Let config_len_disp default to 0.0, in which case its value is set by nominalMinDc

With this commit, the config_len_disp namelist option defaults to 0.0 and is
hidden by default. Additionally, a new variable, nominalMinDc, is read from the
input file and read/written from/to restart files.

If a positive value for config_len_disp is supplied in the &nhyd_model namelist
group, then that value is used for the horizontal length scale in the model;
otherwise, if a positive value for the nominalMinDc variable is found in the
input file, that value is used.

If both config_len_disp and nominalMinDc values are positive real values, and if
they differ by very much (~1.0e-6 relative difference), then a warning is
printed to the log file, and the value specified in the namelist for
config_len_disp is used to set nominalMinDc.

If neither config_len_disp was specified in namelist.atmosphere file nor a valid
value for nominalMinDc was read from the input file, the atmosphere core
initialization will stop with an error:

  ERROR: Both config_len_disp and nominalMinDc are <= 0.0.
  ERROR: Please either specify config_len_disp in the &nhyd_model namelist group,
  ERROR: or use an input file that provides a valid value for the nominalMinDc variable.

Author: mgduda

src/core_atmosphere/Registry.xml

@@ -142,10 +142,10 @@
                      description="Formulation of horizontal mixing"
                      possible_values="`2d_fixed' or `2d_smagorinsky'"/>
 
-                <nml_option name="config_len_disp" type="real" default_value="120000.0"
+                <nml_option name="config_len_disp" type="real" default_value="0.0" in_defaults="false"
                      units="m"
                      description="Horizontal length scale, used by the Smagorinsky formulation of horizontal diffusion and by 3-d divergence damping"
-                     possible_values="Positive real values"/>
+                     possible_values="Positive real values. A zero value implies that the length scale is prescribed by the nominalMinDc value in the input file."/>
 
                 <nml_option name="config_visc4_2dsmag" type="real" default_value="0.05"
                      units="-"
@@ -457,6 +457,7 @@
 			<var name="fEdge"/>
 			<var name="fVertex"/>
 			<var name="meshDensity"/>
+			<var name="nominalMinDc"/>
 			<var name="bdyMaskCell"/>
 			<var name="bdyMaskEdge"/>
 			<var name="bdyMaskVertex"/>
@@ -592,6 +593,7 @@
 			<var name="fEdge"/>
 			<var name="fVertex"/>
 			<var name="meshDensity"/>
+			<var name="nominalMinDc"/>
 			<var name="bdyMaskCell"/>
 			<var name="bdyMaskEdge"/>
 			<var name="bdyMaskVertex"/>
@@ -1305,6 +1307,9 @@
                 <var name="meshDensity" type="real" dimensions="nCells" units="unitless"
                      description="Mesh density function (used when generating the mesh) evaluated at a cell"/>
 
+                <var name="nominalMinDc" type="real" dimensions="" units="m"
+                     description="Nominal minimum dcEdge value where meshDensity == 1.0"/>
+
                 <var name="meshScalingDel2" type="real" dimensions="nEdges" units="unitless"
                      description="Scaling coefficient for $\nabla^2$ eddy viscosity"/>
 

src/core_atmosphere/mpas_atm_core.F

@@ -71,6 +71,9 @@ function atm_core_init(domain, startTimeStamp) result(ierr)
       character (len=StrKIND), pointer :: initial_time1, initial_time2
       type (MPAS_Time_Type) :: startTime
 
+      real (kind=RKIND), pointer :: nominalMinDc
+      real (kind=RKIND), pointer :: config_len_disp
+
       integer, pointer :: nVertLevels, maxEdges, maxEdges2, num_scalars
       character (len=ShortStrKIND) :: init_stream_name
       real (kind=R8KIND) :: input_start_time, input_stop_time
@@ -149,6 +152,56 @@ function atm_core_init(domain, startTimeStamp) result(ierr)
       call MPAS_stream_mgr_reset_alarms(domain % streamManager, streamID='restart', direction=MPAS_STREAM_INPUT, ierr=ierr)
       call mpas_log_write(' ----- done reading initial state -----')
 
+
+      !
+      ! Determine horizontal length scale used by horizontal diffusion and 3-d divergence damping
+      !
+      call mpas_pool_get_subpool(domain % blocklist % structs, 'mesh', mesh)
+      nullify(nominalMinDc)
+      call mpas_pool_get_array(mesh, 'nominalMinDc', nominalMinDc)
+
+      nullify(config_len_disp)
+      call mpas_pool_get_config(domain % blocklist % configs, 'config_len_disp', config_len_disp)
+
+      call mpas_log_write('')
+
+      !
+      ! If config_len_disp was specified as a valid value, use that
+      !
+      if (config_len_disp > 0.0_RKIND) then
+         call mpas_log_write('Setting nominalMinDc to $r based on namelist option config_len_disp', realArgs=[config_len_disp])
+
+         !
+         ! But if nominalMinDc was available in the input file and is different, print a warning
+         !
+         if (nominalMinDc > 0.0_RKIND .and. abs(nominalMinDc - config_len_disp) > 1.0e-6_RKIND * config_len_disp) then
+            call mpas_log_write('nominalMinDc was read from input file as a positive value ($r) that differs', &
+                                realArgs=[nominalMinDc], messageType=MPAS_LOG_WARN)
+            call mpas_log_write('from the specified config_len_disp value ($r)', &
+                                realArgs=[config_len_disp], messageType=MPAS_LOG_WARN)
+         end if
+
+         nominalMinDc = config_len_disp
+
+      !
+      ! Otherwise, try to use nominalMinDc
+      !
+      else
+         if (nominalMinDc > 0.0_RKIND) then
+            call mpas_log_write('Setting config_len_disp to $r based on nominalMinDc value in input file', realArgs=[nominalMinDc])
+            config_len_disp = nominalMinDc
+         else
+            call mpas_log_write('Both config_len_disp and nominalMinDc are <= 0.0.', messageType=MPAS_LOG_ERR)
+            call mpas_log_write('Please either specify config_len_disp in the &nhyd_model namelist group,', &
+                                messageType=MPAS_LOG_ERR)
+            call mpas_log_write('or use an input file that provides a valid value for the nominalMinDc variable.', &
+                                messageType=MPAS_LOG_ERR)
+            ierr = 1
+            return
+         end if
+      end if
+
+
       !
       ! Read all other inputs
       ! For now we don't do this here to match results with previous code; to match requires