Add ability to read external file distribution for KH.

src/parameterizations/lateral/MOM_hor_visc.F90

@@ -88,13 +88,15 @@ module MOM_hor_visc
 
 use MOM_diag_mediator,         only : post_data, register_diag_field, safe_alloc_ptr
 use MOM_diag_mediator,         only : diag_ctrl, time_type
+use MOM_domains,               only : pass_var
 use MOM_error_handler,         only : MOM_error, FATAL, WARNING
 use MOM_file_parser,           only : get_param, log_version, param_file_type
 use MOM_grid,                  only : ocean_grid_type
 use MOM_lateral_mixing_coeffs, only : VarMix_CS
 use MOM_MEKE_types,            only : MEKE_type
 use MOM_open_boundary,         only : ocean_OBC_type, OBC_FLATHER
 use MOM_verticalGrid,          only : verticalGrid_type
+use fms_mod,                   only : read_data
 
 implicit none ; private
 
@@ -131,11 +133,17 @@ module MOM_hor_visc
   logical :: bound_Coriolis  ! If true & SMAGORINSKY_AH is used, the biharmonic
                              ! viscosity is modified to include a term that
                              ! scales quadratically with the velocity shears.
+  logical :: use_Kh_bg_2d    ! Read 2d background viscosity from a file. 
+  real    :: Kh_bg_min       ! The minimum value allowed for Laplacian horizontal
+                             ! viscosity. The default is 0.0
 
   real ALLOCABLE_, dimension(NIMEM_,NJMEM_) :: &
     Kh_bg_xx,        &! The background Laplacian viscosity at h points, in units
                       ! of m2 s-1. The actual viscosity may be the larger of this
                       ! viscosity and the Smagorinsky viscosity.
+    Kh_bg_2d,        &! The background Laplacian viscosity at h points, in units
+                      ! of m2 s-1. The actual viscosity may be the larger of this
+                      ! viscosity and the Smagorinsky viscosity.
     Ah_bg_xx,        &! The background biharmonic viscosity at h points, in units
                       ! of m4 s-1. The actual viscosity may be the larger of this
                       ! viscosity and the Smagorinsky viscosity.
@@ -518,6 +526,9 @@ subroutine horizontal_viscosity(u, v, h, diffu, diffv, MEKE, VarMix, G, GV, CS,
           Kh = Kh + 0.25*( (MEKE%Ku(I,J)+MEKE%Ku(I+1,J+1))    &
                           +(MEKE%Ku(I+1,J)+MEKE%Ku(I,J+1)) )
         endif
+        ! Place a floor on the viscosity, if desired.
+        Kh = MAX(Kh,CS%Kh_bg_min)
+
         if (CS%better_bound_Kh) then
           if (Kh >= hrat_min*CS%Kh_Max_xy(I,J)) then
             visc_bound_rem = 0.0
@@ -785,6 +796,9 @@ subroutine hor_visc_init(Time, G, param_file, diag, CS)
     call get_param(param_file, mod, "KH", Kh,                      &
                  "The background Laplacian horizontal viscosity.", &
                  units = "m2 s-1", default=0.0)
+    call get_param(param_file, mod, "KH_BG_MIN", CS%Kh_bg_min, &
+                 "The minimum value allowed for Laplacian horizontal viscosity, KH.", &
+                 units = "m2 s-1",  default=0.0)
     call get_param(param_file, mod, "KH_VEL_SCALE", Kh_vel_scale, &
                  "The velocity scale which is multiplied by the grid \n"//&
                  "spacing to calculate the Laplacian viscosity. \n"//&
@@ -877,6 +891,12 @@ subroutine hor_visc_init(Time, G, param_file, diag, CS)
                  "is strongly encouraged, and no slip BCs are not used with \n"//&
                  "the biharmonic viscosity.", default=.false.)
 
+  call get_param(param_file, mod, "USE_KH_BG_2D", CS%use_Kh_bg_2d, &
+                 "If true, read a file containing 2-d background harmonic  \n"//&
+                 "viscosities. The final viscosity is the maximum of the other "//&
+                 "terms and this background value.", default=.false.)
+
+
   if (CS%bound_Kh .or. CS%bound_Ah .or. CS%better_bound_Kh .or. CS%better_bound_Ah) &
     call get_param(param_file, mod, "DT", dt, &
                  "The (baroclinic) dynamics time step.", units = "s", &
@@ -914,6 +934,13 @@ subroutine hor_visc_init(Time, G, param_file, diag, CS)
   ALLOC_(CS%reduction_xx(isd:ied,jsd:jed))     ; CS%reduction_xx(:,:) = 0.0
   ALLOC_(CS%reduction_xy(IsdB:IedB,JsdB:JedB)) ; CS%reduction_xy(:,:) = 0.0
 
+  if (CS%use_Kh_bg_2d) then
+    ALLOC_(CS%Kh_bg_2d(isd:ied,jsd:jed))     ; CS%Kh_bg_2d(:,:) = 0.0
+    call read_data('INPUT/KH_background_2d.nc', 'Kh', CS%Kh_bg_2d, &
+                    domain=G%domain%mpp_domain, timelevel=1)
+    call pass_var(CS%Kh_bg_2d, G%domain)
+  endif
+
   if (CS%biharmonic) then
     ALLOC_(CS%Idx2dyCu(IsdB:IedB,jsd:jed)) ; CS%Idx2dyCu(:,:) = 0.0
     ALLOC_(CS%Idx2dyCv(isd:ied,JsdB:JedB)) ; CS%Idx2dyCv(:,:) = 0.0
@@ -986,6 +1013,9 @@ subroutine hor_visc_init(Time, G, param_file, diag, CS)
       if (CS%Smagorinsky_Kh) CS%LAPLAC_CONST_xx(i,j) = Smag_Lap_const * grid_sp_h2
 
       CS%Kh_bg_xx(i,j) = MAX(Kh, Kh_vel_scale * sqrt(grid_sp_h2))
+
+      if (CS%use_Kh_bg_2d) CS%Kh_bg_xx(i,j) = MAX(CS%Kh_bg_2d(i,j), CS%Kh_bg_xx(i,j))
+
       if (CS%bound_Kh .and. .not.CS%better_bound_Kh) then
         CS%Kh_Max_xx(i,j) = Kh_Limit * grid_sp_h2
         CS%Kh_bg_xx(i,j) = MIN(CS%Kh_bg_xx(i,j), CS%Kh_Max_xx(i,j))
@@ -996,6 +1026,9 @@ subroutine hor_visc_init(Time, G, param_file, diag, CS)
       if (CS%Smagorinsky_Kh) CS%LAPLAC_CONST_xy(I,J) = Smag_Lap_const * grid_sp_q2
 
       CS%Kh_bg_xy(I,J) = MAX(Kh, Kh_vel_scale * sqrt(grid_sp_q2))
+
+      if (CS%use_Kh_bg_2d) CS%Kh_bg_xy(i,j) = MAX(CS%Kh_bg_2d(i,j), CS%Kh_bg_xy(i,j))
+
       if (CS%bound_Kh .and. .not.CS%better_bound_Kh) then
         CS%Kh_Max_xy(I,J) = Kh_Limit * grid_sp_q2
         CS%Kh_bg_xy(I,J) = MIN(CS%Kh_bg_xy(I,J), CS%Kh_Max_xy(I,J))