Ensured constant radiation for fixed climate forcing configuration

No answer change incurred.

examples/run_dir/climeConst/climeConst.namelist

@@ -7,7 +7,7 @@ case_name='gh_dray'
 prefix='../../inputs/dryland_maize/'
 do_regression_test=.false.
 pft_file_in='../../../input_data/ecosim_pftpar_20240723.nc'
-grid_file_in='../../../examples/inputs/dryland_maize/dryland_grid_20230221.nc'
+grid_file_in='../../../examples/inputs/climeConst/climeConst_grid_20250223.nc'
 pft_mgmt_in='../../../examples/inputs/dryland_maize/dryland_pft_20230509.nc'
 soil_mgmt_in='../../../examples/inputs/dryland_maize/dryland_soilmgmt_20230210.nc'
 clm_hour_file_in='../../../examples/inputs/dryland_maize/dryland_clm_20230203.nc'

f90src/Modelforc/WthrMod.F90

@@ -5,7 +5,7 @@ module WthrMod
   use data_kind_mod,     only: r8 => DAT_KIND_R8
   use MiniMathMod,       only: safe_adb, vapsat0, isclose
   use MiniFuncMod,       only: get_sun_declin
-  use EcoSIMCtrlMod,     only: etimer, frectyp
+  use EcoSIMCtrlMod,     only: etimer, frectyp,fixClime
   use PlantMgmtDataType, only: NP
   use MiniMathMod,       only: AZMAX1
   use UnitMod,           only: units
@@ -291,8 +291,14 @@ subroutine CalcRadiation(I,J,NHW,NHE,NVN,NVS,RADN_col,PRECUI_col,PRECII_col)
         AZI=SIN(ALAT(NY,NX)*RadianPerDegree)*SIN(DECLIN*RadianPerDegree)
         DEC=COS(ALAT(NY,NX)*RadianPerDegree)*COS(DECLIN*RadianPerDegree)
         !check eq.(11.1) in Campbell and Norman, 1998, p168.
-        SineSunInclAngle_col(NY,NX)       = AZMAX1(AZI+DEC*COS(PICON12*(SolarNoonHour_col(NY,NX)-(J-0.5_r8))))
-        SineSunInclAnglNxtHour_col(NY,NX) = AZMAX1(AZI+DEC*COS(PICON12*(SolarNoonHour_col(NY,NX)-(J+0.5_r8))))
+        if(fixClime)then
+          !always assume the light is from zenith when using fixed climate forcing.
+          SineSunInclAngle_col(NY,NX)       = AZMAX1(AZI+DEC*COS(PICON12*(SolarNoonHour_col(NY,NX)-11.5_r8)))
+          SineSunInclAnglNxtHour_col(NY,NX) = AZMAX1(AZI+DEC*COS(PICON12*(SolarNoonHour_col(NY,NX)-12.5_r8)))
+        else
+          SineSunInclAngle_col(NY,NX)       = AZMAX1(AZI+DEC*COS(PICON12*(SolarNoonHour_col(NY,NX)-(J-0.5_r8))))
+          SineSunInclAnglNxtHour_col(NY,NX) = AZMAX1(AZI+DEC*COS(PICON12*(SolarNoonHour_col(NY,NX)-(J+0.5_r8))))
+        endif  
 
         !IF(SineSunInclAngle_col(NY,NX).GT.0.0_r8 .AND. SineSunInclAngle_col(NY,NX).LT.TWILGT)SineSunInclAngle_col(NY,NX)=TWILGT
         IF(RADN_col(NY,NX).LE.0.0_r8)SineSunInclAngle_col(NY,NX)=0.0_r8