RTE: fluxes

RTE solves the radiative transfer equation for each spectral point independently but this detailed information isn't useful. Class ty_fluxes in module mo_fluxes in the RTE library encapsulates the output from the RTE solvers and provides a way to reduce the highly-detailed information based on precisely what the user needs. Class ty_fluxes_broadband provides an example implementation that reports broadband flux i.e. the sum over all spectral points at all levels.

ty_fluxes is an abstract class that defines two interfaces.

    function reduce(gpt_flux_up, gpt_flux_dn, spectral_disc, top_at_1, gpt_flux_dn_dir) result(error_msg)
      real(kind=wp), dimension(:,:,:),   intent(in   ) :: gpt_flux_up ! Fluxes by gpoint [W/m2](ncol, nlay+1, ngpt)
      real(kind=wp), dimension(:,:,:),   intent(in   ) :: gpt_flux_dn ! Fluxes by gpoint [W/m2](ncol, nlay+1, ngpt)
      class(ty_optical_props),           intent(in   ) :: spectral_disc  !< derived type with spectral information
      logical,                           intent(in   ) :: top_at_1
      real(kind=wp), dimension(:,:,:), optional, &
                                         intent(in   ) :: gpt_flux_dn_dir! Direct flux down
      character(len=128)                               :: error_msg
    end function reduce_abstract

is called within the RTE solvers. The input arguments are the spectrally-resolved fluxes up and down (and, optically, the direct-beam flux), the spectral discretization, and a flag indicating whether the top of the atmosphere is at index 1 or nlay in the vertical dimension.

Logical function fluxes%are_desired() is called by RTE to check if the results of a calculation will be used.

Note that class ty_fluxes defines only the interfaces to these routines. Implementation is deferred to user classes that extend this class.

Broadband fluxes

Class ty_fluxes_broadband in the same module provides an example of how to extend ty_fluxes. This class reports broadband values i.e. the sum over every element in the spectral dimensions. The class contains four data fields

    real(wp), dimension(:,:), pointer :: flux_up => NULL(), flux_dn => NULL()
    real(wp), dimension(:,:), pointer :: flux_net => NULL()    ! Net (down - up)
    real(wp), dimension(:,:), pointer :: flux_dn_dir => NULL() ! Direct flux down

Before calling one of the RTE solvers with this class as output, users either allocate one or more of these output fields or point to an existing array. The fields must have the same number of columns and layers as the problem being solved.

In class ty_fluxes_broadband logical function are_desired() returns true if one or more of the data fields points to storage and false otherwise.

When routine reduce is called from the RTE solver the implementation sums over all elements of the input arrays for which output storage is available. Net broadband flux is computed from the difference of spectrally-resolved values if broadband values of flux_up and flux_dn are not available.

Other extensions

Class ty_fluxes_byband in subdirectory extensions provides another example that makes use of the spectral discretization information.

It would be especially useful to extend the class when particular subsets of fluxes, such as photosynthetically-active radiation at the surface, are required.