we're good.
-  auto dofs_h = m_io_grid->get_dofs_gids().get_view<const AbstractGrid::gid_type*,Host>();
-  if (layout.has_tag(COL)) {
-    const int num_cols = m_io_grid->get_num_local_dofs();
-
-    // Note: col_size might be *larger* than the number of vertical levels, or even smaller.
-    //       E.g., (ncols,2,nlevs), or (ncols,2) respectively.
-    scorpio::offset_t col_size = layout.size() / num_cols;
-
-    for (int icol=0; icol<num_cols; ++icol) {
-      // Get chunk of var_dof to fill
-      auto start = var_dof.begin()+icol*col_size;
-      auto end   = start+col_size;
-
-      // Compute start of the column offset, then fill column adding 1 to each entry
-      auto gid = dofs_h(icol);
-      scorpio::offset_t offset = (gid-min_gid)*col_size;
-      std::iota(start,end,offset);
+  bool has_decomposed_layouts = false;
+  for (const auto& it : m_layouts) {
+    if (it.second.has_tag(decomp_tag)) {
+      has_decomposed_layouts = true;
+      break;
     }
-  } else if (layout.has_tag(EL)) {
-    auto layout2d = m_io_grid->get_2d_scalar_layout();
-    const int num_my_elems = layout2d.dim(0);
-    const int ngp = layout2d.dim(1);
-    const int num_cols = num_my_elems*ngp*ngp;
-
-    // Note: col_size might be *larger* than the number of vertical levels, or even smaller.
-    //       E.g., (ncols,2,nlevs), or (ncols,2) respectively.
-    scorpio::offset_t col_size = layout.size() / num_cols;
-
-    for (int ie=0,icol=0; ie<num_my_elems; ++ie) {
-      for (int igp=0; igp<ngp; ++igp) {
-        for (int jgp=0; jgp<ngp; ++jgp,++icol) {
-          // Get chunk of var_dof to fill
-          auto start = var_dof.begin()+icol*col_size;
-          auto end   = start+col_size;
-
-          // Compute start of the column offset, then fill column adding 1 to each entry
-          auto gid = dofs_h(icol);
-          auto offset = (gid-min_gid)*col_size;
-          std::iota(start,end,offset);
-    }}}
-  } else {
-    // This field is *not* defined over columns, so it is not partitioned.
-    std::iota(var_dof.begin(),var_dof.end(),0);
+  }
+  if (not has_decomposed_layouts) {
+    // If none of the input vars are decomposed on this grid,
+    // then there's nothing to do here
+    return;
   } 
 
-  return var_dof; 
+  // Set the decomposition for the partitioned dimension
+  const int local_dim = m_io_grid->get_partitioned_dim_local_size();
+  std::string decomp_dim = m_io_grid->has_special_tag_name(decomp_tag)
+                         ? m_io_grid->get_special_tag_name(decomp_tag)
+                         : e2str(decomp_tag);
+
+  auto gids_f = m_io_grid->get_partitioned_dim_gids();
+  auto gids_h = gids_f.get_view<const AbstractGrid::gid_type*,Host>();
+  auto min_gid = m_io_grid->get_global_min_partitioned_dim_gid();
+  std::vector<scorpio::offset_t> offsets(local_dim);
+  for (int idof=0; idof<local_dim; ++idof) {
+    offsets[idof] = gids_h[idof] - min_gid;
+  }
+  scorpio::set_dim_decomp(m_filename,decomp_dim,offsets);
 }
 
 } // namespace scream
diff --git a/components/eamxx/src/share/io/scorpio_input.hpp b/components/eamxx/src/share/io/scorpio_input.hpp
index 811d5f6f771..801d224be83 100644
--- a/components/eamxx/src/share/io/scorpio_input.hpp
+++ b/components/eamxx/src/share/io/scorpio_input.hpp
@@ -77,8 +77,13 @@ class AtmosphereInput
                    const std::vector<Field>& fields,
                    const bool skip_grid_checks = false);
 
+  // Due to resource acquisition (in scorpio), avoid copies
+  AtmosphereInput (const AtmosphereInput&) = delete;
   ~AtmosphereInput ();
 
+  // Due to resource acquisition (in scorpio), avoid copies
+  AtmosphereInput& operator= (const AtmosphereInput&) = delete;
+
   // --- Methods --- //
   // Initialize the class for reading into FieldManager-owned fields.
   //  - params: input parameters (must contain at least "Filename")
@@ -123,12 +128,9 @@ class AtmosphereInput
                   const std::map<std::string,FieldLayout>&  layouts);
   void init_scorpio_structures ();
 
-  void register_variables();
-  void set_degrees_of_freedom();
+  void set_decompositions();
 
   std::vector<std::string> get_vec_of_dims (const FieldLayout& layout);
-  std::string get_io_decomp (const FieldLayout& layout);
-  std::vector<scorpio::offset_t> get_var_dof_offsets (const FieldLayout& layout);
 
   // Internal variables
   ekat::ParameterList   m_params;
diff --git a/components/eamxx/src/share/io/scorpio_output.cpp b/components/eamxx/src/share/io/scorpio_output.cpp
index 27eff12a419..b1ce7d3f326 100644
--- a/components/eamxx/src/share/io/scorpio_output.cpp
+++ b/components/eamxx/src/share/io/scorpio_output.cpp
@@ -613,7 +613,7 @@ run (const std::string& filename,
       auto view_host = m_host_views_1d.at(name);
       Kokkos::deep_copy (view_host,view_dev);
       auto func_start = std::chrono::steady_clock::now();
-      grid_write_data_array(filename,name,view_host.data(),view_host.size());
+      scorpio::write_var(filename,name,view_host.data());
       auto func_finish = std::chrono::steady_clock::now();
       auto duration_loc = std::chrono::duration_cast<std::chrono::milliseconds>(func_finish - func_start);
       duration_write += duration_loc.count();
@@ -627,7 +627,7 @@ run (const std::string& filename,
       auto view_host = m_host_views_1d.at(name);
       Kokkos::deep_copy (view_host,view_dev);
       auto func_start = std::chrono::steady_clock::now();
-      grid_write_data_array(filename,name,view_host.data(),view_host.size());
+      scorpio::write_var(filename,name,view_host.data());
       auto func_finish = std::chrono::steady_clock::now();
       auto duration_loc = std::chrono::duration_cast<std::chrono::milliseconds>(func_finish - func_start);
       duration_write += duration_loc.count();
@@ -754,31 +754,29 @@ void AtmosphereOutput::register_dimensions(const std::string& name)
   m_layouts.emplace(fid.name(),layout);
 
   // Now check taht all the dims of this field are already set to be registered.
+  const auto& tags = layout.tags();
+  const auto& dims = layout.dims();
   for (int i=0; i<layout.rank(); ++i) {
     // check tag against m_dims map.  If not in there, then add it.
-    const auto& tags = layout.tags();
-    const auto& dims = layout.dims();
-    auto tag_name = m_io_grid->get_dim_name(layout,i);
-    if (tag_name=="dim") {
-      tag_name += std::to_string(dims[i]);
-    }
-    auto tag_loc = m_dims.find(tag_name);
+    std::string tag_name = m_io_grid->has_special_tag_name(tags[i])
+                         ? m_io_grid->get_special_tag_name(tags[i])
+                         : layout.names()[i];
+
+    // If t==CMP, and the name stored in the layout is the default ("dim"),
+    // we append also the extent, to allow different vector dims in the file
+    tag_name += tag_name=="dim" ? std::to_string(dims[i]) : "";
+
     auto is_partitioned = m_io_grid->get_partitioned_dim_tag()==tags[i];
-    if (tag_loc == m_dims.end()) {
-      int tag_len = 0;
-      if(is_partitioned) {
-        // This is the dimension that is partitioned across ranks.
-        tag_len = m_io_grid->get_partitioned_dim_global_size();
-      } else {
-        tag_len = layout.dim(i);
-      }
-      m_dims[tag_name] = std::make_pair(tag_len,is_partitioned);
-    } else {
-      EKAT_REQUIRE_MSG(m_dims.at(tag_name).first==dims[i] or is_partitioned,
-        "Error! Dimension " + tag_name + " on field " + name + " has conflicting lengths. "
-        "If same name applies to different dims (e.g. PhysicsGLL and PhysicsPG2 define "
-        "\"ncol\" at different lengths), reset tag name for one of the grids.\n");
-    }
+    int dim_len = is_partitioned
+                ? m_io_grid->get_partitioned_dim_global_size()
+                : layout.dim(i);
+    auto it_bool = m_dims.emplace(tag_name,dim_len);
+    EKAT_REQUIRE_MSG(it_bool.second or it_bool.first->second==dim_len,
+      "Error! Dimension " + tag_name + " on field " + name + " has conflicting lengths.\n"
+      "  - old length: " + std::to_string(m_dims[tag_name]) + "\n"
+      "  - new length: " + std::to_string(dim_len) + "\n"
+      "If same name applies to different dims (e.g. PhysicsGLL and PhysicsPG2 define "
+      "\"ncol\" at different lengths), reset tag name for one of the grids.\n");
   }
 } // register_dimensions
 /* ---------------------------------------------------------- */
@@ -854,8 +852,16 @@ void AtmosphereOutput::set_avg_cnt_tracking(const std::string& name, const Field
   const auto tags = layout.tags();
   if (m_track_avg_cnt) {
     std::string avg_cnt_name = "avg_count" + avg_cnt_suffix;
-    for (int ii=0; ii<layout.rank(); ++ii) {
-      auto tag_name = m_io_grid->get_dim_name(layout,ii);
+    for (int i=0; i<layout.rank(); ++i) {
+      const auto t = layout.tag(i);
+      std::string tag_name = m_io_grid->has_special_tag_name(t)
+                           ? m_io_grid->get_special_tag_name(t)
+                           : layout.names()[i];
+
+      // If t==CMP, and the name stored in the layout is the default ("dim"),
+      // we append also the extent, to allow different vector dims in the file
+      tag_name += tag_name=="dim" ? std::to_string(layout.dim(i)) : "";
+
       avg_cnt_name += "_" + tag_name;
     }
     if (std::find(m_avg_cnt_names.begin(),m_avg_cnt_names.end(),avg_cnt_name)==m_avg_cnt_names.end()) {
@@ -903,7 +909,6 @@ register_variables(const std::string& filename,
                    const std::string& fp_precision,
                    const scorpio::FileMode mode)
 {
-  using namespace scorpio;
   using namespace ShortFieldTagsNames;
   using strvec_t = std::vector<std::string>;
 
@@ -913,39 +918,18 @@ register_variables(const std::string& filename,
       "  - supported values: float, single, double, real\n");
 
   // Helper lambdas
-  auto set_decomp_tag = [&](const FieldLayout& layout) {
-    std::string decomp_tag = "dt=real,grid-idx=" + std::to_string(m_io_grid->get_unique_grid_id()) + ",layout=";
-
-    std::vector<int> range(layout.rank());
-    std::iota(range.begin(),range.end(),0);
-    auto tag_and_dim = [&](int i) {
-      return m_io_grid->get_dim_name(layout,i) +
-             std::to_string(layout.dim(i));
-    };
-
-    decomp_tag += ekat::join (range, tag_and_dim,"-");
-
-    if (m_add_time_dim) {
-      decomp_tag += "-time";
-    }
-    return decomp_tag;
-  };
-
   auto set_vec_of_dims = [&](const FieldLayout& layout) {
     std::vector<std::string> vec_of_dims;
     for (int i=0; i<layout.rank(); ++i) {
-      auto tag_name = m_io_grid->get_dim_name(layout,i);
+      const auto t = layout.tag(i);
+      auto tag_name = m_io_grid->has_special_tag_name(t)
+                    ? m_io_grid->get_special_tag_name(t)
+                    : layout.names()[i];
       if (tag_name=="dim") {
         tag_name += std::to_string(layout.dim(i));
       }
       vec_of_dims.push_back(tag_name); // Add dimensions string to vector of dims.
     }
-    // TODO: Reverse order of dimensions to match flip between C++ -> F90 -> PIO,
-    // may need to delete this line when switching to fully C++/C implementation.
-    std::reverse(vec_of_dims.begin(),vec_of_dims.end());
-    if (m_add_time_dim) {
-      vec_of_dims.push_back("time");  //TODO: See the above comment on time.
-    }
     return vec_of_dims;
   };
 
@@ -960,7 +944,6 @@ register_variables(const std::string& filename,
     //   We use real here because the data type for the decomp is the one used
     // in the simulation and not the one used in the output file.
     const auto& layout = fid.get_layout();
-    const auto& io_decomp_tag = set_decomp_tag(layout);
     auto vec_of_dims   = set_vec_of_dims(layout);
     std::string units = fid.get_units().get_string();
 
@@ -971,20 +954,46 @@ register_variables(const std::string& filename,
     // Currently the field_manager only stores Real variables so it is not an issue,
     // but in the future if non-Real variables are added we will want to accomodate that.
 
-    register_variable(filename, name, longname, units, vec_of_dims,
-                      "real",fp_precision, io_decomp_tag);
+    if (mode==scorpio::FileMode::Append) {
+      // Simply check that the var is in the file, and has the right properties
+      EKAT_REQUIRE_MSG (scorpio::has_var(filename,name),
+          "Error! Cannot append, due to variable missing from the file.\n"
+          "  - filename : " + filename + "\n"
+          "  - varname  : " + name + "\n");
+      const auto& var = scorpio::get_var(filename,name);
+      EKAT_REQUIRE_MSG (var.dim_names()==vec_of_dims,
+          "Error! Cannot append, due to variable dimensions mismatch.\n"
+          "  - filename : " + filename + "\n"
+          "  - varname  : " + name + "\n"
+          "  - var dims : " + ekat::join(vec_of_dims,",") + "\n"
+          "  - var dims from file: " + ekat::join(var.dim_names(),",") + "\n");
+      EKAT_REQUIRE_MSG (var.units==units,
+          "Error! Cannot append, due to variable units mismatch.\n"
+          "  - filename : " + filename + "\n"
+          "  - varname  : " + name + "\n"
+          "  - var units: " + units + "\n"
+          "  - var units from file: " + var.units + "\n");
+      EKAT_REQUIRE_MSG (var.time_dep==m_add_time_dim,
+          "Error! Cannot append, due to time dependency mismatch.\n"
+          "  - filename : " + filename + "\n"
+          "  - varname  : " + name + "\n"
+          "  - var time dep: " + (m_add_time_dim ? "yes" : "no") + "\n"
+          "  - var time dep from file: " + (var.time_dep ? "yes" : "no") + "\n");
+    } else {
+      scorpio::define_var (filename, name, units, vec_of_dims,
+                            "real",fp_precision, m_add_time_dim);
+
+      scorpio::set_attribute(filename, name, "long_name", longname);
 
-    // Add any extra attributes for this variable
-    if (mode != FileMode::Append ) {
       // Add FillValue as an attribute of each variable
       // FillValue is a protected metadata, do not add it if it already existed
       if (fp_precision=="double" or
           (fp_precision=="real" and std::is_same<Real,double>::value)) {
         double fill_value = m_fill_value;
-        set_variable_metadata(filename, name, "_FillValue",fill_value);
+        scorpio::set_attribute(filename, name, "_FillValue",fill_value);
       } else {
         float fill_value = m_fill_value;
-        set_variable_metadata(filename, name, "_FillValue",fill_value);
+        scorpio::set_attribute(filename, name, "_FillValue",fill_value);
       }
 
       // If this is has subfields, add list of its children
@@ -1001,20 +1010,20 @@ register_variables(const std::string& filename,
         children_list.pop_back();
         children_list.pop_back();
         children_list += " ]";
-        set_variable_metadata(filename,name,"sub_fields",children_list);
+        scorpio::set_attribute(filename,name,"sub_fields",children_list);
       }
 
       // If tracking average count variables then add the name of the tracking variable for this variable
       if (m_track_avg_cnt) {
         const auto lookup = m_field_to_avg_cnt_map.at(name);
-        set_variable_metadata(filename,name,"averaging_count_tracker",lookup);
+        scorpio::set_attribute(filename,name,"averaging_count_tracker",lookup);
       }
 
       // Atm procs may have set some request for metadata.
       using stratts_t = std::map<std::string,std::string>;
       const auto& str_atts = field.get_header().get_extra_data<stratts_t>("io: string attributes");
       for (const auto& [att_name,att_val] : str_atts) {
-        set_variable_metadata(filename,name,att_name,att_val);
+        scorpio::set_attribute(filename,name,att_name,att_val);
       }
     }
   }
@@ -1022,10 +1031,9 @@ register_variables(const std::string& filename,
   if (m_track_avg_cnt) {
     for (const auto& name : m_avg_cnt_names) {
       const auto layout = m_layouts.at(name);
-      auto io_decomp_tag = set_decomp_tag(layout);
       auto vec_of_dims   = set_vec_of_dims(layout);
-      register_variable(filename, name, name, "unitless", vec_of_dims,
-                        "real",fp_precision, io_decomp_tag);
+      scorpio::define_var(filename, name, "unitless", vec_of_dims,
+                          "real",fp_precision, m_add_time_dim);
     }
   }
 } // register_variables
@@ -1112,48 +1120,71 @@ AtmosphereOutput::get_var_dof_offsets(const FieldLayout& layout)
 
   return var_dof;
 }
-/* ---------------------------------------------------------- */
-void AtmosphereOutput::set_degrees_of_freedom(const std::string& filename)
+
+void AtmosphereOutput::set_decompositions(const std::string& filename)
 {
-  using namespace scorpio;
   using namespace ShortFieldTagsNames;
 
-  // Cycle through all fields and set dof.
-  for (auto const& name : m_fields_names) {
-    auto field = get_field(name,"io");
-    const auto& fid  = field.get_header().get_identifier();
-    auto var_dof = get_var_dof_offsets(fid.get_layout());
-    set_dof(filename,name,var_dof.size(),var_dof.data());
+  // First, check if any of the vars is indeed partitioned
+  const auto decomp_tag  = m_io_grid->get_partitioned_dim_tag();
+
+  bool has_decomposed_layouts = false;
+  for (const auto& it : m_layouts) {
+    if (it.second.has_tag(decomp_tag)) {
+      has_decomposed_layouts = true;
+      break;
+    }
   }
-  // Cycle through the average count fields and set degrees of freedom
-  for (auto const& name : m_avg_cnt_names) {
-    const auto layout = m_layouts.at(name);
-    auto var_dof = get_var_dof_offsets(layout);
-    set_dof(filename,name,var_dof.size(),var_dof.data());
+  if (not has_decomposed_layouts) {
+    // If none of the vars are decomposed on this grid,
+    // then there's nothing to do here
+    return;
+  } 
+
+  // Set the decomposition for the partitioned dimension
+  const int local_dim = m_io_grid->get_partitioned_dim_local_size();
+  std::string decomp_dim = m_io_grid->has_special_tag_name(decomp_tag)
+                         ? m_io_grid->get_special_tag_name(decomp_tag)
+                         : e2str(decomp_tag);
+  auto gids_f = m_io_grid->get_partitioned_dim_gids();
+  auto gids_h = gids_f.get_view<const AbstractGrid::gid_type*,Host>();
+  auto min_gid = m_io_grid->get_global_min_partitioned_dim_gid();
+  std::vector<scorpio::offset_t> offsets(local_dim);
+  for (int idof=0; idof<local_dim; ++idof) {
+    offsets[idof] = gids_h[idof] - min_gid;
   }
+  scorpio::set_dim_decomp(filename,decomp_dim,offsets);
+}
 
-  /* TODO:
-   * Gather DOF info directly from grid manager
-  */
-} // set_degrees_of_freedom
-/* ---------------------------------------------------------- */
 void AtmosphereOutput::
 setup_output_file(const std::string& filename,
                   const std::string& fp_precision,
                   const scorpio::FileMode mode)
 {
-  using namespace scream::scorpio;
-
   // Register dimensions with netCDF file.
   for (auto it : m_dims) {
-    register_dimension(filename,it.first,it.first,it.second.first,it.second.second);
+    if (mode==scorpio::FileMode::Append) {
+      // Simply check that the dim is in the file, and has the right extent
+      EKAT_REQUIRE_MSG (scorpio::has_dim(filename,it.first),
+          "Error! Cannot append, due to missing dim in the file.\n"
+          "  - filename: " + filename + "\n"
+          "  - dimname : " + it.first + "\n");
+      EKAT_REQUIRE_MSG (scorpio::get_dimlen(filename,it.first)==it.second,
+          "Error! Cannot append, due to mismatch dim length.\n"
+          "  - filename: " + filename + "\n"
+          "  - dimname : " + it.first + "\n"
+          "  - old len : " + std::to_string(scorpio::get_dimlen(filename,it.first)) + "\n"
+          "  - new len : " + std::to_string(it.second) + "\n");
+    } else {
+      scorpio::define_dim(filename,it.first,it.second);
+    }
   }
 
   // Register variables with netCDF file.  Must come after dimensions are registered.
   register_variables(filename,fp_precision,mode);
 
   // Set the offsets of the local dofs in the global vector.
-  set_degrees_of_freedom(filename);
+  set_decompositions(filename);
 }
 /* ---------------------------------------------------------- */
 // This routine will evaluate the diagnostics stored in this
diff --git a/components/eamxx/src/share/io/scorpio_output.hpp b/components/eamxx/src/share/io/scorpio_output.hpp
index a07dd4678db..a4468123d1f 100644
--- a/components/eamxx/src/share/io/scorpio_output.hpp
+++ b/components/eamxx/src/share/io/scorpio_output.hpp
@@ -165,7 +165,7 @@ class AtmosphereOutput
 
   void register_dimensions(const std::string& name);
   void register_variables(const std::string& filename, const std::string& fp_precision, const scorpio::FileMode mode);
-  void set_degrees_of_freedom(const std::string& filename);
+  void set_decompositions(const std::string& filename);
   std::vector<scorpio::offset_t> get_var_dof_offsets (const FieldLayout& layout);
   void register_views();
   Field get_field(const std::string& name, const std::string& mode) const;
@@ -200,7 +200,7 @@ class AtmosphereOutput
   std::map<std::string,std::string>                     m_field_to_avg_cnt_map;
   std::map<std::string,std::string>                     m_field_to_avg_cnt_suffix;
   std::map<std::string,FieldLayout>                     m_layouts;
-  std::map<std::string,std::pair<int,bool>>             m_dims;
+  std::map<std::string,int>                             m_dims;
   std::map<std::string,std::shared_ptr<atm_diag_type>>  m_diagnostics;
   std::map<std::string,std::vector<std::string>>        m_diag_depends_on_diags;
   std::map<std::string,bool>                            m_diag_computed;
diff --git a/components/eamxx/src/share/io/scream_io_file_specs.hpp b/components/eamxx/src/share/io/scream_io_file_specs.hpp
index c80db36e094..ec0e2f50d79 100644
--- a/components/eamxx/src/share/io/scream_io_file_specs.hpp
+++ b/components/eamxx/src/share/io/scream_io_file_specs.hpp
@@ -1,6 +1,7 @@
 #ifndef SCREAM_IO_FILE_SPECS_HPP
 #define SCREAM_IO_FILE_SPECS_HPP
 
+#include "share/io/scream_scorpio_types.hpp"
 #include "share/io/scream_io_utils.hpp"
 #include "share/util/scream_time_stamp.hpp"
 
@@ -80,7 +81,7 @@ struct IOFileSpecs {
   bool is_open = false;
   std::string filename;
 
-  int iotype = 0;
+  scorpio::IOType iotype = scorpio::IOType::Invalid;
 
   // If positive, flush the output file every these many snapshots
   int flush_frequency = std::numeric_limits<int>::max();
diff --git a/components/eamxx/src/share/io/scream_io_utils.cpp b/components/eamxx/src/share/io/scream_io_utils.cpp
index 65e5bf030bd..4a0beb813b7 100644
--- a/components/eamxx/src/share/io/scream_io_utils.cpp
+++ b/components/eamxx/src/share/io/scream_io_utils.cpp
@@ -1,4 +1,6 @@
 #include "share/io/scream_io_utils.hpp"
+
+#include "share/io/scream_scorpio_interface.hpp"
 #include "share/util/scream_utils.hpp"
 
 #include <fstream>
@@ -70,4 +72,24 @@ std::string find_filename_in_rpointer (
   return filename;
 }
 
+void write_timestamp (const std::string& filename, const std::string& ts_name,
+                      const util::TimeStamp& ts, const bool write_nsteps)
+{
+  scorpio::set_attribute(filename,"GLOBAL",ts_name,ts.to_string());
+  if (write_nsteps) {
+    scorpio::set_attribute(filename,"GLOBAL",ts_name+"_nsteps",ts.get_num_steps());
+  }
+}
+
+util::TimeStamp read_timestamp (const std::string& filename,
+                                const std::string& ts_name,
+                                const bool read_nsteps)
+{
+  auto ts = util::str_to_time_stamp(scorpio::get_attribute<std::string>(filename,"GLOBAL",ts_name));
+  if (read_nsteps and scorpio::has_attribute(filename,"GLOBAL",ts_name+"_nsteps")) {
+    ts.set_num_steps(scorpio::get_attribute<int>(filename,"GLOBAL",ts_name+"_nsteps"));
+  }
+  return ts;
+}
+
 } // namespace scream
diff --git a/components/eamxx/src/share/io/scream_io_utils.hpp b/components/eamxx/src/share/io/scream_io_utils.hpp
index 6b50fbaba57..781b376858a 100644
--- a/components/eamxx/src/share/io/scream_io_utils.hpp
+++ b/components/eamxx/src/share/io/scream_io_utils.hpp
@@ -87,5 +87,12 @@ struct LongNames {
   
 };
 
+// Shortcut to write/read to/from YYYYMMDD/HHMMSS attributes in the NC file
+void write_timestamp (const std::string& filename, const std::string& ts_name,
+                      const util::TimeStamp& ts, const bool write_nsteps = false);
+util::TimeStamp read_timestamp (const std::string& filename,
+                                const std::string& ts_name,
+                                const bool read_nsteps = false);
+
 } // namespace scream
 #endif // SCREAM_IO_UTILS_HPP
diff --git a/components/eamxx/src/share/io/scream_output_manager.cpp b/components/eamxx/src/share/io/scream_output_manager.cpp
index 2458a4e95c8..35a830465bb 100644
--- a/components/eamxx/src/share/io/scream_output_manager.cpp
+++ b/components/eamxx/src/share/io/scream_output_manager.cpp
@@ -171,7 +171,7 @@ setup (const ekat::Comm& io_comm, const ekat::ParameterList& params,
       // From restart file, get the time of last write, as well as the current size of the avg sample
       m_output_control.last_write_ts = read_timestamp(rhist_file,"last_write",true);
       m_output_control.compute_next_write_ts();
-      m_output_control.nsamples_since_last_write = get_attribute<int>(rhist_file,"num_snapshots_since_last_write");
+      m_output_control.nsamples_since_last_write = get_attribute<int>(rhist_file,"GLOBAL","num_snapshots_since_last_write");
 
       if (m_avg_type!=OutputAvgType::Instant) {
         m_time_bnds.resize(2);
@@ -190,24 +190,23 @@ setup (const ekat::Comm& io_comm, const ekat::ParameterList& params,
 
       // We do NOT allow changing output specs across restart. If you do want to change
       // any of these, you MUST start a new output stream (e.g., setting 'Perform Restart: false')
-      auto old_freq = scorpio::get_attribute<int>(rhist_file,"averaging_frequency");
+      auto old_freq = scorpio::get_attribute<int>(rhist_file,"GLOBAL","averaging_frequency");
       EKAT_REQUIRE_MSG (old_freq == m_output_control.frequency,
           "Error! Cannot change frequency when performing history restart.\n"
           "  - old freq: " << old_freq << "\n"
           "  - new freq: " << m_output_control.frequency << "\n");
-      auto old_freq_units = scorpio::get_attribute<std::string>(rhist_file,"averaging_frequency_units");
+      auto old_freq_units = scorpio::get_attribute<std::string>(rhist_file,"GLOBAL","averaging_frequency_units");
       EKAT_REQUIRE_MSG (old_freq_units == m_output_control.frequency_units,
           "Error! Cannot change frequency units when performing history restart.\n"
           "  - old freq units: " << old_freq_units << "\n"
           "  - new freq units: " << m_output_control.frequency_units << "\n");
-      auto old_avg_type = scorpio::get_attribute<std::string>(rhist_file,"averaging_type");
+      auto old_avg_type = scorpio::get_attribute<std::string>(rhist_file,"GLOBAL","averaging_type");
       EKAT_REQUIRE_MSG (old_avg_type == e2str(m_avg_type),
           "Error! Cannot change avg type when performing history restart.\n"
           "  - old avg type: " << old_avg_type + "\n"
           "  - new avg type: " << e2str(m_avg_type) << "\n");
 
-
-      auto old_storage_type = scorpio::get_attribute<std::string>(rhist_file,"file_max_storage_type");
+      auto old_storage_type = scorpio::get_attribute<std::string>(rhist_file,"GLOBAL","file_max_storage_type");
       EKAT_REQUIRE_MSG (old_storage_type == e2str(m_output_file_specs.storage.type),
           "Error! Cannot change file storage type when performing history restart.\n"
           "  - old file_max_storage_type: " << old_storage_type << "\n"
@@ -216,7 +215,7 @@ setup (const ekat::Comm& io_comm, const ekat::ParameterList& params,
           "  Restart:\n"
           "    force_new_file: true\n");
       if (old_storage_type=="num_snapshot") {
-        auto old_max_snaps = scorpio::get_attribute<int>(rhist_file,"max_snapshots_per_file");
+        auto old_max_snaps = scorpio::get_attribute<int>(rhist_file,"GLOBAL","max_snapshots_per_file");
         EKAT_REQUIRE_MSG (old_max_snaps == m_output_file_specs.storage.max_snapshots_in_file,
             "Error! Cannot change max snapshots per file when performing history restart.\n"
             "  - old max snaps: " << old_max_snaps << "\n"
@@ -226,7 +225,7 @@ setup (const ekat::Comm& io_comm, const ekat::ParameterList& params,
             "    force_new_file: true\n");
       }
       std::string fp_precision = m_params.get<std::string>("Floating Point Precision");
-      auto old_fp_precision = scorpio::get_attribute<std::string>(rhist_file,"fp_precision");
+      auto old_fp_precision = scorpio::get_attribute<std::string>(rhist_file,"GLOBAL","fp_precision");
       EKAT_REQUIRE_MSG (old_fp_precision == fp_precision,
           "Error! Cannot change floating point precision when performing history restart.\n"
           "  - old fp precision: " << old_fp_precision << "\n"
@@ -234,12 +233,12 @@ setup (const ekat::Comm& io_comm, const ekat::ParameterList& params,
 
       // Check if the prev run wrote any output file (it may have not, if the restart was written
       // before the 1st output step). If there is a file, check if there's still room in it.
-      const auto& last_output_filename = get_attribute<std::string>(rhist_file,"last_output_filename");
+      const auto& last_output_filename = get_attribute<std::string>(rhist_file,"GLOBAL","last_output_filename");
       m_resume_output_file = last_output_filename!="" and not restart_pl.get("force_new_file",false);
       if (m_resume_output_file) {
         scorpio::register_file(last_output_filename,scorpio::Read,m_output_file_specs.iotype);
         int num_snaps = scorpio::get_dimlen(last_output_filename,"time");
-        scorpio::eam_pio_closefile(last_output_filename);
+        scorpio::release_file(last_output_filename);
 
         m_output_file_specs.filename = last_output_filename;
         m_output_file_specs.is_open = true;
@@ -249,7 +248,7 @@ setup (const ekat::Comm& io_comm, const ekat::ParameterList& params,
         // since those are a property of the run, not of the file.
         setup_file(m_output_file_specs,m_output_control);
       }
-      scorpio::eam_pio_closefile(rhist_file);
+      scorpio::release_file(rhist_file);
     }
   }
 
@@ -342,7 +341,7 @@ void OutputManager::run(const util::TimeStamp& timestamp)
       snapshot_start += m_time_bnds[0];
     }
     if (not filespecs.storage.snapshot_fits(snapshot_start)) {
-      eam_pio_closefile(filespecs.filename);
+      release_file(filespecs.filename);
       filespecs.close();
     }
 
@@ -388,14 +387,14 @@ void OutputManager::run(const util::TimeStamp& timestamp)
     setup_output_file(m_output_control,m_output_file_specs);
 
     // Update time (must be done _before_ writing fields)
-    pio_update_time(m_output_file_specs.filename,timestamp.days_from(m_case_t0));
+    update_time(m_output_file_specs.filename,timestamp.days_from(m_case_t0));
   }
   if (is_checkpoint_step) {
     setup_output_file(m_checkpoint_control,m_checkpoint_file_specs);
 
     if (is_full_checkpoint_step) {
       // Update time (must be done _before_ writing fields)
-      pio_update_time(m_checkpoint_file_specs.filename,timestamp.days_from(m_case_t0));
+      update_time(m_checkpoint_file_specs.filename,timestamp.days_from(m_case_t0));
     }
   }
   stop_timer(timer_root+"::get_new_file");
@@ -436,44 +435,63 @@ void OutputManager::run(const util::TimeStamp& timestamp)
 
       if (m_is_model_restart_output) {
         // Only write nsteps on model restart
-        set_attribute(filespecs.filename,"nsteps",timestamp.get_num_steps());
+        set_attribute(filespecs.filename,"GLOBAL","nsteps",timestamp.get_num_steps());
       } else {
         if (filespecs.ftype==FileType::HistoryRestart) {
           // Update the date of last write and sample size
-          scorpio::write_timestamp (filespecs.filename,"last_write",m_output_control.last_write_ts,true);
-          scorpio::set_attribute (filespecs.filename,"last_output_filename",m_output_file_specs.filename);
-          scorpio::set_attribute (filespecs.filename,"num_snapshots_since_last_write",m_output_control.nsamples_since_last_write);
+          write_timestamp (filespecs.filename,"last_write",m_output_control.last_write_ts,true);
+          scorpio::set_attribute (filespecs.filename,"GLOBAL","last_output_filename",m_output_file_specs.filename);
+          scorpio::set_attribute (filespecs.filename,"GLOBAL","num_snapshots_since_last_write",m_output_control.nsamples_since_last_write);
         }
         // Write these in both output and rhist file. The former, b/c we need these info when we postprocess
         // output, and the latter b/c we want to make sure these params don't change across restarts
-        set_attribute(filespecs.filename,"averaging_type",e2str(m_avg_type));
-        set_attribute(filespecs.filename,"averaging_frequency_units",m_output_control.frequency_units);
-        set_attribute(filespecs.filename,"averaging_frequency",m_output_control.frequency);
-        set_attribute(filespecs.filename,"file_max_storage_type",e2str(m_output_file_specs.storage.type));
+        set_attribute(filespecs.filename,"GLOBAL","averaging_type",e2str(m_avg_type));
+        set_attribute(filespecs.filename,"GLOBAL","averaging_frequency_units",m_output_control.frequency_units);
+        set_attribute(filespecs.filename,"GLOBAL","averaging_frequency",m_output_control.frequency);
+        set_attribute(filespecs.filename,"GLOBAL","file_max_storage_type",e2str(m_output_file_specs.storage.type));
         if (m_output_file_specs.storage.type==NumSnaps) {
-          set_attribute(filespecs.filename,"max_snapshots_per_file",m_output_file_specs.storage.max_snapshots_in_file);
+          set_attribute(filespecs.filename,"GLOBAL","max_snapshots_per_file",m_output_file_specs.storage.max_snapshots_in_file);
         }
         const auto& fp_precision = m_params.get<std::string>("Floating Point Precision");
-        set_attribute(filespecs.filename,"fp_precision",fp_precision);
+        set_attribute(filespecs.filename,"GLOBAL","fp_precision",fp_precision);
       }
 
       // Write all stored globals
       for (const auto& it : m_globals) {
         const auto& name = it.first;
         const auto& any = it.second;
-        set_any_attribute(filespecs.filename,name,any);
+        if (any.isType<int>()) {
+          set_attribute(filespecs.filename,"GLOBAL",name,ekat::any_cast<int>(any));
+        } else if (any.isType<std::int64_t>()) {
+          set_attribute(filespecs.filename,"GLOBAL",name,ekat::any_cast<std::int64_t>(any));
+        } else if (any.isType<float>()) {
+          set_attribute(filespecs.filename,"GLOBAL",name,ekat::any_cast<float>(any));
+        } else if (any.isType<double>()) {
+          set_attribute(filespecs.filename,"GLOBAL",name,ekat::any_cast<double>(any));
+        } else if (any.isType<std::string>()) {
+          set_attribute(filespecs.filename,"GLOBAL",name,ekat::any_cast<std::string>(any));
+        } else {
+          EKAT_ERROR_MSG (
+              "Error! Invalid concrete type for IO global.\n"
+              " - global name: " + it.first + "\n"
+              " - type id    : " + any.content().type().name() + "\n");
+        }
       }
 
       // We're adding one snapshot to the file
       filespecs.storage.update_storage(timestamp);
 
-      if (m_time_bnds.size()>0) {
-        scorpio::grid_write_data_array(filespecs.filename, "time_bnds", m_time_bnds.data(), 2);
+      // NOTE: for checkpoint files, unless we write restart data, we did not update time,
+      //       which means we cannot write any variable (the check var.num_records==time.length
+      //       would fail)
+      if (m_time_bnds.size()>0 and
+          (filespecs.ftype!=FileType::HistoryRestart or is_full_checkpoint_step)) {
+        scorpio::write_var(filespecs.filename, "time_bnds", m_time_bnds.data());
       }
 
       // Check if we need to flush the output file
       if (filespecs.file_needs_flush()) {
-        eam_flush_file (filespecs.filename);
+        flush_file (filespecs.filename);
       }
     };
 
@@ -500,10 +518,10 @@ void OutputManager::finalize()
 {
   // Close any output file still open
   if (m_output_file_specs.is_open) {
-    scorpio::eam_pio_closefile (m_output_file_specs.filename);
+    scorpio::release_file (m_output_file_specs.filename);
   }
   if (m_checkpoint_file_specs.is_open) {
-    scorpio::eam_pio_closefile (m_checkpoint_file_specs.filename);
+    scorpio::release_file (m_checkpoint_file_specs.filename);
   }
 
   // Swapping with an empty mgr is the easiest way to cleanup.
@@ -691,8 +709,6 @@ void OutputManager::
 setup_file (      IOFileSpecs& filespecs,
             const IOControl& control)
 {
-  using namespace scorpio;
-
   const bool is_checkpoint_step = &control==&m_checkpoint_control;
 
   std::string fp_precision = is_checkpoint_step
@@ -701,59 +717,47 @@ setup_file (      IOFileSpecs& filespecs,
 
   const auto& filename = filespecs.filename;
   // Register new netCDF file for output. Check if we need to append to an existing file
-  auto mode = m_resume_output_file ? Append : Write;
-  register_file(filename,mode,filespecs.iotype);
+  auto mode = m_resume_output_file ? scorpio::Append : scorpio::Write;
+  scorpio::register_file(filename,mode,filespecs.iotype);
   if (m_resume_output_file) {
-    eam_pio_redef(filename);
-  }
+    scorpio::redef(filename);
+  } else {
+    // Register time (and possibly time_bnds) var(s)
+    auto time_units="days since " + m_case_t0.get_date_string() + " " + m_case_t0.get_time_string();
+    scorpio::define_time(filename,time_units,"time");
 
-  // Note: length=0 is how scorpio recognizes that this is an 'unlimited' dimension, which
-  // allows to write as many timesnaps as we desire.
-  register_dimension(filename,"time","time",0,false);
+    scorpio::define_var(filename,"time",time_units,{}, "double", "double",true);
+    if (use_leap_year()) {
+      scorpio::set_attribute (filename,"time","calendar","gregorian");
+    } else {
+      scorpio::set_attribute (filename,"time","calendar","noleap");
+    }
 
-  // Register time (and possibly time_bnds) var(s)
-  auto time_units="days since " + m_case_t0.get_date_string() + " " + m_case_t0.get_time_string();
-  register_variable(filename,"time","time",time_units,{"time"}, "double", "double","time");
-  if (use_leap_year()) {
-    set_variable_metadata (filename,"time","calendar","gregorian");
-  } else {
-    set_variable_metadata (filename,"time","calendar","noleap");
-  }
-  if (m_avg_type!=OutputAvgType::Instant) {
-    // First, ensure a 'dim2' dimension with len=2 is registered.
-    register_dimension(filename,"dim2","dim2",2,false);
-    register_variable(filename,"time_bnds","time_bnds",time_units,{"dim2","time"},"double","double","time-dim2");
-    
-    // Make it clear how the time_bnds should be interpreted
-    set_variable_metadata(filename,"time_bnds","note","right endpoint accumulation");
-
-    // I'm not sure what's the point of this, but CF conventions seem to require it
-    set_variable_metadata (filename,"time","bounds","time_bnds");
-  }
+    if (m_avg_type!=OutputAvgType::Instant) {
+      // First, ensure a 'dim2' dimension with len=2 is registered.
+      scorpio::define_dim(filename,"dim2",2);
+      scorpio::define_var(filename,"time_bnds",time_units,{"dim2"},"double","double",true);
+
+      // Make it clear how the time_bnds should be interpreted
+      scorpio::set_attribute<std::string> (filename,"time_bnds","note","right endpoint accumulation");
+
+      // I'm not sure what's the point of this, but CF conventions seem to require it
+      scorpio::set_attribute<std::string> (filename,"time","bounds","time_bnds");
+    }
 
-  if (not m_resume_output_file) {
-    // Finish the definition phase for this file.
     write_timestamp(filename,"case_t0",m_case_t0);
     write_timestamp(filename,"run_t0",m_run_t0);
-    set_attribute(filename,"averaging_type",e2str(m_avg_type));
-    set_attribute(filename,"averaging_frequency_units",m_output_control.frequency_units);
-    set_attribute(filename,"averaging_frequency",m_output_control.frequency);
-    set_attribute(filespecs.filename,"file_max_storage_type",e2str(m_output_file_specs.storage.type));
+    scorpio::set_attribute(filename,"GLOBAL","averaging_type",e2str(m_avg_type));
+    scorpio::set_attribute(filename,"GLOBAL","averaging_frequency_units",m_output_control.frequency_units);
+    scorpio::set_attribute(filename,"GLOBAL","averaging_frequency",m_output_control.frequency);
+    scorpio::set_attribute(filespecs.filename,"GLOBAL","file_max_storage_type",e2str(m_output_file_specs.storage.type));
     if (m_output_file_specs.storage.type==NumSnaps) {
-      set_attribute(filename,"max_snapshots_per_file",m_output_file_specs.storage.max_snapshots_in_file);
+      scorpio::set_attribute(filename,"GLOBAL","max_snapshots_per_file",m_output_file_specs.storage.max_snapshots_in_file);
     }
-    set_attribute(filename,"fp_precision",fp_precision);
+    scorpio::set_attribute(filename,"GLOBAL","fp_precision",fp_precision);
     set_file_header(filespecs);
   }
 
-  // Set degree of freedom for "time" and "time_bnds"
-  scorpio::offset_t time_dof[1] = {0};
-  set_dof(filename,"time",1,time_dof);
-  if (m_avg_type!=OutputAvgType::Instant) {
-    scorpio::offset_t time_bnds_dofs[2] = {0,1};
-    set_dof(filename,"time_bnds",2,time_bnds_dofs);
-  }
-
   // Make all output streams register their dims/vars
   for (auto& it : m_output_streams) {
     it->setup_output_file(filename,fp_precision,mode);
@@ -767,10 +771,7 @@ setup_file (      IOFileSpecs& filespecs,
     }
   }
 
-  // When resuming a file, PIO opens it in data mode.
-  // NOTE: all the above register_dimension/register_variable are already checking that
-  //       the dims/vars are already in the file (we don't allow adding dims/vars)
-  eam_pio_enddef (filename);
+  scorpio::enddef (filename);
 
   if (m_save_grid_data and not filespecs.is_restart_file() and not m_resume_output_file) {
     // Immediately run the geo data streams
@@ -786,11 +787,6 @@ setup_file (      IOFileSpecs& filespecs,
 /*===============================================================================================*/
 void OutputManager::set_file_header(const IOFileSpecs& file_specs)
 {
-  using namespace scorpio;
-
-  // TODO: All attributes marked TODO below need to be set.  Hopefully by a universal value that reflects
-  // what the attribute is.  For example, git-hash should be the git-hash associated with this version of
-  // the code at build time for this executable.
   auto& p = m_params.sublist("provenance");
   auto now = std::chrono::system_clock::now();
   std::time_t time = std::chrono::system_clock::to_time_t(now);
@@ -801,20 +797,24 @@ void OutputManager::set_file_header(const IOFileSpecs& file_specs)
 
   const auto& filename = file_specs.filename;
 
-  set_attribute<std::string>(filename,"case",p.get<std::string>("caseid","NONE"));
-  set_attribute<std::string>(filename,"source","E3SM Atmosphere Model (EAMxx)");
-  set_attribute<std::string>(filename,"eamxx_version",EAMXX_VERSION);
-  set_attribute<std::string>(filename,"git_version",p.get<std::string>("git_version",EAMXX_GIT_VERSION));
-  set_attribute<std::string>(filename,"hostname",p.get<std::string>("hostname","UNKNOWN"));
-  set_attribute<std::string>(filename,"username",p.get<std::string>("username","UNKNOWN"));
-  set_attribute<std::string>(filename,"atm_initial_conditions_file",p.get<std::string>("initial_conditions_file","NONE"));
-  set_attribute<std::string>(filename,"topography_file",p.get<std::string>("topography_file","NONE"));
-  set_attribute<std::string>(filename,"contact","e3sm-data-support@llnl.gov");
-  set_attribute<std::string>(filename,"institution_id","E3SM-Projet");
-  set_attribute<std::string>(filename,"realm","atmos");
-  set_attribute<std::string>(filename,"history",ts_str);
-  set_attribute<std::string>(filename,"Conventions","CF-1.8");
-  set_attribute<std::string>(filename,"product",e2str(file_specs.ftype));
+  auto set_str_att = [&](const std::string& name, const std::string& val) {
+    scorpio::set_attribute(filename,"GLOBAL",name,val);
+  };
+
+  set_str_att("case",p.get<std::string>("caseid","NONE"));
+  set_str_att("source","E3SM Atmosphere Model (EAMxx)");
+  set_str_att("eamxx_version",EAMXX_VERSION);
+  set_str_att("git_version",p.get<std::string>("git_version",EAMXX_GIT_VERSION));
+  set_str_att("hostname",p.get<std::string>("hostname","UNKNOWN"));
+  set_str_att("username",p.get<std::string>("username","UNKNOWN"));
+  set_str_att("atm_initial_conditions_file",p.get<std::string>("initial_conditions_file","NONE"));
+  set_str_att("topography_file",p.get<std::string>("topography_file","NONE"));
+  set_str_att("contact","e3sm-data-support@llnl.gov");
+  set_str_att("institution_id","E3SM-Project");
+  set_str_att("realm","atmos");
+  set_str_att("history",ts_str);
+  set_str_att("Conventions","CF-1.8");
+  set_str_att("product",e2str(file_specs.ftype));
 }
 /*===============================================================================================*/
 void OutputManager::
diff --git a/components/eamxx/src/share/io/scream_scorpio_interface.F90 b/components/eamxx/src/share/io/scream_scorpio_interface.F90
deleted file mode 100644
index bfd9ad68f2d..00000000000
--- a/components/eamxx/src/share/io/scream_scorpio_interface.F90
+++ /dev/null
@@ -1,1889 +0,0 @@
-module scream_scorpio_interface
-
-!==============================================================================!
-! This module handles the Fortran interface to the PIO library of input/output
-! subroutines.  The essential set of steps to enable and use PIO for creating
-! output are as follows:
-!                                  OUTPUT
-! Initialization:
-! 1) Gather the pio_subsystem and pio_iotype information for the EAM component
-! as assigned by the component coupler.
-!    This is accomplished during eam_init_pio_1 by calling
-!    'eam_init_pio_subsystem'
-! 2) For each output file "create" a file in PIO and record the unique file
-! descriptor.
-!    This is accomplished during the eam_init_pio_1 by calling
-!    'eam_pio_createfile'
-! 3) For each output file define the "header" information, which is essentially
-! a set of metadata strings that describe the output file.
-!    This is accomplished during eam_init_pio_1 by calling 'eam_pio_createHeader'
-! 4) Define all of the dimensions that variables in this file will be defined
-! on.  Examples would time, lat, lon, vertical coordinate, # of consituents,
-! etc.
-!    This is accomplished during 'register_dimension' by which calls 'PIO_def_dim'
-! 5) Define all of the variables that will be written to this file.  This
-! includes any dimension that should also be defined as a variable, such as lat,
-! lon, time.
-!    This is accomplished during 'register_variable' which calls to 'PIO_def_var'
-! 6) Determine the unique PIO identifiers for each domain decomposition.  This
-! is essentially a decomposition of what will be written to the file, multiple
-! variables can have the same decomposition.  Every arrangement of dimensions
-! requires a pio decomposition.
-!    This is accomplished during 'register_variable' by calling
-!    'PIO_initdecomp'
-! 7) Close the PIO file definition step.  In other words, tell PIO that all of
-! the dimensions, variables and decompositions associated with this output have
-! been defined and no new ones will be added.
-!    This is accomplished during eam_pio_enddef by calling 'PIO_enddef' on all
-!    defined files.
-!
-! Writing Output:
-!
-! Finalization:
-!==============================================================================!
-
-  !------------
-  use pio_types,    only: iosystem_desc_t, file_desc_t, var_desc_t, io_desc_t, &
-                          pio_noerr, pio_global, &
-                          PIO_int, PIO_real, PIO_double, PIO_float=>PIO_real,&
-                          pio_iotype_netcdf, pio_iotype_pnetcdf, pio_iotype_adios
-  use pio_kinds,    only: PIO_OFFSET_KIND
-
-  use mpi, only: mpi_abort, mpi_comm_size, mpi_comm_rank
-
-  use iso_c_binding, only: c_float, c_double, c_int
-  implicit none
-  save
-
-  public :: &
-            lookup_pio_atm_file,         & ! Checks if a pio file is present
-            eam_pio_closefile,           & ! Close a specfic pio file.
-            eam_pio_flush_file,          & ! Flushes I/O buffers to file
-            eam_pio_enddef,              & ! Ends define mode phase, enters data mode phase
-            eam_pio_redef,               & ! Pause data mode phase, re-enter define mode phase
-            eam_init_pio_subsystem,      & ! Gather pio specific data from the component coupler
-            is_eam_pio_subsystem_inited, & ! Query whether the pio subsystem is inited already
-            eam_pio_finalize,            & ! Run any final PIO commands
-            register_file,               & ! Creates/opens a pio input/output file
-            register_variable,           & ! Register a variable with a particular pio output file
-            set_variable_metadata_char,  & ! Sets a variable metadata (char data)
-            set_variable_metadata_float, & ! Sets a variable metadata (float data)
-            set_variable_metadata_double,& ! Sets a variable metadata (double data)
-            get_variable_metadata_char,  & ! Gets a variable metadata (char data)
-            get_variable_metadata_float, & ! Gets a variable metadata (float data)
-            get_variable_metadata_double,& ! Gets a variable metadata (double data)
-            register_dimension,          & ! Register a dimension with a particular pio output file
-            set_decomp,                  & ! Set the pio decomposition for all variables in file.
-            set_dof,                     & ! Set the pio dof decomposition for specific variable in file.
-            grid_write_data_array,       & ! Write gridded data to a pio managed netCDF file
-            grid_read_data_array,        & ! Read gridded data from a pio managed netCDF file
-            eam_update_time,             & ! Update the timestamp (i.e. time variable) for a given pio netCDF file
-            read_time_at_index             ! Returns the time stamp for a specific time index
-
-  private :: errorHandle, get_coord, is_read, is_write, is_append, scream_iotype_to_pio_iotype
-
-  ! Universal PIO variables for the module
-  integer               :: atm_mpicom
-  integer               :: pio_iotype
-  type(iosystem_desc_t), pointer, public :: pio_subsystem
-  integer               :: pio_rearranger
-  integer               :: pio_mode
-  integer               :: time_dimid = -1
-
-  ! TYPES to handle history coordinates and files
-  integer,parameter :: max_hcoordname_len = 16
-  integer,parameter :: max_chars = 256
-  integer,parameter :: max_hvarname_len = 64
-  integer,parameter :: max_hvar_dimlen  = 5
-  integer,parameter :: file_purpose_not_set  = 0  ! Not set (to catch uninited stuff errors)
-  integer,parameter :: file_purpose_in  = 1       ! Read
-  integer,parameter :: file_purpose_app = 2       ! Write (append if file exists)
-  integer,parameter :: file_purpose_out = 4       ! Write (replace if file exists)
-
-  type, public :: hist_coord_t
-    character(len=max_hcoordname_len) :: name = ''  ! coordinate name
-    integer                  :: dimid               ! Unique PIO Id for this dimension
-    character(len=max_chars) :: long_name = ''      ! 'long_name' attribute
-    character(len=max_chars) :: units = ''          ! 'units' attribute
-    logical                  :: is_partitioned      ! whether the dimension is partitioned across ranks
-    logical                  :: is_time_dim         ! whether the dimension is the time (unlimited) dim
-  end type hist_coord_t
-
-  type, public :: hist_var_t
-    character(len=max_hvarname_len) :: name   ! coordinate name
-    character(len=max_chars) :: long_name     ! 'long_name' attribute
-    character(len=max_chars) :: pio_decomp_tag ! PIO decomposition label used by this variable.
-    character(len=max_chars) :: units         ! 'units' attribute
-    type(var_desc_t) :: piovar                ! netCDF variable ID
-    integer          :: dtype                 ! data type used to pass data to read/write routines
-    integer          :: nc_dtype              ! data type used in the netcdf files
-    integer          :: numdims               ! Number of dimensions in out field
-    type(io_desc_t), pointer  :: iodesc => NULL()     ! PIO decomp associated with this variable
-    type(iodesc_list_t), pointer  :: iodesc_list ! PIO decomp list with metadata about PIO decomp
-    integer(kind=pio_offset_kind), allocatable :: compdof(:)        ! Global locations in output array for this process
-    integer, allocatable :: dimid(:)          ! array of PIO dimension id's for this variable
-    integer, allocatable :: dimlen(:)         ! array of PIO dimension lengths for this variable
-    logical              :: has_t_dim         ! true, if variable has a time dimension
-    logical              :: is_set = .false.  ! Safety measure to ensure a deallocated hist_var_t is never used
-    logical              :: is_partitioned    ! Whether at least one of the dims is partitioned
-  end type hist_var_t
-
-  ! The iodesc_list allows us to cache existing PIO decompositions
-  ! The tag needs the dim lengths, the dtype and map id (+ optional permutation)
-  ! Define a recursive structure because we do not know ahead of time how many
-  ! decompositions will be require
-  type iodesc_list_t
-    character(max_chars)         :: tag              ! Unique tag associated with this decomposition
-    type(io_desc_t),     pointer :: iodesc => NULL() ! PIO - decomposition
-    type(iodesc_list_t), pointer :: next => NULL()   ! Needed for recursive definition, the next list
-    type(iodesc_list_t), pointer :: prev => NULL()   ! Needed for recursive definition, the list that points to this one
-    logical                      :: iodesc_set = .false.
-    integer                      :: num_customers = 0 ! Track the number of currently active variables that use this pio decomposition
-    integer                      :: location = 0      ! where am in the recursive list
-  end type iodesc_list_t
-
-  ! Define the first iodesc_list_t
-  type(iodesc_list_t), pointer :: iodesc_list_top
-!----------------------------------------------------------------------
-  type hist_coord_list_t
-    type(hist_coord_t),      pointer :: coord => NULL() ! Pointer to a history dimension structure
-    type(hist_coord_list_t), pointer :: next => NULL()  ! Needed for recursive definition
-  end type hist_coord_list_t
-!----------------------------------------------------------------------
-  type hist_var_list_t
-    type(hist_var_t),      pointer :: var => NULL()  ! Pointer to a history variable structure
-    type(hist_var_list_t), pointer :: next => NULL() ! Needed for recursive definition
-  end type hist_var_list_t
-!----------------------------------------------------------------------
-  type pio_file_list_t
-    type(pio_atm_file_t),  pointer :: pio_file => NULL() ! Pointer to an atm. pio file
-    type(pio_file_list_t), pointer :: next => NULL()     ! Needed for recursive definition
-    type(pio_file_list_t), pointer :: prev => NULL()     ! A doubly-linked list is easier to handle
-  end type pio_file_list_t
-  ! Define the first pio_file_list
-  type(pio_file_list_t), pointer :: pio_file_list_front
-  type(pio_file_list_t), pointer :: pio_file_list_back
-
-!----------------------------------------------------------------------
-  type, public :: pio_atm_file_t
-    character(len=max_chars) :: filename = ""
-    integer :: purpose = file_purpose_not_set       ! Input or Output file
-    type(file_desc_t)        :: pioFileDesc         ! Contains data identifying the file.
-    type(hist_coord_list_t)  :: coord_list_top      ! Recursive list of variables
-    type(hist_var_list_t)    :: var_list_top        ! Recursive list of variables
-    integer                  :: numRecs             ! Number of history records on file
-    logical                  :: is_enddef = .false. ! Whether definition phase is open
-    integer                  :: num_customers       ! The number of customer that requested to open the file.
-  end type pio_atm_file_t
-
-!----------------------------------------------------------------------
-  interface grid_read_data_array
-    module procedure grid_read_darray_double
-    module procedure grid_read_darray_float
-    module procedure grid_read_darray_int
-  end interface grid_read_data_array
-!----------------------------------------------------------------------
-  interface grid_write_data_array
-    module procedure grid_write_darray_float
-    module procedure grid_write_darray_double
-    module procedure grid_write_darray_int
-  end interface
-!----------------------------------------------------------------------
-
-contains
-!=====================================================================!
-  ! Register a PIO file to be used for input/output operations.
-  ! If file is already open, ensures file_purpose matches the current one
-  subroutine register_file(filename,file_purpose,iotype)
-
-    character(len=*), intent(in) :: filename
-    integer, intent(in)          :: file_purpose
-    integer, intent(in)          :: iotype
-
-    type(pio_atm_file_t), pointer :: pio_file
-
-    if (.not.associated(pio_subsystem)) then
-      call errorHandle("PIO ERROR: local pio_subsystem pointer has not been established yet.",-999)
-    endif
-
-    call get_pio_atm_file(filename,pio_file,file_purpose,iotype)
-  end subroutine register_file
-!=====================================================================!
-  ! Mandatory call to finish the variable and dimension definition phase
-  ! of a new PIO file.  Once this routine is called it is not possible
-  ! to add new dimensions or variables to the file.
-  subroutine eam_pio_enddef(filename)
-    use pio, only: PIO_enddef
-
-    character(len=*), intent(in) :: filename
-
-    type(pio_atm_file_t), pointer :: current_atm_file
-    integer                       :: ierr
-    logical                       :: found
-
-    call lookup_pio_atm_file(filename,current_atm_file,found)
-    if (.not.found) then
-      call errorHandle("PIO ERROR: error running enddef on file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    ! It could happen that we are running a test, with an input file opening the
-    ! same file that an output stream just wrote. In this case, the def phase ended
-    ! during the output setup.
-    if (.not. current_atm_file%is_enddef) then
-      ! Gather the pio decomposition for all variables in this file, and assign them pointers.
-      call set_decomp(trim(filename))
-      ! Officially close the definition step for this file.
-      ierr = PIO_enddef(current_atm_file%pioFileDesc)
-      call errorHandle("PIO ERROR: issue arose with PIO_enddef for file"//trim(current_atm_file%filename),ierr)
-      current_atm_file%is_enddef = .true.
-    endif
-
-  end subroutine eam_pio_enddef
-!=====================================================================!
-  ! Mandatory call to finish the variable and dimension definition phase
-  ! of a new PIO file.  Once this routine is called it is not possible
-  ! to add new dimensions or variables to the file.
-  subroutine eam_pio_redef(filename)
-    use pio, only: pio_redef
-
-    character(len=*), intent(in) :: filename
-
-    type(pio_atm_file_t), pointer :: current_atm_file
-    integer                       :: ierr
-    logical                       :: found
-
-    call lookup_pio_atm_file(filename,current_atm_file,found)
-    if (.not.found) then
-      call errorHandle("PIO ERROR: error running redef on file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    ! It could happen that we are running a test, with an input file opening the
-    ! same file that an output stream just wrote. In this case, the def phase ended
-    ! during the output setup.
-    if (current_atm_file%is_enddef) then
-      ! Re-open define phase
-      ierr = PIO_redef(current_atm_file%pioFileDesc)
-      call errorHandle("PIO ERROR: issue arose with PIO_redef for file"//trim(current_atm_file%filename),ierr)
-      current_atm_file%is_enddef = .false.
-    endif
-
-  end subroutine eam_pio_redef
-!=====================================================================!
-  ! Register a dimension with a specific pio output file.  Mandatory inputs
-  ! include:
-  ! filename:  Name of file to add the dimension to.
-  ! shortname: Short name descriptor for this dimension.  This will be
-  !            name to find the dimension in the netCDF file.
-  ! longname:  A longer character string with a more descriptive name of
-  !            the dimension.
-  ! length:    The dimension length (must be >=0).  Choosing 0 marks the
-  !            dimensions as having "unlimited" length which is used for
-  !            dimensions such as time.
-  ! NOTE: if the file is in Read or Append mode, we are supposed to have already checked
-  !       that the specs match the ones in the file during the C++ wrapper functions
-  subroutine register_dimension(filename,shortname,longname,length,is_partitioned)
-    use pio_types, only: pio_unlimited
-    use pio,    only: PIO_def_dim
-
-    character(len=*), intent(in)        :: filename   ! Name of file to register the dimension on.
-    character(len=*), intent(in)        :: shortname,longname ! Short- and long- names for this dimension, short: brief identifier and name for netCDF output, long: longer descriptor sentence to be included as meta-data in file.
-    integer, intent(in)                 :: length             ! Length of the dimension, 0: unlimited (like time), >0 actual length of dimension
-    logical, intent(in)                 :: is_partitioned   ! whether this dimension is partitioned across ranks
-
-    type(pio_atm_file_t), pointer       :: pio_atm_file
-    type(hist_coord_t), pointer         :: hist_coord
-    type(hist_coord_list_t), pointer    :: curr, prev
-    logical                             :: found, dim_found
-    integer                             :: ierr
-
-    dim_found = .false.
-
-    ! Make sure the dimension length is reasonable
-    if (length<0) call errorHandle("PIO Error: dimension "//trim(shortname)//", can't have a negative dimension length",-999)
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error registering dimension "//trim(shortname)//" in file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    ! Get a new dimension pointer in coord_list
-    curr => pio_atm_file%coord_list_top
-    do while (associated(curr))
-      if (associated(curr%coord)) then
-        if(trim(curr%coord%name)==trim(shortname)) then
-          dim_found = .true.
-          exit
-        endif
-      end if
-      prev => curr
-      curr => prev%next
-    end do
-
-    ! If the dim was not found, create it
-    if (.not. dim_found) then
-      allocate(prev%next)
-      curr => prev%next
-      allocate(curr%coord)
-      hist_coord => curr%coord
-
-      ! Register this dimension
-      hist_coord%name           = trim(shortname)
-      hist_coord%long_name      = trim(longname)
-      hist_coord%is_partitioned = is_partitioned
-      hist_coord%is_time_dim    = length .eq. 0
-
-      if (is_write(pio_atm_file%purpose)) then
-        if (length.eq.0) then
-          ierr = PIO_def_dim(pio_atm_file%pioFileDesc, trim(shortname), pio_unlimited , hist_coord%dimid)
-          time_dimid = hist_coord%dimid
-        else
-          ierr = PIO_def_dim(pio_atm_file%pioFileDesc, trim(shortname), length , hist_coord%dimid)
-        end if
-        call errorHandle("PIO ERROR: could not define dimension "//trim(shortname)//" on file: "//trim(filename),ierr)
-      endif
-    endif
-  end subroutine register_dimension
-!=====================================================================!
-  ! Register a variable with a specific pio input/output file. Mandatory inputs
-  ! include:
-  ! pio_atm_filename: The name of the netCDF file this variable will be
-  !                   registered with.
-  ! shortname:      A shortname descriptor (tag) for this variable.  This will be
-  !                 used to label the variable in the netCDF file as well.
-  ! longname:       A longer character string describing the variable.
-  ! numdims:        The number of dimensions associated with this variable,
-  !                 including time (if applicable).
-  ! var_dimensions: An array of character strings with the dimension shortnames
-  !                 for each dimension used by this variable.  Should have
-  !                 'numdims' entries.
-  ! dtype:          The data type for this variable using the proper netCDF
-  !                 integer tag.
-  ! pio_decomp_tag: A string that describes this particular dimension
-  !                 arrangement which will be used to create a unique PIO
-  !                 decomposition for reading this variable.  It is ok to reuse
-  !                 the pio_decomp_tag for variables that have the same
-  !                 dimensionality.  See get_decomp for more details.
-  ! NOTE: if the file is in Read or Append mode, we are supposed to have already checked
-  !       that the specs match the ones in the file during the C++ wrapper functions
-  subroutine register_variable(filename,shortname,longname,units, &
-                               numdims,var_dimensions,            &
-                               dtype,nc_dtype,pio_decomp_tag)
-    use pio, only: PIO_def_var, PIO_inq_dimid, PIO_inq_dimlen, PIO_inq_varid, PIO_put_att
-
-    character(len=256), intent(in)  :: filename                 ! Name of the file to register this variable with
-    character(len=256), intent(in)  :: shortname,longname       ! short and long names for the variable.  Short: variable name in file, Long: more descriptive name
-    character(len=256), intent(in)  :: units                    ! units for variable
-    integer, intent(in)             :: numdims                  ! Number of dimensions for this variable, including time dimension
-    character(len=256), intent(in)  :: var_dimensions(numdims)  ! String array with shortname descriptors for each dimension of variable.
-    character(len=256), intent(in)  :: pio_decomp_tag           ! Unique tag for this variables decomposition type, to be used to determine if the io-decomp already exists.
-    integer, intent(in)             :: dtype                    ! datatype for arrays that will be passed to read/write routines
-    integer, intent(in)             :: nc_dtype                 ! datatype for this variable in nc files (unused if file mode is Read)
-
-    ! Local variables
-    type(pio_atm_file_t),pointer :: pio_atm_file
-    type(hist_var_t), pointer    :: hist_var
-    integer                      :: dim_ii
-    logical                      :: found,var_found
-    integer                      :: ierr
-    type(hist_coord_t), pointer  :: hist_coord
-
-    type(hist_var_list_t), pointer :: curr, prev
-
-    var_found = .false.
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error registering variable "//trim(shortname)//" in file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    ! Get a new variable pointer in var_list
-    if (len_trim(shortname)>max_hvarname_len) call errorHandle("PIO Error: variable shortname "//trim(shortname)//" is too long, consider increasing max_hvarname_len or changing the variable shortname",-999)
-    curr => pio_atm_file%var_list_top
-    do while ( associated(curr) )
-      if (associated(curr%var)) then
-        if (trim(curr%var%name)==trim(shortname) .and. curr%var%is_set) then
-          exit
-        end if
-      end if
-      prev => curr
-      curr => prev%next
-    end do
-
-    allocate(prev%next)
-    curr => prev%next
-    allocate(curr%var)
-    hist_var => curr%var
-    ! Populate meta-data associated with this variable
-    hist_var%name      = trim(shortname)
-    hist_var%long_name = trim(longname)
-
-    hist_var%units     = trim(units)
-    hist_var%numdims   = numdims
-    hist_var%dtype     = dtype
-    hist_var%nc_dtype  = nc_dtype
-    hist_var%pio_decomp_tag = trim(pio_decomp_tag)
-    ! Determine the dimension id's saved in the netCDF file and associated with
-    ! this variable, check if variable has a time dimension
-    hist_var%has_t_dim = .false.
-    hist_var%is_partitioned = .false.
-    allocate(hist_var%dimid(numdims),hist_var%dimlen(numdims))
-    do dim_ii = 1,numdims
-      ierr = pio_inq_dimid(pio_atm_file%pioFileDesc,trim(var_dimensions(dim_ii)),hist_var%dimid(dim_ii))
-      call errorHandle("EAM_PIO ERROR: Unable to find dimension id for "//trim(var_dimensions(dim_ii)),ierr)
-      ierr = pio_inq_dimlen(pio_atm_file%pioFileDesc,hist_var%dimid(dim_ii),hist_var%dimlen(dim_ii))
-      call errorHandle("EAM_PIO ERROR: Unable to determine length for dimension "//trim(var_dimensions(dim_ii)),ierr)
-
-      call get_coord (filename,var_dimensions(dim_ii),hist_coord)
-      if (hist_coord%is_partitioned) then
-        hist_var%is_partitioned = .true.
-      endif
-      if (hist_coord%is_time_dim) then
-        hist_var%has_t_dim = .true.
-      endif
-    end do
-
-    if (is_write(pio_atm_file%purpose)) then
-      ierr = PIO_def_var(pio_atm_file%pioFileDesc, trim(shortname), hist_var%nc_dtype, hist_var%dimid(:numdims), hist_var%piovar)
-      call errorHandle("PIO ERROR: could not define variable "//trim(shortname)//" in file "//trim(filename),ierr)
-      ierr=PIO_put_att(pio_atm_file%pioFileDesc, hist_var%piovar, 'units', hist_var%units )
-      call errorHandle("PIO ERROR: could not set attribute 'units' for variable "//trim(shortname)//" in file "//trim(filename),ierr)
-      ierr=PIO_put_att(pio_atm_file%pioFileDesc, hist_var%piovar, 'long_name', hist_var%long_name )
-      call errorHandle("PIO ERROR: could not set attribute 'long_name' for variable "//trim(shortname)//" in file "//trim(filename),ierr)
-    else
-      ierr = PIO_inq_varid(pio_atm_file%pioFileDesc,trim(shortname),hist_var%piovar)
-      call errorHandle("PIO ERROR: could not retrieve id for variable "//trim(shortname)//" from file "//trim(filename),ierr)
-    endif
-
-    ! Set that new variable has been created
-    hist_var%is_set = .true.
-
-  end subroutine register_variable
-!=====================================================================!
-  subroutine set_variable_metadata_float(filename, varname, metaname, metaval)
-    use pio, only: PIO_put_att
-
-    character(len=256), intent(in) :: filename
-    character(len=256), intent(in) :: varname
-    character(len=256), intent(in) :: metaname
-    real(kind=c_float), intent(in) :: metaval
-
-    ! Local variables
-    type(pio_atm_file_t),pointer :: pio_file
-    type(hist_var_t),    pointer :: var
-    integer                      :: ierr
-    logical                      :: found
-
-    type(hist_var_list_t), pointer :: curr
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error setting metadata for variable "//trim(varname)//" in file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    ! Find the variable in the file
-    curr => pio_file%var_list_top
-
-    found = .false.
-    do while (associated(curr))
-      if (associated(curr%var)) then
-        if (trim(curr%var%name)==trim(varname) .and. curr%var%is_set) then
-          found = .true.
-          var => curr%var
-          exit
-        endif
-      endif
-      curr => curr%next
-    end do
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error setting metadata for variable "//trim(varname)//" in file "//trim(filename)//".\n Variable not found.",-999)
-    endif
-
-    ierr = PIO_put_att(pio_file%pioFileDesc, var%piovar, metaname, metaval)
-    if (ierr .ne. 0) then
-      call errorHandle("Error setting attribute '" // trim(metaname) &
-                       // "' on variable '" // trim(varname) &
-                       // "' in pio file " // trim(filename) // ".", -999)
-    endif
-
-  end subroutine set_variable_metadata_float
-!=====================================================================!
-  subroutine set_variable_metadata_double(filename, varname, metaname, metaval)
-    use pio, only: PIO_put_att
-
-    character(len=256), intent(in) :: filename
-    character(len=256), intent(in) :: varname
-    character(len=256), intent(in) :: metaname
-    real(kind=c_double), intent(in) :: metaval
-
-    ! Local variables
-    type(pio_atm_file_t),pointer :: pio_file
-    type(hist_var_t),    pointer :: var
-    integer                      :: ierr
-    logical                      :: found
-
-    type(hist_var_list_t), pointer :: curr
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error setting metadata for variable "//trim(varname)//" in file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    ! Find the variable in the file
-    curr => pio_file%var_list_top
-
-    found = .false.
-    do while (associated(curr))
-      if (associated(curr%var)) then
-        if (trim(curr%var%name)==trim(varname) .and. curr%var%is_set) then
-          found = .true.
-          var => curr%var
-          exit
-        endif
-      endif
-      curr => curr%next
-    end do
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error setting metadata for variable "//trim(varname)//" in file "//trim(filename)//".\n Variable not found.",-999)
-    endif
-
-    ierr = PIO_put_att(pio_file%pioFileDesc, var%piovar, metaname, metaval)
-    if (ierr .ne. 0) then
-      call errorHandle("Error setting attribute '" // trim(metaname) &
-                       // "' on variable '" // trim(varname) &
-                       // "' in pio file " // trim(filename) // ".", -999)
-    endif
-
-  end subroutine set_variable_metadata_double
-!=====================================================================!
-  function get_variable_metadata_float(filename, varname, metaname) result(metaval)
-    use pio, only: PIO_get_att
-
-    character(len=256), intent(in) :: filename
-    character(len=256), intent(in) :: varname
-    character(len=256), intent(in) :: metaname
-    real(kind=c_float)             :: metaval
-
-
-    ! Local variables
-    type(pio_atm_file_t),pointer :: pio_file
-    type(hist_var_t),    pointer :: var
-    integer                      :: ierr
-    logical                      :: found
-
-    type(hist_var_list_t), pointer :: curr
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: PIO file not open.\nError getting metadata for variable "//trim(varname)//" in file "//trim(filename)//".",-999)
-    endif
-
-    ! Find the variable in the file
-    curr => pio_file%var_list_top
-
-    found = .false.
-    do while (associated(curr))
-      if (associated(curr%var)) then
-        if (trim(curr%var%name)==trim(varname) .and. curr%var%is_set) then
-          found = .true.
-          var => curr%var
-          exit
-        endif
-      endif
-      curr => curr%next
-    end do
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: PIO file not open.\nError getting metadata for variable "//trim(varname)//" in file "//trim(filename)//".",-999)
-    endif
-
-    ! TODO: Maybe we shouldn't throw an error when the metadata isn't there, maybe we provide an output like ierr as an integer?
-    ! That way we can query for a metadata and on the EAMxx side decide what to do if the metadata is missing.
-    ierr = PIO_get_att(pio_file%pioFileDesc, var%piovar, metaname, metaval)
-    if (ierr .ne. 0) then
-      call errorHandle("Error getting attribute '" // trim(metaname) &
-                       // "' on variable '" // trim(varname) &
-                       // "' in pio file " // trim(filename) // ".", -999)
-    endif
-
-  end function get_variable_metadata_float
-!=====================================================================!
-  function get_variable_metadata_double(filename, varname, metaname) result(metaval)
-    use pio, only: PIO_get_att
-
-    character(len=256), intent(in) :: filename
-    character(len=256), intent(in) :: varname
-    character(len=256), intent(in) :: metaname
-    real(kind=c_double)            :: metaval
-
-    ! Local variables
-    type(pio_atm_file_t),pointer :: pio_file
-    type(hist_var_t),    pointer :: var
-    integer                      :: ierr
-    logical                      :: found
-
-    type(hist_var_list_t), pointer :: curr
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: PIO file not open.\nError getting metadata for variable "//trim(varname)//" in file "//trim(filename)//".",-999)
-    endif
-
-    ! Find the variable in the file
-    curr => pio_file%var_list_top
-
-    found = .false.
-    do while (associated(curr))
-      if (associated(curr%var)) then
-        if (trim(curr%var%name)==trim(varname) .and. curr%var%is_set) then
-          found = .true.
-          var => curr%var
-          exit
-        endif
-      endif
-      curr => curr%next
-    end do
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: PIO file not open.\nError getting metadata for variable "//trim(varname)//" in file "//trim(filename)//".",-999)
-    endif
-
-    ierr = PIO_get_att(pio_file%pioFileDesc, var%piovar, metaname, metaval)
-    if (ierr .ne. 0) then
-      call errorHandle("Error getting attribute '" // trim(metaname) &
-                       // "' on variable '" // trim(varname) &
-                       // "' in pio file " // trim(filename) // ".", -999)
-    endif
-
-  end function get_variable_metadata_double
-!=====================================================================!
-  subroutine set_variable_metadata_char(filename, varname, metaname, metaval)
-    use pio, only: PIO_put_att
-
-    character(len=256), intent(in) :: filename
-    character(len=256), intent(in) :: varname
-    character(len=256), intent(in) :: metaname
-    character(len=256), intent(in) :: metaval
-
-    ! Local variables
-    type(pio_atm_file_t),pointer :: pio_file
-    type(hist_var_t),    pointer :: var
-    integer                      :: ierr
-    logical                      :: found
-
-    type(hist_var_list_t), pointer :: curr
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error setting metadata for variable "//trim(varname)//" in file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    ! Find the variable in the file
-    curr => pio_file%var_list_top
-
-    found = .false.
-    do while (associated(curr))
-      if (associated(curr%var)) then
-        if (trim(curr%var%name)==trim(varname) .and. curr%var%is_set) then
-          found = .true.
-          var => curr%var
-          exit
-        endif
-      endif
-      curr => curr%next
-    end do
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: error setting metadata for variable "//trim(varname)//" in file "//trim(filename)//".\n Variable not found.",-999)
-    endif
-
-    ierr = PIO_put_att(pio_file%pioFileDesc, var%piovar, metaname, metaval)
-    if (ierr .ne. 0) then
-      call errorHandle("Error setting attribute '" // trim(metaname) &
-                       // "' on variable '" // trim(varname) &
-                       // "' in pio file " // trim(filename) // ".", -999)
-    endif
-
-  end subroutine set_variable_metadata_char
-!=====================================================================!
-  function get_variable_metadata_char(filename, varname, metaname) result(metaval)
-    use pio, only: PIO_get_att
-
-    character(len=256), intent(in) :: filename
-    character(len=256), intent(in) :: varname
-    character(len=256), intent(in) :: metaname
-    character(len=256)             :: metaval
-
-    ! Local variables
-    type(pio_atm_file_t),pointer :: pio_file
-    type(hist_var_t),    pointer :: var
-    integer                      :: ierr
-    logical                      :: found
-
-    type(hist_var_list_t), pointer :: curr
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(filename),pio_file,found)
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: PIO file not open.\nError getting metadata for variable "//trim(varname)//" in file "//trim(filename)//".",-999)
-    endif
-
-    ! Find the variable in the file
-    curr => pio_file%var_list_top
-
-    found = .false.
-    do while (associated(curr))
-      if (associated(curr%var)) then
-        if (trim(curr%var%name)==trim(varname) .and. curr%var%is_set) then
-          found = .true.
-          var => curr%var
-          exit
-        endif
-      endif
-      curr => curr%next
-    end do
-    if (.not.found ) then
-      call errorHandle("PIO ERROR: PIO file not open.\nError getting metadata for variable "//trim(varname)//" in file "//trim(filename)//".",-999)
-    endif
-
-    ! TODO: Maybe we shouldn't throw an error when the metadata isn't there, maybe we provide an output like ierr as an integer?
-    ! That way we can query for a metadata and on the EAMxx side decide what to do if the metadata is missing.
-    ierr = PIO_get_att(pio_file%pioFileDesc, var%piovar, metaname, metaval)
-    if (ierr .ne. 0) then
-      call errorHandle("Error getting attribute '" // trim(metaname) &
-                       // "' on variable '" // trim(varname) &
-                       // "' in pio file " // trim(filename) // ".", -999)
-    endif
-  end function get_variable_metadata_char
-!=====================================================================!
-  ! Update the time dimension for a specific PIO file.  This is needed when
-  ! reading or writing multiple time levels.  Unlimited dimensions are treated
-  ! differently in netCDF than typical static length variables.  Note, here
-  ! "time" is hardcoded as the only unlimited variable.  If, in the future,
-  ! scream decides to allow for other "unlimited" dimensions to be used our
-  ! input/output than this routine will need to be adjusted.
-  subroutine eam_update_time(filename,time)
-    use pio, only: PIO_put_var
-
-    character(len=*), intent(in) :: filename       ! PIO filename
-    real(c_double), intent(in)   :: time
-
-    type(hist_var_t), pointer    :: var
-    type(pio_atm_file_t),pointer :: pio_atm_file
-    integer                      :: ierr
-    logical                      :: found
-
-    call lookup_pio_atm_file(filename,pio_atm_file,found)
-    pio_atm_file%numRecs = pio_atm_file%numRecs + 1
-    call get_var(pio_atm_file,'time',var)
-    ! Only update time on the file if a valid time is provided
-    if (time>=0) then
-      ierr = pio_put_var(pio_atm_file%pioFileDesc,var%piovar,(/ pio_atm_file%numRecs /), (/ 1 /), (/ time /))
-      call errorHandle("PIO ERROR: something went wrong while writing time var on file="//trim(filename),ierr)
-    endif
-  end subroutine eam_update_time
-!=====================================================================!
-  ! Assign institutions to header metadata for a specific pio output file.
-  subroutine eam_pio_createHeader(File)
-    use pio, only: PIO_put_att
-
-    type(file_desc_t), intent(in) :: File             ! Pio file Handle
-    integer                       :: retval
-
-    ! We are able to have EAMxx directly set most attributes in the HEADER
-    ! except the list of institutions which appears to have a string that is too
-    ! long to accomodate using `set_str_attribute` as it is currently defined.
-    ! So we keep the setting of institutions here.
-    ! TODO: revise the set_str_attribute code to allow the
-    ! scream_output_manager.cpp to handle institutions too.
-    ! NOTE: The use of //char(10)// causes each institution to be written on it's own line, makes it easier to read.
-    retval=pio_put_att (File, PIO_GLOBAL, 'institutions', 'LLNL (Lawrence Livermore National Laboratory, Livermore, CA 94550, USA);'  &
-      //char(10)//'ANL (Argonne National Laboratory, Argonne, IL 60439, USA); '  &
-      //char(10)//'BNL (Brookhaven National Laboratory, Upton, NY 11973, USA);'  &
-      //char(10)//'LANL (Los Alamos National Laboratory, Los Alamos, NM 87545, USA);'  &
-      //char(10)//'LBNL (Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA);'  &
-      //char(10)//'ORNL (Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA);'  &
-      //char(10)//'PNNL (Pacific Northwest National Laboratory, Richland, WA 99352, USA);'  &
-      //char(10)//'SNL (Sandia National Laboratories, Albuquerque, NM 87185, USA).'  &
-      //char(10)//'Mailing address: LLNL Climate Program, c/o David C. Bader, Principal Investigator, L-103, 7000 East Avenue, Livermore, CA 94550, USA')
-
-  end subroutine eam_pio_createHeader
-!=====================================================================!
-  ! Ensures a pio system is in place, by either creating a new one
-  ! or getting the one created by CIME (for CIME builds)
-  subroutine eam_init_pio_subsystem(mpicom,atm_id)
-#ifdef SCREAM_CIME_BUILD
-    use shr_pio_mod,  only: shr_pio_getrearranger, shr_pio_getiosys, &
-                            shr_pio_getiotype, shr_pio_getioformat
-#else
-    use pio_types,  only: pio_rearr_subset, PIO_iotype_netcdf, PIO_64BIT_DATA
-    use pio, only: pio_init
-
-    integer :: ierr, stride, atm_rank, atm_size, num_aggregator
-#endif
-
-    integer, intent(in) :: mpicom
-    integer, intent(in) :: atm_id
-
-    if (associated(pio_subsystem)) call errorHandle("PIO ERROR: local pio_subsystem pointer has already been established.",-999)
-
-    atm_mpicom = mpicom
-
-#ifdef SCREAM_CIME_BUILD
-    pio_subsystem  => shr_pio_getiosys(atm_id)
-    pio_iotype     = shr_pio_getiotype(atm_id)
-    pio_rearranger = shr_pio_getrearranger(atm_id)
-    pio_mode       = shr_pio_getioformat(atm_id)
-#else
-    ! WARNING: we're assuming *every atm rank* is an I/O rank
-    call MPI_Comm_rank(atm_mpicom, atm_rank, ierr)
-    call MPI_Comm_size(atm_mpicom, atm_size, ierr)
-
-    ! Just for removing unused dummy warnings
-    if (.false.) print *, atm_id
-
-    stride = 1
-    num_aggregator = 0
-
-    allocate(pio_subsystem)
-    pio_rearranger = pio_rearr_subset
-    pio_iotype     = PIO_iotype_netcdf
-    pio_mode       = PIO_64BIT_DATA ! Default to 64 bit
-    call PIO_init(atm_rank, atm_mpicom, atm_size, num_aggregator, stride, &
-                  pio_rearr_subset, pio_subsystem, base=0)
-#endif
-
-    ! Init the list of pio files so that begin==end==null
-    pio_file_list_back   => null()
-    pio_file_list_front => null()
-
-    ! Init the iodecomp
-    iodesc_list_top => null()
-
-  end subroutine eam_init_pio_subsystem
-!=====================================================================!
-  ! Query whether the pio subsystem is inited already
-  ! This can be useful to avoid double-init or double-finalize calls.
-  function is_eam_pio_subsystem_inited() result(is_it) bind(c)
-    use iso_c_binding, only: c_bool
-
-    logical(kind=c_bool) :: is_it
-
-    is_it = LOGICAL(associated(pio_subsystem),kind=c_bool)
-  end function is_eam_pio_subsystem_inited
-!=====================================================================!
-  function scream_iotype_to_pio_iotype(siotype) result(piotype)
-    integer, intent(in) :: siotype
-    integer :: piotype
-
-    if(siotype == 0) then
-      piotype = pio_iotype
-    else if(siotype == 1) then
-      piotype = pio_iotype_netcdf
-    else if(siotype == 2) then
-      piotype = pio_iotype_pnetcdf
-    else if(siotype == 3) then
-      piotype = pio_iotype_adios
-    else
-      piotype = pio_iotype
-    end if
-  end function scream_iotype_to_pio_iotype
-!=====================================================================!
-  ! Create a pio netCDF file with the appropriate name.
-  subroutine eam_pio_createfile(File,fname,iotype)
-    use pio, only: pio_createfile
-    use pio_types,  only: pio_clobber
-
-    type(file_desc_t), intent(inout) :: File             ! Pio file Handle
-    character(len=*),  intent(in)    :: fname            ! Pio file name
-    integer, intent(in)              :: iotype
-    !--
-    integer                          :: retval           ! PIO error return value
-    integer                          :: mode             ! Mode for how to handle the new file
-    integer                           :: piotype
-
-    mode = ior(pio_mode,pio_clobber) ! Set to CLOBBER for now, TODO: fix to allow for optional mode type like in CAM
-    piotype = scream_iotype_to_pio_iotype(iotype)
-    retval = pio_createfile(pio_subsystem,File,piotype,fname,mode)
-    call errorHandle("PIO ERROR: unable to create file: "//trim(fname),retval)
-
-  end subroutine eam_pio_createfile
-!=====================================================================!
-  ! Open an already existing netCDF file.
-  subroutine eam_pio_openfile(pio_file,fname,iotype)
-    use pio, only: pio_openfile
-    use pio_types,  only: pio_write, pio_nowrite
-
-    type(pio_atm_file_t), pointer, intent(in) :: pio_file     ! Pointer to pio file struct associated with this filename
-    character(len=*),  intent(in)    :: fname            ! Pio file name
-    !--
-    integer                          :: retval           ! PIO error return value
-    integer                          :: mode             ! Mode for how to handle the new file
-    integer, intent(in)              :: iotype
-
-    integer                           :: piotype
-
-    if (is_read(pio_file%purpose)) then
-      mode = pio_nowrite
-    else
-      mode = pio_write
-    endif
-    piotype = scream_iotype_to_pio_iotype(iotype)
-    retval = pio_openfile(pio_subsystem,pio_file%pioFileDesc,piotype,fname,mode)
-    call errorHandle("PIO ERROR: unable to open file: "//trim(fname),retval)
-
-    if (is_append(pio_file%purpose)) then
-      pio_file%is_enddef = .true.
-    endif
-
-  end subroutine eam_pio_openfile
-!=====================================================================!
-  ! Close a netCDF file.  To be done as a last step after all input or output
-  ! for that file has been finished.
-  subroutine eam_pio_closefile(fname)
-    use pio, only: PIO_syncfile, PIO_closefile
-
-    character(len=*),  intent(in)    :: fname            ! Pio file name
-    !--
-    type(pio_atm_file_t),pointer     :: pio_atm_file
-    type(pio_file_list_t), pointer   :: pio_file_list_ptr
-    logical                          :: found
-    type(hist_var_list_t), pointer   :: curr_var_list
-    type(hist_var_t), pointer        :: var
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(fname),pio_atm_file,found,pio_file_list_ptr)
-
-    if (found) then
-      if (pio_atm_file%num_customers .eq. 1) then
-        if ( is_write(pio_atm_file%purpose) ) then
-          call PIO_syncfile(pio_atm_file%pioFileDesc)
-        endif
-        call PIO_closefile(pio_atm_file%pioFileDesc)
-        pio_atm_file%num_customers = pio_atm_file%num_customers - 1
-
-        ! Remove all variables from this file as customers for the stored pio
-        ! decompostions
-        curr_var_list => pio_atm_file%var_list_top  ! Start with the first variable in the file
-        do while (associated(curr_var_list))
-          var => curr_var_list%var  ! The actual variable pointer
-          if (associated(var)) then
-            if (associated(var%iodesc_list)) then
-              ! Remove this variable as a customer of the associated iodesc
-              var%iodesc_list%num_customers = var%iodesc_list%num_customers - 1
-              ! Dellocate select memory from this variable.  Note we can't just
-              ! deallocate the whole var structure because this would also
-              ! deallocate the iodesc_list.
-              call deallocate_hist_var_t(var)
-            end if ! associated(var%iodesc_list)
-          end if ! associated(var)
-          curr_var_list => curr_var_list%next  ! Move on to the next variable
-        end do ! associated(curr_var_list)
-
-        ! Adjust pointers in the pio file list
-        if (associated(pio_file_list_ptr%prev)) then
-          pio_file_list_ptr%prev%next => pio_file_list_ptr%next
-        else
-          ! We're deleting the first item in the lists. Update pio_file_list_front
-          pio_file_list_front => pio_file_list_ptr%next
-        endif
-        if (associated(pio_file_list_ptr%next)) then
-          pio_file_list_ptr%next%prev => pio_file_list_ptr%prev
-        else
-          ! We're deleting the last item in the lists. Update pio_file_list_back
-          pio_file_list_back => pio_file_list_ptr%prev
-        endif
-
-        ! Now that we have closed this pio file and purged it from the list we
-        ! can deallocate the structure.
-        deallocate(pio_atm_file)
-      else if (pio_atm_file%num_customers .gt. 1) then
-        pio_atm_file%num_customers = pio_atm_file%num_customers - 1
-      else
-        call errorHandle("PIO ERROR: while closing file: "//trim(fname)//", found num_customers<=0",-999)
-      endif
-    else
-      call errorHandle("PIO ERROR: unable to close file: "//trim(fname)//", was not found",-999)
-    end if
-
-    ! Final step, free any pio decompostion memory that is no longer needed.
-    !   Update: We are trying to reuse decompostions maximally, so we're
-    ! skipping this step.
-    !call free_decomp()
-
-  end subroutine eam_pio_closefile
-!=====================================================================!
-  ! Flushes IO buffers to file
-  subroutine eam_pio_flush_file(fname)
-    use pio, only: PIO_syncfile
-
-    character(len=*),  intent(in)    :: fname            ! Pio file name
-    !--
-    type(pio_atm_file_t),pointer     :: pio_atm_file
-    logical                          :: found
-
-    ! Find the pointer for this file
-    call lookup_pio_atm_file(trim(fname),pio_atm_file,found)
-
-    if (found) then
-      if ( is_write(pio_atm_file%purpose) .or. is_append(pio_atm_file%purpose) ) then
-        call PIO_syncfile(pio_atm_file%pioFileDesc)
-      else
-        call errorHandle("PIO ERROR: unable to flush file: "//trim(fname)//", is not open in write mode",-999)
-      endif
-    else
-      call errorHandle("PIO ERROR: unable to flush file: "//trim(fname)//", was not found",-999)
-    end if
-  end subroutine eam_pio_flush_file
-!=====================================================================!
-  ! Helper function to debug list of decomps
-  subroutine print_decomp()
-    type(iodesc_list_t),   pointer :: iodesc_ptr
-
-    integer :: total
-    integer :: cnt
-    logical :: assoc
-
-    if (associated(iodesc_list_top)) then
-      total = 0
-      cnt   = 0
-      write(*,*) "            PRINT DECOMP            "
-      write(*,*) "            ------------            "
-      write(*,'(8X,A10,A15,A50,A15)') "Location", "Associated?", "IODESC TAG", "# Customers"
-    else
-      write(*,*) "No DECOMP List to print"
-      return
-    end if
-    iodesc_ptr => iodesc_list_top
-    do while(associated(iodesc_ptr))
-      total = total + 1
-      assoc = .false.
-      if (associated(iodesc_ptr%iodesc).and.iodesc_ptr%iodesc_set) then
-        cnt = cnt + 1
-        assoc = .true.
-      end if
-      write(*,'(I3,A5,I10,L15,A50,I15)') total, ": ", iodesc_ptr%location, assoc , trim(iodesc_ptr%tag), iodesc_ptr%num_customers
-      iodesc_ptr => iodesc_ptr%next
-    end do
-    write(*,*) "            total: ", total, ", cnt: ",cnt
-    write(*,*) "            ------------            "
-
-  end subroutine print_decomp
-!=====================================================================!
-  ! Free the memory stored in a hist_var_t derived type
-  subroutine deallocate_hist_var_t(var)
-
-    type(hist_var_t), pointer        :: var
-
-    deallocate(var%compdof)
-    deallocate(var%dimid)
-    deallocate(var%dimlen)
-    var%is_set = .false.
-
-  end subroutine deallocate_hist_var_t
-  !=====================================================================!
-  ! Free pio decomposition memory in PIO for any decompositions that are no
-  ! longer needed.  Previously, we thought that this is an important memory
-  ! management step that should be taken whenever a file is closed.  Now we're
-  ! trying to keep decomps persistent so they can be reused.  Thus, calling
-  ! this routine is optional.
-  subroutine free_decomp()
-    use pio, only: PIO_freedecomp
-    type(iodesc_list_t),   pointer :: iodesc_ptr, next
-
-    ! Free all decompositions from PIO
-    iodesc_ptr => iodesc_list_top
-    do while(associated(iodesc_ptr))
-      next => iodesc_ptr%next
-      if (associated(iodesc_ptr%iodesc).and.iodesc_ptr%iodesc_set) then
-        if (iodesc_ptr%num_customers .eq. 0) then
-          ! Free decomp
-          call pio_freedecomp(pio_subsystem,iodesc_ptr%iodesc)
-          ! Nullify this decomp
-          ! If we are at iodesc_list_top we need to make iodesc_ptr%next the new
-          ! iodesc_list_top:
-          if (associated(iodesc_ptr%prev)) then
-            iodesc_ptr%prev%next => iodesc_ptr%next
-          else
-            ! We are deleting the first item in the list, update
-            ! iodesc_list_front
-            iodesc_list_top => iodesc_ptr%next
-          end if
-          if (associated(iodesc_ptr%next)) then
-            iodesc_ptr%next%prev => iodesc_ptr%prev
-          end if
-          deallocate(iodesc_ptr)
-        end if
-      end if
-      iodesc_ptr => next
-    end do
-
-  end subroutine free_decomp
-!=====================================================================!
-  ! Finalize a PIO session within scream.  Close all open files and deallocate
-  ! the pio_subsystem session.
-  subroutine eam_pio_finalize()
-    use pio, only: PIO_finalize, pio_freedecomp
-    ! May not be needed, possibly handled by PIO directly.
-
-#if !defined(SCREAM_CIME_BUILD)
-    integer :: ierr
-#endif
-    type(pio_file_list_t), pointer :: curr_file_ptr, prev_file_ptr
-    type(iodesc_list_t),   pointer :: iodesc_ptr
-
-    ! Close all the PIO Files
-    curr_file_ptr => pio_file_list_front
-    do while (associated(curr_file_ptr))
-      call eam_pio_closefile(curr_file_ptr%pio_file%filename)
-      prev_file_ptr => curr_file_ptr
-      curr_file_ptr => curr_file_ptr%next
-      deallocate(prev_file_ptr)
-      pio_file_list_front => curr_file_ptr ! be sure not to iterate over deallocated item
-    end do
-    ! Free all decompositions from PIO
-    iodesc_ptr => iodesc_list_top
-    do while(associated(iodesc_ptr))
-      if (associated(iodesc_ptr%iodesc).and.iodesc_ptr%iodesc_set) then
-        call pio_freedecomp(pio_subsystem,iodesc_ptr%iodesc)
-      end if
-      iodesc_ptr => iodesc_ptr%next
-    end do
-
-#if !defined(SCREAM_CIME_BUILD)
-    call PIO_finalize(pio_subsystem, ierr)
-    call errorHandle("PIO ERROR: something went wrong when calling PIO_finalize.",ierr)
-    nullify(pio_subsystem)
-#endif
-
-  end subroutine eam_pio_finalize
-!=====================================================================!
-  ! Handle any errors that occur in this module and print to screen an error
-  ! message.
-  subroutine errorHandle(errMsg, retVal)
-    use iso_c_binding
-    implicit none
-
-    interface
-      subroutine finalize_scream_session() bind(C)
-        ! No inputs or anything, just interface to C code.
-      end subroutine finalize_scream_session
-    end interface
-
-    character(len=*),  intent(in)    :: errMsg
-    integer,           intent(in)    :: retVal
-
-    integer :: ierr
-
-    if (retVal .ne. PIO_NOERR) then
-      write(*,'(I8,2x,A512)') retVal,trim(errMsg)
-      ! Kill run
-      call eam_pio_finalize()
-      call finalize_scream_session()
-      call mpi_abort(atm_mpicom,retVal,ierr)
-    end if
-
-  end subroutine errorHandle
-!=====================================================================!
- ! Determine the unique pio_decomposition for this output grid, if it hasn't
- ! been defined create a new one.
-  subroutine get_decomp(tag,dtype,dimension_len,compdof,iodesc_list)
-    use pio, only: pio_initdecomp
-    ! TODO: CAM code creates the decomp tag for the user.  Theoretically it is
-    ! unique because it is based on dimensions and datatype.  But the tag ends
-    ! up not being very descriptive.  The todo item is to revisit how tags are
-    ! handled and decide if we want the code to create a tag or let the use
-    ! assign a tag.
-    character(len=*)          :: tag              ! Unique tag string describing this output grid
-    integer, intent(in)       :: dtype            ! Datatype associated with the output
-    integer, intent(in)       :: dimension_len(:) ! Array of the dimension lengths for this decomp
-    integer(kind=pio_offset_kind), intent(in) :: compdof(:)       ! The degrees of freedom this rank is responsible for
-    type(iodesc_list_t), pointer :: iodesc_list   ! The pio decomposition list that holds this iodesc
-
-    logical                     :: found            ! Whether a decomp has been found among the previously defined decompositions
-    type(iodesc_list_t),pointer :: curr, prev       ! Used to toggle through the recursive list of decompositions
-    integer                     :: loc_len          ! Used to keep track of how many dimensions there are in decomp
-
-    ! Assign a PIO decomposition to variable, if none exists, create a new one:
-    found = .false.
-    curr => iodesc_list_top
-    prev => iodesc_list_top
-    ! Cycle through all current iodesc to see if the decomp has already been
-    ! created
-    do while(associated(curr) .and. (.not.found))
-      if (trim(tag) == trim(curr%tag)) then
-        found = .true.
-      else
-        prev => curr
-        curr => curr%next
-      end if
-    end do
-    ! If we didn't find an iodesc then we need to create one
-    if (.not.found) then
-      curr => prev ! Go back and allocate the new iodesc in curr%next
-      ! We may have no iodesc to begin with, so we need to associate the
-      ! beginning of the list.
-      if(.not.associated(curr)) then
-        allocate(curr)
-        curr%location = 1
-        iodesc_list_top => curr
-      end if
-      if(associated(curr%iodesc)) then
-        allocate(curr%next)
-        curr%next%prev => curr
-        curr => curr%next
-        nullify(curr%iodesc)  ! Extra step to ensure clean iodesc
-        nullify(curr%next)  ! Extra step to ensure clean iodesc
-      end if
-      allocate(curr%iodesc)
-      curr%tag = trim(tag)
-      if (associated(curr%prev)) then
-        curr%location = prev%location+1
-      end if
-      loc_len = size(dimension_len)
-      if ( loc_len.eq.1 .and. dimension_len(loc_len).eq.0 ) then
-        allocate(curr%iodesc)
-      else
-        call pio_initdecomp(pio_subsystem, dtype, dimension_len, compdof, curr%iodesc, rearr=pio_rearranger)
-        curr%iodesc_set = .true.
-      end if
-      curr%num_customers = 0
-    end if
-    iodesc_list => curr
-
-  end subroutine get_decomp
-!=====================================================================!
-  ! Set the degrees of freedom (dof) this MPI rank is responsible for
-  ! reading/writing from/to file.
-  ! Briefly, PIO distributes the work of reading/writing the total array
-  ! of any variable data over all of the MPI ranks assigned to PIO.
-  ! DOF's are assigned considering a 1D flattening of any array, ignoring
-  ! unlimited dimensions, which are handled elsewhere.
-  ! Once it is known which dof a rank is responsible for this routine is used to
-  ! set those locally for use with all read and write statements.
-  ! Arguments:
-  ! filename: name of PIO input/output file.
-  ! varname:  shortname of variable to set the dof for.
-  ! dof_len:  number of dof associated for this rank and this variable
-  ! dof_vec:  a vector of length dof_len which includes the global indices of
-  !           the flattened "varname" array that this MPI rank is responsible
-  !           for.
-  ! --- Example: If variable F has dimensions (x,y,t) of size (2,5,t), which means a ---
-  ! total of 2x5=10 dof, not counting the time dimension.
-  ! If 3 MPI ranks are used then a typical breakdown for dof might be:
-  ! Rank 1: (1,2,3)
-  ! Rank 2: (4,5,6)
-  ! Rank 3: (7,8,9,10)
-  subroutine set_dof(filename,varname,dof_len,dof_vec)
-    character(len=*), intent(in)              :: filename
-    character(len=*), intent(in)              :: varname
-    integer, intent(in)                       :: dof_len
-    integer(kind=pio_offset_kind), intent(in) :: dof_vec(dof_len)
-
-    type(pio_atm_file_t),pointer              :: pio_atm_file
-    type(hist_var_t), pointer                 :: var
-    logical                                   :: found
-    integer                                   :: ii
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    call get_var(pio_atm_file,varname,var)
-    if (allocated(var%compdof)) deallocate(var%compdof)
-    allocate( var%compdof(dof_len) )
-    do ii = 1,dof_len
-      var%compdof(ii) = dof_vec(ii)
-    end do
-
-  end subroutine set_dof
-!=====================================================================!
-  ! Get and assign all pio decompositions for a specific PIO file.  This is a
-  ! mandatory step to be taken after all dimensions and variables have been
-  ! registered with an input or output file.
-  subroutine set_decomp(filename)
-
-    character(len=*)               :: filename  ! Name of the pio file to set decomp for
-
-    type(pio_atm_file_t), pointer  :: current_atm_file
-    type(hist_var_list_t), pointer :: curr     ! Used to cycle through recursive list of variables
-    type(hist_var_t), pointer      :: hist_var ! Pointer to the variable structure that has been found
-    integer                        :: loc_len
-    logical                        :: found
-
-    call lookup_pio_atm_file(filename,current_atm_file,found)
-    if (.not. found) then
-      call errorHandle("PIO ERROR: pio file '"//trim(filename)//"' not found.",999)
-    endif
-
-    curr => current_atm_file%var_list_top
-    do while (associated(curr))
-      ! Skip already deallocated vars, and vars for which decomp was already set
-      ! NOTE: fortran does not mandate/prohibit logical op short circuit, so do the
-      !       two following if statements separately
-      if (associated(curr%var)) then
-        if (.not. associated(curr%var%iodesc)) then
-          hist_var => curr%var
-          if (.not.associated(hist_var)) call errorHandle("PIO ERROR: unable to set decomp for file, var: "//trim(current_atm_file%filename)//", "//trim(hist_var%name)//". Set DOF.",999)
-          ! Assign decomp
-          if (hist_var%has_t_dim) then
-            loc_len = max(1,hist_var%numdims-1)
-            call get_decomp(hist_var%pio_decomp_tag,hist_var%dtype,hist_var%dimlen(:loc_len),hist_var%compdof,hist_var%iodesc_list)
-          else
-            call get_decomp(hist_var%pio_decomp_tag,hist_var%dtype,hist_var%dimlen,hist_var%compdof,hist_var%iodesc_list)
-          end if
-          hist_var%iodesc => hist_var%iodesc_list%iodesc
-          hist_var%iodesc_list%num_customers = hist_var%iodesc_list%num_customers + 1  ! Add this variable as a customer of this pio decomposition
-        endif
-      end if
-      curr => curr%next
-    end do
-
-  end subroutine set_decomp
-!=====================================================================!
-  ! Query the hist_var_t pointer for a specific variable on a specific file.
-  subroutine get_var(pio_file,varname,var)
-
-    type(pio_atm_file_t), pointer  :: pio_file ! Pio output file structure
-    character(len=*)               :: varname  ! Name of the variable to query
-    type(hist_var_t), pointer      :: var      ! Pointer to the variable structure that has been found
-
-    type(hist_var_list_t), pointer :: curr     ! Used to cycle through recursive list of variables
-
-    curr => pio_file%var_list_top
-    do while (associated(curr))
-      var => curr%var
-      if (associated(var)) then
-        if (trim(varname) == trim(var%name) .and. var%is_set) return
-      end if
-      curr => curr%next
-    end do
-
-    ! If we got this far we didn't find the variable
-    call errorHandle("PIO ERROR: unable to find variable: "//trim(varname)//" in file: "//trim(pio_file%filename),999)
-
-  end subroutine get_var
-!=====================================================================!
-  ! Lookup pointer for pio file based on filename.
-  subroutine lookup_pio_atm_file(filename,pio_file,found,pio_file_list_ptr_in)
-
-    character(len=*),intent(in)   :: filename     ! Name of file to be found
-    type(pio_atm_file_t), pointer :: pio_file     ! Pointer to pio_atm_output structure associated with this filename
-    logical, intent(out)          :: found        ! whether or not the file was found
-    type(pio_file_list_t), pointer, optional :: pio_file_list_ptr_in
-
-    type(pio_file_list_t), pointer :: pio_file_list_ptr
-
-    ! Scan pio file list, search for this filename
-    found = .false.
-    pio_file_list_ptr => pio_file_list_front
-    pio_file => null()
-    do while (associated(pio_file_list_ptr))
-      if (trim(filename)==trim(pio_file_list_ptr%pio_file%filename)) then
-        pio_file => pio_file_list_ptr%pio_file
-        found = .true.
-        if (present(pio_file_list_ptr_in)) then
-          pio_file_list_ptr_in => pio_file_list_ptr
-        endif
-        return
-      end if
-      pio_file_list_ptr => pio_file_list_ptr%next
-    end do
-
-  end subroutine lookup_pio_atm_file
-!=====================================================================!
-  ! Create a new pio file pointer based on filename.
-  subroutine get_pio_atm_file(filename,pio_file,purpose,iotype)
-    use pio, only: PIO_inq_dimid, PIO_inq_dimlen
-
-    character(len=*),intent(in)   :: filename     ! Name of file to be found
-    type(pio_atm_file_t), pointer :: pio_file     ! Pointer to pio_atm_output structure associated with this filename
-    integer,intent(in)            :: purpose      ! Purpose for this file lookup, 0 = find already existing, 1 = create new as output, 2 = open new as input
-    integer,intent(in)            :: iotype
-
-    logical                        :: found
-    type(pio_file_list_t), pointer :: new_list_item
-
-    integer                        :: ierr, time_id
-
-    ! Sanity checks
-    if ( .not. (is_read(purpose) .or. is_write(purpose) .or. is_append(purpose)) ) then
-      call errorHandle("PIO Error: unrecognized open mode requested for file '"//filename//"'.",-999)
-    endif
-    if ( is_read(purpose) .and. is_write(purpose) ) then
-      call errorHandle("PIO Error: both READ and WRITE mode requested for file '"//filename//"'.",-999)
-    endif
-    if ( is_read(purpose) .and. is_append(purpose) ) then
-      call errorHandle("PIO Error: APPEND mode requested along with READ mode for file '"//filename//"'.",-999)
-    endif
-
-    ! If the file already exists, return that file
-    call lookup_pio_atm_file(trim(filename),pio_file,found)
-    if (found) then
-      if (is_write(purpose) .or. is_write(pio_file%purpose) ) then
-        ! We only allow multiple customers of the file if they all use it in read mode.
-        call errorHandle("PIO Error: file '"//trim(filename)//"' was already open for writing.",-999)
-      endif
-      pio_file%num_customers = pio_file%num_customers + 1
-    else
-      allocate(new_list_item)
-      allocate(new_list_item%pio_file)
-      pio_file => new_list_item%pio_file
-
-      ! Create and initialize the new pio file:
-      pio_file%filename = trim(filename)
-      pio_file%numRecs = 0
-      pio_file%num_customers = 1
-      pio_file%purpose = purpose
-      if (is_read(purpose) .or. is_append(purpose)) then
-        ! Either read or append to existing file. Either way, file must exist on disk
-        call eam_pio_openfile(pio_file,trim(pio_file%filename),iotype)
-        ! Update the numRecs to match the number of recs in this file.
-        ierr = pio_inq_dimid(pio_file%pioFileDesc,"time",time_id)
-        if (ierr.ne.0) then
-          ! time is not present in the file, set the number of Recs to 1
-          pio_file%numRecs = 1
-        else
-          ! time is present, set the number of Recs accordingly
-          ierr = pio_inq_dimlen(pio_file%pioFileDesc,time_id,pio_file%numRecs)
-          call errorHandle("EAM_PIO ERROR: Unable to determine length for dimension time in file "//trim(pio_file%filename),ierr)
-        end if
-      elseif (is_write(purpose)) then
-        ! New output file
-        call eam_pio_createfile(pio_file%pioFileDesc,trim(pio_file%filename),iotype)
-        call eam_pio_createHeader(pio_file%pioFileDesc)
-      else
-        call errorHandle("PIO Error: get_pio_atm_file with filename = "//trim(filename)//", purpose (int) assigned to this lookup is not valid" ,-999)
-      end if
-
-      ! Update the pio file list
-      if (associated(pio_file_list_back)) then
-        ! 1) Link new file to the new_list_itement back of the list
-        new_list_item%prev => pio_file_list_back
-        ! 2) Link the current last element of the list to the new one
-        pio_file_list_back%next => new_list_item
-        ! 3) and update the pointer to the last
-        pio_file_list_back => new_list_item
-      else
-        ! The list was empty. Set both front/back to point to the new item
-        pio_file_list_front => new_list_item
-        pio_file_list_back  => new_list_item
-      endif
-    endif
-  end subroutine get_pio_atm_file
-!=====================================================================!
-  ! Retrieve the time value for a specific time_index
-  ! If the input arg time_index is not provided, then it is assumed the user wants
-  ! the last time entry. If time_index is present, it MUST be valid
-  function read_time_at_index(filename,time_index) result(val)
-    use pio,          only: PIO_get_var, PIO_inq_varid, PIO_inq_dimid, PIO_inq_dimlen
-
-    character(len=*), intent(in)   :: filename
-    integer, intent(in), optional  :: time_index
-    real(c_double)                 :: val
-    real(c_double)                 :: val_buf(1)
-
-    type(pio_atm_file_t), pointer :: pio_atm_file
-    logical                       :: found
-    integer                       :: dim_id, time_len, ierr
-    type(var_desc_t)              :: varid ! netCDF variable ID
-    integer                       :: strt(1), cnt(1), timeidx
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    if (.not.found) call errorHandle("read_time_at_index ERROR: File "//trim(filename)//" not found",-999)
-    ierr = PIO_inq_varid(pio_atm_file%pioFileDesc,"time",varid)
-    call errorHandle('read_time_at_index: Error finding variable ID for "time" in file '//trim(filename)//'.',ierr);
-
-    ierr = pio_inq_dimid(pio_atm_file%pioFileDesc,trim("time"),dim_id)
-    call errorHandle("read_time_at_index ERROR: dimension 'time' not found in file "//trim(filename)//".",ierr)
-    ierr = pio_inq_dimlen(pio_atm_file%pioFileDesc,dim_id,time_len)
-    call errorHandle("PIO Error! Something went wrong when inquiring time dim length on file file "//trim(filename)//".",ierr)
-
-    if (present(time_index)) then
-      timeidx = time_index
-    else
-      timeidx = time_len
-    endif
-    if (timeidx .gt. time_len) then
-      call errorHandle("read_time_at_index ERROR: time_index arg larger than length of time dimension",-999)
-    elseif (timeidx .le. 0) then
-      call errorHandle("read_time_at_index ERROR: time_index arg must be positive",-999)
-    end if
-
-    strt(1) = timeidx
-    cnt(1)  = 1
-    ierr = PIO_get_var(pio_atm_file%pioFileDesc,varid,strt,cnt,val_buf)
-    call errorHandle('read_time_at_index: Error reading variable "time" in file '//trim(filename)//'.',ierr);
-    val  = val_buf(1)
-  end function read_time_at_index
-!=====================================================================!
-  ! Write output to file based on type (int or real)
-  ! --Note-- that any dimensionality could be written if it is flattened to 1D
-  ! before calling a write routine.
-  ! Mandatory inputs are:
-  ! filename:     the netCDF filename to be written to.
-  ! varname:      The shortname for the variable being written.
-  ! var_data_ptr: An array of data that will be used to write the output.  NOTE:
-  !               If PIO MPI ranks > 1, var_data_ptr should be the subset of the global array
-  !               which includes only those degrees of freedom that have been
-  !               assigned to this rank.  See set_dof above.
-  !---------------------------------------------------------------------------
-  !
-  !  grid_write_darray_1d: Write a variable defined on this grid
-  !
-  !---------------------------------------------------------------------------
-  subroutine grid_write_darray_float(filename, varname, buf, buf_size)
-    use pio, only: PIO_put_var, PIO_setframe, PIO_write_darray
-    use pio_types, only: PIO_max_var_dims
-
-    ! Dummy arguments
-    character(len=*),    intent(in) :: filename       ! PIO filename
-    character(len=*),    intent(in) :: varname
-    integer(kind=c_int), intent(in) :: buf_size
-    real(kind=c_float),  intent(in) :: buf(buf_size)
-
-    ! Local variables
-
-    type(pio_atm_file_t), pointer :: pio_atm_file
-    type(hist_var_t), pointer     :: var
-    integer                       :: ierr,jdim
-    integer                       :: start(pio_max_var_dims), count(pio_max_var_dims)
-    logical                       :: found
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    call get_var(pio_atm_file,varname,var)
-
-    if (var%has_t_dim) then
-      ! Set the time index we are writing
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(max(1,pio_atm_file%numRecs),kind=pio_offset_kind))
-    endif
-
-    if (var%is_partitioned) then
-      call pio_write_darray(pio_atm_file%pioFileDesc, var%piovar, var%iodesc, buf, ierr)
-    else
-      if (var%has_t_dim) then
-        do jdim=1,var%numdims
-          if (var%dimid(jdim) .eq. time_dimid) then
-            start (jdim) = int(max(1,pio_atm_file%numRecs))
-            count (jdim) = 1
-          else
-            start (jdim) = 1
-            count (jdim) = var%dimlen(jdim)
-          endif
-        enddo
-        ierr = pio_put_var(pio_atm_file%pioFileDesc,var%piovar,start(:var%numdims),count(:var%numdims),buf)
-      else
-        ierr = pio_put_var(pio_atm_file%pioFileDesc,var%piovar,buf)
-      endif
-    endif
-
-    call errorHandle( 'eam_grid_write_darray_float: Error writing variable '//trim(varname),ierr)
-  end subroutine grid_write_darray_float
-  subroutine grid_write_darray_double(filename, varname, buf, buf_size)
-    use pio, only: PIO_put_var, PIO_setframe, PIO_write_darray
-    use pio_types, only: PIO_max_var_dims
-
-    ! Dummy arguments
-    character(len=*),    intent(in) :: filename       ! PIO filename
-    character(len=*),    intent(in) :: varname
-    integer(kind=c_int), intent(in) :: buf_size
-    real(kind=c_double), intent(in) :: buf(buf_size)
-
-    ! Local variables
-
-    type(pio_atm_file_t), pointer :: pio_atm_file
-    type(hist_var_t), pointer     :: var
-    integer                       :: ierr,jdim
-    integer                       :: start(pio_max_var_dims), count(pio_max_var_dims)
-    logical                       :: found
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    call get_var(pio_atm_file,varname,var)
-
-    if (var%has_t_dim) then
-      ! Set the time index we are writing
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(max(1,pio_atm_file%numRecs),kind=pio_offset_kind))
-    endif
-
-    if (var%is_partitioned) then
-      call pio_write_darray(pio_atm_file%pioFileDesc, var%piovar, var%iodesc, buf, ierr)
-    else
-      if (var%has_t_dim) then
-        do jdim=1,var%numdims
-          if (var%dimid(jdim) .eq. time_dimid) then
-            start (jdim) = int(max(1,pio_atm_file%numRecs))
-            count (jdim) = 1
-          else
-            start (jdim) = 1
-            count (jdim) = var%dimlen(jdim)
-          endif
-        enddo
-        ierr = pio_put_var(pio_atm_file%pioFileDesc,var%piovar,start(:var%numdims),count(:var%numdims),buf)
-      else
-        ierr = pio_put_var(pio_atm_file%pioFileDesc,var%piovar,buf)
-      endif
-    endif
-
-    call errorHandle( 'eam_grid_write_darray_double: Error writing variable '//trim(varname),ierr)
-  end subroutine grid_write_darray_double
-  subroutine grid_write_darray_int(filename, varname, buf, buf_size)
-    use pio, only: PIO_put_var, PIO_setframe, PIO_write_darray
-    use pio_types, only: PIO_max_var_dims
-
-    ! Dummy arguments
-    character(len=*),    intent(in) :: filename       ! PIO filename
-    character(len=*),    intent(in) :: varname
-    integer(kind=c_int), intent(in) :: buf_size
-    integer(kind=c_int), intent(in) :: buf(buf_size)
-
-    ! Local variables
-
-    type(pio_atm_file_t), pointer :: pio_atm_file
-    type(hist_var_t), pointer     :: var
-    integer                       :: ierr,jdim
-    integer                       :: start(pio_max_var_dims), count(pio_max_var_dims)
-    logical                       :: found
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    call get_var(pio_atm_file,varname,var)
-
-    if (var%has_t_dim) then
-      ! Set the time index we are writing
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(max(1,pio_atm_file%numRecs),kind=pio_offset_kind))
-    endif
-
-    if (var%is_partitioned) then
-      call pio_write_darray(pio_atm_file%pioFileDesc, var%piovar, var%iodesc, buf, ierr)
-    else
-      if (var%has_t_dim) then
-        do jdim=1,var%numdims
-          if (var%dimid(jdim) .eq. time_dimid) then
-            start (jdim) = int(max(1,pio_atm_file%numRecs))
-            count (jdim) = 1
-          else
-            start (jdim) = 1
-            count (jdim) = var%dimlen(jdim)
-          endif
-        enddo
-        ierr = pio_put_var(pio_atm_file%pioFileDesc,var%piovar,start(:var%numdims),count(:var%numdims),buf)
-      else
-        ierr = pio_put_var(pio_atm_file%pioFileDesc,var%piovar,buf)
-      endif
-    endif
-
-    call errorHandle( 'eam_grid_write_darray_int: Error writing variable '//trim(varname),ierr)
-  end subroutine grid_write_darray_int
-!=====================================================================!
-  ! Read output from file based on type (int or real)
-  ! --Note-- that any dimensionality could be read if it is flattened to 1D
-  ! before calling a write routine.
-  ! Mandatory inputs are:
-  ! filename:     the netCDF filename to be read from.
-  ! varname:      The shortname for the variable being read.i
-  ! var_data_ptr: An c_ptr of data that will be used to read the input.  NOTE:
-  !               If PIO MPI ranks > 1, var_data_ptr should be the subset of the global array
-  !               which includes only those degrees of freedom that have been
-  !               assigned to this rank.  See set_dof above.
-  ! time_index:   The 1-based time index for this variable (0 is ignored).
-  !---------------------------------------------------------------------------
-  !
-  !  grid_read_darray_1d: Read a variable defined on this grid
-  !
-  !---------------------------------------------------------------------------
-  subroutine grid_read_darray_double(filename, varname, buf, buf_size, time_index)
-    use pio, only: PIO_setframe, PIO_read_darray
-
-    ! Dummy arguments
-    character(len=*),     intent(in) :: filename       ! PIO filename
-    character(len=*),     intent(in) :: varname
-    integer (kind=c_int), intent(in) :: buf_size
-    real(kind=c_double),  intent(out) :: buf(buf_size)
-    integer, intent(in)          :: time_index
-
-    ! Local variables
-    type(pio_atm_file_t),pointer       :: pio_atm_file
-    type(hist_var_t), pointer          :: var
-    integer                            :: ierr, var_size
-    logical                            :: found
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    call get_var(pio_atm_file,varname,var)
-    ! Set the timesnap we are reading
-    if (time_index .gt. 0) then
-      ! The user has set a valid time index to read from
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(time_index,kind=pio_offset_kind))
-    else
-      ! Otherwise default to the last time_index in the file
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(pio_atm_file%numRecs,kind=pio_offset_kind))
-    end if
-
-    ! We don't want the extent along the 'time' dimension
-    var_size = SIZE(var%compdof)
-
-    ! Now we know the exact size of the array, and can shape the f90 pointer
-    call pio_read_darray(pio_atm_file%pioFileDesc, var%piovar, var%iodesc, buf, ierr)
-    call errorHandle( 'eam_grid_read_darray_double: Error reading variable '//trim(varname),ierr)
-  end subroutine grid_read_darray_double
-  subroutine grid_read_darray_float(filename, varname, buf, buf_size, time_index)
-    use pio, only: PIO_setframe, PIO_read_darray
-
-    ! Dummy arguments
-    character(len=*),     intent(in) :: filename       ! PIO filename
-    character(len=*),     intent(in) :: varname
-    integer (kind=c_int), intent(in) :: buf_size
-    real(kind=c_float),  intent(out) :: buf(buf_size)
-    integer, intent(in)          :: time_index
-
-    ! Local variables
-    type(pio_atm_file_t),pointer       :: pio_atm_file
-    type(hist_var_t), pointer          :: var
-    integer                            :: ierr, var_size
-    logical                            :: found
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    call get_var(pio_atm_file,varname,var)
-
-    ! Set the timesnap we are reading
-    if (time_index .gt. 0) then
-      ! The user has set a valid time index to read from
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(time_index,kind=pio_offset_kind))
-    else
-      ! Otherwise default to the last time_index in the file
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(pio_atm_file%numRecs,kind=pio_offset_kind))
-    end if
-
-    ! We don't want the extent along the 'time' dimension
-    var_size = SIZE(var%compdof)
-
-    ! Now we know the exact size of the array, and can shape the f90 pointer
-    call pio_read_darray(pio_atm_file%pioFileDesc, var%piovar, var%iodesc, buf, ierr)
-    call errorHandle( 'eam_grid_read_darray_float: Error reading variable '//trim(varname),ierr)
-  end subroutine grid_read_darray_float
-  subroutine grid_read_darray_int(filename, varname, buf, buf_size, time_index)
-    use pio, only: PIO_setframe, PIO_read_darray
-
-    ! Dummy arguments
-    character(len=*),     intent(in) :: filename       ! PIO filename
-    character(len=*),     intent(in) :: varname
-    integer (kind=c_int), intent(in) :: buf_size
-    integer (kind=c_int), intent(out) :: buf(buf_size)
-    integer, intent(in)          :: time_index
-
-    ! Local variables
-    type(pio_atm_file_t),pointer       :: pio_atm_file
-    type(hist_var_t), pointer          :: var
-    integer                            :: ierr, var_size
-    logical                            :: found
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,found)
-    call get_var(pio_atm_file,varname,var)
-
-    ! Set the timesnap we are reading
-    if (time_index .gt. 0) then
-      ! The user has set a valid time index to read from
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(time_index,kind=pio_offset_kind))
-    else
-      ! Otherwise default to the last time_index in the file
-      call PIO_setframe(pio_atm_file%pioFileDesc,var%piovar,int(pio_atm_file%numRecs,kind=pio_offset_kind))
-    end if
-
-    ! We don't want the extent along the 'time' dimension
-    var_size = SIZE(var%compdof)
-
-    ! Now we know the exact size of the array, and can shape the f90 pointer
-    call pio_read_darray(pio_atm_file%pioFileDesc, var%piovar, var%iodesc, buf, ierr)
-    call errorHandle( 'eam_grid_read_darray_int: Error reading variable '//trim(varname),ierr)
-  end subroutine grid_read_darray_int
-!=====================================================================!
-  subroutine convert_int_2_str(int_in,str_out)
-    integer, intent(in)           :: int_in
-    character(len=*), intent(out) :: str_out
-
-    character(len=8) :: fmt_str
-
-    if (int_in < 0) then
-      fmt_str = "(A1,"
-    else
-      fmt_str = "("
-    end if
-
-    if (abs(int_in)<10) then
-      fmt_str = trim(fmt_str)//"I1)"
-    elseif (abs(int_in)<1e2) then
-      fmt_str = trim(fmt_str)//"I2)"
-    elseif (abs(int_in)<1e3) then
-      fmt_str = trim(fmt_str)//"I3)"
-    elseif (abs(int_in)<1e4) then
-      fmt_str = trim(fmt_str)//"I4)"
-    elseif (abs(int_in)<1e5) then
-      fmt_str = trim(fmt_str)//"I5)"
-    elseif (abs(int_in)<1e6) then
-      fmt_str = trim(fmt_str)//"I6)"
-    elseif (abs(int_in)<1e7) then
-      fmt_str = trim(fmt_str)//"I7)"
-    elseif (abs(int_in)<1e8) then
-      fmt_str = trim(fmt_str)//"I8)"
-    elseif (abs(int_in)<1e9) then
-      fmt_str = trim(fmt_str)//"I9)"
-    endif
-
-    if (int_in < 0) then
-      write(str_out,fmt_str) "n", int_in
-    else
-      write(str_out,fmt_str) int_in
-    end if
-
-  end subroutine convert_int_2_str
-
-  subroutine get_coord (filename,shortname,hist_coord)
-    character(len=256), intent(in)           :: filename
-    character(len=256), intent(in)           :: shortname
-    type(hist_coord_t), pointer, intent(out) :: hist_coord
-
-    type(pio_atm_file_t), pointer    :: pio_atm_file
-    type(hist_coord_list_t), pointer :: curr, prev
-    logical                          :: file_found, dim_found
-
-    hist_coord => NULL()
-
-    call lookup_pio_atm_file(trim(filename),pio_atm_file,file_found)
-    if (.not. file_found ) then
-      call errorHandle("PIO ERROR: error retrieving dimension "//trim(shortname)//" in file "//trim(filename)//".\n PIO file not found or not open.",-999)
-    endif
-
-    curr => pio_atm_file%coord_list_top
-    do while (associated(curr))
-      if (associated(curr%coord)) then
-        if(trim(curr%coord%name)==trim(shortname)) then
-          dim_found = .true.
-          exit
-        endif
-      end if
-      prev => curr
-      curr => prev%next
-    end do
-
-    if (.not. dim_found ) then
-      call errorHandle("PIO ERROR: error retrieving dimension "//trim(shortname)//" from file "//trim(filename)//". Dimension not found.",-999)
-    endif
-
-    hist_coord => curr%coord
-  end subroutine get_coord
-
-  function is_read (purpose)
-    integer, intent(in) :: purpose
-    logical :: is_read
-    is_read = iand(purpose,file_purpose_in) .ne. 0
-  end function is_read
-  function is_write (purpose)
-    integer, intent(in) :: purpose
-    logical :: is_write
-    is_write = iand(purpose,file_purpose_out) .ne. 0
-  end function is_write
-  function is_append (purpose)
-    integer, intent(in) :: purpose
-    logical :: is_append
-    is_append = iand(purpose,file_purpose_app) .ne. 0
-  end function is_append
-!=====================================================================!
-end module scream_scorpio_interface
diff --git a/components/eamxx/src/share/io/scream_scorpio_interface.cpp b/components/eamxx/src/share/io/scream_scorpio_interface.cpp
index ead1aa0fbd6..0d4918ad230 100644
--- a/components/eamxx/src/share/io/scream_scorpio_interface.cpp
+++ b/components/eamxx/src/share/io/scream_scorpio_interface.cpp
@@ -1,54 +1,125 @@
 #include "scream_scorpio_interface.hpp"
-#include "ekat/ekat_scalar_traits.hpp"
+#include "scream_shr_interface_c2f.hpp"
+
 #include "scream_config.h"
 
-#include "ekat/ekat_assert.hpp"
-#include "share/scream_types.hpp"
+#include <ekat/ekat_assert.hpp>
+#include <ekat/util/ekat_string_utils.hpp>
 
 #include <pio.h>
 
-#include <string>
-
-
-using scream::Real;
-using scream::Int;
-extern "C" {
-
-// Fortran routines to be called from C++
-  void register_file_c2f(const char*&& filename, const int& mode, const int& iotype);
-  int get_file_mode_c2f(const char*&& filename);
-  void set_decomp_c2f(const char*&& filename);
-  void set_dof_c2f(const char*&& filename,const char*&& varname,const Int dof_len,const std::int64_t *x_dof);
-  void grid_read_data_array_c2f_int(const char*&& filename, const char*&& varname, const Int time_index, int *buf, const int buf_size);
-  void grid_read_data_array_c2f_float(const char*&& filename, const char*&& varname, const Int time_index, float *buf, const int buf_size);
-  void grid_read_data_array_c2f_double(const char*&& filename, const char*&& varname, const Int time_index, double *buf, const int buf_size);
-
-  void grid_write_data_array_c2f_int(const char*&& filename, const char*&& varname, const int* buf, const int buf_size);
-  void grid_write_data_array_c2f_float(const char*&& filename, const char*&& varname, const float* buf, const int buf_size);
-  void grid_write_data_array_c2f_double(const char*&& filename, const char*&& varname, const double* buf, const int buf_size);
-  void eam_init_pio_subsystem_c2f(const int mpicom, const int atm_id);
-  void eam_pio_finalize_c2f();
-  void eam_pio_closefile_c2f(const char*&& filename);
-  void eam_pio_flush_file_c2f(const char*&& filename);
-  void pio_update_time_c2f(const char*&& filename,const double time);
-  void register_dimension_c2f(const char*&& filename, const char*&& shortname, const char*&& longname, const int global_length, const bool partitioned);
-  void register_variable_c2f(const char*&& filename, const char*&& shortname, const char*&& longname,
-                             const char*&& units, const int numdims, const char** var_dimensions,
-                             const int dtype, const int nc_dtype, const char*&& pio_decomp_tag);
-  void set_variable_metadata_char_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name, const char*&& meta_val);
-  void set_variable_metadata_float_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name, const float meta_val);
-  void set_variable_metadata_double_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name, const double meta_val);
-  float get_variable_metadata_float_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name);
-  double get_variable_metadata_double_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name);
-  void get_variable_metadata_char_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name, char*&& meta_val);
-  void eam_pio_redef_c2f(const char*&& filename);
-  void eam_pio_enddef_c2f(const char*&& filename);
-  bool is_enddef_c2f(const char*&& filename);
-} // extern C
+#include <numeric>
 
 namespace scream {
 namespace scorpio {
 
+// This class is an implementation detail, and therefore it is hidden inside
+// a cpp file. All customers of IO capabilities must use the common interfaces
+// exposed in the header file of this source file.
+// This class simply serves as a container for persistent IO data.
+struct ScorpioSession
+{
+public:
+  static ScorpioSession& instance () {
+    static ScorpioSession s;
+    return s;
+  }
+
+  template<typename T>
+  using strmap_t = std::map<std::string,T>;
+
+  strmap_t<PIOFile>                     files;
+  strmap_t<std::shared_ptr<PIODecomp>>  decomps;
+
+  // In the above map, we would like to label decomps as dtype_dim1$N1_dim2$N2...
+  // where N$i is the global length of dim$i. However, it *may* happen that we use
+  // two different decompositions for the same global layout, which would clash
+  // the names. For this reason, we append at the end an increasing counter,
+  // which disambiguate between globally-equivalent partitions.
+  // When adding a new decomp, we check this map to see if another decomp
+  // already exists with the same global layout. If so, we first check to see
+  // if that decomp is equivalent to the new one *on all ranks*. If yes, we
+  // recycle it, otherwise we create a new PIO decomp.
+  // strmap_t<std::list<std::string>>    decomp_global_layout_to_decomp_name;
+  // strmap_t<int>                       decomp_global_layout_to_counter;
+
+  int         pio_sysid        = -1;
+  int         pio_type_default = -1;
+  int         pio_rearranger   = -1;
+  int         pio_format       = -1;
+
+  ekat::Comm  comm;
+
+private:
+
+  ScorpioSession () = default;
+};
+
+// --------------------------------------------------------------------------------------------- //
+
+template<typename S, typename D>
+void copy_data (const S* src, D* dst, int n) {
+  for (int i=0; i<n; ++i) {
+    dst[i] = src[i];
+  }
+}
+
+// Utility for common IO operation failure
+void check_scorpio_noerr (const int err,
+                          const std::string& func_name,
+                          const std::string& pioc_func_name)
+{
+  EKAT_REQUIRE_MSG (err==PIO_NOERR,
+      "Error! Something went wrong while performing a pio operation.\n"
+      " - pio error code: " + std::to_string(err) + "\n"
+      " - from interface function: scorpio::" + func_name + "\n"
+      " - calling PIOc function: PIOc_" + pioc_func_name + "\n");
+}
+
+void check_scorpio_noerr (const int err, const std::string& filename,
+                          const std::string& func_name,
+                          const std::string& pioc_func_name)
+{
+  EKAT_REQUIRE_MSG (err==PIO_NOERR,
+      "Error! Something went wrong while performing a pio operation.\n"
+      " - pio error code: " + std::to_string(err) + "\n"
+      " - filename: " + filename + "\n" 
+      " - from interface function: scorpio::" + func_name + "\n"
+      " - calling PIOc function: " + pioc_func_name + "\n");
+}
+
+void check_scorpio_noerr (const int err,
+                          const std::string& filename,
+                          const std::string& entity_type,
+                          const std::string& entity_name,
+                          const std::string& func_name,
+                          const std::string& pioc_func_name)
+{
+  EKAT_REQUIRE_MSG (err==PIO_NOERR,
+      "Error! Something went wrong while performing a pio operation.\n"
+      " - pio error code: " + std::to_string(err) + "\n"
+      " - filename: " + filename + "\n" 
+      " - " + entity_type + ": " + entity_name + "\n" 
+      " - from interface function: scorpio::" + func_name + "\n"
+      " - calling PIOc function: " + pioc_func_name + "\n");
+}
+
+// Return name of a shared ptr to PIO entity (to use inside ekat::join)
+std::string get_entity_name (const std::shared_ptr<const PIOEntity>& e)
+{
+  return e->name;
+}
+
+template<typename T>
+std::string print_map_keys (const std::map<std::string,T>& map) {
+  std::string s;
+  for (const auto& it : map) {
+    s += it.first + ",";
+  }
+  s.pop_back();
+  return s;
+}
+
 // Retrieve the int codes PIO uses to specify data types
 int nctype (const std::string& type) {
   if (type=="int") {
@@ -65,637 +136,1351 @@ int nctype (const std::string& type) {
 #else
     return PIO_FLOAT;
 #endif
+  } else if (type=="char") {
+    return PIO_CHAR;
   } else {
     EKAT_ERROR_MSG ("Error! Unrecognized/unsupported data type '" + type + "'.\n");
   }
 }
-std::string nctype2str (const int type) {
-  for (auto t : {"int", "int64", "float", "double"}) {
-    if (nctype(t)==type) return t;
+
+template<typename T>
+int nctype () {
+  if (std::is_same<T,int>::value) {
+    return PIO_INT;
+  } else if (std::is_same<T,std::int64_t>::value) {
+    return PIO_INT64;
+  } else if (std::is_same<T,float>::value) {
+    return PIO_FLOAT;
+  } else if (std::is_same<T,double>::value) {
+    return PIO_DOUBLE;
+  } else if (std::is_same<T,std::string>::value) {
+    return PIO_CHAR;
+  } else {
+    EKAT_ERROR_MSG ("Error! Unrecognized/unsupported data type.\n");
   }
-  return "UNKNOWN";
 }
-/* ----------------------------------------------------------------- */
-void eam_init_pio_subsystem(const ekat::Comm& comm) {
-  MPI_Fint fcomm = MPI_Comm_c2f(comm.mpi_comm());
-  eam_init_pio_subsystem(fcomm);
+
+template<typename T>
+const void* ncdata (const T& v) {
+  return reinterpret_cast<const void*>(&v);
+}
+template<>
+const void* ncdata (const std::string& v) {
+  return reinterpret_cast<const void*>(v.data());
 }
 
-void eam_init_pio_subsystem(const int mpicom, const int atm_id) {
-  // TODO: Right now the compid has been hardcoded to 0 and the flag
-  // to create a init a subsystem in SCREAM is hardcoded to true.
-  // When surface coupling is established we will need to refactor this
-  // routine to pass the appropriate values depending on if we are running
-  // the full model or a unit test.
-  eam_init_pio_subsystem_c2f(mpicom,atm_id);
+template<typename T>
+PIO_Offset nclen (const T& v) {
+  return 1;
+}
+template<>
+PIO_Offset nclen (const std::string& v) {
+  return v.size();
 }
-/* ----------------------------------------------------------------- */
-void eam_pio_finalize() {
-  eam_pio_finalize_c2f();
+
+std::string refine_dtype (const std::string& dtype) {
+  if (dtype=="real") {
+#if defined(SCREAM_DOUBLE_PRECISION)
+    return "double";
+#else
+    return "float";
+#endif
+  } else if (dtype=="single") {
+    return "float";
+  } else {
+    return dtype;
+  }
 }
-/* ----------------------------------------------------------------- */
-void register_file(const std::string& filename, const FileMode mode, const int iotype) {
-  register_file_c2f(filename.c_str(),mode,iotype);
+
+size_t dtype_size (const std::string& dtype) {
+  if (dtype=="int") {
+    return sizeof(int);
+  } else if (dtype=="int64") {
+    return sizeof(long long);
+  } else if (dtype=="float") {
+    return sizeof(float);
+  } else if (dtype=="double") {
+    return sizeof(double);
+  } else {
+    EKAT_ERROR_MSG ("Error! Unrecognized/unsupported data type '" + dtype + "'.\n");
+  }
+  return 0;
 }
-/* ----------------------------------------------------------------- */
-void eam_pio_closefile(const std::string& filename) {
 
-  eam_pio_closefile_c2f(filename.c_str());
+// ====================== Local utilities ========================== //
+
+namespace impl {
+// Note: these utilities are used in this file to retrieve PIO entities,
+//       so that we implement all checks once (rather than in every function)
+
+// Small struct that allows to quickly open a file (in Read mode) if it wasn't open.
+// If the file had to be open, when the struct is deleted, it will release the file.
+struct PeekFile {
+  PeekFile(const std::string& filename_in) {
+    filename = filename_in;
+    was_open = is_file_open(filename);
+    if (not was_open) {
+      register_file(filename,Read);
+    }
+    auto& s = ScorpioSession::instance();
+    file = &s.files[filename];
+  }
+
+  ~PeekFile () {
+    if (not was_open) {
+      // Note: this function _could_ throw, but it should not happen (unless someone
+      //       else called release_file twice). That's b/c we either are not the only
+      //       customer (so nothing to be done other than a ref count decrement) or
+      //       the file was open in Read mode, in which case it doesn't need to do
+      //       much in scorpio.
+      release_file(filename);
+    }
+  }
+
+  const PIOFile*  file;
+  std::string     filename;
+  bool            was_open;
+};
+
+PIOFile& get_file (const std::string& filename,
+                   const std::string& context)
+{
+  auto& s = ScorpioSession::instance();
+
+  EKAT_REQUIRE_MSG (s.files.count(filename)==1,
+      "Error! Could not retrieve the file. File not open.\n"
+      " - filename: " + filename + "\n"
+      "Context:\n"
+      " " + context + "\n");
+
+  return s.files.at(filename);
 }
-void eam_flush_file(const std::string& filename) {
-  eam_pio_flush_file_c2f(filename.c_str());
+
+PIODim& get_dim (const std::string& filename,
+                 const std::string& dimname,
+                 const std::string& context)
+{
+  const auto& f = get_file(filename,context);
+  EKAT_REQUIRE_MSG (f.dims.count(dimname)==1,
+      "Error! Could not retrieve dimension. Dimension not found.\n"
+      " - filename: " + filename + "\n"
+      " - dimname : " + dimname + "\n"
+      " - dims on file: " + print_map_keys(f.dims) + "\n"
+      "Context:\n"
+      " " + context + "\n");
+
+  return *f.dims.at(dimname);
 }
-/* ----------------------------------------------------------------- */
-void set_decomp(const std::string& filename) {
 
-  set_decomp_c2f(filename.c_str());
+PIOVar& get_var (const std::string& filename,
+                 const std::string& varname,
+                 const std::string& context)
+{
+  const auto& f = get_file(filename,context);
+  EKAT_REQUIRE_MSG (f.vars.count(varname)==1,
+      "Error! Could not retrieve variable. Variable not found.\n"
+      " - filename: " + filename + "\n"
+      " - varname : " + varname + "\n"
+      " - vars on file : " + print_map_keys(f.vars) + "\n"
+      "Context:\n"
+      " " + context + "\n");
+
+  return *f.vars.at(varname);
 }
-/* ----------------------------------------------------------------- */
-int get_dimlen(const std::string& filename, const std::string& dimname)
+
+} // namespace impl
+
+// ====================== Global IO operations ======================= // 
+
+void init_subsystem(const ekat::Comm& comm, const int atm_id)
 {
-  int ncid, dimid, err;
-  PIO_Offset len;
+  auto& s = ScorpioSession::instance();
+  s.comm = comm;
 
-  bool was_open = is_file_open_c2f(filename.c_str(),-1);
-  if (not was_open) {
-    register_file(filename,Read);
-  }
+  EKAT_REQUIRE_MSG (s.pio_sysid==-1,
+      "Error! Attmept to re-initialize pio subsystem.\n");
 
-  ncid = get_file_ncid_c2f (filename.c_str());
-  err = PIOc_inq_dimid(ncid,dimname.c_str(),&dimid);
-  EKAT_REQUIRE_MSG (err!=PIO_EBADDIM,
-      "Error! Could not find dimension in the file.\n"
-      " - filename : " + filename + "\n"
-      " - dimname  : " + dimname + "\n"
-      " - pio error: " + std::to_string(err) + "\n");
-  EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "Error! Something went wrong while retrieving dimension id.\n"
-      " - filename : " + filename + "\n"
-      " - dimname  : " + dimname + "\n"
-      " - pio error: " + std::to_string(err) + "\n");
+#ifdef SCREAM_CIME_BUILD
+  s.pio_sysid        = shr_get_iosysid_c2f(atm_id);
+  s.pio_type_default = shr_get_iotype_c2f(atm_id);
+  s.pio_rearranger   = shr_get_rearranger_c2f(atm_id);
+  s.pio_format       = shr_get_ioformat_c2f(atm_id);
+#else
+  // Use some reasonable defaults for standalone EAMxx tests
+  int stride = 1;
+  int base = 0;
 
-  err = PIOc_inq_dimlen(ncid,dimid,&len);
-  EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "Error! Something went wrong while querying dimension length.\n"
-      " - filename : " + filename + "\n"
-      " - dimname  : " + dimname + "\n"
-      " - pio error: " + std::to_string(err) + "\n");
+  s.pio_rearranger = PIO_REARR_SUBSET;
+  s.pio_format     = PIO_64BIT_DATA;
+#if PIO_USE_PNETCDF
+  s.pio_type_default = PIO_IOTYPE_PNETCDF;
+#elif PIO_USE_NETCDF
+  s.pio_type_default = PIO_IOTYPE_NETCDF;
+#else
+#error "Standalone EAMxx requires either PNETCDF or NETCDF iotype to be available in Scorpio"
+#endif
 
-  if (not was_open) {
-    eam_pio_closefile(filename);
-  }
+  auto err = PIOc_Init_Intracomm(comm.mpi_comm(), comm.size(), stride, base, s.pio_rearranger, &s.pio_sysid);
+  check_scorpio_noerr (err,"init_subsystem", "Init_Intracomm");
+
+  // Unused in standalone mode
+  (void) atm_id;
+#endif
+
+  static_assert (sizeof(offset_t)==sizeof(PIO_Offset),
+      "Error! PIO was configured with PIO_OFFSET not a 64-bit int.\n");
+}
 
-  return len;
+bool is_subsystem_inited () {
+  return ScorpioSession::instance().pio_sysid!=-1;
 }
-/* ----------------------------------------------------------------- */
-bool has_dim (const std::string& filename, const std::string& dimname)
+
+void finalize_subsystem ()
 {
-  int ncid, dimid, err;
+  auto& s = ScorpioSession::instance();
 
-  bool was_open = is_file_open_c2f(filename.c_str(),-1);
-  if (not was_open) {
-    register_file(filename,Read);
-  }
+  // TODO: should we simply return instead? I think trying to finalize twice
+  //       *may* be a sign of possible bugs, though with Catch2 testing
+  //       I *think* there may be some issue with how the code is run.
+  EKAT_REQUIRE_MSG (s.pio_sysid!=-1,
+      "Error! PIO subsystem was already finalized.\n");
 
-  ncid = get_file_ncid_c2f (filename.c_str());
-  err = PIOc_inq_dimid(ncid,dimname.c_str(),&dimid);
-  if (err==PIO_EBADDIM) {
-    return false;
+  for (auto& it : s.files) {
+    EKAT_REQUIRE_MSG (it.second.num_customers==0,
+      "Error! ScorpioSession::finalize called, but a file is still in use elsewhere.\n"
+      " - filename: " + it.first + "\n");
   }
+  s.files.clear();
 
-  EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "Error! Something went wrong while retrieving dimension id.\n"
-      " - filename : " + filename + "\n"
-      " - dimname  : " + dimname + "\n"
-      " - pio error: " + std::to_string(err) + "\n");
-  if (not was_open) {
-    eam_pio_closefile(filename);
+  for (auto& it : s.decomps) {
+    EKAT_REQUIRE_MSG (it.second.use_count()==1,
+      "Error! ScorpioSession::finalize called, but a decomp is still stored elsewhere.\n"
+      " - decomp name: " + it.first + "\n");
+
+    int err = PIOc_freedecomp(s.pio_sysid,it.second->ncid);
+    check_scorpio_noerr(err,"finalize_subsystem","freedecomp");
   }
+  s.decomps.clear();
 
-  return true;
+#ifndef SCREAM_CIME_BUILD
+  // Don't finalize in CIME builds, since the coupler will take care of it
+  PIOc_finalize (s.pio_sysid);
+#endif
+
+  s.pio_sysid        = -1;
+  s.pio_type_default = -1;
+  s.pio_format       = -1;
+  s.pio_rearranger   = -1;
 }
-/* ----------------------------------------------------------------- */
-bool has_variable (const std::string& filename, const std::string& varname)
+
+// ========================= File operations ===================== //
+
+void register_file (const std::string& filename,
+                    const FileMode mode,
+                    const IOType iotype)
 {
-  int ncid, varid, err;
+  auto& s = ScorpioSession::instance();
+  auto& f = s.files[filename];
+  EKAT_REQUIRE_MSG (f.mode==Unset || f.mode==mode,
+      "Error! File was already opened with a different mode.\n"
+      " - filename: " + filename + "\n"
+      " - old mode: " + e2str(f.mode) + "\n"
+      " - new mode: " + e2str(mode) + "\n");
+  EKAT_REQUIRE_MSG (f.mode==Unset || f.iotype==iotype,
+      "Error! File was already opened with a different iotype.\n"
+      " - filename: " + filename + "\n"
+      " - old type: " + iotype2str(f.iotype) + "\n"
+      " - new type: " + iotype2str(iotype) + "\n");
+
+  if (f.mode == Unset) {
+    // First time we ask for this file. Call PIO open routine(s)
+    int err;
+    int iotype_int = iotype==IOType::DefaultIOType
+                   ? s.pio_type_default
+                   : static_cast<int>(iotype);
+    if (mode & Read) {
+      auto write = mode & Write ? PIO_WRITE : PIO_NOWRITE;
+      err = PIOc_openfile(s.pio_sysid,&f.ncid,&iotype_int,filename.c_str(),write);
+      f.enddef = true;
+    } else {
+      err = PIOc_createfile(s.pio_sysid,&f.ncid,&iotype_int,filename.c_str(),s.pio_format);
+      f.enddef = false;
+    }
+
+    EKAT_REQUIRE_MSG (err==PIO_NOERR,
+        "Error! Something went wrong while opening a file.\n"
+        " - filename : " + filename + "\n"
+        " - file mode: " + e2str(mode) + "\n"
+        " - pio error: " + std::to_string(err) + "\n");
+
+    f.mode = mode;
+    f.iotype = iotype;
+    f.name = filename;
+
+    if (mode & Read) {
+      // Read all dims/vars from file
+      PIO_Offset len;
+      int ndims, nvars, ngatts, unlimdimid;
+      err = PIOc_inq(f.ncid, &ndims, &nvars, &ngatts, &unlimdimid);
+      check_scorpio_noerr(err,f.name,"register_file","inq");
+
+      char name[PIO_MAX_NAME];
+      for (int idim=0; idim<ndims; ++idim) {
+        err = PIOc_inq_dim(f.ncid,idim,name,&len);
+        check_scorpio_noerr (err,f.name,"register_file","inq_dim");
+        auto dim = f.dims[name] = std::make_shared<PIODim>();
+        dim->name = name;
+        dim->fid = f.ncid;
+        dim->length = len;
+        dim->ncid = idim;
+        dim->unlimited = idim==unlimdimid;
+
+        if (dim->unlimited) {
+          f.time_dim = dim;
+        }
+      }
+
+      auto find_dim = [&](int dimid) -> std::shared_ptr<const PIODim> {
+        std::shared_ptr<const PIODim> d;
+        for (auto it : f.dims) {
+          if (it.second->ncid==dimid) {
+            d = it.second;
+          }
+        }
+        EKAT_REQUIRE_MSG (d!=nullptr,
+            "Error! Could not locat dimension id in the file.\n"
+            " - filename: " + f.name + "\n"
+            " - dim id  : " + std::to_string(dimid) + "\n");
+        return d;
+      };
+      int dtype,natts;
+      int dimids[PIO_MAX_DIMS];
+      for (int ivar=0; ivar<nvars; ++ivar) {
+        err = PIOc_inq_var(f.ncid,ivar,name,PIO_MAX_NAME,&dtype,&ndims,dimids,&natts);
+        check_scorpio_noerr(err,f.name,"register_file","inq_var");
+
+        auto var = f.vars[name] = std::make_shared<PIOVar>();
+        var->name = name;
+        var->ncid = ivar;
+        var->fid = f.ncid;
+        for (int idim=0; idim<ndims; ++idim) {
+          auto dim = find_dim(dimids[idim]);
+          if (dim->unlimited) {
+            var->time_dep = true;
+            var->num_records = dim->length;
+          } else {
+            var->dims.push_back(find_dim(dimids[idim]));
+          }
+        }
 
-  bool was_open = is_file_open_c2f(filename.c_str(),-1);
-  if (not was_open) {
-    register_file(filename,Read);
+        for (const auto& dt : {"int","int64","float","double","char"}) {
+          if (nctype(dt)==dtype) {
+            var->dtype = var->nc_dtype = dt;
+            break;
+          }
+        }
+        EKAT_REQUIRE_MSG (var->dtype!="",
+            "Error! Variable data type not supported.\n"
+            " - filename: " + filename + "\n"
+            " - varname : " + var->name + "\n"
+            " - nc dtype: " + std::to_string(dtype) + "\n");
+
+        for (int iatt=0; iatt<natts; ++iatt) {
+          err = PIOc_inq_attname(f.ncid,ivar,iatt,name);
+          check_scorpio_noerr(err,f.name,"register_file","inq_attname");
+          err = PIOc_inq_attlen(f.ncid,ivar,name,&len);
+          check_scorpio_noerr(err,f.name,"register_file","inq_attlen");
+          if (std::string(name)=="units") {
+            err = PIOc_get_att_text(f.ncid,ivar,"units",name);
+            name[len] = '\0';
+            check_scorpio_noerr(err,f.name,"register_file","get_att_text");
+            var->units = name;
+            break;
+          }
+        }
+      }
+    }
   }
+  ++f.num_customers;
+}
 
-  ncid = get_file_ncid_c2f (filename.c_str());
-  err = PIOc_inq_varid(ncid,varname.c_str(),&varid);
-  if (err==PIO_ENOTVAR) {
-    return false;
+void release_file  (const std::string& filename)
+{
+  auto& f = impl::get_file(filename,"scorpio::release_file");
+
+  --f.num_customers;
+  if (f.num_customers>0) {
+    return;
   }
-  EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "Error! Something went wrong while retrieving variable id.\n"
-      " - filename : " + filename + "\n"
-      " - varname  : " + varname + "\n"
-      " - pio error: " + std::to_string(err) + "\n");
-  if (not was_open) {
-    eam_pio_closefile(filename);
+
+  int err;
+  if (f.mode & Write) {
+    err = PIOc_sync(f.ncid);
+    check_scorpio_noerr (err,f.name,"release_file","sync");
   }
 
-  return true;
+  err = PIOc_closefile(f.ncid);
+  check_scorpio_noerr (err,f.name,"release_file","closefile");
+
+  auto& s = ScorpioSession::instance();
+  s.files.erase(filename);
 }
 
-bool has_attribute (const std::string& filename, const std::string& attname)
+void flush_file (const std::string &filename)
 {
-  return has_attribute(filename,"GLOBAL",attname);
+  auto& f = impl::get_file(filename,"scorpio::sync_file");
+  
+  EKAT_REQUIRE_MSG (f.mode & Write,
+      "Error! Cannot call sync_file. File is read-only.\n"
+      " - filename: " + filename + "\n");
+
+  int err = PIOc_sync(f.ncid);
+  check_scorpio_noerr (err,f.name,"sync_file","sync");
 }
 
-bool has_attribute (const std::string& filename, const std::string& varname, const std::string& attname)
+void redef(const std::string &filename)
 {
-  int ncid, varid, attid, err;
+  auto& f = impl::get_file(filename,"scorpio::redef");
+
+  EKAT_REQUIRE_MSG (f.mode & Write,
+      "Error! Could not call redef on the input file. File is read-only.\n"
+      " - filename: " + filename + "\n");
 
-  bool was_open = is_file_open_c2f(filename.c_str(),-1);
-  if (not was_open) {
-    register_file(filename,Read);
+  if (f.enddef) {
+    int err = PIOc_redef(f.ncid);
+    check_scorpio_noerr (err,f.name,"redef","redef");
+    f.enddef = false;
   }
+}
 
-  // Get file id
-  ncid = get_file_ncid_c2f (filename.c_str());
+void enddef(const std::string &filename)
+{
+  auto& f = impl::get_file(filename,"scorpio::enddef");
 
-  // Get var id
-  if (varname=="GLOBAL") {
-    varid = PIO_GLOBAL;
+  if (not f.enddef) {
+    int err = PIOc_enddef(f.ncid);
+    check_scorpio_noerr (err,f.name,"enddef","enddef");
+    f.enddef = true;
+  }
+}
+
+bool is_file_open (const std::string& filename, const FileMode mode)
+{
+  auto& s = ScorpioSession::instance();
+  auto it = s.files.find(filename);
+  if (it==s.files.end()) return false;
+
+  return mode==Unset || (mode & it->second.mode);
+}
+
+// =================== Dimensions operations ======================= //
+
+void define_dim (const std::string& filename, const std::string& dimname, const int length)
+{
+  auto& f = impl::get_file(filename,"scorpio::define_dim");
+
+  EKAT_REQUIRE_MSG (f.mode & Write,
+      "Error! Could not define dimension. File is read-only.\n"
+      " - filename: " + filename + "\n"
+      " - dimname : " + dimname + "\n");
+
+  auto& dim = f.dims[dimname];
+
+  bool unlimited = length==0;
+
+  if (dim==nullptr) {
+    EKAT_REQUIRE_MSG (f.mode!=Append,
+        "Error! Cannot add a new dim when the file is open in append mode.\n"
+        " - filename: " + filename + "\n"
+        " - dimname : " + dimname + "\n");
+    // Create new dimension
+    dim = std::make_shared<PIODim>();
+    dim->name = dimname;
+    dim->fid = f.ncid;
+    dim->length = length;
+    dim->unlimited = unlimited;
+
+    // Define the dimension in PIO
+    int err = PIOc_def_dim(f.ncid,dimname.c_str(),dim->length,&dim->ncid);
+    check_scorpio_noerr (err,f.name,"dimension",dimname,"define_dim","def_dim");
   } else {
-    err = PIOc_inq_varid(ncid,varname.c_str(),&varid);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Something went wrong while retrieving variable id.\n"
-        " - filename : " + filename + "\n"
-        " - varname  : " + varname + "\n"
-        " - pio error: " + std::to_string(err) + "\n");
+    // Already defined. Check that the dim specs are the same.
+    EKAT_REQUIRE_MSG (unlimited==dim->unlimited,
+        "Error! Redefining dimension with different unlimited flag.\n"
+        " - filename: " + filename + "\n"
+        " - dimname : " + dimname + "\n"
+        " - old unlimited:" + (dim->unlimited ? "yes" : "no" )+ "\n"
+        " - new unlimited:" + (unlimited ? "yes" : "no") + "\n");
+
+    EKAT_REQUIRE_MSG (unlimited || length==dim->length,
+        "Error! Redefining dimension with a different (local) length.\n"
+        " - filename: " + filename + "\n"
+        " - dimname : " + dimname + "\n"
+        " - old length:" + std::to_string(dim->length)+ "\n"
+        " - new length:" + std::to_string(length) + "\n");
   }
+}
 
-  // Get att id
-  err = PIOc_inq_attid(ncid,varid,attname.c_str(),&attid);
-  if (err==PIO_ENOTATT) {
+bool has_dim (const std::string& filename,
+              const std::string& dimname,
+              const int length)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  auto it = pf.file->dims.find(dimname);
+  if (it==pf.file->dims.end()) {
     return false;
+  } else if (length==0) {
+    return it->second->unlimited;
+  } else if (length>0) {
+    return it->second->length==length;
   }
-  EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "Error! Something went wrong while retrieving attribute id.\n"
-      " - filename : " + filename + "\n"
-      " - varname  : " + varname + "\n"
-      " - attname  : " + attname + "\n"
-      " - pio error: " + std::to_string(err) + "\n");
+  return true;
+}
 
-  if (not was_open) {
-    eam_pio_closefile(filename);
-  }
+int get_dimlen (const std::string& filename, const std::string& dimname)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
 
-  return true;
+  EKAT_REQUIRE_MSG (has_dim(filename,dimname),
+      "Error! Could not inquire dimension length. The dimension is not in the file.\n"
+      " - filename: " + filename + "\n"
+      " - dimname : " + dimname + "\n");
+
+  return pf.file->dims.at(dimname)->length;
 }
-/* ----------------------------------------------------------------- */
-void set_dof(const std::string& filename, const std::string& varname, const Int dof_len, const std::int64_t* x_dof) {
 
-  set_dof_c2f(filename.c_str(),varname.c_str(),dof_len,x_dof);
+int get_dimlen_local (const std::string& filename, const std::string& dimname)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  EKAT_REQUIRE_MSG (has_dim(filename,dimname),
+      "Error! Could not inquire dimension local length. The dimension is not in the file.\n"
+      " - filename: " + filename + "\n"
+      " - dimname : " + dimname + "\n");
+
+  const auto& dim = pf.file->dims.at(dimname);
+  return dim->offsets==nullptr ? dim->length : dim->offsets->size();
 }
-/* ----------------------------------------------------------------- */
-void pio_update_time(const std::string& filename, const double time) {
 
-  pio_update_time_c2f(filename.c_str(),time);
+bool is_dim_unlimited (const std::string& filename,
+                       const std::string& dimname)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  EKAT_REQUIRE_MSG (has_dim(filename,dimname),
+      "Error! Could not inquire if dimension is unlimited. The dimension is not in the file.\n"
+      " - filename: " + filename + "\n"
+      " - dimname : " + dimname + "\n");
+
+  return pf.file->dims.at(dimname)->unlimited;
 }
-/* ----------------------------------------------------------------- */
-void register_dimension(const std::string &filename, const std::string& shortname, const std::string& longname, const int length, const bool partitioned)
+
+int get_time_len (const std::string& filename)
 {
-  int mode = get_file_mode_c2f(filename.c_str());
-  std::string mode_str = mode==Read ? "Read" : (mode==Write ? "Write" : "Append");
-  if (mode!=Write) {
-    // Ensure the dimension already exists, and that it has the correct size (if not unlimited)
-    int ncid,dimid,unlimid,err;
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
 
-    ncid = get_file_ncid_c2f (filename.c_str());
-    err = PIOc_inq_dimid(ncid,shortname.c_str(),&dimid);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Could not retrieve dimension id from file open in " + mode_str + " mode.\n"
-        " - filename: " + filename + "\n"
-        " - dimension : " + shortname + "\n"
-        " - pio error: " + std::to_string(err) + "\n");
+  EKAT_REQUIRE_MSG (pf.file->time_dim!=nullptr,
+      "Error! Could not inquire time dimension length. The time dimension is not in the file.\n"
+      " - filename: " + filename + "\n");
 
-    err = PIOc_inq_unlimdim(ncid,&unlimid);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Something went wrong querying for the unlimited dimension id.\n"
+  return pf.file->time_dim->length;
+}
+
+std::string get_time_name (const std::string& filename)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  EKAT_REQUIRE_MSG (pf.file->time_dim!=nullptr,
+      "Error! Could not inquire time dimension name. The time dimension is not in the file.\n"
+      " - filename: " + filename + "\n");
+
+  return pf.file->time_dim->name;
+}
+
+// =================== Decompositions operations ==================== //
+
+// NOTES:
+//  - this is a local function, we don't expose it. It's only called inside other scorpio utilities
+//  - we don't really *need* filename, it's only to print more context in case of errors
+void set_var_decomp (PIOVar& var,
+                     const std::string& filename)
+{
+  for (size_t i=1; i<var.dims.size(); ++i) {
+    EKAT_REQUIRE_MSG (var.dims[i]->offsets==nullptr,
+        "Error! We currently only allow decomposition on slowest-striding dimension.\n"
+        "       Generalizing is not complicated, but it was not a priority.\n"
         " - filename: " + filename + "\n"
-        " - dimension : " + shortname + "\n"
-        " - pio error: " + std::to_string(err) + "\n");
-    if (length==0) {
-      EKAT_REQUIRE_MSG ( unlimid==dimid,
-          "Error! Input dimension is unlimited, but does not appear to be unlimited in the file (open in " + mode_str + " mode).\n"
-          " - filename: " + filename + "\n"
-          " - dimension : " + shortname + "\n"
-          " - pio error: " + std::to_string(err) + "\n");
-    } else {
-      EKAT_REQUIRE_MSG ( unlimid!=dimid,
-          "Error! Input dimension is not unlimited, but it appears to be unlimited in the file (open in " + mode_str + " mode).\n"
-          " - filename: " + filename + "\n"
-          " - dimension : " + shortname + "\n"
-          " - pio error: " + std::to_string(err) + "\n");
+        " - varname : " + var.name + "\n"
+        " - var dims: " + ekat::join(var.dims,get_entity_name,",") + "\n"
+        " - bad dim : " + var.dims[i]->name + "\n");
+  }
+  EKAT_REQUIRE_MSG (var.dims[0]->offsets!=nullptr,
+      "Error! Calling set_var_decomp, but the var first dimension does not appear to be decomposed.\n"
+      " - filename: " + filename + "\n"
+      " - varname : " + var.name  + "\n"
+      " - var dims: " + ekat::join(var.dims,get_entity_name,",") + "\n");
+  EKAT_REQUIRE_MSG (var.decomp==nullptr,
+      "Error! You should have invalidated var.decomp before attempting to reset it.\n"
+      " - filename  : " + filename + "\n"
+      " - varname   : " + var.name  + "\n"
+      " - var decomp: " + var.decomp->name  + "\n");
 
-      int len_from_file = get_dimlen(filename,shortname);
-      EKAT_REQUIRE_MSG (length==len_from_file,
-          "Error! Input dimension length does not match the one from the file  (open in " + mode_str + " mode).\n"
-          " - filename: " + filename + "\n"
-          " - dimension : " + shortname + "\n"
-          " - input dim length: " + std::to_string(length) + "\n"
-          " - file dim length : " + std::to_string(len_from_file) + "\n");
+  // Create decomp name: dtype-dim1<len1>_dim2<len2>_..._dimk<lenN>
+  std::shared_ptr<const PIODim> decomp_dim;
+  std::string decomp_tag = var.dtype + "-";
+  for (auto d : var.dims) {
+    decomp_tag += d->name + "<" + std::to_string(d->length) + ">_";
+  }
+  decomp_tag.pop_back(); // remove trailing underscore
+
+  // Check if a decomp with this name already exists
+  auto& s = ScorpioSession::instance();
+  auto& decomp = s.decomps[decomp_tag];
+#ifndef NDEBUG
+  // Extra check: all ranks must agree on whether they have the decomposition!
+  // If they don't agree, some rank will be stuck in a PIO call, waiting for others
+  int found = decomp==nullptr ? 0 : 1;
+  int min_found, max_found;
+  const auto& comm = ScorpioSession::instance().comm;
+  comm.all_reduce(&found,&min_found,1,MPI_MIN);
+  comm.all_reduce(&found,&max_found,1,MPI_MAX);
+  EKAT_REQUIRE_MSG(min_found==max_found,
+      "Error! Decomposition already present on some ranks but not all.\n"
+      " - filename: " + filename + "\n"
+      " - varname : " + var.name + "\n"
+      " - var dims: " + ekat::join(var.dims,get_entity_name,",") + "\n"
+      " - decopm tag: " + decomp_tag + "\n");
+#endif
+
+  if (decomp==nullptr) {
+    // We haven't create this decomp yet. Go ahead and create one
+    decomp = std::make_shared<PIODecomp>();
+    decomp->name = decomp_tag;
+    decomp->dim = var.dims[0];
+
+    int ndims = var.dims.size();
+
+    // Get ALL dims global lengths, and compute prod of *non-decomposed* dims
+    std::vector<int> gdimlen = {decomp->dim->length};
+    int non_decomp_dim_prod = 1;
+    for (int idim=1; idim<ndims; ++idim) {
+      auto d = var.dims[idim];
+      gdimlen.push_back(d->length);
+      non_decomp_dim_prod *= d->length;
+    }
+
+    // Create offsets list
+    const auto& dim_offsets = *decomp->dim->offsets;
+    int dim_loc_len = dim_offsets.size();
+    decomp->offsets.resize (non_decomp_dim_prod*dim_loc_len);
+    for (int idof=0; idof<dim_loc_len; ++idof) {
+      auto dof_offset = dim_offsets[idof];
+      auto beg = decomp->offsets.begin()+ idof*non_decomp_dim_prod;
+      auto end = beg + non_decomp_dim_prod;
+      std::iota (beg,end,non_decomp_dim_prod*dof_offset);
     }
+
+    // Create PIO decomp
+    int maplen = decomp->offsets.size();
+    PIO_Offset* compmap = reinterpret_cast<PIO_Offset*>(decomp->offsets.data());
+    int err = PIOc_init_decomp(s.pio_sysid,nctype(var.dtype),ndims,gdimlen.data(),
+                               maplen,compmap, &decomp->ncid,s.pio_rearranger,
+                               nullptr,nullptr);
+
+    check_scorpio_noerr(err,filename,"decomp",decomp_tag,"set_var_decomp","InitDecomp");
   }
 
-  register_dimension_c2f(filename.c_str(), shortname.c_str(), longname.c_str(), length, partitioned);
+  // Set decomp data in the var
+  var.decomp = decomp;
 }
-/* ----------------------------------------------------------------- */
-void register_variable(const std::string& filename, const std::string& shortname, const std::string& longname,
-                       const std::vector<std::string>& var_dimensions,
-                       const std::string& dtype, const std::string& pio_decomp_tag)
+
+void set_dim_decomp (const std::string& filename,
+                     const std::string& dimname,
+                     const std::vector<offset_t>& my_offsets,
+                     const bool allow_reset)
 {
-  // This overload does not require to specify an nc data type, so it *MUST* be used when the
-  // file access mode is either Read or Append. Either way, a) the var should be on file already,
-  // and b) so should be the dimensions
-  EKAT_REQUIRE_MSG (has_variable(filename,shortname),
-      "Error! This overload of register_variable *assumes* the variable is already in the file, but wasn't found.\n"
+  auto& s = ScorpioSession::instance();
+  auto& f = impl::get_file(filename,"scorpio::set_decomp");
+  auto& dim = impl::get_dim(filename,dimname,"scorpio::set_dim_decomp");
+
+  EKAT_REQUIRE_MSG (not dim.unlimited,
+      "Error! Cannot partition an unlimited dimension.\n"
       " - filename: " + filename + "\n"
-      " - varname : " + shortname + "\n");
-  for (const auto& dimname : var_dimensions) {
-    int len = get_dimlen (filename,dimname);
-    // WARNING! If the dimension was not yet registered, it will be registered as a NOT partitioned dim.
-    //          If this dim should be partitioned, then register it *before* the variable
-    register_dimension(filename,dimname,dimname,len,false);
-  }
-  register_variable(filename,shortname,longname,"",var_dimensions,dtype,"",pio_decomp_tag);
-}
-void register_variable(const std::string &filename, const std::string& shortname, const std::string& longname,
-                       const std::string& units_in, const std::vector<std::string>& var_dimensions,
-                       const std::string& dtype, const std::string& nc_dtype_in, const std::string& pio_decomp_tag)
-{
-  // Local copies, since we can modify them in case of defaults
-  auto units = units_in;
-  auto nc_dtype = nc_dtype_in;
-
-  int mode = get_file_mode_c2f(filename.c_str());
-  std::string mode_str = mode==Read ? "Read" : (mode==Write ? "Write" : "Append");
-
-  bool has_var = has_variable(filename,shortname);
-  if (mode==Write) {
-    EKAT_REQUIRE_MSG ( units!="" and nc_dtype!="",
-        "Error! Missing valid units and/or nc_dtype arguments for file open in Write mode.\n"
-        " - filename: " + filename + "\n"
-        " - varname : " + shortname + "\n");
-  } else {
-    EKAT_REQUIRE_MSG ( has_var,
-        "Error! Variable not found in file open in " + mode_str + " mode.\n"
+      " - dimname : " + dimname + "\n");
+
+  if (dim.offsets!=nullptr) {
+    if (allow_reset) {
+      // We likely won't need the previously created decomps that included this dimension.
+      // So, as we remove decomps from vars that have this dim, keep track of their name,
+      // so that we can free them later *if no other users of them remain*.
+      std::set<std::string> decomps_to_remove;
+      for (auto it : f.vars) {
+        auto v = it.second;
+        if (v->decomp!=nullptr and v->decomp->dim->name==dimname) {
+          decomps_to_remove.insert(v->decomp->name);
+          v->decomp = nullptr;
+        }
+      }
+      for (const auto& dn : decomps_to_remove) {
+        if (s.decomps.at(dn).use_count()==1) {
+          auto decomp = s.decomps.at(dn);
+          // There is no other customer of this decomposition, so we can safely free it
+          int err = PIOc_freedecomp(s.pio_sysid,decomp->ncid);
+          check_scorpio_noerr(err,filename,"decomp",dn,"set_dim_decomp","freedecomp");
+          s.decomps.erase(dn);
+        }
+      }
+    } else {
+      // Check that the offsets are (globally) the same
+      int same = *dim.offsets==my_offsets;
+      const auto& comm = ScorpioSession::instance().comm;
+      comm.all_reduce(&same,1,MPI_MIN);
+      EKAT_REQUIRE_MSG(same==1,
+          "Error! Attempt to redefine a decomposition with a different dofs distribution.\n"
+          " - filename: " + filename + "\n"
+          " - dimname : " + dimname + "\n"
+          "If you are attempting to redefine the decomp, call this function with throw_if_changing_decomp=false.\n");
+
+      // Same decomposition, so we can just return
+      return;
+    }
+  }
+  
+  // Check that offsets are less than the global dimension length
+  for (auto o : my_offsets) {
+    EKAT_REQUIRE_MSG (o>=0 && o<dim.length,
+        "Error! Offset for dimension decomposition is out of bounds.\n"
         " - filename: " + filename + "\n"
-        " - varname : " + shortname + "\n");
+        " - dimname : " + dimname + "\n"
+        " - dim glen: " + std::to_string(dim.length) + "\n"
+        " - offset  : " + std::to_string(o) + "\n");
   }
 
+  dim.offsets = std::make_shared<std::vector<offset_t>>(my_offsets);
 
-  if (has_var) {
-    // The file already exists or the var was already registered.
-    // Make sure we're registering the var with the same specs
-    int ncid = get_file_ncid_c2f (filename.c_str());
-    int vid,ndims,err;
-    err = PIOc_inq_varid(ncid,shortname.c_str(),&vid);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Something went wrong retrieving variable id.\n"
-        " - filename: " + filename + "\n"
-        " - varname : " + shortname + "\n"
-        " - pio error: " + std::to_string(err) + "\n");
-    err = PIOc_inq_varndims(ncid,vid,&ndims);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Something went wrong inquiring the number of dimensions of a variable.\n"
-        " - filename: " + filename + "\n"
-        " - varname : " + shortname + "\n"
-        " - pio error: " + std::to_string(err) + "\n");
-    std::vector<int> dims(ndims);
-    err = PIOc_inq_vardimid(ncid,vid,dims.data());
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Something went wrong inquiring the dimensions ids of a variable.\n"
+  // If vars were already defined, we need to process them,
+  // and create the proper PIODecomp objects.
+  for (auto it : f.vars) {
+    if (ekat::contains(it.second->dim_names(),dimname)) {
+      set_var_decomp (*it.second,filename);
+    }
+  }
+}
+
+void set_dim_decomp (const std::string& filename,
+                     const std::string& dimname,
+                     const offset_t start, const offset_t count,
+                     const bool allow_reset)
+{
+  std::vector<offset_t> offsets(count);
+  std::iota(offsets.begin(),offsets.end(),start);
+  set_dim_decomp(filename,dimname,offsets,allow_reset);
+}
+
+void set_dim_decomp (const std::string& filename,
+                     const std::string& dimname,
+                     const bool allow_reset)
+{
+  const auto& comm = ScorpioSession::instance().comm;
+
+  const int glen = get_dimlen(filename,dimname);
+  int len = glen / comm.size();
+  if (comm.rank() < (glen % comm.size())) {
+    ++len;
+  }
+
+  offset_t offset = len;
+  comm.scan(&offset,1,MPI_SUM);
+  offset -= len; // scan is inclusive, but we need exclusive
+
+  set_dim_decomp (filename,dimname,offset,len,allow_reset);
+}
+
+// ================== Variable operations ================== //
+
+// Define var on output file (cannot call on Read/Append files)
+void define_var (const std::string& filename, const std::string& varname,
+                 const std::string& units, const std::vector<std::string>& dimensions,
+                 const std::string& dtype, const std::string& nc_dtype,
+                 const bool time_dep)
+{
+  auto& f = impl::get_file(filename,"scorpio::define_var");
+
+  EKAT_REQUIRE_MSG (f.mode & Write,
+      "Error! Could not define variable. File is read-only.\n"
+      " - filename: " + filename + "\n"
+      " - varname : " + varname + "\n");
+
+  EKAT_REQUIRE_MSG (not time_dep || f.time_dim!=nullptr,
+      "Error! Cannot define time-dependent variable: no time dimension defined.\n"
+      " - filename: " + filename + "\n"
+      " - varname : " + varname + "\n");
+
+  if (f.vars.count(varname)==0) {
+    EKAT_REQUIRE_MSG (f.mode!=Append,
+        "Error! Cannot add a new var when the file is open in append mode.\n"
         " - filename: " + filename + "\n"
-        " - varname : " + shortname + "\n"
-        " - pio error: " + std::to_string(err) + "\n");
-    std::vector<std::string> dims_from_file(ndims);
-    for (int i=0; i<ndims; ++i) {
-      dims_from_file[i].resize(PIO_MAX_NAME);
-      err =  PIOc_inq_dimname(ncid,dims[i],&dims_from_file[i][0]);
-      // IMPORTANT: must remove trailing null chars, to get *correct* string size
-      dims_from_file[i] = ekat::trim(dims_from_file[i],'\0');
-      EKAT_REQUIRE_MSG (err==PIO_NOERR,
-          "Error! Something went wrong inquiring dimension name.\n"
-          " - filename: " + filename + "\n"
-          " - dimid   : " + std::to_string(dims[i]) + "\n"
-          " - pio error: " + std::to_string(err) + "\n");
+        " - varname : " + varname + "\n");
+    // Create new variable
+    auto var = std::make_shared<PIOVar>();
+    var->name = varname;
+    var->fid = f.ncid;
+    var->units = units;
+    var->dtype = refine_dtype(dtype);
+    var->nc_dtype = refine_dtype(nc_dtype);
+    var->time_dep = time_dep;
+    int ndims = dimensions.size() + (time_dep ? 1 : 0);
+    std::vector<int> dimids;
+    if (time_dep) {
+      dimids.push_back(f.time_dim->ncid);
+    }
+    for (const auto& dname : dimensions) {
+      EKAT_REQUIRE_MSG (has_dim(filename,dname),
+          "Error! Cannot create variable. Dimension not found.\n"
+          " - filename : " + filename + "\n"
+          " - varname  : " + varname + "\n"
+          " - var dims : " + ekat::join(dimensions,",") + "\n"
+          " - file dims: " + print_map_keys(f.dims) + "\n");
+      auto dim = f.dims.at(dname);
+      var->dims.push_back(dim);
+      dimids.push_back(dim->ncid);
     }
 
-    // Here, let's only try to access var_dimensions[0] when we know for sure
-    // that var_dimensions is actually dimensioned (i.e., .size()>0)
-    if (var_dimensions.size()>0) {
-      if (mode==Read && (dims_from_file[0]=="time" && var_dimensions[0]!="time")) {
-        // For Read operations, we may not consider "time" as a field dimension, so if the
-        // input file has "time", simply disregard it in this check.
-        dims_from_file.erase(dims_from_file.begin());
-      }
-    } else {
-      if (mode==Read && (dims_from_file[0]=="time")) {
-        // For Read operations, we may not consider "time" as a field dimension, so if the
-        // input file has "time", simply disregard it in this check.
-        dims_from_file.erase(dims_from_file.begin());
-      }      
+    // Define the variable in PIO
+    int err = PIOc_def_var(f.ncid,varname.c_str(),nctype(nc_dtype),ndims,dimids.data(),&var->ncid);
+    check_scorpio_noerr(err,f.name,"variable",varname,"define_var","def_var");
+
+    f.vars[varname] = var;
+
+    if (units!="") {
+      // Add units attribute
+      set_attribute(filename,varname,"units",units);
     }
-    std::reverse(dims_from_file.begin(),dims_from_file.end());
-    EKAT_REQUIRE_MSG(var_dimensions==dims_from_file,
-        "Error! Input variable dimensions do not match the ones from the file.\n"
-        " - filename  : " + filename + "\n"
-        " - varname   : " + shortname + "\n"
-        " - input dims: (" + ekat::join(var_dimensions,",") + ")\n"
-        " - file dims : (" + ekat::join(dims_from_file,",") + ")\n");
-
-    // Check nc dtype only if user bothered specifying it (if mode=Read, probably the user doesn't care)
-    nc_type type;
-    err = PIOc_inq_vartype(ncid,vid,&type);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Something went wrong while inquiring variable data type.\n"
-        " - filename: " + filename + "\n"
-        " - varname : " + shortname + "\n"
-        " - pio error: " + std::to_string(err) + "\n");
-    EKAT_REQUIRE_MSG (nc_dtype=="" or type==nctype(nc_dtype),
-        "Error! Input NC data type does not match the one from the file.\n"
-        " - filename: " + filename + "\n"
-        " - varname : " + shortname + "\n"
-        " - input dtype : " + nc_dtype + "\n"
-        " - file dtype  : " + nctype2str(type) + "\n");
-    nc_dtype = nctype2str(type);
-
-    // Get var units (if set)
-    int natts;
-    err = PIOc_inq_varnatts(ncid,vid,&natts);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "Error! Something went wrong while inquiring a variable's number of attributes.\n"
-          " - filename: " + filename + "\n"
-          " - varname : " + shortname + "\n"
-          " - pio error: " + std::to_string(err) + "\n");
-    std::string units_from_file(PIO_MAX_NAME,'\0');
-    std::string att_name(PIO_MAX_NAME,'\0');
-    for (int i=0; i<natts; ++i) {
-      err = PIOc_inq_attname(ncid,vid,i,&att_name[0]);
-      EKAT_REQUIRE_MSG (err==PIO_NOERR,
-          "Error! Something went wrong while inquiring the name of a variable attribute.\n"
-            " - filename: " + filename + "\n"
-            " - varname : " + shortname + "\n"
-            " - pio error: " + std::to_string(err) + "\n");
-      if (att_name=="units") {
-        err = PIOc_get_att_text(ncid,vid,"units",&units_from_file[0]);
-        EKAT_REQUIRE_MSG (err==PIO_NOERR,
-            "Error! Something went wrong while retrieving a variable units.\n"
-              " - filename: " + filename + "\n"
-              " - varname : " + shortname + "\n"
-              " - pio error: " + std::to_string(err) + "\n");
-        EKAT_REQUIRE_MSG (units=="" or units==units_from_file,
-            "Error! Input variable units do not match the ones from the file.\n"
-            " - filename: " + filename + "\n"
-            " - varname : " + shortname + "\n"
-            " - input units: " + units + "\n"
-            " - file units : " + units_from_file + "\n");
 
-        // If mode=Read and user didn't bother with units, but units _are_ in the file, then
-        // make sure we call register_variable with correct units (to avoid later checks failures)
-        units = units_from_file;
-      }
+    if (var->dims.size()>0 and var->dims[0]->offsets!=nullptr) {
+      set_var_decomp (*var,filename);
     }
+  } else {
+    const auto& var = f.vars.at(varname);
+    // The variable was already defined. Check that important metadata is the same
+    EKAT_REQUIRE_MSG (var->units==units,
+        "Error! Attempt to redefine variable with different units.\n"
+          " - filename : " + filename + "\n"
+          " - varname  : " + varname + "\n"
+          " - old units: " + var->units + "\n"
+          " - new units: " +      units + "\n");
+    EKAT_REQUIRE_MSG (var->dtype==refine_dtype(dtype),
+        "Error! Attempt to redefine variable with different data type.\n"
+          " - filename : " + filename + "\n"
+          " - varname  : " + varname + "\n"
+          " - old dtype: " + var->dtype + "\n"
+          " - new dtype: " +      refine_dtype(dtype) + "\n");
+    EKAT_REQUIRE_MSG (var->nc_dtype==refine_dtype(nc_dtype),
+        "Error! Attempt to redefine variable with different PIO data type.\n"
+          " - filename : " + filename + "\n"
+          " - varname  : " + varname + "\n"
+          " - old pio dtype: " + var->nc_dtype + "\n"
+          " - new pio dtype: " +      refine_dtype(nc_dtype) + "\n");
+    EKAT_REQUIRE_MSG (var->time_dep==time_dep,
+        "Error! Attempt to redefine variable with different time dep flag.\n"
+          " - filename : " + filename + "\n"
+          " - varname  : " + varname + "\n"
+          " - old time_dep: " + (var->time_dep ? "yes" : "no") + "\n"
+          " - new time_dep: " + (     time_dep ? "yes" : "no") + "\n");
+    const auto var_dims = ekat::join(var->dims,get_entity_name,",");
+    EKAT_REQUIRE_MSG (var_dims==ekat::join(dimensions,","),
+        "Error! Attempt to redefine variable with different dimensions.\n"
+          " - filename: " + filename + "\n"
+          " - varname : " + varname + "\n"
+          " - old dims: " + var_dims + "\n"
+          " - new dims: " + ekat::join(dimensions,",") + "\n");
   }
+}
 
-  // Convert the vector of strings that contains the variable dimensions to a char array
-  const int numdims = var_dimensions.size();
-  std::vector<const char*> var_dimensions_c(numdims);
-  for (int ii = 0;ii<numdims;++ii)
-  {
-    var_dimensions_c[ii] = var_dimensions[ii].c_str();
-  }
-  register_variable_c2f(filename.c_str(), shortname.c_str(), longname.c_str(),
-                        units.c_str(), numdims, var_dimensions_c.data(),
-                        nctype(dtype), nctype(nc_dtype), pio_decomp_tag.c_str());
+void define_var (const std::string& filename, const std::string& varname,
+                 const std::vector<std::string>& dimensions,
+                 const std::string& dtype,
+                 const bool time_dependent)
+{
+  define_var(filename,varname,"",dimensions,dtype,dtype,time_dependent);
 }
-/* ----------------------------------------------------------------- */
-void set_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, const float meta_val) {
-  set_variable_metadata_float_c2f(filename.c_str(),varname.c_str(),meta_name.c_str(),meta_val);
+
+// This overload is not exposed externally. Also, filename is only
+// used to print it in case there are errors
+void change_var_dtype (PIOVar& var,
+                       const std::string& dtype,
+                       const std::string& filename)
+{
+  if (refine_dtype(dtype)==refine_dtype(var.dtype)) {
+    // The type is not changing, nothing to do
+    return;
+  }
+
+  var.dtype = refine_dtype(dtype);
+  if (var.decomp) {
+    // Re-decompose the variable, with new data type
+    var.decomp = nullptr;
+    set_var_decomp (var,filename);
+  }
 }
-/* ----------------------------------------------------------------- */
-void set_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, const double meta_val) {
-  set_variable_metadata_double_c2f(filename.c_str(),varname.c_str(),meta_name.c_str(),meta_val);
+
+void change_var_dtype (const std::string& filename,
+                       const std::string& varname,
+                       const std::string& dtype)
+{
+  auto& var = impl::get_var(filename,varname,"scorpio::change_var_dtype");
+  change_var_dtype(var,dtype,filename);
 }
-/* ----------------------------------------------------------------- */
-void set_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, const std::string& meta_val) {
-  set_variable_metadata_char_c2f(filename.c_str(),varname.c_str(),meta_name.c_str(),meta_val.c_str());
+
+bool has_var (const std::string& filename, const std::string& varname)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  return pf.file->vars.count(varname)==1;
 }
-/* ----------------------------------------------------------------- */
-void get_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, float& meta_val) {
-  meta_val = get_variable_metadata_float_c2f(filename.c_str(),varname.c_str(),meta_name.c_str());
+
+const PIOVar& get_var (const std::string& filename,
+                       const std::string& varname)
+{
+  return impl::get_var(filename,varname,"scorpio::get_var");
 }
-/* ----------------------------------------------------------------- */
-void get_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, double& meta_val) {
-  meta_val = get_variable_metadata_double_c2f(filename.c_str(),varname.c_str(),meta_name.c_str());
+
+void define_time (const std::string& filename, const std::string& units, const std::string& time_name)
+{
+  auto& f = impl::get_file(filename,"scorpio::define_time");
+  EKAT_REQUIRE_MSG (f.time_dim==nullptr,
+      "Error! Attempt to redeclare unlimited dimension.\n"
+      " - filename: " + filename + "\n");
+
+  define_dim(filename,time_name,0);
+  f.time_dim = f.dims.at(time_name);
+
+  define_var(filename,time_name,units,{},"double","double",true);
 }
-/* ----------------------------------------------------------------- */
-void get_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, std::string& meta_val) {
-  meta_val.resize(256);
-  get_variable_metadata_char_c2f(filename.c_str(),varname.c_str(),meta_name.c_str(),&meta_val[0]);
 
-  // If terminating char is not found, meta_val simply uses all 256 chars
-  if (meta_val.find('\0')!=std::string::npos) {
-    meta_val.resize(meta_val.find('\0'));
+void pretend_dim_is_unlimited (const std::string& filename, const std::string& dimname)
+{
+  auto& f = impl::get_file(filename,"scorpio::mark_dim_as_time");
+  EKAT_REQUIRE_MSG (f.mode==Read,
+      "Error! Cannot interpret dimension as 'time' dim. File not in Read mode.\n"
+      " - filename : " + filename + "\n"
+      " - file mode: " + e2str(f.mode) + "\n");
+
+  if (f.time_dim==nullptr) {
+    EKAT_REQUIRE_MSG (has_dim(filename,dimname),
+        "Error! Cannot interpret dimension as 'time' dim. Dimension not found.\n"
+        " - filename: " + filename + "\n"
+        " - dimname : " + dimname + "\n");
+
+    auto dim = f.dims.at(dimname);
+    f.time_dim = dim;
+
+    // If a var has "time" in its dims (must be the 1st dim!),
+    // remove it. Recall that we only store non-time dims in
+    // the list of var dims.
+    for (auto& it : f.vars) {
+      auto& v = it.second;
+      if (v->dims.size()>0 and v->dims[0]->name==dimname) {
+        v->dims.erase(v->dims.begin());
+        v->size = -1;
+        v->time_dep = true;
+      }
+    }
+  } else {
+    EKAT_REQUIRE_MSG (f.time_dim->name==dimname,
+        "Error! Attempt to change the time dimension.\n"
+        " - filenama    : " + filename + "\n"
+        " - old time dim: " + f.time_dim->name + "\n"
+        " - new time dim: " + dimname + "\n");
   }
 }
-/* ----------------------------------------------------------------- */
-ekat::any get_any_attribute (const std::string& filename, const std::string& att_name) {
-  auto out = get_any_attribute(filename,"GLOBAL",att_name);
-  return out;
+
+// Update value of time variable, increasing time dim length
+void update_time(const std::string &filename, const double time) {
+  const auto& f = impl::get_file(filename,"scorpio::update_time");
+        auto& time_dim = *f.time_dim;
+  const auto& var = impl::get_var(filename,time_dim.name,"scorpio::update_time");
+
+  PIO_Offset index = time_dim.length;
+  int err = PIOc_put_var1(f.ncid,var.ncid,&index,&time);
+  check_scorpio_noerr (err,f.name,"update time","put_var1");
+  ++time_dim.length;
 }
-/* ----------------------------------------------------------------- */
-ekat::any get_any_attribute (const std::string& filename, const std::string& var_name, const std::string& att_name) {
-  register_file(filename,Read);
-  auto ncid = get_file_ncid_c2f (filename.c_str());
-  EKAT_REQUIRE_MSG (ncid>=0,
-      "[get_any_attribute] Error! Could not retrieve file ncid.\n"
-        " - filename : " + filename + "\n");
 
-  int varid;
+double get_time (const std::string& filename, const int time_index)
+{
+  impl::PeekFile pf (filename);
+
+  const auto& time_name = pf.file->time_dim->name;
+  double t;
+  read_var(filename,time_name,&t,time_index);
+  return t;
+}
+
+std::vector<double> get_all_times (const std::string& filename)
+{
+  impl::PeekFile pf (filename);
+  const auto& dim = *pf.file->time_dim;
+
+  std::vector<double> times (dim.length);
+  for (int i=0; i<dim.length; ++i) {
+    read_var (filename, dim.name, &times[i], i);
+  }
+  return times;
+}
+
+// Read variable into user provided buffer.
+// If time dim is present, read given time slice (time_index=-1 means "read last record).
+// If time dim is not present, time_index must be -1 (error out otherwise)
+template<typename T>
+void read_var (const std::string &filename, const std::string &varname, T* buf, const int time_index)
+{
+  EKAT_REQUIRE_MSG (buf!=nullptr,
+      "Error! Cannot read from provided pointer. Invalid buffer pointer.\n"
+      " - filename: " + filename + "\n"
+      " - varname : " + varname + "\n");
+
+  const auto& f = impl::get_file(filename,"scorpio::read_var");
+        auto& var = impl::get_var(filename,varname,"scorpio::read_var");
+
+  // If the input pointer type already matches var.dtype, this is a no-op
+  change_var_dtype(var,get_dtype<T>(),filename);
+
   int err;
-  if (var_name=="GLOBAL") {
-    varid = PIO_GLOBAL;
+  int frame = -1;
+  if (var.time_dep) {
+    frame = time_index>=0 ? time_index : f.time_dim->length-1;
+    EKAT_REQUIRE_MSG (frame<f.time_dim->length,
+        "Error! Time index out of bounds.\n"
+        " - filename: " + filename + "\n"
+        " - varname : " + varname + "\n"
+        " - time idx: " + std::to_string(time_index) + "\n"
+        " - time len: " + std::to_string(f.time_dim->length));
+    err = PIOc_setframe(f.ncid,var.ncid,frame);
+    check_scorpio_noerr (err,f.name,"variable",varname,"read_var","setframe");
+  } else if (time_index>=0) {
+    // This is a bit of a hacky usage. We want to read a time index of a var,
+    // but the time dim is NOT unlimited in the input file. Apparently, SCORPIO
+    // supports this, and some E3SM input files are indeed like this, so we
+    // need to support it here too, hacky as it may be.
+    frame = time_index;
+
+    EKAT_REQUIRE_MSG (frame<var.dims[0]->length,
+        "Error! First dim index out of bounds.\n"
+        " - filename     : " + filename + "\n"
+        " - varname      : " + varname + "\n"
+        " - first dim idx: " + std::to_string(time_index) + "\n"
+        " - first dim len: " + std::to_string(var.dims[0]->length) + "\n");
+  }
+
+  std::string pioc_func;
+  if (var.decomp) {
+    // A decomposed variable, requires read_darray
+    err = PIOc_read_darray(f.ncid,var.ncid,var.decomp->ncid,var.decomp->offsets.size(),buf);
+    pioc_func = "read_darray";
   } else {
-    err = PIOc_inq_varid(ncid, var_name.c_str(), &varid);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "[get_any_attribute] Error! Something went wrong while inquiring variable id.\n"
-          " - filename : " + filename + "\n"
-          " - variable : " + var_name + "\n"
-          " - attribute: " + att_name + "\n"
-          " - pio error: " << err << "\n");
+    // A non-decomposed variable, use PIOc_get_var(a)
+
+    // If nc data type doesn't match the input pointer, we need to use the var internal buffer
+    void* io_buf = buf;
+    if (var.dtype!=var.nc_dtype) {
+      if (var.size==-1) {
+        var.size = 1;
+        for (auto d : var.dims) {
+          var.size *= d->length;
+        }
+        var.buf.resize(var.size*dtype_size(var.nc_dtype));
+      }
+      io_buf = var.buf.data();
+    }
+
+    if (frame>=0) {
+      // We need to get the start/count for each dimension
+      int ndims = var.dims.size();
+      std::vector<PIO_Offset> start (ndims+1,0), count(ndims+1); // +1 for time
+      start[0] = frame;
+      count[0] = 1;
+      for (int idim=0; idim<ndims; ++idim) {
+        count[idim+1] = var.dims[idim]->length;
+      }
+      err = PIOc_get_vara(f.ncid,var.ncid,start.data(),count.data(),io_buf);
+      pioc_func = "get_vara";
+    } else {
+      err = PIOc_get_var(f.ncid,var.ncid,io_buf);
+      pioc_func = "get_var";
+    }
+
+    // If we used the var tmp buffer, copy back into the user-provided pointer
+    if (var.dtype!=var.nc_dtype) {
+      if (var.nc_dtype=="int") {
+        copy_data(reinterpret_cast<int*>(io_buf),buf,var.size);
+      } else if (var.nc_dtype=="int64") {
+        copy_data(reinterpret_cast<long long*>(io_buf),buf,var.size);
+      } else if (var.nc_dtype=="float") {
+        copy_data(reinterpret_cast<float*>(io_buf),buf,var.size);
+      } else if (var.nc_dtype=="double") {
+        copy_data(reinterpret_cast<double*>(io_buf),buf,var.size);
+      }
+    }
   }
+  check_scorpio_noerr (err,f.name,"variable",varname,"read_var",pioc_func);
+}
 
-  nc_type type;
-  PIO_Offset len;
-  err = PIOc_inq_att(ncid,varid,att_name.c_str(),&type,&len);
-  EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "[get_any_attribute] Error! Something went wrong while inquiring global attribute.\n"
-        " - filename : " + filename + "\n"
-        " - variable : " + var_name + "\n"
-        " - attribute: " + att_name + "\n"
-        " - pio error: " << err << "\n");
+// Write data from user provided buffer into the requested variable
+template<typename T>
+void write_var (const std::string &filename, const std::string &varname, const T* buf, const T* fillValue)
+{
+  EKAT_REQUIRE_MSG (buf!=nullptr,
+      "Error! Cannot write in provided pointer. Invalid buffer pointer.\n"
+      " - filename: " + filename + "\n"
+      " - varname : " + varname + "\n");
 
-  EKAT_REQUIRE_MSG (len==1 || type==PIO_CHAR,
-      "[get_any_attribute] Error! Only single value attributes allowed.\n"
-        " - filename : " + filename + "\n"
-        " - variable : " + var_name + "\n"
-        " - attribute: " + att_name + "\n"
-        " - nc type  : " << type << "\n"
-        " - att len  : " << len << "\n");
-
-  ekat::any att;
-  if (type==PIO_INT) {
-    int val;
-    err = PIOc_get_att(ncid,varid,att_name.c_str(),&val);
-    att.reset(val);
-  } else if (type==PIO_DOUBLE) {
-    double val;
-    err = PIOc_get_att(ncid,varid,att_name.c_str(),&val);
-    att.reset(val);
-  } else if (type==PIO_FLOAT) {
-    float val;
-    err = PIOc_get_att(ncid,varid,att_name.c_str(),&val);
-    att.reset(val);
-  } else if (type==PIO_CHAR) {
-    std::string val(len,'\0');
-    err = PIOc_get_att(ncid,varid,att_name.c_str(),&val[0]);
-    att.reset(val);
+  const auto& f = impl::get_file(filename,"scorpio::write_var");
+  auto& var = impl::get_var(filename,varname,"scorpio::write_var");
+
+  // If the input pointer type already matches var.dtype, this is a no-op
+  change_var_dtype(var,get_dtype<T>(),filename);
+
+  int err;
+
+  if (var.time_dep) {
+    ++var.num_records;
+    EKAT_REQUIRE_MSG (var.num_records==f.time_dim->length,
+        "Error! Number of records for variable does not match time length.\n"
+        " - filename: " + filename + "\n"
+        " - varname : " + varname + "\n"
+        " - time len: " + std::to_string(f.time_dim->length) + "\n"
+        " - nrecords: " + std::to_string(var.num_records) + "\n");
+    err = PIOc_setframe (f.ncid,var.ncid,var.num_records-1);
+    check_scorpio_noerr (err,f.name,"variable",varname,"write_var","setframe");
+  }
+
+  std::string pioc_func;
+  if (var.decomp) {
+    // A decomposed variable, requires write_darray
+    err = PIOc_write_darray(f.ncid,var.ncid,var.decomp->ncid,var.decomp->offsets.size(),buf,fillValue);
+    pioc_func = "write_darray";
   } else {
-    EKAT_ERROR_MSG ("[get_any_attribute] Error! Unsupported/unrecognized nc type.\n"
-        " - filename : " + filename + "\n"
-        " - variable : " + var_name + "\n"
-        " - attribute: " + att_name + "\n"
-        " - nc type  : " << type << "\n");
+    // A non-decomposed variable, use PIOc_put_var(a)
+    // If nc data type doesn't match the input pointer, we need to use the var internal buffer
+    const void* io_buf = buf;
+    if (var.dtype!=var.nc_dtype) {
+      if (var.size==-1) {
+        var.size = 1;
+        for (auto d : var.dims) {
+          var.size *= d->length;
+        }
+        var.buf.resize(var.size*dtype_size(var.nc_dtype));
+      }
+      io_buf = var.buf.data();
+      void* var_buf = var.buf.data();
+      if (var.nc_dtype=="int") {
+        copy_data(buf,reinterpret_cast<int*>(var_buf),var.size);
+      } else if (var.nc_dtype=="int64") {
+        copy_data(buf,reinterpret_cast<long long*>(var_buf),var.size);
+      } else if (var.nc_dtype=="float") {
+        copy_data(buf,reinterpret_cast<float*>(var_buf),var.size);
+      } else if (var.nc_dtype=="double") {
+        copy_data(buf,reinterpret_cast<double*>(var_buf),var.size);
+      }
+    }
+
+    if (var.time_dep) {
+      // We need to get the start/count for each dimension
+      int ndims = var.dims.size();
+      std::vector<PIO_Offset> start (ndims+1,0), count(ndims+1);
+      start[0] = f.time_dim->length-1;
+      count[0] = 1;
+      for (int idim=0; idim<ndims; ++idim) {
+        count[idim+1] = var.dims[idim]->length;
+      }
+      err = PIOc_put_vara(f.ncid,var.ncid,start.data(),count.data(),io_buf);
+      pioc_func = "put_vara";
+    } else {
+      // Easy: just pass the buffer, and write all entries
+      err = PIOc_put_var(f.ncid,var.ncid,io_buf);
+      pioc_func = "put_var";
+    }
   }
-  EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "[get_any_attribute] Error! Something went wrong while inquiring global attribute.\n"
-        " - filename : " + filename + "\n"
-        " - variable : " + var_name + "\n"
-        " - attribute: " + att_name + "\n"
-        " - pio error: " << err << "\n");
+  check_scorpio_noerr (err,f.name,"variable",varname,"write_var",pioc_func);
+}
+
+// ========================== READ/WRITE ETI ========================== //
 
-  eam_pio_closefile(filename);
-  return att;
+template void read_var<int>       (const std::string&, const std::string&, int*,       const int);
+template void read_var<long long> (const std::string&, const std::string&, long long*, const int);
+template void read_var<float>     (const std::string&, const std::string&, float*,     const int);
+template void read_var<double>    (const std::string&, const std::string&, double*,    const int);
+template void read_var<char>      (const std::string&, const std::string&, char*,      const int);
+
+template void write_var<int>       (const std::string&, const std::string&, const int*,       const int*);
+template void write_var<long long> (const std::string&, const std::string&, const long long*, const long long*);
+template void write_var<float>     (const std::string&, const std::string&, const float*,     const float*);
+template void write_var<double>    (const std::string&, const std::string&, const double*,    const double*);
+template void write_var<char>      (const std::string&, const std::string&, const char*,      const char*);
+
+// =============== Attributes operations ================== //
+
+bool has_global_attribute (const std::string& filename, const std::string& attname)
+{
+  return has_attribute(filename,"GLOBAL",attname);
 }
-void set_any_attribute (const std::string& filename, const std::string& att_name, const ekat::any& att) {
-  auto ncid = get_file_ncid_c2f (filename.c_str());
-  int err;
 
-  EKAT_REQUIRE_MSG (ncid>=0,
-      "[set_any_attribute] Error! Could not retrieve file ncid.\n"
-        " - filename : " + filename + "\n");
+bool has_attribute (const std::string& filename, const std::string& varname, const std::string& attname)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  const int ncid = pf.file->ncid;
 
-  bool redef = is_enddef_c2f(filename.c_str());
-  if (redef) {
-    err = PIOc_redef(ncid);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "[set_any_attribute] Error! Something went wrong while re-opening def phase.\n"
-          " - filename : " + filename + "\n"
-          " - attribute: " + att_name + "\n"
-          " - pio error: " << err << "\n");
-  }
-
-  int varid = PIO_GLOBAL;
-  if (att.isType<int>()) {
-    const int& data = ekat::any_cast<int>(att);
-    err = PIOc_put_att(ncid,varid,att_name.c_str(),PIO_INT,1,&data);
-  } else if (att.isType<double>()) {
-    const double& data = ekat::any_cast<double>(att);
-    err = PIOc_put_att(ncid,varid,att_name.c_str(),PIO_DOUBLE,1,&data);
-  } else if (att.isType<float>()) {
-    const float& data = ekat::any_cast<float>(att);
-    err = PIOc_put_att(ncid,varid,att_name.c_str(),PIO_FLOAT,1,&data);
-  } else if (att.isType<std::string>()) {
-    const std::string& data = ekat::any_cast<std::string>(att);
-    err = PIOc_put_att(ncid,varid,att_name.c_str(),PIO_CHAR,data.size(),data.data());
+  // Get var id
+  int varid;
+  if (varname=="GLOBAL") {
+    varid = PIO_GLOBAL;
   } else {
-    EKAT_ERROR_MSG ("[set_any_attribute] Error! Unsupported/unrecognized att type.\n"
-        " - filename : " + filename + "\n"
-        " - att name : " + att_name + "\n"
-        " - att value: " << att << "\n"
-        " - type info: " << att.content().type().name() << "\n");
+    const auto& var = impl::get_var(filename,varname,"scorpio::has_attribute");
+    varid = var.ncid;
   }
 
+  // Get att id
+  int attid;
+  int err = PIOc_inq_attid(ncid,varid,attname.c_str(),&attid);
+  if (err==PIO_ENOTATT) {
+    return false;
+  }
   EKAT_REQUIRE_MSG (err==PIO_NOERR,
-      "[set_any_attribute] Error! Something went wrong while setting global attribute.\n"
-        " - filename : " + filename + "\n"
-        " - attribute: " + att_name + "\n"
-        " - pio error: " << err << "\n");
+      "Error! Something went wrong while retrieving attribute id.\n"
+      " - filename : " + filename + "\n"
+      " - varname  : " + varname + "\n"
+      " - attname  : " + attname + "\n"
+      " - pio error: " + std::to_string(err) + "\n");
 
-  if (redef) {
-    err = PIOc_enddef(ncid);
-    EKAT_REQUIRE_MSG (err==PIO_NOERR,
-        "[set_any_attribute] Error! Something went wrong while re-closing def phase.\n"
-          " - filename : " + filename + "\n"
-          " - attribute: " + att_name + "\n"
-          " - pio error: " << err << "\n");
-  }
-}
-/* ----------------------------------------------------------------- */
-void eam_pio_enddef(const std::string &filename) {
-  eam_pio_enddef_c2f(filename.c_str());
-}
-/* ----------------------------------------------------------------- */
-void eam_pio_redef(const std::string &filename) {
-  eam_pio_redef_c2f(filename.c_str());
-}
-/* ----------------------------------------------------------------- */
-template<>
-void grid_read_data_array<int>(const std::string &filename, const std::string &varname,
-                          const int time_index, int *hbuf, const int buf_size) {
-  grid_read_data_array_c2f_int(filename.c_str(),varname.c_str(),time_index,hbuf,buf_size);
-}
-template<>
-void grid_read_data_array<float>(const std::string &filename, const std::string &varname,
-                                const int time_index, float *hbuf, const int buf_size) {
-  grid_read_data_array_c2f_float(filename.c_str(),varname.c_str(),time_index,hbuf,buf_size);
-}
-template<>
-void grid_read_data_array<double>(const std::string &filename, const std::string &varname,
-                                  const int time_index, double *hbuf, const int buf_size) {
-  grid_read_data_array_c2f_double(filename.c_str(),varname.c_str(),time_index,hbuf,buf_size);
-}
-/* ----------------------------------------------------------------- */
-template<>
-void grid_write_data_array<int>(const std::string &filename, const std::string &varname, const int* hbuf, const int buf_size) {
-  grid_write_data_array_c2f_int(filename.c_str(),varname.c_str(),hbuf,buf_size);
+  return true;
 }
-template<>
-void grid_write_data_array<float>(const std::string &filename, const std::string &varname, const float* hbuf, const int buf_size) {
-  grid_write_data_array_c2f_float(filename.c_str(),varname.c_str(),hbuf,buf_size);
+
+template<typename T>
+T get_attribute (const std::string& filename,
+                 const std::string& varname,
+                 const std::string& attname)
+{
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  int varid;
+  if (varname=="GLOBAL") {
+    varid = PIO_GLOBAL;
+  } else {
+    varid = impl::get_var(filename,varname,"scorpio::set_any_attribute").ncid;
+  }
+
+  T val;
+  int err = PIOc_get_att(pf.file->ncid,varid,attname.c_str(),reinterpret_cast<void*>(&val));
+  check_scorpio_noerr(err,filename,"attribute",attname,"set_attribute","put_att");
+
+  return val;
 }
+
+// Explicit instantiation
+template int get_attribute (const std::string& filename,
+                            const std::string& varname,
+                            const std::string& attname);
+template std::int64_t get_attribute (const std::string& filename,
+                                     const std::string& varname,
+                                     const std::string& attname);
+template float get_attribute (const std::string& filename,
+                              const std::string& varname,
+                              const std::string& attname);
+template double get_attribute (const std::string& filename,
+                               const std::string& varname,
+                               const std::string& attname);
+
+// Full specialization for strings
 template<>
-void grid_write_data_array<double>(const std::string &filename, const std::string &varname, const double* hbuf, const int buf_size) {
-  grid_write_data_array_c2f_double(filename.c_str(),varname.c_str(),hbuf,buf_size);
-}
-/* ----------------------------------------------------------------- */
-void write_timestamp (const std::string& filename, const std::string& ts_name,
-                      const util::TimeStamp& ts, const bool write_nsteps)
+std::string get_attribute (const std::string& filename,
+                           const std::string& varname,
+                           const std::string& attname)
 {
-  set_attribute(filename,ts_name,ts.to_string());
-  if (write_nsteps) {
-    set_attribute(filename,ts_name+"_nsteps",ts.get_num_steps());
+  // If file wasn't open, open it on the fly. See comment in PeekFile class above.
+  impl::PeekFile pf(filename);
+
+  int varid;
+  if (varname=="GLOBAL") {
+    varid = PIO_GLOBAL;
+  } else {
+    varid = impl::get_var(filename,varname,"scorpio::set_any_attribute").ncid;
   }
+
+  int err;
+  PIO_Offset len;
+  err = PIOc_inq_attlen(pf.file->ncid,varid,attname.c_str(),&len);
+  check_scorpio_noerr(err,filename,"attribute",attname,"set_attribute","inq_attlen");
+
+  std::string val(len,'\0');
+
+  err = PIOc_get_att(pf.file->ncid,varid,attname.c_str(),val.data());
+  check_scorpio_noerr(err,filename,"attribute",attname,"set_attribute","put_att");
+
+  return val;
 }
-/* ----------------------------------------------------------------- */
-util::TimeStamp read_timestamp (const std::string& filename,
-                                const std::string& ts_name,
-                                const bool read_nsteps)
+
+template<typename T>
+void set_attribute (const std::string& filename,
+                    const std::string& varname,
+                    const std::string& attname,
+                    const T& att)
 {
-  auto ts = util::str_to_time_stamp(get_attribute<std::string>(filename,ts_name));
-  if (read_nsteps and has_attribute(filename,ts_name+"_nsteps")) {
-    ts.set_num_steps(get_attribute<int>(filename,ts_name+"_nsteps"));
+  const auto& f = impl::get_file (filename,"scorpio::set_any_attribute");
+
+  int varid;
+  if (varname=="GLOBAL") {
+    varid = PIO_GLOBAL;
+  } else {
+    varid = impl::get_var(filename,varname,"scorpio::set_any_attribute").ncid;
+  }
+
+  // If the file was not in define mode, we must call enddef at the end
+  const bool needs_redef = f.enddef;
+  if (needs_redef) {
+    redef(filename);
+  }
+  
+  int err = PIOc_put_att(f.ncid,varid,attname.c_str(),nctype<T>(),nclen(att),ncdata(att));
+  check_scorpio_noerr(err,filename,"attribute",attname,"set_attribute","put_att");
+
+  if (needs_redef) {
+    enddef(filename);
   }
-  return ts;
 }
-/* ----------------------------------------------------------------- */
+
+// Explicit instantiation
+template void set_attribute (const std::string& filename,
+                             const std::string& varname,
+                             const std::string& attname,
+                             const int& att);
+template void set_attribute (const std::string& filename,
+                             const std::string& varname,
+                             const std::string& attname,
+                             const std::int64_t& att);
+template void set_attribute (const std::string& filename,
+                             const std::string& varname,
+                             const std::string& attname,
+                             const float& att);
+template void set_attribute (const std::string& filename,
+                             const std::string& varname,
+                             const std::string& attname,
+                             const double& att);
+template void set_attribute (const std::string& filename,
+                             const std::string& varname,
+                             const std::string& attname,
+                             const std::string& att);
+
 } // namespace scorpio
 } // namespace scream
diff --git a/components/eamxx/src/share/io/scream_scorpio_interface.hpp b/components/eamxx/src/share/io/scream_scorpio_interface.hpp
index c5ae69ea6c6..549de680fe4 100644
--- a/components/eamxx/src/share/io/scream_scorpio_interface.hpp
+++ b/components/eamxx/src/share/io/scream_scorpio_interface.hpp
@@ -1,168 +1,240 @@
 #ifndef SCREAM_SCORPIO_INTERFACE_HPP
 #define SCREAM_SCORPIO_INTERFACE_HPP
 
-#include "share/field/field_tag.hpp"
-#include "share/scream_types.hpp"
-#include "share/util/scream_time_stamp.hpp"
+#include "scream_scorpio_types.hpp"
 
-#include "ekat/mpi/ekat_comm.hpp"
-#include "ekat/util/ekat_string_utils.hpp"
+#include <ekat/mpi/ekat_comm.hpp>
+#include <ekat/ekat_assert.hpp>
 
+#include <string>
 #include <vector>
 
-/* C++/F90 bridge to F90 SCORPIO routines */
+/*
+ * This file contains interfaces to scorpio C library routines
+ * 
+ * There are two reasons for these interfaces:
+ * 
+ * - allow better context when exceptions/errors occour: throwing exceptions
+ *   can even allow host code to use try-catch blocks to figure out what works.
+ *   Moreover, the user does not need to continuously check return codes, since
+ *   we throw any time scorpio returns something different from PIO_NOERR.
+ * - allow using simpler interfaces: by using string/vector and templates,
+ *   the host code can have more compact interfaces.
+ *
+ * Most of the "get" interfaces can open a file in read mode on the fly.
+ * This allows easier usage from the user point of view, but has some drawbacks:
+ *  - the file is open/closed every time you query it
+ *  - the file is open with default IOType
+ * If you need to do several queries, you should consider registering the file manually
+ * before doing any query, and release it once you are done.
+ */
 
 namespace scream {
 namespace scorpio {
 
-  using offset_t = std::int64_t;
-
-  // WARNING: these values must match the ones of file_purpose_in and file_purpose_out
-  // in the scream_scorpio_interface F90 module
-  enum FileMode {
-    Read = 1,
-    Append = 2,
-    Write = 4
-  };
-
-  // I/O types supported
-  enum IOType {
-    // Default I/O type is used to let the code choose I/O type as needed (via CIME)
-    DefaultIOType = 0,
-    NetCDF,
-    PnetCDF,
-    Adios,
-    Hdf5
-  };
-
-  inline int str2iotype(const std::string &str)
-  {
-    if(str == "default"){
-      return static_cast<int>(IOType::DefaultIOType);
-    }
-    else if(str == "netcdf"){
-      return static_cast<int>(IOType::NetCDF);
-    }
-    else if(str == "pnetcdf"){
-      return static_cast<int>(IOType::PnetCDF);
-    }
-    else if(str == "adios"){
-      return static_cast<int>(IOType::Adios);
-    }
-    else if(str == "hdf5"){
-      return static_cast<int>(IOType::Hdf5);
-    }
-    else{
-      return static_cast<int>(IOType::DefaultIOType);
-    }
+inline std::string default_time_name () { return "time"; }
+
+// Handles aliases for same type:
+//  single -> float
+//  float  -> float
+//  double -> double
+//  real   -> float or double (depending on SCREAM_DOUBLE_PRECISION)
+std::string refine_dtype (const std::string& dtype);
+
+template<typename T>
+std::string get_dtype () {
+  using raw_t = typename std::remove_cv<T>::type;
+  std::string s;
+  if constexpr (std::is_same<raw_t,int>::value) {
+    s = "int";
+  } else if constexpr (std::is_same<raw_t,float>::value) {
+    s = "float";
+  } else if constexpr (std::is_same<raw_t,double>::value) {
+    s = "double";
+  } else if constexpr (std::is_integral<raw_t>::value &&
+              std::is_signed<raw_t>::value &&
+              sizeof(raw_t)==sizeof(long long)) {
+    s = "int64";
+  } else if constexpr (std::is_same<raw_t,char>::value) {
+    s = "char";
+  } else {
+    EKAT_ERROR_MSG ("Error! Invalid/unsupported data type.\n");
   }
-
-  inline std::string iotype2str(int iotype)
-  {
-    switch(iotype){
-      case static_cast<int>(IOType::DefaultIOType): return "default";
-      case static_cast<int>(IOType::NetCDF): return "netcdf";
-      case static_cast<int>(IOType::PnetCDF): return "pnetcdf";
-      case static_cast<int>(IOType::Adios): return "adios";
-      case static_cast<int>(IOType::Hdf5): return "hdf5";
-      default: return "default";
-    }
-  }
-
-  /* All scorpio usage requires that the pio_subsystem is initialized. Happens only once per simulation */
-  void eam_init_pio_subsystem(const ekat::Comm& comm);
-  void eam_init_pio_subsystem(const int mpicom, const int atm_id = 0);
-  /* Cleanup scorpio with pio_finalize */
-  void eam_pio_finalize();
-  /* Close a file currently open in scorpio */
-  void eam_pio_closefile(const std::string& filename);
-  void eam_flush_file(const std::string& filename);
-  /* Register a new file to be used for input/output with the scorpio module */
-  void register_file(const std::string& filename, const FileMode mode, int iotype = IOType::DefaultIOType);
-  /* Sets the IO decompostion for all variables in a particular filename.  Required after all variables have been registered.  Called once per file. */
-  int get_dimlen(const std::string& filename, const std::string& dimname);
-  bool has_dim(const std::string& filename, const std::string& dimname);
-  bool has_variable (const std::string& filename, const std::string& varname);
-  bool has_attribute (const std::string& filename, const std::string& attname);
-  bool has_attribute (const std::string& filename, const std::string& varname, const std::string& attname);
-  void set_decomp(const std::string& filename);
-  /* Sets the degrees-of-freedom for a particular variable in a particular file.  Called once for each variable, for each file. */
-  void set_dof(const std::string &filename, const std::string &varname, const Int dof_len, const offset_t* x_dof);
-  /* Register a dimension coordinate with a file. Called during the file setup. */
-  void register_dimension(const std::string& filename,const std::string& shortname, const std::string& longname, const int length, const bool partitioned);
-  /* Register a variable with a file.  Called during the file setup, for an output stream. */
-  void register_variable(const std::string& filename, const std::string& shortname, const std::string& longname,
-                         const std::string& units, const std::vector<std::string>& var_dimensions,
-                         const std::string& dtype, const std::string& nc_dtype, const std::string& pio_decomp_tag);
-  void register_variable(const std::string& filename, const std::string& shortname, const std::string& longname,
-                         const std::vector<std::string>& var_dimensions,
-                         const std::string& dtype, const std::string& pio_decomp_tag);
-  void set_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, const std::string& meta_val);
-  void set_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, const float meta_val);
-  void set_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, const double meta_val);
-  void get_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, float& meta_val);
-  void get_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, double& meta_val);
-  void get_variable_metadata (const std::string& filename, const std::string& varname, const std::string& meta_name, std::string& meta_val);
-  /* Register a variable with a file.  Called during the file setup, for an input stream. */
-  ekat::any get_any_attribute (const std::string& filename, const std::string& att_name);
-  ekat::any get_any_attribute (const std::string& filename, const std::string& var_name, const std::string& att_name);
-  void set_any_attribute (const std::string& filename, const std::string& att_name, const ekat::any& att);
-  /* End the definition phase for a scorpio file.  Last thing called after all dimensions, variables, dof's and decomps have been set.  Called once per file.
-   * Mandatory before writing or reading can happend on file. */
-  void eam_pio_enddef(const std::string &filename);
-  void eam_pio_redef(const std::string &filename);
-  /* Called each timestep to update the timesnap for the last written output. */
-  void pio_update_time(const std::string &filename, const double time);
-
-  // Read data for a specific variable from a specific file. To read data that
-  // isn't associated with a time index, or to read data at the most recent
-  // time, set time_index to -1. Otherwise use the proper zero-based time index.
-  template<typename T>
-  void grid_read_data_array (const std::string &filename, const std::string &varname,
-                             const int time_index, T* hbuf, const int buf_size);
-  /* Write data for a specific variable to a specific file. */
-  template<typename T>
-  void grid_write_data_array(const std::string &filename, const std::string &varname,
-                             const T* hbuf, const int buf_size);
-
-  template<typename T>
-  T get_attribute (const std::string& filename, const std::string& att_name)
-  {
-    auto att = get_any_attribute(filename,att_name);
-    return ekat::any_cast<T>(att);
-  }
-
-  template<typename T>
-  void set_attribute (const std::string& filename, const std::string& att_name, const T& att)
-  {
-    ekat::any a(att);
-    set_any_attribute(filename,att_name,a);
-  }
-
-  // Shortcut to write/read to/from YYYYMMDD/HHMMSS attributes in the NC file
-  void write_timestamp (const std::string& filename, const std::string& ts_name,
-                        const util::TimeStamp& ts, const bool write_nsteps = false);
-  util::TimeStamp read_timestamp (const std::string& filename,
-                                  const std::string& ts_name,
-                                  const bool read_nsteps = false);
-
-extern "C" {
-  /* Query whether the pio subsystem is inited or not */
-  bool is_eam_pio_subsystem_inited();
-  /* Checks if a file is already open, with the given mode */
-  int get_file_ncid_c2f(const char*&& filename);
-  // If mode<0, then simply checks if file is open, regardless of mode
-  bool is_file_open_c2f(const char*&& filename, const int& mode);
-  /* Query a netCDF file for the time variable */
-  bool is_enddef_c2f(const char*&& filename);
-  double read_time_at_index_c2f(const char*&& filename, const int& time_index);
-  double read_curr_time_c2f(const char*&& filename);
-  /* Query a netCDF file for the metadata associated w/ a variable */
-  float get_variable_metadata_float_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name);
-  double get_variable_metadata_double_c2f (const char*&& filename, const char*&& varname, const char*&& meta_name);
-} // extern "C"
+  return s;
+}
+
+// =================== Global operations ================= //
+
+void init_subsystem(const ekat::Comm& comm, const int atm_id = 0);
+bool is_subsystem_inited ();
+void finalize_subsystem ();
+
+// =================== File operations ================= //
+
+// Opens a file, returns const handle to it (useful for Read mode, to get dims/vars)
+void register_file(const std::string& filename, const FileMode mode, const IOType iotype = IOType::DefaultIOType);
+
+// Release a file (if in Write mode, sync and close the file);
+void release_file  (const std::string& filename);
+
+// Check if file is open. If mode!=Unset, also checks that it's open with given mode
+bool is_file_open (const std::string& filename, const FileMode mode = Unset);
+
+// Force a flush to file (for Write mode only)
+void flush_file (const std::string &filename);
+
+// Reopen/ends the definition phase
+void redef (const std::string &filename);
+void enddef (const std::string &filename);
+
+// =================== Dimensions operations ======================= //
+
+// Define dim on output file (cannot call on Read/Append files)
+void define_dim (const std::string& filename, const std::string& dimname, const int length);
+
+// Check that the given dimension is in the file. If length>0, also check that the length is as expected.
+bool has_dim (const std::string& filename,
+              const std::string& dimname,
+              const int length = -1);
+
+int get_dimlen (const std::string& filename, const std::string& dimname);
+int get_dimlen_local (const std::string& filename, const std::string& dimname);
+
+// Checks if the dimension is unlimited
+bool is_dim_unlimited (const std::string& filename,
+                       const std::string& dimname);
+
+// Get len/name of the time dimension (i.e., the unlimited one)
+// NOTE: these throw if time dim is not present. Use has_dim to check first.
+int get_time_len (const std::string& filename);
+std::string get_time_name (const std::string& filename);
+
+// =================== Decompositions operations ==================== //
+
+// Create a decomposition along a particular dimension
+// Notes:
+// - we declare a decomposition along a single dimension.
+// - set_dim_decomp requires *offsets* in the global array, not global indices
+//   (for 0-based indices, they're the same, but for 1-based indices they're not)
+// - the second version is a shortcut for contiguous decompositions. Notice that NO
+//   check is performed to ensure that the decomposition covers the entire dimension,
+//   or that there are no overlaps (in fact, one *may* need overlap, in certain reads).
+// - the third version is a shortcut of the second, where we compute start/count based
+//   on a linear decomposition of the dimension along all ranks in the IO comm stored
+//   in the ScorpioInstance. The return value is the local length of the dimension
+// - if allow_reset=true, we simply reset the decomposition (if present).
+// - if allow_reset=false, if a decomposition for this dim is already set, we error out
+
+void set_dim_decomp (const std::string& filename,
+                     const std::string& dimname,
+                     const std::vector<offset_t>& my_offsets,
+                     const bool allow_reset = false);
+
+void set_dim_decomp (const std::string& filename,
+                     const std::string& dimname,
+                     const offset_t start, const offset_t count,
+                     const bool allow_reset = false);
+
+void set_dim_decomp (const std::string& filename,
+                     const std::string& dimname,
+                     const bool allow_reset = false);
+
+// ================== Variable operations ================== //
+
+// Define var on output file (cannot call on Read/Append files)
+void define_var (const std::string& filename, const std::string& varname,
+                 const std::string& units, const std::vector<std::string>& dimensions,
+                 const std::string& dtype, const std::string& nc_dtype,
+                 const bool time_dependent = false);
+
+// Shortcut when units are not used, and dtype==nc_dtype
+void define_var (const std::string& filename, const std::string& varname,
+                 const std::vector<std::string>& dimensions,
+                 const std::string& dtype,
+                 const bool time_dependent = false);
+
+// This is useful when reading data sets. E.g., if the pio file is storing
+// a var as float, but we need to read it as double, we need to call this.
+// NOTE: read_var/write_var automatically change the dtype if the input
+//       pointer type does not match the var dtype. However, changing dtype
+//       forces a rebuild of the var decomp (if any). Hence, if you know
+//       the var WILL be read/written as decomposed, you should call this method
+//       BEFORE calling set_dim_decomp, so that the decomp is built directly
+//       with the correct data type (PIO decomps depend on var dtype).
+void change_var_dtype (const std::string& filename,
+                       const std::string& varname,
+                       const std::string& dtype);
+
+// Check that the given variable is in the file.
+bool has_var (const std::string& filename, const std::string& varname);
+
+// Allows to easily query var metadata, such as dims, units, data type,...
+const PIOVar& get_var (const std::string& filename,
+                       const std::string& varname);
+
+// Defines both a time dimension and a time variable
+void define_time (const std::string& filename, const std::string& units,
+                  const std::string& time_name = default_time_name());
+
+// When we read a file, and there is a "time" dimension that is FIXED rather than UNLIMITED,
+// we may have some issues with our read/write logics. Hence, we can use mark a dimension
+// as if it was the UNLIMITED time dim.
+void pretend_dim_is_unlimited (const std::string& filename, const std::string& dimname);
+
+// Update value of time variable, increasing time dim length
+void update_time(const std::string &filename, const double time);
+
+// Retrieves the time variable value(s)
+double get_time (const std::string& filename, const int time_index = -1);
+std::vector<double> get_all_times (const std::string& filename);
+
+// Read variable into user provided buffer.
+// If time dim is present, read given time slice (time_index=-1 means "read last record).
+// If time dim is not present and time_index>=0, it is interpreted as the index of the
+// first dimension (which is not unlimited).
+// NOTE: ETI in the cpp file for int, float, double.
+template<typename T>
+void read_var (const std::string &filename, const std::string &varname, T* buf, const int time_index = -1);
+
+// Write data from user provided buffer into the requested variable
+// NOTE: ETI in the cpp file for int, float, double.
+template<typename T>
+void write_var (const std::string &filename, const std::string &varname, const T* buf, const T* fillValue = nullptr);
+
+// =============== Attributes operations ================== //
+
+// To specify GLOBAL attributes, pass "GLOBAL" as varname
+// NOTE: set/get_attribute are implemented in the cpp file,
+//       with Explicit Instantiation only for:
+//         int, std::int64_t, float, double, std::string
+
+bool has_attribute (const std::string& filename,
+                    const std::string& varname,
+                    const std::string& attname);
+
+template<typename T>
+T get_attribute (const std::string& filename,
+                 const std::string& varname,
+                 const std::string& attname);
+
+template<typename T>
+void set_attribute (const std::string& filename,
+                    const std::string& varname,
+                    const std::string& attname,
+                    const T& att);
+
+// Shortcut, to allow calling set_attribute with compile-time strings, like so
+//   set_attribute(my_file,my_var,my_att_name,"my_value");
+template<int N>
+inline void set_attribute (const std::string& filename,
+                    const std::string& varname,
+                    const std::string& attname,
+                    const char (&att)[N])
+{
+  set_attribute<std::string>(filename,varname,attname,att);
+}
 
 } // namespace scorpio
 } // namespace scream
 
-#endif // define SCREAM_SCORPIO_INTERFACE_HPP
+#endif // define SCREAM_SCORPIO_INTERFACE_HPP 
diff --git a/components/eamxx/src/share/io/scream_scorpio_interface_iso_c2f.F90 b/components/eamxx/src/share/io/scream_scorpio_interface_iso_c2f.F90
deleted file mode 100644
index 2f1263beef7..00000000000
--- a/components/eamxx/src/share/io/scream_scorpio_interface_iso_c2f.F90
+++ /dev/null
@@ -1,520 +0,0 @@
-module scream_scorpio_interface_iso_c2f
-  use iso_c_binding, only: c_int, c_double, c_float, c_bool, c_ptr
-  implicit none
-
-!
-! This file contains bridges from scream c++ to shoc fortran.
-!
-contains
-!=====================================================================!
-  subroutine eam_init_pio_subsystem_c2f(mpicom,compid) bind(c)
-    use scream_scorpio_interface, only : eam_init_pio_subsystem
-    integer(kind=c_int), value, intent(in) :: mpicom,compid
-
-    call eam_init_pio_subsystem(mpicom,compid)
-  end subroutine eam_init_pio_subsystem_c2f
-!=====================================================================!
-  subroutine eam_pio_finalize_c2f() bind(c)
-    use scream_scorpio_interface, only : eam_pio_finalize
-
-    call eam_pio_finalize()
-  end subroutine eam_pio_finalize_c2f
-!=====================================================================!
-  function get_file_ncid_c2f(filename_in) result(ncid) bind(c)
-    use scream_scorpio_interface, only : lookup_pio_atm_file, pio_atm_file_t
-    type(c_ptr), intent(in)         :: filename_in
-
-    type(pio_atm_file_t), pointer :: atm_file
-    character(len=256)      :: filename
-    integer(kind=c_int) :: ncid
-    logical :: found
-
-    call convert_c_string(filename_in,filename)
-    call lookup_pio_atm_file(filename,atm_file,found)
-    if (found) then
-      ncid = int(atm_file%pioFileDesc%fh,kind=c_int)
-    else
-      ncid = -1
-    endif
-  end function get_file_ncid_c2f
-!=====================================================================!
-  function get_file_mode_c2f(filename_in) result(mode) bind(c)
-    use scream_scorpio_interface, only : lookup_pio_atm_file, pio_atm_file_t
-
-    type(c_ptr), intent(in)         :: filename_in
-
-    type(pio_atm_file_t), pointer :: atm_file
-    character(len=256)      :: filename
-    integer(kind=c_int)     :: mode
-    logical :: found
-
-    call convert_c_string(filename_in,filename)
-    call lookup_pio_atm_file(filename,atm_file,found)
-    if (found) then
-      mode = atm_file%purpose
-    else
-      mode = 0
-    endif
-  end function get_file_mode_c2f
-  function is_file_open_c2f(filename_in,purpose) result(res) bind(c)
-    use scream_scorpio_interface, only : lookup_pio_atm_file, pio_atm_file_t
-
-    type(c_ptr), intent(in)         :: filename_in
-    integer(kind=c_int), intent(in) :: purpose
-
-    type(pio_atm_file_t), pointer :: atm_file
-    character(len=256)      :: filename
-    logical (kind=c_bool)   :: res
-    logical :: found
-
-    call convert_c_string(filename_in,filename)
-    call lookup_pio_atm_file(filename,atm_file,found)
-    if (found) then
-      res = LOGICAL(purpose .lt. 0 .or. atm_file%purpose .eq. purpose,kind=c_bool)
-    else
-      res = .false.
-    endif
-  end function is_file_open_c2f
-!=====================================================================!
-  subroutine register_file_c2f(filename_in,purpose,iotype) bind(c)
-    use scream_scorpio_interface, only : register_file
-    type(c_ptr), intent(in)         :: filename_in
-    integer(kind=c_int), intent(in) :: purpose
-    integer(kind=c_int), intent(in) :: iotype
-
-    character(len=256)      :: filename
-
-    call convert_c_string(filename_in,filename)
-    call register_file(trim(filename),purpose,iotype)
-
-  end subroutine register_file_c2f
-!=====================================================================!
-  subroutine set_decomp_c2f(filename_in) bind(c)
-    use scream_scorpio_interface, only : set_decomp
-    type(c_ptr), intent(in) :: filename_in
-
-    character(len=256)       :: filename
-
-    call convert_c_string(filename_in,filename)
-    call set_decomp(trim(filename))
-  end subroutine set_decomp_c2f
-!=====================================================================!
-  subroutine set_dof_c2f(filename_in,varname_in,dof_len,dof_vec) bind(c)
-    use scream_scorpio_interface, only : set_dof, pio_offset_kind
-    use iso_c_binding, only: c_int64_t
-    type(c_ptr), intent(in)                             :: filename_in
-    type(c_ptr), intent(in)                             :: varname_in
-    integer(kind=c_int), value, intent(in)              :: dof_len
-    integer(kind=c_int64_t), intent(in), dimension(dof_len) :: dof_vec
-
-    character(len=256)            :: filename
-    character(len=256)            :: varname
-    integer                       :: ii
-    integer(kind=pio_offset_kind), allocatable :: dof_vec_f90(:)
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    ! Need to add 1 to the dof_vec because C++ starts indices at 0 not 1:
-    allocate(dof_vec_f90(dof_len))
-    do ii = 1,dof_len
-      dof_vec_f90(ii) = dof_vec(ii) + 1
-    end do
-    call set_dof(trim(filename),trim(varname),dof_len,dof_vec_f90)
-    deallocate(dof_vec_f90)
-  end subroutine set_dof_c2f
-!=====================================================================!
-  subroutine eam_pio_closefile_c2f(filename_in) bind(c)
-    use scream_scorpio_interface, only : eam_pio_closefile
-    type(c_ptr), intent(in) :: filename_in
-    character(len=256)      :: filename
-
-    call convert_c_string(filename_in,filename)
-    call eam_pio_closefile(trim(filename))
-
-  end subroutine eam_pio_closefile_c2f
-!=====================================================================!
-  subroutine eam_pio_flush_file_c2f(filename_in) bind(c)
-    use scream_scorpio_interface, only : eam_pio_flush_file
-    type(c_ptr), intent(in) :: filename_in
-    character(len=256)      :: filename
-
-    call convert_c_string(filename_in,filename)
-    call eam_pio_flush_file(trim(filename))
-
-  end subroutine eam_pio_flush_file_c2f
-!=====================================================================!
-  subroutine pio_update_time_c2f(filename_in,time) bind(c)
-    use scream_scorpio_interface, only : eam_update_time
-    type(c_ptr), intent(in) :: filename_in
-    real(kind=c_double), value, intent(in) :: time
-
-    character(len=256)       :: filename
-
-    call convert_c_string(filename_in,filename)
-    call eam_update_time(trim(filename),time)
-
-  end subroutine pio_update_time_c2f
-!=====================================================================!
-  subroutine register_variable_c2f(filename_in, shortname_in, longname_in, &
-                                   units_in, numdims, var_dimensions_in,   &
-                                   dtype, nc_dtype, pio_decomp_tag_in) bind(c)
-    use scream_scorpio_interface, only : register_variable
-    type(c_ptr), intent(in)                :: filename_in
-    type(c_ptr), intent(in)                :: shortname_in
-    type(c_ptr), intent(in)                :: longname_in
-    type(c_ptr), intent(in)                :: units_in
-    integer(kind=c_int), value, intent(in) :: numdims
-    type(c_ptr), intent(in)                :: var_dimensions_in(numdims)
-    integer(kind=c_int), value, intent(in) :: dtype, nc_dtype
-    type(c_ptr), intent(in)                :: pio_decomp_tag_in
-
-    character(len=256) :: filename
-    character(len=256) :: shortname
-    character(len=256) :: longname
-    character(len=256) :: units
-    character(len=256) :: var_dimensions(numdims)
-    character(len=256) :: pio_decomp_tag
-    integer            :: ii
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(shortname_in,shortname)
-    call convert_c_string(longname_in,longname)
-    call convert_c_string(units_in,units)
-    call convert_c_string(pio_decomp_tag_in,pio_decomp_tag)
-    do ii = 1,numdims
-      call convert_c_string(var_dimensions_in(ii), var_dimensions(ii))
-    end do
-
-    call register_variable(filename,shortname,longname,units,numdims,var_dimensions,dtype,nc_dtype,pio_decomp_tag)
-
-  end subroutine register_variable_c2f
-!=====================================================================!
-  subroutine set_variable_metadata_char_c2f(filename_in, varname_in, metaname_in, metaval_in) bind(c)
-    use scream_scorpio_interface, only : set_variable_metadata_char
-    type(c_ptr), intent(in)                :: filename_in
-    type(c_ptr), intent(in)                :: varname_in
-    type(c_ptr), intent(in)                :: metaname_in
-    type(c_ptr), intent(in)                :: metaval_in
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-    character(len=256) :: metaname
-    character(len=256) :: metaval
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call convert_c_string(metaname_in,metaname)
-    call convert_c_string(metaval_in,metaval)
-
-    call set_variable_metadata_char(filename,varname,metaname,metaval)
-
-  end subroutine set_variable_metadata_char_c2f
-!=====================================================================!
-  subroutine set_variable_metadata_float_c2f(filename_in, varname_in, metaname_in, metaval_in) bind(c)
-    use scream_scorpio_interface, only : set_variable_metadata_float
-    type(c_ptr), intent(in)                :: filename_in
-    type(c_ptr), intent(in)                :: varname_in
-    type(c_ptr), intent(in)                :: metaname_in
-    real(kind=c_float), value, intent(in)  :: metaval_in
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-    character(len=256) :: metaname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call convert_c_string(metaname_in,metaname)
-
-    call set_variable_metadata_float(filename,varname,metaname,metaval_in)
-
-  end subroutine set_variable_metadata_float_c2f
-!=====================================================================!
-  subroutine set_variable_metadata_double_c2f(filename_in, varname_in, metaname_in, metaval_in) bind(c)
-    use scream_scorpio_interface, only : set_variable_metadata_double
-    type(c_ptr), intent(in)                :: filename_in
-    type(c_ptr), intent(in)                :: varname_in
-    type(c_ptr), intent(in)                :: metaname_in
-    real(kind=c_double), value, intent(in) :: metaval_in
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-    character(len=256) :: metaname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call convert_c_string(metaname_in,metaname)
-
-    call set_variable_metadata_double(filename,varname,metaname,metaval_in)
-
-  end subroutine set_variable_metadata_double_c2f
-!=====================================================================!
-  function get_variable_metadata_float_c2f(filename_in, varname_in, metaname_in) result(metaval_out) bind(c)
-    use scream_scorpio_interface, only : get_variable_metadata_float
-    type(c_ptr), intent(in)                :: filename_in
-    type(c_ptr), intent(in)                :: varname_in
-    type(c_ptr), intent(in)                :: metaname_in
-    real(kind=c_float)                     :: metaval_out
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-    character(len=256) :: metaname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call convert_c_string(metaname_in,metaname)
-
-    metaval_out = get_variable_metadata_float(filename,varname,metaname)
-
-  end function get_variable_metadata_float_c2f
-!=====================================================================!
-  function get_variable_metadata_double_c2f(filename_in, varname_in, metaname_in) result(metaval_out) bind(c)
-    use scream_scorpio_interface, only : get_variable_metadata_double
-    type(c_ptr), intent(in)                :: filename_in
-    type(c_ptr), intent(in)                :: varname_in
-    type(c_ptr), intent(in)                :: metaname_in
-    real(kind=c_double)                    :: metaval_out
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-    character(len=256) :: metaname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call convert_c_string(metaname_in,metaname)
-
-    metaval_out = get_variable_metadata_double(filename,varname,metaname)
-
-  end function get_variable_metadata_double_c2f
-!=====================================================================!
-  subroutine get_variable_metadata_char_c2f(filename_in, varname_in, metaname_in, metaval_out) bind(c)
-    use scream_scorpio_interface, only : get_variable_metadata_char
-    use iso_c_binding, only: C_NULL_CHAR, c_char, c_f_pointer
-    type(c_ptr), intent(in) :: filename_in
-    type(c_ptr), intent(in) :: varname_in
-    type(c_ptr), intent(in) :: metaname_in
-    type(c_ptr), intent(in) :: metaval_out
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-    character(len=256) :: metaname
-    character(len=256) :: metaval
-    character(len=256, kind=c_char), pointer :: temp_string
-    integer :: slen
-
-    call c_f_pointer(metaval_out,temp_string)
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call convert_c_string(metaname_in,metaname)
-
-    metaval = get_variable_metadata_char(filename,varname,metaname)
-
-    slen = len(trim(metaval))
-    ! If string is 255 or less, add terminating char. If not, it's still
-    ! ok (the C++ string will have length=max_length=256)
-    if (slen .le. 255) then
-      temp_string = trim(metaval) // C_NULL_CHAR
-    else
-      temp_string = metaval
-    endif
-  end subroutine get_variable_metadata_char_c2f
-!=====================================================================!
-  subroutine register_dimension_c2f(filename_in, shortname_in, longname_in, length, partitioned) bind(c)
-    use scream_scorpio_interface, only : register_dimension
-
-    type(c_ptr), intent(in)                 :: filename_in
-    type(c_ptr), intent(in)                 :: shortname_in
-    type(c_ptr), intent(in)                 :: longname_in
-    integer(kind=c_int), value, intent(in)  :: length
-    logical(kind=c_bool), value, intent(in) :: partitioned
-
-    character(len=256) :: filename
-    character(len=256) :: shortname
-    character(len=256) :: longname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(shortname_in,shortname)
-    call convert_c_string(longname_in,longname)
-    call register_dimension(filename,shortname,longname,length,LOGICAL(partitioned))
-
-  end subroutine register_dimension_c2f
-!=====================================================================!
-  function read_curr_time_c2f(filename_in) result(val) bind(c)
-    use scream_scorpio_interface, only : read_time_at_index
-    type(c_ptr), intent(in)                :: filename_in
-    real(kind=c_double)                    :: val
-
-    character(len=256) :: filename
-
-    call convert_c_string(filename_in,filename)
-    val        = read_time_at_index(filename)
-
-  end function read_curr_time_c2f
-!=====================================================================!
-  function read_time_at_index_c2f(filename_in,time_index) result(val) bind(c)
-    use scream_scorpio_interface, only : read_time_at_index
-    type(c_ptr), intent(in)                :: filename_in
-    integer(kind=c_int), intent(in)        :: time_index ! zero-based
-    real(kind=c_double)                    :: val
-
-    character(len=256) :: filename
-
-    call convert_c_string(filename_in,filename)
-    val = read_time_at_index(filename,time_index)
-
-  end function read_time_at_index_c2f
-!=====================================================================!
-  function is_enddef_c2f(filename_in) bind(c) result(enddef)
-    use scream_scorpio_interface, only : lookup_pio_atm_file, pio_atm_file_t
-    type(c_ptr), intent(in) :: filename_in
-
-    type(pio_atm_file_t), pointer :: atm_file
-    character(len=256)    :: filename
-    logical (kind=c_bool) :: enddef
-    logical :: found
-
-    call convert_c_string(filename_in,filename)
-    call lookup_pio_atm_file(filename,atm_file,found)
-    if (found) then
-      enddef = LOGICAL(atm_file%is_enddef, kind=c_bool)
-    endif
-  end function is_enddef_c2f
-!=====================================================================!
-  subroutine eam_pio_enddef_c2f(filename_in) bind(c)
-    use scream_scorpio_interface, only : eam_pio_enddef
-    type(c_ptr), intent(in) :: filename_in
-
-    character(len=256)      :: filename
-
-    call convert_c_string(filename_in,filename)
-    call eam_pio_enddef(filename)
-  end subroutine eam_pio_enddef_c2f
-!=====================================================================!
-  subroutine eam_pio_redef_c2f(filename_in) bind(c)
-    use scream_scorpio_interface, only : eam_pio_redef
-    type(c_ptr), intent(in) :: filename_in
-
-    character(len=256)      :: filename
-
-    call convert_c_string(filename_in,filename)
-    call eam_pio_redef(filename)
-  end subroutine eam_pio_redef_c2f
-!=====================================================================!
-  subroutine convert_c_string(c_string_ptr,f_string)
-    use iso_c_binding, only: c_f_pointer, C_NULL_CHAR
-  ! Purpose: To convert a c_string pointer to the proper fortran string format.
-    type(c_ptr), intent(in) :: c_string_ptr
-    character(len=256), intent(out) :: f_string
-    character(len=256), pointer :: temp_string
-    integer :: str_len
-
-    call c_f_pointer(c_string_ptr,temp_string)
-    str_len = index(temp_string, C_NULL_CHAR) - 1
-    f_string = trim(temp_string(1:str_len))
-
-  end subroutine convert_c_string
-!=====================================================================!
-  subroutine grid_write_data_array_c2f_int(filename_in,varname_in,buf,buf_size) bind(c)
-    use scream_scorpio_interface, only: grid_write_data_array
-
-    type(c_ptr), intent(in) :: filename_in
-    type(c_ptr), intent(in) :: varname_in
-    integer(kind=c_int), intent(in), value :: buf_size
-    integer(kind=c_int), intent(in) :: buf(buf_size)
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call grid_write_data_array(filename,varname,buf,buf_size)
-
-  end subroutine grid_write_data_array_c2f_int
-  subroutine grid_write_data_array_c2f_float(filename_in,varname_in,buf,buf_size) bind(c)
-    use scream_scorpio_interface, only: grid_write_data_array
-
-    type(c_ptr), intent(in) :: filename_in
-    type(c_ptr), intent(in) :: varname_in
-    integer(kind=c_int), intent(in), value :: buf_size
-    real(kind=c_float), intent(in) :: buf(buf_size)
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call grid_write_data_array(filename,varname,buf,buf_size)
-
-  end subroutine grid_write_data_array_c2f_float
-  subroutine grid_write_data_array_c2f_double(filename_in,varname_in,buf,buf_size) bind(c)
-    use scream_scorpio_interface, only: grid_write_data_array
-
-    type(c_ptr), intent(in) :: filename_in
-    type(c_ptr), intent(in) :: varname_in
-    integer(kind=c_int), intent(in), value :: buf_size
-    real(kind=c_double), intent(in) :: buf(buf_size)
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call grid_write_data_array(filename,varname,buf,buf_size)
-
-  end subroutine grid_write_data_array_c2f_double
-!=====================================================================!
-  subroutine grid_read_data_array_c2f_int(filename_in,varname_in,time_index,buf,buf_size) bind(c)
-    use scream_scorpio_interface, only: grid_read_data_array
-
-    type(c_ptr), intent(in) :: filename_in
-    type(c_ptr), intent(in) :: varname_in
-    integer(kind=c_int), value, intent(in) :: time_index ! zero-based
-    integer(kind=c_int), intent(in), value :: buf_size
-    integer(kind=c_int), intent(out) :: buf(buf_size)
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call grid_read_data_array(filename,varname,buf,buf_size,time_index+1)
-
-  end subroutine grid_read_data_array_c2f_int
-!=====================================================================!
-  subroutine grid_read_data_array_c2f_float(filename_in,varname_in,time_index,buf,buf_size) bind(c)
-    use scream_scorpio_interface, only: grid_read_data_array
-
-    type(c_ptr), intent(in) :: filename_in
-    type(c_ptr), intent(in) :: varname_in
-    integer(kind=c_int), value, intent(in) :: time_index ! zero-based
-    integer(kind=c_int), intent(in), value :: buf_size
-    real(kind=c_float), intent(out) :: buf(buf_size)
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call grid_read_data_array(filename,varname,buf,buf_size,time_index+1)
-
-  end subroutine grid_read_data_array_c2f_float
-!=====================================================================!
-  subroutine grid_read_data_array_c2f_double(filename_in,varname_in,time_index,buf,buf_size) bind(c)
-    use scream_scorpio_interface, only: grid_read_data_array
-
-    type(c_ptr), intent(in) :: filename_in
-    type(c_ptr), intent(in) :: varname_in
-    integer(kind=c_int), value, intent(in) :: time_index ! zero-based
-    integer(kind=c_int), intent(in), value :: buf_size
-    real(kind=c_double), intent(out) :: buf(buf_size)
-
-    character(len=256) :: filename
-    character(len=256) :: varname
-
-    call convert_c_string(filename_in,filename)
-    call convert_c_string(varname_in,varname)
-    call grid_read_data_array(filename,varname,buf,buf_size,time_index+1)
-
-  end subroutine grid_read_data_array_c2f_double
-!=====================================================================!
-end module scream_scorpio_interface_iso_c2f
diff --git a/components/eamxx/src/share/io/scream_scorpio_types.cpp b/components/eamxx/src/share/io/scream_scorpio_types.cpp
new file mode 100644
index 00000000000..71c3325c465
--- /dev/null
+++ b/components/eamxx/src/share/io/scream_scorpio_types.cpp
@@ -0,0 +1,59 @@
+#include "scream_scorpio_types.hpp"
+
+#include <ekat/ekat_assert.hpp>
+
+namespace scream {
+namespace scorpio {
+
+std::string e2str (const FileMode mode)
+{
+  auto mode_int = static_cast<typename std::underlying_type<FileMode>::type>(mode);
+  std::string s;
+  switch (mode) {
+    case Unset:  s = "UNSET";  break;
+    case Read:   s = "READ";   break;
+    case Write:  s = "WRITE";  break;
+    case Append: s = "APPEND"; break;
+    default:
+      EKAT_ERROR_MSG (
+          "Error! Unsupported/unrecognized FileMode value.\n"
+          " - value: " + std::to_string(mode_int) + "\n");
+  }
+  return s;
+}
+
+IOType str2iotype(const std::string &str)
+{
+  if(str == "default"){
+    return IOType::DefaultIOType;
+  } else if(str == "netcdf") {
+    return IOType::NetCDF;
+  } else if(str == "pnetcdf") {
+    return IOType::PnetCDF;
+  } else if(str == "adios") {
+    return IOType::Adios;
+  } else if(str == "hdf5") {
+    return IOType::Hdf5;
+  } else {
+    return IOType::Invalid;
+  }
+}
+
+std::string iotype2str(const IOType iotype)
+{
+  std::string s;
+  switch(iotype){
+    case IOType::DefaultIOType: s = "default";  break;
+    case IOType::NetCDF:        s = "netcdf";   break;
+    case IOType::PnetCDF:       s = "pnetcdf";  break;
+    case IOType::Adios:         s = "adios";    break;
+    case IOType::Hdf5:          s = "hdf5";     break;
+    case IOType::Invalid:       s = "invalid";  break;
+    default:
+      EKAT_ERROR_MSG ("Unrecognized iotype.\n");
+  }
+  return s;
+}
+
+} // namespace scorpio
+} // namespace scream
diff --git a/components/eamxx/src/share/io/scream_scorpio_types.hpp b/components/eamxx/src/share/io/scream_scorpio_types.hpp
new file mode 100644
index 00000000000..645b1b26937
--- /dev/null
+++ b/components/eamxx/src/share/io/scream_scorpio_types.hpp
@@ -0,0 +1,135 @@
+#ifndef SCREAM_SCORPIO_TYPES_HPP
+#define SCREAM_SCORPIO_TYPES_HPP
+
+#include <string>
+#include <map>
+#include <vector>
+#include <memory>
+
+namespace scream {
+namespace scorpio {
+
+// Enum denoting how we open a file
+enum FileMode {
+  Unset = 0,
+  Read = 1,
+  Write = 2,
+  Append = Read | Write
+};
+std::string e2str (const FileMode mode);
+
+// I/O types supported
+enum IOType {
+  // Default I/O type is used to let the code choose I/O type as needed (via CIME)
+  DefaultIOType = 0,
+  NetCDF,
+  PnetCDF,
+  Adios,
+  Hdf5,
+  Invalid
+};
+
+IOType str2iotype(const std::string &str);
+std::string iotype2str(const IOType iotype);
+
+// The type used by PIOc for offsets
+using offset_t = std::int64_t;
+
+/*
+ * The following PIOxyz types each represent an entity that
+ * is associated in scorpio with an id. For each of them, we add some
+ * additional metadata, to avoid having to call PIOc_inq_xyz every time
+ * we need such information.
+ * While these types are defined in this public header, the customers
+ * of scream_io will never be able to get any object of these types out
+ * of the internal database. In particular, all data is stored in a
+ * ScorpioSession singleton class, whose declaration is hidden inside
+ * scream_scorpio_interface.cpp.
+ */
+
+// The basic common data of any PIO entity
+struct PIOEntity {
+  int ncid = -1;      // PIO access all data via their id
+  std::string name;   // In EAMxx, we prefer to use a string name than a number id
+};
+
+// An entity that is linked to a specific file
+// This allows an entity to retrieve its file
+struct PIOFileEntity : public PIOEntity {
+  int fid = -1;       // Allow retrieving file from the entity
+};
+
+// A dimension
+struct PIODim : public PIOFileEntity {
+  int length       = -1;
+  bool unlimited   = false;
+
+  // In case we decompose the dimension, this will store
+  // the owned offsets on this rank
+  // NOTE: use a pointer, so we can detect if a decomposition already
+  //       existed or not when we set one.
+  std::shared_ptr<std::vector<offset_t>> offsets;
+};
+
+// A decomposition
+// NOTE: the offsets of a PIODecomp are not the same as the offsets of
+//       stored in its dim. The latter are the offsets *along that dim*.
+//       A PIODecomp is associated with a Nd layout, which includes decomp_dim
+//       among its dimensions. PIODecomp::offsets are the offsets of the full
+//       array layout owned by this rank. Hence, there can be many PIODecomp
+//       all storing the same dim
+struct PIODecomp : public PIOEntity {
+  std::vector<offset_t>           offsets;  // Owned offsets
+  std::shared_ptr<const PIODim>   dim; 
+};
+
+// A variable
+struct PIOVar : public PIOFileEntity {
+  // Note: if time_dep=true, we will add it to the list of dims passed
+  // to scorpio, but the time dim will not appear in this list.
+  std::vector<std::shared_ptr<const PIODim>>          dims;
+
+  std::vector<std::string> dim_names () const {
+    std::vector<std::string> n;
+    for (auto d : dims) {
+      n.push_back(d->name);
+    }
+    return n;
+  }
+
+  std::string dtype;
+  std::string nc_dtype;
+  std::string units;
+
+  bool time_dep = false;
+  
+  // Extra safety measure: for time_dep vars, use this to check that
+  // we are not writing more slices than the current time dim length.
+  int num_records = 0;
+
+  std::shared_ptr<const PIODecomp> decomp;
+
+  // Used only if a) var is not decomposed, and b) dtype!=nc_dtype
+  int size = -1; // Product of all dims
+  std::vector<char> buf;
+};
+
+// A file, which is basically a container for dims and vars
+struct PIOFile : public PIOEntity {
+  std::map<std::string,std::shared_ptr<PIODim>>   dims;
+  std::map<std::string,std::shared_ptr<PIOVar>>   vars;
+
+  std::shared_ptr<PIODim> time_dim;
+  FileMode mode;
+  IOType   iotype;
+  bool enddef = false;
+
+  // We keep track of how many places are currently using this file, so that we
+  // can close it only when they are all done.
+  int num_customers = 0;
+};
+
+} // namespace scorpio
+} // namespace scream
+
+#endif // define SCREAM_SCORPIO_INTERFACE_HPP 
diff --git a/components/eamxx/src/share/io/scream_shr_interface_c2f.F90 b/components/eamxx/src/share/io/scream_shr_interface_c2f.F90
new file mode 100644
index 00000000000..514a1478648
--- /dev/null
+++ b/components/eamxx/src/share/io/scream_shr_interface_c2f.F90
@@ -0,0 +1,53 @@
+module eamxx_shr_interface_mod
+  use iso_c_binding, only: c_int
+  implicit none
+
+!
+! This file contains bridges from EAMxx to E3SM shr module
+!
+contains
+
+!=====================================================================!
+  function shr_get_iosysid_c2f(atm_id) result (iosysid) bind(c)
+    use pio, only: iosystem_desc_t
+    use shr_pio_mod, only: shr_pio_getiosys
+    integer(kind=c_int), value, intent(in) :: atm_id
+
+    integer (kind=c_int) :: iosysid
+    type(iosystem_desc_t), pointer :: iosystem
+
+    iosystem => shr_pio_getiosys(atm_id)
+    iosysid = iosystem%iosysid
+  end function shr_get_iosysid_c2f
+
+!=====================================================================!
+  function shr_get_iotype_c2f(atm_id) result (iotype) bind(c)
+    use shr_pio_mod, only: shr_pio_getiotype
+    integer(kind=c_int), value, intent(in) :: atm_id
+
+    integer (kind=c_int) :: iotype
+
+    iotype = shr_pio_getiotype(atm_id)
+  end function shr_get_iotype_c2f
+
+!=====================================================================!
+  function shr_get_rearranger_c2f(atm_id) result (rearr) bind(c)
+    use shr_pio_mod, only: shr_pio_getrearranger
+    integer(kind=c_int), value, intent(in) :: atm_id
+
+    integer (kind=c_int) :: rearr
+
+    rearr = shr_pio_getrearranger(atm_id)
+  end function shr_get_rearranger_c2f
+
+!=====================================================================!
+  function shr_get_ioformat_c2f(atm_id) result (ioformat) bind(c)
+    use shr_pio_mod, only: shr_pio_getioformat
+    integer(kind=c_int), value, intent(in) :: atm_id
+
+    integer (kind=c_int) :: ioformat
+
+    ioformat = shr_pio_getioformat(atm_id)
+  end function shr_get_ioformat_c2f
+
+end module eamxx_shr_interface_mod
diff --git a/components/eamxx/src/share/io/scream_shr_interface_c2f.hpp b/components/eamxx/src/share/io/scream_shr_interface_c2f.hpp
new file mode 100644
index 00000000000..4e861542515
--- /dev/null
+++ b/components/eamxx/src/share/io/scream_shr_interface_c2f.hpp
@@ -0,0 +1,16 @@
+#ifndef SCREAM_SHR_INTERFACE_HPP
+#define SCREAM_SHR_INTERFACE_HPP
+
+extern "C"
+{
+
+#ifdef SCREAM_CIME_BUILD
+int shr_get_iosysid_c2f(int atm_id);
+int shr_get_iotype_c2f(int atm_id);
+int shr_get_rearranger_c2f(int atm_id);
+int shr_get_ioformat_c2f(int atm_id);
+#endif
+
+} // extern "C"
+
+#endif // SCREAM_SHR_INTERFACE_HPP
diff --git a/components/eamxx/src/share/io/tests/CMakeLists.txt b/components/eamxx/src/share/io/tests/CMakeLists.txt
index 94bcee1790b..16ce2efd437 100644
--- a/components/eamxx/src/share/io/tests/CMakeLists.txt
+++ b/components/eamxx/src/share/io/tests/CMakeLists.txt
@@ -5,6 +5,12 @@ include(ScreamUtils)
 include (BuildCprnc)
 BuildCprnc()
 
+## Test scorpio interfaces
+CreateUnitTest(scorpio_interface_tests "scorpio_interface_tests.cpp"
+  LIBS scream_scorpio_interface LABELS "io"
+  MPI_RANKS 1 ${SCREAM_TEST_MAX_RANKS}
+)
+
 ## Test io utils
 CreateUnitTest(io_utils "io_utils.cpp"
   LIBS scream_io LABELS io
diff --git a/components/eamxx/src/share/io/tests/io_basic.cpp b/components/eamxx/src/share/io/tests/io_basic.cpp
index 378a956f893..11905fd8480 100644
--- a/components/eamxx/src/share/io/tests/io_basic.cpp
+++ b/components/eamxx/src/share/io/tests/io_basic.cpp
@@ -257,14 +257,12 @@ void read (const std::string& avg_type, const std::string& freq_units,
   }
 
   // Check that the expected metadata was appropriately set for each variable
-  Real fill_out;
-  std::string att_test;
   for (const auto& fn: fnames) {
-    scorpio::get_variable_metadata(filename,fn,"_FillValue",fill_out);
-    REQUIRE(fill_out==constants::DefaultFillValue<float>().value);
+    auto att_fill = scorpio::get_attribute<float>(filename,fn,"_FillValue");
+    REQUIRE(att_fill==constants::DefaultFillValue<float>().value);
 
-    scorpio::get_variable_metadata(filename,fn,"test",att_test);
-    REQUIRE (att_test==fn);
+    auto att_str = scorpio::get_attribute<std::string>(filename,fn,"test");
+    REQUIRE (att_str==fn);
   }
 }
 
@@ -284,7 +282,7 @@ TEST_CASE ("io_basic") {
   };
 
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   auto seed = get_random_test_seed(&comm);
 
@@ -308,7 +306,7 @@ TEST_CASE ("io_basic") {
       print(" PASS\n");
     }
   }
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // anonymous namespace
diff --git a/components/eamxx/src/share/io/tests/io_diags.cpp b/components/eamxx/src/share/io/tests/io_diags.cpp
index b2fe7f994db..7daa13c1904 100644
--- a/components/eamxx/src/share/io/tests/io_diags.cpp
+++ b/components/eamxx/src/share/io/tests/io_diags.cpp
@@ -250,7 +250,7 @@ void read (const int seed, const ekat::Comm& comm)
 
 TEST_CASE ("io_diags") {
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   // Make MyDiag available via diag factory
   auto& diag_factory = AtmosphereDiagnosticFactory::instance();
@@ -272,7 +272,7 @@ TEST_CASE ("io_diags") {
   write(seed,comm);
   read(seed,comm);
   print(" PASS\n");
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // anonymous namespace
diff --git a/components/eamxx/src/share/io/tests/io_filled.cpp b/components/eamxx/src/share/io/tests/io_filled.cpp
index ba5eb7d871d..0901e7e7c9e 100644
--- a/components/eamxx/src/share/io/tests/io_filled.cpp
+++ b/components/eamxx/src/share/io/tests/io_filled.cpp
@@ -247,10 +247,10 @@ void read (const std::string& avg_type, const std::string& freq_units,
   }
 
   // Check that the fill value gets appropriately set for each variable
-  Real fill_out;
   for (const auto& fn: fnames) {
-    scorpio::get_variable_metadata(filename,fn,"_FillValue",fill_out);
-    REQUIRE(fill_out==constants::DefaultFillValue<float>().value);
+    // NOTE: use float, since default fp_precision for I/O is 'single'
+    auto att_fill = scorpio::get_attribute<float>(filename,fn,"_FillValue");
+    REQUIRE(att_fill==constants::DefaultFillValue<float>().value);
   }
 }
 
@@ -270,7 +270,7 @@ TEST_CASE ("io_filled") {
   };
 
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   auto seed = get_random_test_seed(&comm);
 
@@ -294,7 +294,7 @@ TEST_CASE ("io_filled") {
       print(" PASS\n");
     }
   }
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // anonymous namespace
diff --git a/components/eamxx/src/share/io/tests/io_monthly.cpp b/components/eamxx/src/share/io/tests/io_monthly.cpp
index 4cf18fff1c7..82b06421196 100644
--- a/components/eamxx/src/share/io/tests/io_monthly.cpp
+++ b/components/eamxx/src/share/io/tests/io_monthly.cpp
@@ -212,7 +212,7 @@ void read (const int seed, const ekat::Comm& comm)
 
 TEST_CASE ("io_monthly") {
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   auto seed = get_random_test_seed(&comm);
 
@@ -224,7 +224,7 @@ TEST_CASE ("io_monthly") {
   if (comm.am_i_root()) {
     std::cout << "   -> Testing output with one file per month ... PASS\n";
   }
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // anonymous namespace
diff --git a/components/eamxx/src/share/io/tests/io_packed.cpp b/components/eamxx/src/share/io/tests/io_packed.cpp
index 585fc7b26f6..5796dbbe8b2 100644
--- a/components/eamxx/src/share/io/tests/io_packed.cpp
+++ b/components/eamxx/src/share/io/tests/io_packed.cpp
@@ -178,7 +178,7 @@ void read (const int freq, const int seed, const int ps_write, const int ps_read
 
 TEST_CASE ("io_packs") {
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
 
   auto seed = get_random_test_seed(&comm);
 
@@ -202,7 +202,7 @@ TEST_CASE ("io_packs") {
       print(" PASS\n");
     }
   }
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // anonymous namespace
diff --git a/components/eamxx/src/share/io/tests/io_remap_test.cpp b/components/eamxx/src/share/io/tests/io_remap_test.cpp
index bfed937636e..c579dea5c7d 100644
--- a/components/eamxx/src/share/io/tests/io_remap_test.cpp
+++ b/components/eamxx/src/share/io/tests/io_remap_test.cpp
@@ -54,8 +54,7 @@ TEST_CASE("io_remap_test","io_remap_test")
 
 
   print (" -> Test Setup ...\n",io_comm);
-  MPI_Fint fcomm = MPI_Comm_c2f(io_comm.mpi_comm());  // MPI communicator group used for I/O.  In our simple test we use MPI_COMM_WORLD, however a subset could be used.
-  scorpio::eam_init_pio_subsystem(fcomm);   // Gather the initial PIO subsystem data creater by component coupler
+  scorpio::init_subsystem(io_comm);
   const int ncols_src = 64*io_comm.size();
   const int nlevs_src = 2*packsize + 1;
   // Construct a timestamp
@@ -81,7 +80,8 @@ TEST_CASE("io_remap_test","io_remap_test")
   print (" -> Create remap file ... \n",io_comm);
   const int ncols_tgt_l = ncols_src_l/2;
   const int ncols_tgt = ncols_src/2;
-  std::vector<Real> col, row, S;
+  std::vector<int> col, row;
+  std::vector<Real> S;
   const Real wgt = 0.4;
   for (int ii=0; ii<ncols_tgt_l; ii++) {
     const int src_col = 2*ii + ncols_src_l*io_comm.rank();
@@ -92,13 +92,9 @@ TEST_CASE("io_remap_test","io_remap_test")
     S.push_back(wgt);
     S.push_back(1.0-wgt);
   }
-  std::vector<std::int64_t> dofs_cols (ncols_src_l);
-  std::iota(dofs_cols.begin(),dofs_cols.end(),io_comm.rank()*ncols_src_l);
   // For vertical remapping we will prokject onto a set of equally
   // spaced pressure levels from p_top to b_bot that is nearly half
   // the number of source columns.
-  std::vector<std::int64_t> dofs_levs(nlevs_tgt);
-  std::iota(dofs_levs.begin(),dofs_levs.end(),0);
   std::vector<Real> p_tgt;
   for (int ii=0; ii<nlevs_tgt; ++ii) {
     p_tgt.push_back(set_pressure(p_top, p_bot, nlevs_tgt, ii));
@@ -108,29 +104,25 @@ TEST_CASE("io_remap_test","io_remap_test")
   const std::string remap_filename = "remap_weights_np"+std::to_string(io_comm.size())+".nc";
   scorpio::register_file(remap_filename, scorpio::FileMode::Write);
 
-  scorpio::register_dimension(remap_filename,"n_a",  "n_a",    ncols_src, true);
-  scorpio::register_dimension(remap_filename,"n_b",  "n_b",    ncols_tgt, true);
-  scorpio::register_dimension(remap_filename,"n_s",  "n_s",    ncols_src, true);
-  scorpio::register_dimension(remap_filename,"lev",  "lev",    nlevs_tgt, false);
+  scorpio::define_dim(remap_filename,"n_a",ncols_src);
+  scorpio::define_dim(remap_filename,"n_b",ncols_tgt);
+  scorpio::define_dim(remap_filename,"n_s",ncols_src);
+  scorpio::define_dim(remap_filename,"lev",nlevs_tgt);
 
-  scorpio::register_variable(remap_filename,"col","col","none",{"n_s"},"real","int","int-nnz");
-  scorpio::register_variable(remap_filename,"row","row","none",{"n_s"},"real","int","int-nnz");
-  scorpio::register_variable(remap_filename,"S","S","none",{"n_s"},"real","real","Real-nnz");
-  scorpio::register_variable(remap_filename,"p_levs","p_levs","none",{"lev"},"real","real","Real-lev");
+  scorpio::define_var(remap_filename,"col",   {"n_s"},"int");
+  scorpio::define_var(remap_filename,"row",   {"n_s"},"int");
+  scorpio::define_var(remap_filename,"S",     {"n_s"},"real");
+  scorpio::define_var(remap_filename,"p_levs",{"lev"},"real");
 
-  scorpio::set_dof(remap_filename,"col",dofs_cols.size(),dofs_cols.data());
-  scorpio::set_dof(remap_filename,"row",dofs_cols.size(),dofs_cols.data());
-  scorpio::set_dof(remap_filename,"S",  dofs_cols.size(),dofs_cols.data());
-  scorpio::set_dof(remap_filename,"p_levs",dofs_levs.size(),dofs_levs.data()); 
-  
-  scorpio::eam_pio_enddef(remap_filename);
+  scorpio::set_dim_decomp(remap_filename,"n_s",io_comm.rank()*ncols_src_l,ncols_src_l);
+  scorpio::enddef(remap_filename);
 
-  scorpio::grid_write_data_array(remap_filename,"row",row.data(),ncols_src);
-  scorpio::grid_write_data_array(remap_filename,"col",col.data(),ncols_src);
-  scorpio::grid_write_data_array(remap_filename,"S",    S.data(),ncols_src);
-  scorpio::grid_write_data_array(remap_filename,"p_levs",p_tgt.data(),nlevs_tgt);
+  scorpio::write_var(remap_filename,"row",   row.data());
+  scorpio::write_var(remap_filename,"col",   col.data());
+  scorpio::write_var(remap_filename,"S",     S.data());
+  scorpio::write_var(remap_filename,"p_levs",p_tgt.data());
 
-  scorpio::eam_pio_closefile(remap_filename);
+  scorpio::release_file(remap_filename);
   print (" -> Create remap file ... done\n",io_comm);
 
   /*
@@ -296,11 +288,11 @@ TEST_CASE("io_remap_test","io_remap_test")
     std::string att_val;
     const auto& filename = vert_in.get<std::string>("Filename");
     for (auto& fname : fnames) {
-      scorpio::get_variable_metadata(filename,fname,"test",att_val);
+      att_val = scorpio::get_attribute<std::string>(filename,fname,"test");
       REQUIRE (att_val==fname);
     }
     std::string f_at_lev_name = "Y_int_at_" + std::to_string(p_ref) + "Pa";
-    scorpio::get_variable_metadata(filename,f_at_lev_name,"test",att_val);
+    att_val = scorpio::get_attribute<std::string>(filename,f_at_lev_name,"test");
     REQUIRE (att_val=="Y_int");
 
     test_input.finalize();
@@ -366,11 +358,11 @@ TEST_CASE("io_remap_test","io_remap_test")
     std::string att_val;
     const auto& filename = horiz_in.get<std::string>("Filename");
     for (auto& fname : fnames) {
-      scorpio::get_variable_metadata(filename,fname,"test",att_val);
+      att_val = scorpio::get_attribute<std::string>(filename,fname,"test");
       REQUIRE (att_val==fname);
     }
     std::string f_at_lev_name = "Y_int_at_" + std::to_string(p_ref) + "Pa";
-    scorpio::get_variable_metadata(filename,f_at_lev_name,"test",att_val);
+    att_val = scorpio::get_attribute<std::string>(filename,f_at_lev_name,"test");
     REQUIRE (att_val=="Y_int");
     test_input.finalize();
 
@@ -452,11 +444,11 @@ TEST_CASE("io_remap_test","io_remap_test")
     std::string att_val;
     const auto& filename = vh_in.get<std::string>("Filename");
     for (auto& fname : fnames) {
-      scorpio::get_variable_metadata(filename,fname,"test",att_val);
+      att_val = scorpio::get_attribute<std::string>(filename,fname,"test");
       REQUIRE (att_val==fname);
     }
     std::string f_at_lev_name = "Y_int_at_" + std::to_string(p_ref) + "Pa";
-    scorpio::get_variable_metadata(filename,f_at_lev_name,"test",att_val);
+    att_val = scorpio::get_attribute<std::string>(filename,f_at_lev_name,"test");
     REQUIRE (att_val=="Y_int");
     test_input.finalize();
 
@@ -551,7 +543,7 @@ TEST_CASE("io_remap_test","io_remap_test")
   // ------------------------------------------------------------------------------------------------------
   // All Done 
   print (" -> Test Remapped Output ... done\n",io_comm);
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 
 }
 /*==========================================================================================================*/
diff --git a/components/eamxx/src/share/io/tests/io_se_grid.cpp b/components/eamxx/src/share/io/tests/io_se_grid.cpp
index edf5f5dbbcd..b610002c8ac 100644
--- a/components/eamxx/src/share/io/tests/io_se_grid.cpp
+++ b/components/eamxx/src/share/io/tests/io_se_grid.cpp
@@ -47,8 +47,7 @@ TEST_CASE("se_grid_io")
   int num_levs = 2 + SCREAM_PACK_SIZE;
 
   // Initialize the pio_subsystem for this test:
-  MPI_Fint fcomm = MPI_Comm_c2f(io_comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm);   // Gather the initial PIO subsystem data creater by component coupler
+  scorpio::init_subsystem(io_comm);
 
   // First set up a field manager and grids manager to interact with the output functions
   auto gm = get_test_gm(io_comm,num_my_elems,np,num_levs);
@@ -95,7 +94,7 @@ TEST_CASE("se_grid_io")
   ins_input.finalize();
 
   // All Done 
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 /*===================================================================================================*/
diff --git a/components/eamxx/src/share/io/tests/output_restart.cpp b/components/eamxx/src/share/io/tests/output_restart.cpp
index 7e59574b1b9..40c8ffee528 100644
--- a/components/eamxx/src/share/io/tests/output_restart.cpp
+++ b/components/eamxx/src/share/io/tests/output_restart.cpp
@@ -68,8 +68,7 @@ TEST_CASE("output_restart","io")
   const auto& out_fields = fm0->get_groups_info().at("output")->m_fields_names;
 
   // Initialize the pio_subsystem for this test:
-  MPI_Fint fcomm = MPI_Comm_c2f(comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm);
+  scorpio::init_subsystem(comm);
 
   // Timestamp of the simulation initial time
   util::TimeStamp t0 ({2000,1,1},{0,0,0});
@@ -150,7 +149,7 @@ TEST_CASE("output_restart","io")
     print(" DONE\n");
   }
   // Finalize everything
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 } 
 
 /*=============================================================================================*/
diff --git a/components/eamxx/src/share/io/tests/scorpio_interface_tests.cpp b/components/eamxx/src/share/io/tests/scorpio_interface_tests.cpp
new file mode 100644
index 00000000000..ea2999eef57
--- /dev/null
+++ b/components/eamxx/src/share/io/tests/scorpio_interface_tests.cpp
@@ -0,0 +1,217 @@
+#include <catch2/catch.hpp>
+
+#include "share/io/scream_scorpio_interface.hpp"
+#include <ekat/util/ekat_string_utils.hpp>
+
+namespace scream {
+
+using namespace scorpio;
+
+TEST_CASE ("io_subsystem") {
+  ekat::Comm comm (MPI_COMM_WORLD);
+
+  init_subsystem (comm);
+  REQUIRE_THROWS (init_subsystem(comm)); // ERROR: already inited
+
+  finalize_subsystem ();
+  REQUIRE_THROWS (finalize_subsystem()); // ERROR: no subsystem active
+}
+
+TEST_CASE ("write_and_read") {
+  ekat::Comm comm (MPI_COMM_WORLD);
+
+  EKAT_REQUIRE_MSG (comm.size()<=4,
+      "Error! This test is tailored for an MPI_Comm of size 1, 2, 3, or 4.\n"
+      " - MPI_Comm size: " + std::to_string(comm.size()) + "\n");
+
+  init_subsystem (comm);
+
+  std::string filename = "scorpio_interface_write_test_np" + std::to_string(comm.size()) + ".nc";
+
+  const int dim1 = 2;
+  const int dim2 = 4;
+  const int dim3 = 12;
+  const int ldim3 = dim3 / comm.size();
+
+  // Offsets for dim3 decomp owned by this rank
+  std::vector<offset_t> my_offsets;
+  for (int i=0; i<ldim3; ++i) {
+    my_offsets.push_back(ldim3*comm.rank() + i);
+  }
+
+  // Write phase
+  {
+    register_file (filename,Write);
+    REQUIRE_THROWS (register_file (filename,Read)); // ERROR: cannot open in both read and write modes
+    REQUIRE (is_file_open(filename));
+    REQUIRE (is_file_open(filename,Write));
+    REQUIRE (not is_file_open(filename,Read));
+
+    define_dim (filename,"dim1",dim1);
+    define_dim (filename,"dim2",dim2);
+    define_dim (filename,"dim2",dim2); // OK, same specs
+    REQUIRE_THROWS (define_dim (filename,"dim2",dim2+3)); // ERROR: changing dim length
+    define_dim (filename,"dim3",dim3);
+
+    REQUIRE_THROWS (set_dim_decomp (filename,"dim4",my_offsets)); // ERROR: dimension not found
+
+    set_dim_decomp (filename,"dim3",my_offsets);
+
+    REQUIRE_THROWS (define_var (filename,"var1",{"dim1"},"double",true)); // ERROR: no time dimension (yet)
+    REQUIRE_THROWS (define_var (filename,"var1",{"dim0"},"double",false)); // ERROR: dim0 not found
+    REQUIRE_THROWS (define_var (filename,"var1",{"dim1"},"complex",false)); // ERROR: unsupported dtype
+    define_var (filename,"var1",{"dim1"},"double",false);
+    define_var (filename,"var1",{"dim1"},"double",false); // OK, same specs
+    REQUIRE_THROWS (define_var (filename,"var1",{"dim2"},"double",false)); // ERROR: changing var dimensions
+    REQUIRE_THROWS (define_var (filename,"var1",{"dim1"},"int",false)); // ERROR: changing dtype
+
+    define_time(filename,"some_units","the_time");
+    REQUIRE_THROWS (define_time(filename,"","another_name")); // ERROR: time already defined with another name
+
+    define_var (filename,"var2",{"dim1","dim2"},"float",true);
+    define_var (filename,"var3",{},"int",true);
+    REQUIRE_THROWS (define_var (filename,"var3",{},"int",false)); // ERROR: changing time_dep flag
+    define_var (filename,"var4",{"dim3","dim1"},"double",false);
+    define_var (filename,"var5",{"dim3","dim1"},"double",true);
+
+    enddef (filename);
+
+    std::vector<double> var1 (dim1);
+    std::vector<float> var2 (dim1*dim2);
+    std::vector<int> var3 (1);
+    std::vector<double> var45 (ldim3*dim1);
+
+    // Write first time slice
+    update_time (filename,0.0);
+    std::iota (var1.begin(),var1.end(),100);
+    std::iota (var2.begin(),var2.end(),100);
+    std::iota (var3.begin(),var3.end(),100);
+    std::iota (var45.begin(),var45.end(),100+comm.rank()*ldim3*dim1);
+    write_var (filename,"var1",var1.data());
+    write_var (filename,"var2",var2.data());
+    write_var (filename,"var3",var3.data());
+    write_var (filename,"var4",var45.data());
+    write_var (filename,"var5",var45.data());
+
+    REQUIRE_THROWS (write_var (filename,"var3",static_cast<int*>(nullptr))); // ERROR: invalid pointer
+
+    // Write second time slice
+    update_time (filename,0.5);
+    std::iota (var2.begin(),var2.end(),  200);
+    std::iota (var3.begin(),var3.end(),  200);
+    std::iota (var45.begin(),var45.end(),200+comm.rank()*ldim3*dim1);
+    write_var (filename,"var2",var2.data());
+    write_var (filename,"var3",var3.data());
+    double minus_one = -1;
+    write_var (filename,"var5",var45.data(),&minus_one);
+
+    // Cleanup
+    release_file (filename);
+
+    REQUIRE_THROWS (release_file (filename)); // ERROR: file not open
+    REQUIRE (not is_file_open(filename));
+  }
+
+  // Read phase
+  {
+    using strvec_t = std::vector<std::string>;
+
+    register_file (filename,Read);
+    REQUIRE (is_file_open(filename));
+
+    // Check dims
+    REQUIRE (has_dim(filename,"the_time",2));
+    REQUIRE (has_dim(filename,"dim1",dim1));
+    REQUIRE (has_dim(filename,"dim2",dim2));
+    REQUIRE (has_dim(filename,"dim3",dim3));
+
+    // Check vars
+    REQUIRE (has_var(filename,"the_time"));
+    const auto& timevar = get_var(filename,"the_time");
+    REQUIRE (timevar.dim_names().size()==0);
+    REQUIRE (timevar.time_dep==true);
+
+    REQUIRE (has_var(filename,"var1"));
+    const auto& piovar1 = get_var(filename,"var1");
+    REQUIRE (piovar1.dim_names()==strvec_t{"dim1"});
+    REQUIRE (piovar1.time_dep==false);
+
+    REQUIRE (has_var(filename,"var2"));
+    const auto& piovar2 = get_var(filename,"var2");
+    REQUIRE (piovar2.dim_names()==strvec_t{"dim1","dim2"});
+    REQUIRE (piovar2.time_dep==true);
+
+    REQUIRE (has_var(filename,"var3"));
+    const auto& piovar3 = get_var(filename,"var3");
+    REQUIRE (piovar3.dim_names().size()==0);
+    REQUIRE (piovar3.time_dep==true);
+
+    REQUIRE (has_var(filename,"var4"));
+    const auto& piovar4 = get_var(filename,"var4");
+    REQUIRE (piovar4.dim_names()==strvec_t{"dim3","dim1"});
+    REQUIRE (piovar4.time_dep==false);
+
+    REQUIRE (has_var(filename,"var5"));
+    const auto piovar5= get_var(filename,"var5");
+    REQUIRE (piovar5.dim_names()==strvec_t{"dim3","dim1"});
+    REQUIRE (piovar5.time_dep==true);
+
+    REQUIRE (not has_var(filename,"var0")); // Var not in file
+
+    set_dim_decomp (filename,"dim3",my_offsets);
+
+    std::vector<double> var1 (dim1);
+    std::vector<float> var2 (dim1*dim2);
+    std::vector<int> var3 (1);
+    std::vector<double> var45 (ldim3*dim1);
+
+    std::vector<double> tgt_var1 (dim1);
+    std::vector<float> tgt_var2 (dim1*dim2);
+    std::vector<int> tgt_var3 (1);
+    std::vector<double> tgt_var45 (ldim3*dim1);
+    std::iota (tgt_var1.begin(),tgt_var1.end(),  100);
+    std::iota (tgt_var2.begin(),tgt_var2.end(),  100);
+    std::iota (tgt_var3.begin(),tgt_var3.end(),  100);
+    std::iota (tgt_var45.begin(),tgt_var45.end(),100+comm.rank()*ldim3*dim1);
+
+    read_var (filename,"var1",var1.data());
+    REQUIRE (tgt_var1==var1);
+
+    // Read first time slice
+    REQUIRE_THROWS (read_var (filename,"var3",var3.data(),3)); // ERROR: time_idx out of bounds
+    REQUIRE_THROWS (read_var (filename,"var3",static_cast<int*>(nullptr))); // ERROR: invalid pointer
+
+    read_var (filename,"var2",var2.data(),0);
+    REQUIRE (tgt_var2==var2);
+
+    read_var (filename,"var3",var3.data(),0);
+    REQUIRE (tgt_var3==var3);
+
+    read_var (filename,"var4",var45.data(),0);
+    REQUIRE (tgt_var45==var45);
+
+    read_var (filename,"var5",var45.data(),0);
+    REQUIRE (tgt_var45==var45);
+
+    // Read second time slice
+    std::iota (tgt_var2.begin(),tgt_var2.end(),  200);
+    std::iota (tgt_var3.begin(),tgt_var3.end(),  200);
+    std::iota (tgt_var45.begin(),tgt_var45.end(),200+comm.rank()*ldim3*dim1);
+
+    read_var (filename,"var2",var2.data(),1);
+    REQUIRE (tgt_var2==var2);
+
+    read_var (filename,"var3",var3.data(),1);
+    REQUIRE (tgt_var3==var3);
+
+    read_var (filename,"var5",var45.data(),1);
+    REQUIRE (tgt_var45==var45);
+
+    // Cleanup
+    release_file (filename);
+  }
+
+  finalize_subsystem ();
+}
+
+} // namespace scream
diff --git a/components/eamxx/src/share/tests/coarsening_remapper_tests.cpp b/components/eamxx/src/share/tests/coarsening_remapper_tests.cpp
index 7f1a3c20c7b..c6223b67dbf 100644
--- a/components/eamxx/src/share/tests/coarsening_remapper_tests.cpp
+++ b/components/eamxx/src/share/tests/coarsening_remapper_tests.cpp
@@ -236,22 +236,15 @@ void create_remap_file(const std::string& filename, const int ngdofs_tgt)
 
   scorpio::register_file(filename, scorpio::FileMode::Write);
 
-  scorpio::register_dimension(filename,"n_a", "n_a", ngdofs_src, true);
-  scorpio::register_dimension(filename,"n_b", "n_b", ngdofs_tgt, true);
-  scorpio::register_dimension(filename,"n_s", "n_s", nnz, true);
+  scorpio::define_dim(filename,"n_a", ngdofs_src);
+  scorpio::define_dim(filename,"n_b", ngdofs_tgt);
+  scorpio::define_dim(filename,"n_s", nnz);
 
-  scorpio::register_variable(filename,"col","col","none",{"n_s"},"int","int","int-nnz");
-  scorpio::register_variable(filename,"row","row","none",{"n_s"},"int","int","int-nnz");
-  scorpio::register_variable(filename,"S","S","none",{"n_s"},"double","double","Real-nnz");
+  scorpio::define_var(filename,"col",{"n_s"},"int");
+  scorpio::define_var(filename,"row",{"n_s"},"int");
+  scorpio::define_var(filename,"S"  ,{"n_s"},"double");
 
-  std::vector<scorpio::offset_t> dofs(nnz);
-  std::iota(dofs.begin(),dofs.end(),0);
-
-  scorpio::set_dof(filename,"col",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"row",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"S",  dofs.size(),dofs.data());
-  
-  scorpio::eam_pio_enddef(filename);
+  scorpio::enddef(filename);
 
   std::vector<int> col(nnz), row(nnz);
   std::vector<double> S(nnz,0.5);
@@ -262,11 +255,11 @@ void create_remap_file(const std::string& filename, const int ngdofs_tgt)
     col[2*i+1] = i+1;
   }
 
-  scorpio::grid_write_data_array(filename,"row",row.data(),nnz);
-  scorpio::grid_write_data_array(filename,"col",col.data(),nnz);
-  scorpio::grid_write_data_array(filename,"S",    S.data(),nnz);
+  scorpio::write_var(filename,"row",row.data());
+  scorpio::write_var(filename,"col",col.data());
+  scorpio::write_var(filename,"S",    S.data());
 
-  scorpio::eam_pio_closefile(filename);
+  scorpio::release_file(filename);
 }
 
 TEST_CASE("coarsening_remap")
@@ -288,8 +281,7 @@ TEST_CASE("coarsening_remap")
   root_print (" |   Testing coarsening remapper   |\n",comm);
   root_print (" +---------------------------------+\n\n",comm);
 
-  MPI_Fint fcomm = MPI_Comm_c2f(comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm);
+  scorpio::init_subsystem(comm);
   auto engine = setup_random_test (&comm);
 
   // -------------------------------------- //
@@ -507,7 +499,7 @@ TEST_CASE("coarsening_remap")
   }
 
   // Clean up scorpio stuff
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // namespace scream
diff --git a/components/eamxx/src/share/tests/eamxx_time_interpolation_tests.cpp b/components/eamxx/src/share/tests/eamxx_time_interpolation_tests.cpp
index 53e423dfa4d..c8551d08126 100644
--- a/components/eamxx/src/share/tests/eamxx_time_interpolation_tests.cpp
+++ b/components/eamxx/src/share/tests/eamxx_time_interpolation_tests.cpp
@@ -139,7 +139,7 @@ TEST_CASE ("eamxx_time_interpolation_data_from_file") {
   // Setup basic test
   printf("   - Test Basics...\n");
   ekat::Comm comm(MPI_COMM_WORLD);
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
   auto seed = get_random_test_seed(&comm);
   std::mt19937_64 engine(seed); 
   const auto t0 = init_timestamp();
@@ -229,7 +229,7 @@ TEST_CASE ("eamxx_time_interpolation_data_from_file") {
   printf("                        ... DONE\n");
 
   // All done with IO
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 
   printf("TimeInterpolation - From File Case...DONE\n\n\n");
 } // TEST_CASE eamxx_time_interpolation_data_from_file
@@ -350,7 +350,9 @@ std::shared_ptr<FieldManager> get_fm (const std::shared_ptr<const AbstractGrid>&
 
   const auto units = ekat::units::Units::nondimensional();
   for (const auto& fl : layouts) {
-    FID fid("f_"+std::to_string(fl.size()),fl,units,grid->name());
+    int gl_size = fl.size();
+    grid->get_comm().all_reduce(&gl_size,1,MPI_SUM);
+    FID fid("f_"+std::to_string(gl_size),fl,units,grid->name());
     Field f(fid);
     f.allocate_view();
     randomize (f,engine,my_pdf);
diff --git a/components/eamxx/src/share/tests/refining_remapper_p2p_tests.cpp b/components/eamxx/src/share/tests/refining_remapper_p2p_tests.cpp
index 75ea20f8130..56d0de8a47a 100644
--- a/components/eamxx/src/share/tests/refining_remapper_p2p_tests.cpp
+++ b/components/eamxx/src/share/tests/refining_remapper_p2p_tests.cpp
@@ -123,21 +123,15 @@ void write_map_file (const std::string& filename, const int ngdofs_src) {
 
   scorpio::register_file(filename, scorpio::FileMode::Write);
 
-  scorpio::register_dimension(filename, "n_a", "n_a", ngdofs_src, false);
-  scorpio::register_dimension(filename, "n_b", "n_b", ngdofs_tgt, false);
-  scorpio::register_dimension(filename, "n_s", "n_s", nnz,        false);
-
-  scorpio::register_variable(filename, "col", "col", "1", {"n_s"}, "int",    "int",    "");
-  scorpio::register_variable(filename, "row", "row", "1", {"n_s"}, "int",    "int",    "");
-  scorpio::register_variable(filename, "S",   "S",   "1", {"n_s"}, "double", "double", "");
-
-  std::vector<scorpio::offset_t> dofs(nnz);
-  std::iota(dofs.begin(),dofs.end(),0);
-  scorpio::set_dof(filename,"col",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"row",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"S",  dofs.size(),dofs.data());
-  
-  scorpio::eam_pio_enddef(filename);
+  scorpio::define_dim(filename, "n_a", ngdofs_src);
+  scorpio::define_dim(filename, "n_b", ngdofs_tgt);
+  scorpio::define_dim(filename, "n_s", nnz);
+
+  scorpio::define_var(filename, "col", {"n_s"}, "int");
+  scorpio::define_var(filename, "row", {"n_s"}, "int");
+  scorpio::define_var(filename, "S",   {"n_s"}, "double");
+
+  scorpio::enddef(filename);
 
   std::vector<int> col(nnz), row(nnz);
   std::vector<double> S(nnz);
@@ -156,11 +150,11 @@ void write_map_file (const std::string& filename, const int ngdofs_src) {
       S[ngdofs_src+2*i+1] = 0.5;
   }
 
-  scorpio::grid_write_data_array(filename,"row",row.data(),nnz);
-  scorpio::grid_write_data_array(filename,"col",col.data(),nnz);
-  scorpio::grid_write_data_array(filename,"S",  S.data(),  nnz);
+  scorpio::write_var(filename,"row",row.data());
+  scorpio::write_var(filename,"col",col.data());
+  scorpio::write_var(filename,"S",  S.data());
 
-  scorpio::eam_pio_closefile(filename);
+  scorpio::release_file(filename);
 }
 
 TEST_CASE ("refining_remapper") {
@@ -172,8 +166,7 @@ TEST_CASE ("refining_remapper") {
 
   auto engine = setup_random_test (&comm);
 
-  MPI_Fint fcomm = MPI_Comm_c2f(comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm);
+  scorpio::init_subsystem(comm);
 
   // Create a map file
   const int ngdofs_src = 4*comm.size();
@@ -417,7 +410,7 @@ TEST_CASE ("refining_remapper") {
 
   // Clean up
   r = nullptr;
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // namespace scream
diff --git a/components/eamxx/src/share/tests/refining_remapper_rma_tests.cpp b/components/eamxx/src/share/tests/refining_remapper_rma_tests.cpp
index 53fb79321d4..b37bd2df139 100644
--- a/components/eamxx/src/share/tests/refining_remapper_rma_tests.cpp
+++ b/components/eamxx/src/share/tests/refining_remapper_rma_tests.cpp
@@ -178,21 +178,15 @@ void write_map_file (const std::string& filename, const int ngdofs_src) {
 
   scorpio::register_file(filename, scorpio::FileMode::Write);
 
-  scorpio::register_dimension(filename, "n_a", "n_a", ngdofs_src, false);
-  scorpio::register_dimension(filename, "n_b", "n_b", ngdofs_tgt, false);
-  scorpio::register_dimension(filename, "n_s", "n_s", nnz,        false);
-
-  scorpio::register_variable(filename, "col", "col", "1", {"n_s"}, "int",    "int",    "");
-  scorpio::register_variable(filename, "row", "row", "1", {"n_s"}, "int",    "int",    "");
-  scorpio::register_variable(filename, "S",   "S",   "1", {"n_s"}, "double", "double", "");
-
-  std::vector<scorpio::offset_t> dofs(nnz);
-  std::iota(dofs.begin(),dofs.end(),0);
-  scorpio::set_dof(filename,"col",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"row",dofs.size(),dofs.data());
-  scorpio::set_dof(filename,"S",  dofs.size(),dofs.data());
-  
-  scorpio::eam_pio_enddef(filename);
+  scorpio::define_dim(filename, "n_a", ngdofs_src);
+  scorpio::define_dim(filename, "n_b", ngdofs_tgt);
+  scorpio::define_dim(filename, "n_s", nnz);
+
+  scorpio::define_var(filename, "col", {"n_s"}, "int");
+  scorpio::define_var(filename, "row", {"n_s"}, "int");
+  scorpio::define_var(filename, "S",   {"n_s"}, "double");
+
+  scorpio::enddef(filename);
 
   std::vector<int> col(nnz), row(nnz);
   std::vector<double> S(nnz);
@@ -211,11 +205,11 @@ void write_map_file (const std::string& filename, const int ngdofs_src) {
       S[ngdofs_src+2*i+1] = 0.5;
   }
 
-  scorpio::grid_write_data_array(filename,"row",row.data(),nnz);
-  scorpio::grid_write_data_array(filename,"col",col.data(),nnz);
-  scorpio::grid_write_data_array(filename,"S",  S.data(),  nnz);
+  scorpio::write_var(filename,"row",row.data());
+  scorpio::write_var(filename,"col",col.data());
+  scorpio::write_var(filename,"S",  S.data());
 
-  scorpio::eam_pio_closefile(filename);
+  scorpio::release_file(filename);
 }
 
 TEST_CASE ("refining_remapper") {
@@ -227,8 +221,7 @@ TEST_CASE ("refining_remapper") {
 
   auto engine = setup_random_test (&comm);
 
-  MPI_Fint fcomm = MPI_Comm_c2f(comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm);
+  scorpio::init_subsystem(comm);
 
   // Create a map file
   const int ngdofs_src = 4*comm.size();
@@ -475,7 +468,7 @@ TEST_CASE ("refining_remapper") {
 
   // Clean up
   r = nullptr;
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // namespace scream
diff --git a/components/eamxx/src/share/tests/vertical_remapper_tests.cpp b/components/eamxx/src/share/tests/vertical_remapper_tests.cpp
index 131f6380f52..f7bd62b7998 100644
--- a/components/eamxx/src/share/tests/vertical_remapper_tests.cpp
+++ b/components/eamxx/src/share/tests/vertical_remapper_tests.cpp
@@ -96,20 +96,14 @@ Real data_func(const int col, const int vec, const Real pres) {
 // Helper function to create a remap file
 void create_remap_file(const std::string& filename, const int nlevs, const std::vector<std::int64_t>& dofs_p, const std::vector<Real>& p_tgt) 
 {
-
   scorpio::register_file(filename, scorpio::FileMode::Write);
+  scorpio::define_dim(filename,"lev",nlevs);
+  scorpio::define_var(filename,"p_levs",{"lev"},"real");
+  scorpio::enddef(filename);
 
-  scorpio::register_dimension(filename,"lev","lev",nlevs, false);
-
-  scorpio::register_variable(filename,"p_levs","p_levs","none",{"lev"},"real","real","Real-lev");
-
-  scorpio::set_dof(filename,"p_levs",dofs_p.size(),dofs_p.data()); 
-  
-  scorpio::eam_pio_enddef(filename);
-
-  scorpio::grid_write_data_array(filename,"p_levs",p_tgt.data(),nlevs);
+  scorpio::write_var(filename,"p_levs",p_tgt.data());
 
-  scorpio::eam_pio_closefile(filename);
+  scorpio::release_file(filename);
 }
 
 TEST_CASE ("vertical_remap") {
@@ -121,8 +115,7 @@ TEST_CASE ("vertical_remap") {
 
   ekat::Comm comm(MPI_COMM_WORLD);
 
-  MPI_Fint fcomm = MPI_Comm_c2f(comm.mpi_comm());
-  scorpio::eam_init_pio_subsystem(fcomm);
+  scorpio::init_subsystem(comm);
 
   // -------------------------------------- //
   //           Set grid/map sizes           //
@@ -389,7 +382,7 @@ TEST_CASE ("vertical_remap") {
   }
 
   // Clean up scorpio stuff
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
 }
 
 } // namespace scream
diff --git a/components/eamxx/src/share/util/eamxx_time_interpolation.cpp b/components/eamxx/src/share/util/eamxx_time_interpolation.cpp
index 3515bcdaac9..e0dba0cf838 100644
--- a/components/eamxx/src/share/util/eamxx_time_interpolation.cpp
+++ b/components/eamxx/src/share/util/eamxx_time_interpolation.cpp
@@ -1,4 +1,5 @@
 #include "share/util/eamxx_time_interpolation.hpp"
+#include "share/io/scream_io_utils.hpp"
 
 namespace scream{
 namespace util {
@@ -30,8 +31,8 @@ TimeInterpolation::TimeInterpolation(
 void TimeInterpolation::finalize()
 {
   if (m_is_data_from_file) {
-    m_file_data_atm_input.finalize();
-    m_is_data_from_file=false;
+    m_file_data_atm_input = nullptr;
+    m_is_data_from_file = false;
   }
 }
 /*-----------------------------------------------------------------------------------------------*/
@@ -86,6 +87,10 @@ void TimeInterpolation::add_field(const Field& field_in, const bool store_shallo
   const std::string name = field_in.name();
   EKAT_REQUIRE_MSG(!m_fm_time0->has_field(name) and !m_fm_time1->has_field(name),
 		  "Error!! TimeInterpolation:add_field, field + " << name << " has already been added." << "\n");
+  EKAT_REQUIRE_MSG (field_in.data_type()==DataType::FloatType or field_in.data_type()==DataType::DoubleType,
+      "[TimeInterpolation] Error! Input field must have floating-point data type.\n"
+      " - field name: " + field_in.name() + "\n"
+      " - data type : " + e2str(field_in.data_type()) + "\n");
 
   // Clone the field for each field manager to get all the metadata correct.
   auto field0 = field_in.clone();
@@ -113,7 +118,7 @@ void TimeInterpolation::shift_data()
     auto& field1 = m_fm_time1->get_field(name);
     std::swap(field0,field1);
   }
-  m_file_data_atm_input.set_field_manager(m_fm_time1);
+  m_file_data_atm_input->set_field_manager(m_fm_time1);
 }
 /*-----------------------------------------------------------------------------------------------*/
 /* Function which will initialize the TimeStamps.
@@ -160,19 +165,48 @@ void TimeInterpolation::initialize_data_from_files()
   ekat::ParameterList input_params;
   input_params.set("Field Names",m_field_names);
   input_params.set("Filename",triplet_curr.filename);
-  m_file_data_atm_input = AtmosphereInput(input_params,m_fm_time1);
-  m_file_data_atm_input.set_logger(m_logger);
+  m_file_data_atm_input = std::make_shared<AtmosphereInput>(input_params,m_fm_time1);
+  m_file_data_atm_input->set_logger(m_logger);
   // Assign the mask value gathered from the FillValue found in the source file.
   // TODO: Should we make it possible to check if FillValue is in the metadata and only assign mask_value if it is?
-  float var_fill_value;
   for (auto& name : m_field_names) {
-    scorpio::get_variable_metadata(triplet_curr.filename,name,"_FillValue",var_fill_value);
     auto& field0 = m_fm_time0->get_field(name);
-    field0.get_header().set_extra_data("mask_value",var_fill_value);
     auto& field1 = m_fm_time1->get_field(name);
-    field1.get_header().set_extra_data("mask_value",var_fill_value);
     auto& field_out = m_interp_fields.at(name);
-    field_out.get_header().set_extra_data("mask_value",var_fill_value);
+
+    auto set_fill_value = [&](const auto var_fill_value) {
+      const auto dt = field_out.data_type();
+      if (dt==DataType::FloatType) {
+        field0.get_header().set_extra_data("mask_value",static_cast<float>(var_fill_value));
+        field1.get_header().set_extra_data("mask_value",static_cast<float>(var_fill_value));
+        field_out.get_header().set_extra_data("mask_value",static_cast<float>(var_fill_value));
+      } else if (dt==DataType::DoubleType) {
+        field0.get_header().set_extra_data("mask_value",static_cast<double>(var_fill_value));
+        field1.get_header().set_extra_data("mask_value",static_cast<double>(var_fill_value));
+        field_out.get_header().set_extra_data("mask_value",static_cast<double>(var_fill_value));
+      } else {
+        EKAT_ERROR_MSG (
+            "[TimeInterpolation] Unexpected/unsupported field data type.\n"
+            " - field name: " + field_out.name() + "\n"
+            " - data type : " + e2str(dt) + "\n");
+      }
+    };
+
+    const auto& pio_var = scorpio::get_var(triplet_curr.filename,name);
+    if (scorpio::refine_dtype(pio_var.nc_dtype)=="float") {
+      auto var_fill_value = scorpio::get_attribute<float>(triplet_curr.filename,name,"_FillValue");
+      set_fill_value(var_fill_value);
+    } else if (scorpio::refine_dtype(pio_var.nc_dtype)=="double") {
+      auto var_fill_value = scorpio::get_attribute<double>(triplet_curr.filename,name,"_FillValue");
+      set_fill_value(var_fill_value);
+    } else {
+      EKAT_ERROR_MSG (
+          "Unrecognized/unsupported data type\n"
+          " - filename: " + triplet_curr.filename + "\n"
+          " - varname : " + name + "\n"
+          " - dtype   : " + pio_var.dtype + "\n");
+    }
+
   }
   // Read first snap of data and shift to time0
   read_data();
@@ -253,10 +287,10 @@ void TimeInterpolation::set_file_data_triplets(const vos_type& list_of_files) {
   for (size_t ii=0; ii<list_of_files.size(); ii++) {
     const auto filename = list_of_files[ii];
     // Reference TimeStamp
-    auto ts_file_start = scorpio::read_timestamp(filename,"case_t0");
+    scorpio::register_file(filename,scorpio::FileMode::Read);
+    auto ts_file_start = read_timestamp(filename,"case_t0");
     // Gather the units of time
-    auto time_units_tmp = scorpio::get_any_attribute(filename,"time","units");
-    auto& time_units = ekat::any_cast<std::string>(time_units_tmp);
+    auto time_units = scorpio::get_attribute<std::string>(filename,"time","units");
     int time_mult;
     if (time_units.find("seconds") != std::string::npos) {
       time_mult = 1;
@@ -273,10 +307,9 @@ void TimeInterpolation::set_file_data_triplets(const vos_type& list_of_files) {
     if (ii==0) {
       ts_ref = ts_file_start;
     }
-    scorpio::register_file(filename,scorpio::Read);
     const int ntime = scorpio::get_dimlen(filename,"time");
     for (int tt=0; tt<ntime; tt++) {
-      auto time_snap = scorpio::read_time_at_index_c2f(filename.c_str(),tt+1);
+      auto time_snap = scorpio::get_time(filename,tt);
       TimeStamp ts_snap = ts_file_start;
       if (time_snap>0) {
         ts_snap += (time_snap*time_mult);
@@ -292,6 +325,7 @@ void TimeInterpolation::set_file_data_triplets(const vos_type& list_of_files) {
       time_idx_tmp.push_back(tt);
       ++running_idx;
     }
+    scorpio::release_file(filename);
   }
   // Now that we have gathered all of the timesnaps we can arrange them in order as DataFromFileTriplet objects.
   // Taking advantage of maps automatically self-sorting by the first arg.
@@ -313,21 +347,30 @@ void TimeInterpolation::set_file_data_triplets(const vos_type& list_of_files) {
 void TimeInterpolation::read_data()
 {
   const auto triplet_curr = m_file_data_triplets[m_triplet_idx];
-  if (triplet_curr.filename != m_file_data_atm_input.get_filename()) {
+  if (not m_file_data_atm_input or triplet_curr.filename != m_file_data_atm_input->get_filename()) {
     // Then we need to close this input stream and open a new one
-    m_file_data_atm_input.finalize();
     ekat::ParameterList input_params;
     input_params.set("Field Names",m_field_names);
     input_params.set("Filename",triplet_curr.filename);
-    m_file_data_atm_input = AtmosphereInput(input_params,m_fm_time1);
-    m_file_data_atm_input.set_logger(m_logger);
+    m_file_data_atm_input = std::make_shared<AtmosphereInput>(input_params,m_fm_time1);
+    m_file_data_atm_input->set_logger(m_logger);
     // Also determine the FillValue, if used
     // TODO: Should we make it possible to check if FillValue is in the metadata and only assign mask_value if it is?
-    float var_fill_value;
     for (auto& name : m_field_names) {
-      scorpio::get_variable_metadata(triplet_curr.filename,name,"_FillValue",var_fill_value);
       auto& field = m_fm_time1->get_field(name);
-      field.get_header().set_extra_data("mask_value",var_fill_value);
+      const auto dt = field.data_type();
+      if (dt==DataType::FloatType) {
+        auto var_fill_value = scorpio::get_attribute<float>(triplet_curr.filename,name,"_FillValue");
+        field.get_header().set_extra_data("mask_value",var_fill_value);
+      } else if (dt==DataType::DoubleType) {
+        auto var_fill_value = scorpio::get_attribute<double>(triplet_curr.filename,name,"_FillValue");
+        field.get_header().set_extra_data("mask_value",var_fill_value);
+      } else {
+        EKAT_ERROR_MSG (
+            "[TimeInterpolation] Unexpected/unsupported field data type.\n"
+            " - field name: " + field.name() + "\n"
+            " - data type : " + e2str(dt) + "\n");
+      }
     }
   }
 
@@ -335,7 +378,7 @@ void TimeInterpolation::read_data()
     m_logger->info(m_header);
     m_logger->info("[EAMxx:time_interpolation] Reading data at time " + triplet_curr.timestamp.to_string());
   }
-  m_file_data_atm_input.read_variables(triplet_curr.time_idx);
+  m_file_data_atm_input->read_variables(triplet_curr.time_idx);
   m_time1 = triplet_curr.timestamp;
 }
 /*-----------------------------------------------------------------------------------------------*/
diff --git a/components/eamxx/src/share/util/eamxx_time_interpolation.hpp b/components/eamxx/src/share/util/eamxx_time_interpolation.hpp
index 870dad33013..5e5fa5112f2 100644
--- a/components/eamxx/src/share/util/eamxx_time_interpolation.hpp
+++ b/components/eamxx/src/share/util/eamxx_time_interpolation.hpp
@@ -89,7 +89,7 @@ class TimeInterpolation {
   // Variables related to the case where we use data from file
   std::vector<DataFromFileTriplet>           m_file_data_triplets;
   int                                        m_triplet_idx;
-  AtmosphereInput                            m_file_data_atm_input;
+  std::shared_ptr<AtmosphereInput>           m_file_data_atm_input;
   bool                                       m_is_data_from_file=false;
 
   std::shared_ptr<ekat::logger::LoggerBase>  m_logger;
diff --git a/components/eamxx/tests/multi-process/physics_only/shoc_p3_nudging/create_vert_remap_and_weights.cpp b/components/eamxx/tests/multi-process/physics_only/shoc_p3_nudging/create_vert_remap_and_weights.cpp
index 702d83f16d3..8cedad048a6 100644
--- a/components/eamxx/tests/multi-process/physics_only/shoc_p3_nudging/create_vert_remap_and_weights.cpp
+++ b/components/eamxx/tests/multi-process/physics_only/shoc_p3_nudging/create_vert_remap_and_weights.cpp
@@ -8,13 +8,10 @@ using namespace scream;
 
 void create_vert_remap() {
   // Simple function to create a 1D remap column to test nudging w/ remapped data
-  ekat::Comm io_comm(MPI_COMM_WORLD);  // MPI communicator group used for I/O set as ekat object.
-  MPI_Fint fcomm = MPI_Comm_c2f(io_comm.mpi_comm());  // MPI communicator group used for I/O.  In our simple test we use MPI_COMM_WORLD, however a subset could be used.
-  scorpio::eam_init_pio_subsystem(fcomm);   // Gather the initial PIO subsystem data creater by component coupler
+  ekat::Comm comm(MPI_COMM_WORLD);
+  scorpio::init_subsystem(comm);
 
   int nlevs = 5*SCREAM_PACK_SIZE+1;
-  std::vector<std::int64_t> dofs_levs(nlevs);
-  std::iota(dofs_levs.begin(),dofs_levs.end(),0);
   std::vector<Real> p_tgt;
   Real p_top=0, p_bot=102500;
   Real dp = (p_bot - p_top) / (nlevs-1);
@@ -26,24 +23,20 @@ void create_vert_remap() {
   std::string remap_filename = "vertical_remap.nc";
 
   scorpio::register_file(remap_filename, scorpio::FileMode::Write);
-  scorpio::register_dimension(remap_filename,"lev", "lev", nlevs, false);
-  scorpio::register_variable(remap_filename,"p_levs","p_levs","none",{"lev"},"real","real","Real-lev");
-  scorpio::set_dof(remap_filename,"p_levs",dofs_levs.size(),dofs_levs.data());
-  scorpio::eam_pio_enddef(remap_filename);
-  scorpio::grid_write_data_array(remap_filename,"p_levs",p_tgt.data(),nlevs);
-  scorpio::eam_pio_closefile(remap_filename);
-  scorpio::eam_pio_finalize();
+  scorpio::define_dim(remap_filename, "lev", nlevs);
+  scorpio::define_var(remap_filename,"p_levs",{"lev"},"real");
+  scorpio::enddef(remap_filename);
+  scorpio::write_var(remap_filename,"p_levs",p_tgt.data());
+  scorpio::release_file(remap_filename);
+  scorpio::finalize_subsystem();
 }
 
 void create_nudging_weights_ncfile(int ntimes, int ncols, int nlevs, const std::string& filename)
 {
   // Simple function to create a 1D remap column to test nudging w/ remapped data
-  ekat::Comm io_comm(MPI_COMM_WORLD);  // MPI communicator group used for I/O set as ekat object.
-  MPI_Fint fcomm = MPI_Comm_c2f(io_comm.mpi_comm());  // MPI communicator group used for I/O.  In our simple test we use MPI_COMM_WORLD, however a subset could be used.
-  scorpio::eam_init_pio_subsystem(fcomm);   // Gather the initial PIO subsystem data creater by component coupler
+  ekat::Comm comm(MPI_COMM_WORLD);
+  scorpio::init_subsystem(comm);
 
-  std::vector<std::int64_t> dofs(ntimes*ncols*nlevs);
-  std::iota(dofs.begin(),dofs.end(),0);
   Real plev[nlevs];
   Real p_top=0, p_bot=102500;
   Real dp = (p_bot - p_top) / (nlevs-1);
@@ -64,16 +57,18 @@ void create_nudging_weights_ncfile(int ntimes, int ncols, int nlevs, const std::
     }
   }
 
+  // NOTE: we are generating a file with "time" dimension that is not unlimited.
+  //       This should stress test AtmosphereInput, which will 'pretend' that
+  //       a dimension called 'time' is unlimited, even though it isn't in the file
   scorpio::register_file(filename, scorpio::FileMode::Write);
-  scorpio::register_dimension(filename,"ncol", "ncol", ncols, false);
-  scorpio::register_dimension(filename,"lev", "lev", nlevs, false);
-  scorpio::register_dimension(filename,"time","time",ntimes, false);
-  scorpio::register_variable(filename,"nudging_weights","nudging_weights","none",{"lev", "ncol", "time"},"real","real","Real-lev");
-  scorpio::set_dof(filename,"nudging_weights",dofs.size(),dofs.data());
-  scorpio::eam_pio_enddef(filename);
-  scorpio::grid_write_data_array(filename,"nudging_weights",&weights[0][0][0],ntimes*ncols*nlevs);
-  scorpio::eam_pio_closefile(filename);
-  scorpio::eam_pio_finalize();
+  scorpio::define_dim(filename,"ncol",ncols);
+  scorpio::define_dim(filename,"lev", nlevs);
+  scorpio::define_dim(filename,"time",ntimes);
+  scorpio::define_var(filename,"nudging_weights",{"time","ncol","lev"},"real");
+  scorpio::enddef(filename);
+  scorpio::write_var(filename,"nudging_weights",&weights[0][0][0]);
+  scorpio::release_file(filename);
+  scorpio::finalize_subsystem();
 }
 
 TEST_CASE("create_vert_remap_and_weights","create_vert_remap_and_weights")
diff --git a/components/eamxx/tests/single-process/surface_coupling/surface_coupling.cpp b/components/eamxx/tests/single-process/surface_coupling/surface_coupling.cpp
index d34059f8559..a4e2a18cbfb 100644
--- a/components/eamxx/tests/single-process/surface_coupling/surface_coupling.cpp
+++ b/components/eamxx/tests/single-process/surface_coupling/surface_coupling.cpp
@@ -88,7 +88,7 @@ std::vector<std::string> create_from_file_test_data(const ekat::Comm& comm, cons
   }
 
   // Create output manager to handle the data
-  scorpio::eam_init_pio_subsystem(comm);
+  scorpio::init_subsystem(comm);
   ekat::ParameterList om_pl;
   om_pl.set("filename_prefix",std::string("surface_coupling_forcing"));
   om_pl.set("Field Names",fnames);
@@ -119,7 +119,7 @@ std::vector<std::string> create_from_file_test_data(const ekat::Comm& comm, cons
 
   // Done, finalize
   om.finalize();
-  scorpio::eam_pio_finalize();
+  scorpio::finalize_subsystem();
   return om.get_list_of_files();
 }