Merge branch 'whannah/eamxx/create-gwd-atm-proc-rebase' (PR #8219)

This adds support for the C++ GW drag schemes in EAMxx. Nothing has been 
validated yet, but we can save this effort for later when ZM and frontogenesis 
values are available. For now this PR just adds a working GW interface to EAMxx, 
but keeps it as a stealth feature.

[BFB]

Author: tcclevenger

components/eamxx/cime_config/namelist_defaults_eamxx.xml

@@ -296,6 +296,30 @@ be lost if SCREAM_HACK_XML is not enabled.
       <mcsp_v_coeff type="real" doc="MCSP V-wind coefficient"         >0.0</mcsp_v_coeff>
     </zm>
 
+    <!-- Gravity Wave Drag -->
+    <gw inherit="atm_proc_base">
+      <use_gw_convect type="logical" doc="Flag for convective GWD">false</use_gw_convect>
+      <use_gw_frontal type="logical" doc="Flag for frontal GWD">false</use_gw_frontal>
+      <use_gw_orographic type="logical" doc="Flag for orographic GWD">false</use_gw_orographic>
+      <gw_drag_file type="string" doc="GW source spectra file">${DIN_LOC_ROOT}/atm/waccm/gw/newmfspectra40_dc25.nc</gw_drag_file>
+      <pgwv type="integer" doc="Maximum number of waves allowed">32</pgwv>
+      <gw_dc type="real" doc="Bin width for spectrum">2.5</gw_dc>
+      <tau_0_ubc type="logical" doc="flag to enforce an upper boundary condition of tau=0">false</tau_0_ubc>
+      <fcrit2 type="real" doc="Critical Froude number">1.0</fcrit2>
+      <gw_orographic_eff type="real" doc="Efficiency of orographic GW tendencies">0.375</gw_orographic_eff>
+      <gw_frontal_taubgnd type="real" doc="Background stress source strength for frontal GW scheme">2.5E-3</gw_frontal_taubgnd>
+      <gw_frontal_eff type="real" doc="Efficiency of frontal GW tendencies">1.0</gw_frontal_eff>
+      <gw_frontal_fgfc hgrid="ne30np4.pg2"  type="real" doc="Frontogenesis function critical threshold for frontal GW scheme">1.25E-15</gw_frontal_fgfc>
+      <gw_frontal_fgfc hgrid="ne120np4.pg2" type="real" doc="Frontogenesis function critical threshold for frontal GW scheme">2.00E-14</gw_frontal_fgfc>
+      <gw_convect_eff type="real" doc="Efficiency of convective GW tendencies">0.35</gw_convect_eff>
+      <gw_convect_hcf type="real" doc="Convective heating rate conversion factor">10.0</gw_convect_hcf>
+      <gw_convect_hdepth_scale type="real" doc="Scaling factor for convective heating depth">0.50</gw_convect_hdepth_scale>
+      <gw_convect_hdepth_min type="real" doc="Minimum hdepth for for convective GWD spectrum lookup table [km]">2.5</gw_convect_hdepth_min>
+      <gw_convect_storm_speed_min type="real" doc="Minimum convective storm speed for convective GWD [m/s]">10.0</gw_convect_storm_speed_min>
+      <gw_convect_plev_src_wind type="real" doc="Reference pressure level for source wind for convective GWD [Pa]">70000</gw_convect_plev_src_wind>
+      <use_gw_convect_old type="logical" doc="Switch to enable legacy behavior">false</use_gw_convect_old>
+    </gw>
+
     <!-- Basic options for each mam4 atm process -->
     <mam4_atm_proc_base inherit="atm_proc_base">
       <create_fields_interval_checks type="logical" doc="Create field interval checks for all fields that are computed and requested in mam4xx." >false</create_fields_interval_checks>

components/eamxx/src/control/atmosphere_driver.cpp

@@ -1094,8 +1094,13 @@ void AtmosphereDriver::set_initial_conditions ()
                         "double or string, or vector double arguments are allowed");
       }
       m_fields_inited[grid_name].push_back(fname);
-    } else if (fname == "phis" or fname == "sgh30") {
-      // Both phis and sgh30 need to be loaded from the topography file
+    } else if (fname == "phis" or fname == "sgh30" or fname == "sgh") {
+      // these fields need to be loaded from the topography file
+	  // - phis is the surface geopotential height
+	  // - sgh30 - sub-grid std dev of surface height (on phys grid) between source grid and a 3km ref grid
+	  //   needed for turbulent mountain stress scheme (i.e. TMS)
+	  // - sgh - sub-grid std dev of surface height (on phys grid) between source grid and target grid
+	  //   needed for orographic gravity wave drag scheme (i.e. GWD)
       auto& this_grid_topo_file_fnames = topography_file_fields_names[grid_name];
       auto& this_grid_topo_eamxx_fnames = topography_eamxx_fields_names[grid_name];
 
@@ -1122,6 +1127,15 @@ void AtmosphereDriver::set_initial_conditions ()
         topography_file_fields_names[grid_name].push_back("SGH30");
         topography_eamxx_fields_names[grid_name].push_back(fname);
         m_fields_inited[grid_name].push_back(fname);
+      } else if (fname == "sgh") {
+        // The eamxx field "sgh" is called "SGH" in the
+        // topography file and is only available on the PG2 grid.
+        EKAT_ASSERT_MSG(grid_name == "physics_pg2",
+                        "Error! Requesting sgh field on " + grid_name +
+                        " topo file only has sgh for physics_pg2.\n");
+        topography_file_fields_names[grid_name].push_back("SGH");
+        topography_eamxx_fields_names[grid_name].push_back(fname);
+        m_fields_inited[grid_name].push_back(fname);
       }
     } else if (not (fvphyshack and grid_name == "physics_pg2")) {
       // The IC file is written for the GLL grid, so we only load

components/eamxx/src/mct_coupling/CMakeLists.txt

@@ -49,6 +49,11 @@ if (TARGET zm)
   list(APPEND SCREAM_LIBS zm)
 endif()
 
+# GW is not always on yet
+if (TARGET gw)
+  list(APPEND SCREAM_LIBS gw)
+endif()
+
 if (SCREAM_ENABLE_MAM)
   list (APPEND SCREAM_LIBS mam)
 endif()

components/eamxx/src/physics/gw/CMakeLists.txt

@@ -33,6 +33,8 @@ endif()
 
 add_library(gw ${GW_SRCS})
 
+target_compile_definitions(gw PUBLIC EAMXX_HAS_GW)
+
 target_include_directories(gw PUBLIC
   ${CMAKE_CURRENT_SOURCE_DIR}
   ${CMAKE_CURRENT_SOURCE_DIR}/impl