+Add user-controlled underflow of tracers

src/ALE/MOM_ALE.F90

@@ -882,6 +882,11 @@ subroutine remap_all_state_vars(CS, G, GV, h_old, h_new, Reg, OBC, &
                                 h_neglect, h_neglect_edge)
         endif
 
+        ! Possibly underflow any very tiny tracer concentrations to 0.  Note that this is not conservative!
+        if (Tr%conc_underflow > 0.0) then ; do k=1,GV%ke
+          if (abs(tr_column(k)) < Tr%conc_underflow) tr_column(k) = 0.0
+        enddo ; endif
+
         ! Intermediate steps for tendency of tracer concentration and tracer content.
         if (present(dt)) then
           if (Tr%id_remap_conc > 0) then
@@ -895,6 +900,7 @@ subroutine remap_all_state_vars(CS, G, GV, h_old, h_new, Reg, OBC, &
             enddo
           endif
         endif
+
         ! update tracer concentration
         Tr%t(i,j,:) = tr_column(:)
       endif ; enddo ; enddo

src/core/MOM.F90

@@ -1799,6 +1799,8 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, restart_CSp, &
   integer :: nkml, nkbl, verbosity, write_geom
   integer :: dynamics_stencil  ! The computational stencil for the calculations
                                ! in the dynamic core.
+  real :: salin_underflow      ! A tiny value of salinity below which the it is set to 0 [S ~> ppt]
+  real :: temp_underflow       ! A tiny magnitude of temperatures below which they are set to 0 [C ~> degC]
   real :: conv2watt            ! A conversion factor from temperature fluxes to heat
                                ! fluxes [J m-2 H-1 degC-1 ~> J m-3 degC-1 or J kg-1 degC-1]
   real :: conv2salt            ! A conversion factor for salt fluxes [m H-1 ~> 1] or [kg m-2 H-1 ~> 1]
@@ -2022,6 +2024,13 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, restart_CSp, &
     call get_param(param_file, "MOM", "MIN_SALINITY", CS%tv%min_salinity, &
                  "The minimum value of salinity when BOUND_SALINITY=True.", &
                  units="PPT", default=0.0, scale=US%ppt_to_S, do_not_log=.not.bound_salinity)
+    call get_param(param_file, "MOM", "SALINITY_UNDERFLOW", salin_underflow, &
+                 "A tiny value of salinity below which the it is set to 0.  For reference, "//&
+                 "one molecule of salt per square meter of ocean is of order 1e-29 ppt.", &
+                 units="PPT", default=0.0, scale=US%ppt_to_S)
+    call get_param(param_file, "MOM", "TEMPERATURE_UNDERFLOW", temp_underflow, &
+                 "A tiny magnitude of temperatures below which they are set to 0.", &
+                 units="degC", default=0.0, scale=US%degC_to_C)
     call get_param(param_file, "MOM", "C_P", CS%tv%C_p, &
                  "The heat capacity of sea water, approximated as a "//&
                  "constant. This is only used if ENABLE_THERMODYNAMICS is "//&
@@ -2324,12 +2333,14 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, restart_CSp, &
                            tr_desc=vd_T, registry_diags=.true., conc_scale=US%C_to_degC, &
                            flux_nameroot='T', flux_units='W', flux_longname='Heat', &
                            flux_scale=conv2watt, convergence_units='W m-2', &
-                           convergence_scale=conv2watt, CMOR_tendprefix="opottemp", diag_form=2)
+                           convergence_scale=conv2watt, CMOR_tendprefix="opottemp", &
+                           diag_form=2, underflow_conc=temp_underflow)
       call register_tracer(CS%tv%S, CS%tracer_Reg, param_file, HI, GV, &
                            tr_desc=vd_S, registry_diags=.true., conc_scale=US%S_to_ppt, &
                            flux_nameroot='S', flux_units=S_flux_units, flux_longname='Salt', &
                            flux_scale=conv2salt, convergence_units='kg m-2 s-1', &
-                           convergence_scale=0.001*US%S_to_ppt*GV%H_to_kg_m2, CMOR_tendprefix="osalt", diag_form=2)
+                           convergence_scale=0.001*US%S_to_ppt*GV%H_to_kg_m2, CMOR_tendprefix="osalt", &
+                           diag_form=2, underflow_conc=salin_underflow)
     endif
   endif
 

src/tracer/MOM_lateral_boundary_diffusion.F90

@@ -231,6 +231,13 @@ subroutine lateral_boundary_diffusion(G, GV, US, h, Coef_x, Coef_y, dt, Reg, CS)
       endif
     enddo ; enddo ; enddo
 
+    ! Do user controlled underflow of the tracer concentrations.
+    if (tracer%conc_underflow > 0.0) then
+      do k=1,GV%ke ; do j=G%jsc,G%jec ; do i=G%isc,G%iec
+        if (abs(tracer%t(i,j,k)) < tracer%conc_underflow) tracer%t(i,j,k) = 0.0
+      enddo ; enddo ; enddo
+    endif
+
     if (CS%debug) then
       call hchksum(tracer%t, "after LBD "//tracer%name,G%HI)
       ! tracer (native grid) integrated tracer amounts before and after LBD

src/tracer/MOM_neutral_diffusion.F90

@@ -640,6 +640,7 @@ subroutine neutral_diffusion(G, GV, h, Coef_x, Coef_y, dt, Reg, US, CS)
         do k = 1, GV%ke
           tracer%t(i,j,k) = tracer%t(i,j,k) + dTracer(k) * &
                           ( G%IareaT(i,j) / ( h(i,j,k) + GV%H_subroundoff ) )
+          if (abs(tracer%t(i,j,k)) < tracer%conc_underflow) tracer%t(i,j,k) = 0.0
         enddo
 
         if (tracer%id_dfxy_conc > 0  .or. tracer%id_dfxy_cont > 0 .or. tracer%id_dfxy_cont_2d > 0 ) then
@@ -651,6 +652,13 @@ subroutine neutral_diffusion(G, GV, h, Coef_x, Coef_y, dt, Reg, US, CS)
       endif
     enddo ; enddo
 
+    ! Do user controlled underflow of the tracer concentrations.
+    if (tracer%conc_underflow > 0.0) then
+      do k=1,GV%ke ; do j=G%jsc,G%jec ; do i=G%isc,G%iec
+        if (abs(tracer%t(i,j,k)) < tracer%conc_underflow) tracer%t(i,j,k) = 0.0
+      enddo ; enddo ; enddo
+    endif
+
     ! Diagnose vertically summed zonal flux, giving zonal tracer transport from ndiff.
     ! Note sign corresponds to downgradient flux convention.
     if (tracer%id_dfx_2d > 0) then

src/tracer/MOM_tracer_advect.F90

@@ -670,10 +670,14 @@ subroutine advect_x(Tr, hprev, uhr, uh_neglect, OBC, domore_u, ntr, Idt, &
 
     enddo
 
-  endif
-
+  endif ; enddo ! End of j-loop.
 
-  enddo ! End of j-loop.
+  ! Do user controlled underflow of the tracer concentrations.
+  do m=1,ntr ; if (Tr(m)%conc_underflow > 0.0) then
+    do j=js,je ; do i=is,ie
+      if (abs(Tr(m)%t(i,j,k)) < Tr(m)%conc_underflow) Tr(m)%t(i,j,k) = 0.0
+    enddo ; enddo
+  endif ; enddo
 
   ! compute ad2d_x diagnostic outside above j-loop so as to make the summation ordered when OMP is active.
 
@@ -1047,6 +1051,13 @@ subroutine advect_y(Tr, hprev, vhr, vh_neglect, OBC, domore_v, ntr, Idt, &
     enddo
   endif ; enddo ! End of j-loop.
 
+  ! Do user controlled underflow of the tracer concentrations.
+  do m=1,ntr ; if (Tr(m)%conc_underflow > 0.0) then
+    do j=js,je ; do i=is,ie
+      if (abs(Tr(m)%t(i,j,k)) < Tr(m)%conc_underflow) Tr(m)%t(i,j,k) = 0.0
+    enddo ; enddo
+  endif ; enddo
+
   ! compute ad2d_y diagnostic outside above j-loop so as to make the summation ordered when OMP is active.
 
   !$OMP ordered

src/tracer/MOM_tracer_hor_diff.F90

@@ -512,6 +512,14 @@ subroutine tracer_hordiff(h, dt, MEKE, VarMix, G, GV, US, CS, Reg, tv, do_online
 
       enddo ! End of k loop.
 
+      ! Do user controlled underflow of the tracer concentrations.
+      do m=1,ntr ; if (Reg%Tr(m)%conc_underflow > 0.0) then
+        !$OMP parallel do default(shared)
+        do k=1,nz ; do j=js,je ; do i=is,ie
+          if (abs(Reg%Tr(m)%t(i,j,k)) < Reg%Tr(m)%conc_underflow) Reg%Tr(m)%t(i,j,k) = 0.0
+        enddo ; enddo ; enddo
+      endif ; enddo
+
     enddo ! End of "while" loop.
 
   endif   ! endif for CS%use_neutral_diffusion
@@ -1398,7 +1406,7 @@ subroutine tracer_epipycnal_ML_diff(h, dt, Tr, ntr, khdt_epi_x, khdt_epi_y, G, &
           endif
         enddo
       endif ; enddo ; enddo
-!$OMP parallel do default(none) shared(PEmax_kRho,is,ie,js,je,G,h,Tr,tr_flux_conv,m)
+      !$OMP parallel do default(shared)
       do k=1,PEmax_kRho ; do j=js,je ; do i=is,ie
         if ((G%mask2dT(i,j) > 0.0) .and. (h(i,j,k) > 0.0)) then
           Tr(m)%t(i,j,k) = Tr(m)%t(i,j,k) + tr_flux_conv(i,j,k) / &
@@ -1407,6 +1415,14 @@ subroutine tracer_epipycnal_ML_diff(h, dt, Tr, ntr, khdt_epi_x, khdt_epi_y, G, &
         endif
       enddo ; enddo ; enddo
 
+      ! Do user controlled underflow of the tracer concentrations.
+      if (Tr(m)%conc_underflow > 0.0) then
+        !$OMP parallel do default(shared)
+        do k=1,nz ; do j=js,je ; do i=is,ie
+          if (abs(Tr(m)%t(i,j,k)) < Tr(m)%conc_underflow) Tr(m)%t(i,j,k) = 0.0
+        enddo ; enddo ; enddo
+      endif
+
     enddo ! Loop over tracers
   enddo ! Loop over iterations