Merge branch 'master-v7.0/initialization_seaice_threshold' into develop (PR #972)

This merge adjusts the initialization of xice for cold sea-surface temperatures

Setting xice to 1.0 for sea-surface temperatures colder than 271 K has proved to
produce too much sea ice at high latitudes. Furthermore, many datasets provide a
sea ice fraction field. Determination of using actual sea ice fraction input or
setting xice to 1.0 for sea-surface temperatures colder than a pre-defined value
in the case where fractional sea ice is not provided in the input is now moved
to the subroutine physics_init_seaice in module mpas_atmphys_initialize_real.F.

Now, the temperature threshold for converting water points to sea ice with a
fraction of 1.0 is set by a new namelist option, config_tsk_seaice_threshold, in
a new &physics namelist group. The default value for this threshold is 100 K,
which effectively shuts off the conversion of water to sea ice, which is
reasonable when ingesting datasets that already provide a fractional sea ice
field.

Author: mgduda

src/core_atmosphere/physics/mpas_atmphys_initialize_real.F

@@ -55,6 +55,10 @@ module mpas_atmphys_initialize_real
 ! * In subroutine physics_init_seaice, added the initialization of the annual maximum snow albedo over seaice
 !   points to 0.75.
 ! * Laura D. Fowler (laura@ucar.edu) / 2022-03-15).
+! * In subroutine physics_init_seaice, corrected the initialization of seaice points when the surface
+!   temperature was originally colder than 271K. We now use the seaice threshold config_tsk_seaice_threshold
+!   that has a default value set to 100K. This leads to decreased seaice at high latitudes.
+!   Laura D. Fowler (laura@ucar.edu) / 2022-03-25.
 
 
  contains
@@ -599,6 +603,7 @@ subroutine physics_init_seaice(mesh, input, dims, configs)
 
  real(kind=RKIND):: xice_threshold
  real(kind=RKIND):: mid_point_depth
+ real(kind=RKIND),pointer:: tsk_seaice_threshold
  real(kind=RKIND),dimension(:),pointer  :: vegfra
  real(kind=RKIND),dimension(:),pointer  :: seaice,snoalb,xice
  real(kind=RKIND),dimension(:),pointer  :: skintemp,tmn,xland
@@ -611,15 +616,15 @@ subroutine physics_init_seaice(mesh, input, dims, configs)
 !note that this threshold is also defined in module_physics_vars.F.It is defined here to avoid
 !adding "use module_physics_vars" since this subroutine is only used for the initialization of
 !a "real" forecast with $CORE = init_nhyd_atmos.
- real(kind=RKIND),parameter:: xice_tsk_threshold = 271.
  real(kind=RKIND),parameter:: total_depth        = 3.   ! 3-meter soil depth.
 
 !-----------------------------------------------------------------------------------------------------------------
 !call mpas_log_write('')
 !call mpas_log_write('--- enter physics_init_seaice:')
 
- call mpas_pool_get_config(configs, 'config_frac_seaice', config_frac_seaice)
- call mpas_pool_get_config(configs, 'config_landuse_data', config_landuse_data)
+ call mpas_pool_get_config(configs, 'config_frac_seaice'         , config_frac_seaice)
+ call mpas_pool_get_config(configs, 'config_tsk_seaice_threshold', tsk_seaice_threshold)
+ call mpas_pool_get_config(configs, 'config_landuse_data'        , config_landuse_data)
 
  call mpas_pool_get_dimension(dims, 'nCellsSolve', nCellsSolve)
  call mpas_pool_get_dimension(dims, 'nSoilLevels', nSoilLevels)
@@ -660,13 +665,14 @@ subroutine physics_init_seaice(mesh, input, dims, configs)
  endif
  call mpas_log_write('--- config_frac_seaice      : $l', logicArgs=(/config_frac_seaice/))
  call mpas_log_write('--- xice_threshold          : $r', realArgs=(/xice_threshold/))
+ call mpas_log_write('--- tsk_seaice_threshold    : $r', realArgs=(/tsk_seaice_threshold/))
 
 !convert seaice points to land points when the sea-ice fraction is greater than the
 !prescribed threshold:
  num_seaice_changes = 0
  do iCell = 1, nCellsSolve
     if(xice(iCell) .ge. xice_threshold .or. &
-      (landmask(iCell).eq.0 .and. skintemp(iCell).lt.xice_tsk_threshold)) then
+      (landmask(iCell).eq.0 .and. skintemp(iCell).lt.tsk_seaice_threshold)) then
 
        num_seaice_changes = num_seaice_changes + 1
        !... sea-ice points are converted to land points:

src/core_init_atmosphere/Registry.xml

@@ -278,7 +278,12 @@
                      units="-"
                      description="Whether to switch sea-ice threshold from 0.5 to 0.02"
                      possible_values="true or false"/>
+        </nml_record>
 
+        <nml_record name="physics" in_defaults="false">
+                <nml_option name="config_tsk_seaice_threshold" type="real" default_value="100." units="K"
+                     description="surface temperature threshold below which water points are set to seaice points"
+                     possible_values="Positive real values"/>
         </nml_record>
 
         <nml_record name="io" in_defaults="true">

src/core_init_atmosphere/mpas_init_atm_cases.F

@@ -4559,9 +4559,6 @@ subroutine init_atm_case_gfs(block, mesh, nCells, nEdges, nVertLevels, fg, state
 
       if (allocated(maskslab)) deallocate(maskslab)
 
-      ! Freeze really cold ocean
-      where (sst < 271.0 .and. landmask == 0) xice = 1.0
-
       ! Limit XICE to values between 0 and 1. Although the input meteorological field is between 0.
       ! and 1., interpolation to the MPAS grid can yield values of XiCE less than 0. and greater
       ! than 1.: