Option to homogenize forces and fluxes (mom-ocean#51)

* Adds option to homogenize forces and fluxes fields

- Adds functions to do global averages on U and V grids in MOM_spatial_means
- Adds functionality to average all forcing and fluxes fields in MOM_forcing_types
- Adds flag to average all forcing and fluxes in MOM.F90
- This new feature is primarily for running in single column like configurations with the coupler, which requires perfectly equal forcing across all cells.

* Fixing ustar calculation in homogenize_mech_forcing

- Adds in irho0 and sqrt that were missing in homogenize mech forcing.

* Updates to homogenize_forcings options.

- Correct issues in global_area_mean_u and global_area_mean_v to work with symmetric and rotated grids.
- Add options to compute mean ustar or compute ustar from mean tau.
- Add subroutines to replace averaging blocks in MOM_forcing_type.

* Minor formatting updates

- Move a division and reformat alignment in MOM_spatial_means.F90.
- Remove a unused parameter in MOM_forcing_type.F90
- Reformat misalignment of an "if-block" in MOM_forcing_type.F90

* Remove obsolete netSalt flux homogenization

- netSalt has been removed so no longer needs homogenized in the fluxes.

* Fix 2d mean on U grid to use U mask

* Remove whitespacace

* Add do_not_log option to UPDATE_USTAR get_param

src/core/MOM.F90

@@ -82,6 +82,8 @@ module MOM
 use MOM_forcing_type,          only : allocate_forcing_type, allocate_mech_forcing
 use MOM_forcing_type,          only : deallocate_mech_forcing, deallocate_forcing_type
 use MOM_forcing_type,          only : rotate_forcing, rotate_mech_forcing
+use MOM_forcing_type,          only : copy_common_forcing_fields, set_derived_forcing_fields
+use MOM_forcing_type,          only : homogenize_forcing, homogenize_mech_forcing
 use MOM_grid,                  only : ocean_grid_type, MOM_grid_init, MOM_grid_end
 use MOM_grid,                  only : set_first_direction, rescale_grid_bathymetry
 use MOM_hor_index,             only : hor_index_type, hor_index_init
@@ -207,6 +209,8 @@ module MOM
   type(ocean_grid_type) :: G_in                   !< Input grid metric
   type(ocean_grid_type), pointer :: G => NULL()   !< Model grid metric
   logical :: rotate_index = .false.   !< True if index map is rotated
+  logical :: homogenize_forcings = .false. !< True if all inputs are homogenized
+  logical :: update_ustar = .false.   !< True to update ustar from homogenized tau
 
   type(verticalGrid_type), pointer :: &
     GV => NULL()    !< structure containing vertical grid info
@@ -579,6 +583,20 @@ subroutine step_MOM(forces_in, fluxes_in, sfc_state, Time_start, time_int_in, CS
     fluxes => fluxes_in
   endif
 
+  ! Homogenize the forces
+  if (CS%homogenize_forcings) then
+    ! Homogenize all forcing and fluxes fields.
+    call homogenize_mech_forcing(forces, G, US, GV%Rho0, CS%update_ustar)
+    ! Note the following computes the mean ustar as the mean of ustar rather than
+    !  ustar of the mean of tau.
+    call homogenize_forcing(fluxes, G)
+    if (CS%update_ustar) then
+      ! These calls corrects the ustar values
+      call copy_common_forcing_fields(forces, fluxes, G)
+      call set_derived_forcing_fields(forces, fluxes, G, US, GV%Rho0)
+    endif
+  endif
+
   ! First determine the time step that is consistent with this call and an
   ! integer fraction of time_interval.
   if (do_dyn) then
@@ -2144,6 +2162,14 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, restart_CSp, &
 
   call callTree_waypoint("MOM parameters read (initialize_MOM)")
 
+  call get_param(param_file, "MOM", "HOMOGENIZE_FORCINGS", CS%homogenize_forcings, &
+                 "If True, homogenize the forces and fluxes.", default=.false.)
+  call get_param(param_file, "MOM", "UPDATE_USTAR",CS%update_ustar, &
+                 "If True, update ustar from homogenized tau when using the "//&
+                 "HOMOGENIZE_FORCINGS option.  Note that this will not work "//&
+                 "with a non-zero gustiness factor.", default=.false., &
+                 do_not_log=.not.CS%homogenize_forcings)
+
   ! Grid rotation test
   call get_param(param_file, "MOM", "ROTATE_INDEX", CS%rotate_index, &
       "Enable rotation of the horizontal indices.", default=.false., &

src/core/MOM_forcing_type.F90

@@ -17,6 +17,7 @@ module MOM_forcing_type
 use MOM_grid,          only : ocean_grid_type
 use MOM_opacity,       only : sumSWoverBands, optics_type, extract_optics_slice, optics_nbands
 use MOM_spatial_means, only : global_area_integral, global_area_mean
+use MOM_spatial_means, only : global_area_mean_u, global_area_mean_v
 use MOM_unit_scaling,  only : unit_scale_type
 use MOM_variables,     only : surface, thermo_var_ptrs
 use MOM_verticalGrid,  only : verticalGrid_type
@@ -35,6 +36,7 @@ module MOM_forcing_type
 public set_derived_forcing_fields, copy_back_forcing_fields
 public set_net_mass_forcing, get_net_mass_forcing
 public rotate_forcing, rotate_mech_forcing
+public homogenize_forcing, homogenize_mech_forcing
 
 !> Allocate the fields of a (flux) forcing type, based on either a set of input
 !! flags for each group of fields, or a pre-allocated reference forcing.
@@ -3358,6 +3360,7 @@ subroutine rotate_forcing(fluxes_in, fluxes, turns)
   if (do_iceberg) then
     call rotate_array(fluxes_in%ustar_berg, turns, fluxes%ustar_berg)
     call rotate_array(fluxes_in%area_berg, turns, fluxes%area_berg)
+    !BGR: pretty sure the following line isn't supposed to be here.
     call rotate_array(fluxes_in%iceshelf_melt, turns, fluxes%iceshelf_melt)
   endif
 
@@ -3463,6 +3466,234 @@ subroutine rotate_mech_forcing(forces_in, turns, forces)
   forces%initialized = forces_in%initialized
 end subroutine rotate_mech_forcing
 
+!< Homogenize the forcing fields from the input domain
+subroutine homogenize_mech_forcing(forces, G, US, Rho0, UpdateUstar)
+  type(mech_forcing),    intent(inout) :: forces !< Forcing on the input domain
+  type(ocean_grid_type),    intent(in) :: G      !< Grid metric of target forcing
+  type(unit_scale_type),    intent(in) :: US     !< A dimensional unit scaling type
+  real,                     intent(in) :: Rho0   !< A reference density of seawater [R ~> kg m-3],
+                                              !! as used to calculate ustar.
+  logical, optional,        intent(in) :: UpdateUstar !< A logical to determine if Ustar should be directly averaged
+                                                   !! or updated from mean tau.
+
+  real :: tx_mean, ty_mean, avg
+  real :: iRho0
+  logical :: do_stress, do_ustar, do_shelf, do_press, do_iceberg, tau2ustar
+  integer :: i, j, is, ie, js, je, isB, ieB, jsB, jeB
+  is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec
+  isB = G%iscB ; ieB = G%iecB ; jsB = G%jscB ; jeB = G%jecB
+
+  iRho0 = US%L_to_Z / Rho0
+
+  tau2ustar = .false.
+  if (present(UpdateUstar)) tau2ustar = UpdateUstar
+
+  call get_mech_forcing_groups(forces, do_stress, do_ustar, do_shelf, &
+                              do_press, do_iceberg)
+
+  if (do_stress) then
+    tx_mean = global_area_mean_u(forces%taux, G)
+    do j=js,je ; do i=isB,ieB
+      if (G%mask2dCu(I,j) > 0.) forces%taux(I,j) = tx_mean
+    enddo ; enddo
+    ty_mean = global_area_mean_v(forces%tauy, G)
+    do j=jsB,jeB ; do i=is,ie
+      if (G%mask2dCv(i,J) > 0.) forces%tauy(i,J) = ty_mean
+    enddo ; enddo
+    if (tau2ustar) then
+      do j=js,je ; do i=is,ie
+        if (G%mask2dT(i,j) > 0.) forces%ustar(i,j) = sqrt(sqrt(tx_mean**2 + ty_mean**2)*iRho0)
+      enddo ; enddo
+    else
+      call homogenize_field_t(forces%ustar, G)
+    endif
+  else
+    if (do_ustar) then
+      call homogenize_field_t(forces%ustar, G)
+    endif
+  endif
+
+  if (do_shelf) then
+    call homogenize_field_u(forces%rigidity_ice_u, G)
+    call homogenize_field_v(forces%rigidity_ice_v, G)
+    call homogenize_field_u(forces%frac_shelf_u, G)
+    call homogenize_field_v(forces%frac_shelf_v, G)
+  endif
+
+  if (do_press) then
+    ! NOTE: p_surf_SSH either points to p_surf or p_surf_full
+    call homogenize_field_t(forces%p_surf, G)
+    call homogenize_field_t(forces%p_surf_full, G)
+    call homogenize_field_t(forces%net_mass_src, G)
+  endif
+
+  if (do_iceberg) then
+    call homogenize_field_t(forces%area_berg, G)
+    call homogenize_field_t(forces%mass_berg, G)
+  endif
+
+end subroutine homogenize_mech_forcing
+
+!< Homogenize the fluxes
+subroutine homogenize_forcing(fluxes, G)
+  type(forcing), intent(inout)  :: fluxes     !< Input forcing struct
+  type(ocean_grid_type), intent(in) :: G      !< Grid metric of target forcing
+
+  real :: avg
+  logical :: do_ustar, do_water, do_heat, do_salt, do_press, do_shelf, &
+      do_iceberg, do_heat_added, do_buoy
+  integer :: i, j, is, ie, js, je, isB, ieB, jsB, jeB
+  is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec
+  isB = G%iscB ; ieB = G%iecB ; jsB = G%jscB ; jeB = G%jecB
+
+  call get_forcing_groups(fluxes, do_water, do_heat, do_ustar, do_press, &
+      do_shelf, do_iceberg, do_salt, do_heat_added, do_buoy)
+
+  if (do_ustar) then
+    call homogenize_field_t(fluxes%ustar, G)
+    call homogenize_field_t(fluxes%ustar_gustless, G)
+  endif
+
+  if (do_water) then
+    call homogenize_field_t(fluxes%evap, G)
+    call homogenize_field_t(fluxes%lprec, G)
+    call homogenize_field_t(fluxes%lprec, G)
+    call homogenize_field_t(fluxes%fprec, G)
+    call homogenize_field_t(fluxes%vprec, G)
+    call homogenize_field_t(fluxes%lrunoff, G)
+    call homogenize_field_t(fluxes%frunoff, G)
+    call homogenize_field_t(fluxes%seaice_melt, G)
+    call homogenize_field_t(fluxes%netMassOut, G)
+    call homogenize_field_t(fluxes%netMassIn, G)
+    !This was removed and I don't think replaced. Not needed?
+    !call homogenize_field_t(fluxes%netSalt, G)
+  endif
+
+  if (do_heat) then
+    call homogenize_field_t(fluxes%seaice_melt_heat, G)
+    call homogenize_field_t(fluxes%sw, G)
+    call homogenize_field_t(fluxes%lw, G)
+    call homogenize_field_t(fluxes%latent, G)
+    call homogenize_field_t(fluxes%sens, G)
+    call homogenize_field_t(fluxes%latent_evap_diag, G)
+    call homogenize_field_t(fluxes%latent_fprec_diag, G)
+    call homogenize_field_t(fluxes%latent_frunoff_diag, G)
+  endif
+
+  if (do_salt) call homogenize_field_t(fluxes%salt_flux, G)
+
+  if (do_heat .and. do_water) then
+    call homogenize_field_t(fluxes%heat_content_cond, G)
+    call homogenize_field_t(fluxes%heat_content_icemelt, G)
+    call homogenize_field_t(fluxes%heat_content_lprec, G)
+    call homogenize_field_t(fluxes%heat_content_fprec, G)
+    call homogenize_field_t(fluxes%heat_content_vprec, G)
+    call homogenize_field_t(fluxes%heat_content_lrunoff, G)
+    call homogenize_field_t(fluxes%heat_content_frunoff, G)
+    call homogenize_field_t(fluxes%heat_content_massout, G)
+    call homogenize_field_t(fluxes%heat_content_massin, G)
+  endif
+
+  if (do_press) call homogenize_field_t(fluxes%p_surf, G)
+
+  if (do_shelf) then
+    call homogenize_field_t(fluxes%frac_shelf_h, G)
+    call homogenize_field_t(fluxes%ustar_shelf, G)
+    call homogenize_field_t(fluxes%iceshelf_melt, G)
+  endif
+
+  if (do_iceberg) then
+    call homogenize_field_t(fluxes%ustar_berg, G)
+    call homogenize_field_t(fluxes%area_berg, G)
+  endif
+
+  if (do_heat_added) then
+    call homogenize_field_t(fluxes%heat_added, G)
+  endif
+
+  ! The following fields are handled by drivers rather than control flags.
+  if (associated(fluxes%sw_vis_dir)) &
+    call homogenize_field_t(fluxes%sw_vis_dir, G)
+
+  if (associated(fluxes%sw_vis_dif)) &
+    call homogenize_field_t(fluxes%sw_vis_dif, G)
+
+  if (associated(fluxes%sw_nir_dir)) &
+    call homogenize_field_t(fluxes%sw_nir_dir, G)
+
+  if (associated(fluxes%sw_nir_dif)) &
+    call homogenize_field_t(fluxes%sw_nir_dif, G)
+
+  if (associated(fluxes%salt_flux_in)) &
+    call homogenize_field_t(fluxes%salt_flux_in, G)
+
+  if (associated(fluxes%salt_flux_added)) &
+    call homogenize_field_t(fluxes%salt_flux_added, G)
+
+  if (associated(fluxes%p_surf_full)) &
+    call homogenize_field_t(fluxes%p_surf_full, G)
+
+  if (associated(fluxes%buoy)) &
+    call homogenize_field_t(fluxes%buoy, G)
+
+  if (associated(fluxes%TKE_tidal)) &
+    call homogenize_field_t(fluxes%TKE_tidal, G)
+
+  if (associated(fluxes%ustar_tidal)) &
+    call homogenize_field_t(fluxes%ustar_tidal, G)
+
+  ! TODO: tracer flux homogenization
+  ! Having a warning causes a lot of errors (each time step).
+  !if (coupler_type_initialized(fluxes%tr_fluxes)) &
+  !  call MOM_error(WARNING, "Homogenization of tracer BC fluxes not yet implemented.")
+
+end subroutine homogenize_forcing
+
+subroutine homogenize_field_t(var, G)
+  type(ocean_grid_type),                intent(in) :: G   !< The ocean's grid structure
+  real, dimension(SZI_(G), SZJ_(G)), intent(inout) :: var !< The variable to homogenize
+
+  real    :: avg
+  integer :: i, j, is, ie, js, je
+  is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec
+
+  avg = global_area_mean(var, G)
+  do j=js,je ; do i=is,ie
+    if (G%mask2dT(i,j) > 0.) var(i,j) = avg
+  enddo ; enddo
+
+end subroutine homogenize_field_t
+
+subroutine homogenize_field_v(var, G)
+  type(ocean_grid_type),             intent(in)    :: G    !< The ocean's grid structure
+  real, dimension(SZI_(G), SZJB_(G)), intent(inout) :: var  !< The variable to homogenize
+
+  real    :: avg
+  integer :: i, j, is, ie, jsB, jeB
+  is = G%isc ; ie = G%iec ; jsB = G%jscB ; jeB = G%jecB
+
+  avg = global_area_mean_v(var, G)
+  do J=jsB,jeB ; do i=is,ie
+    if (G%mask2dCv(i,J) > 0.) var(i,J) = avg
+  enddo ; enddo
+
+end subroutine homogenize_field_v
+
+subroutine homogenize_field_u(var, G)
+  type(ocean_grid_type),             intent(in)    :: G    !< The ocean's grid structure
+  real, dimension(SZI_(G), SZJB_(G)), intent(inout) :: var  !< The variable to homogenize
+
+  real    :: avg
+  integer :: i, j, isB, ieB, js, je
+  isB = G%iscB ; ieB = G%iecB ; js = G%jsc ; je = G%jec
+
+  avg = global_area_mean_u(var, G)
+  do j=js,je ; do I=isB,ieB
+    if (G%mask2dCu(I,j) > 0.) var(I,j) = avg
+  enddo ; enddo
+
+end subroutine homogenize_field_u
+
 !> \namespace mom_forcing_type
 !!
 !! \section section_fluxes Boundary fluxes

src/diagnostics/MOM_spatial_means.F90

@@ -17,7 +17,7 @@ module MOM_spatial_means
 #include <MOM_memory.h>
 
 public :: global_i_mean, global_j_mean
-public :: global_area_mean, global_layer_mean
+public :: global_area_mean, global_area_mean_u, global_area_mean_v, global_layer_mean
 public :: global_area_integral
 public :: global_volume_mean, global_mass_integral
 public :: adjust_area_mean_to_zero
@@ -47,6 +47,50 @@ function global_area_mean(var, G, scale)
 
 end function global_area_mean
 
+!> Return the global area mean of a variable. This uses reproducing sums.
+function global_area_mean_v(var, G)
+  type(ocean_grid_type),             intent(in)  :: G    !< The ocean's grid structure
+  real, dimension(SZI_(G), SZJB_(G)), intent(in)  :: var  !< The variable to average
+
+  real, dimension(SZI_(G), SZJ_(G))              :: tmpForSumming
+  real :: global_area_mean_v
+  integer :: i, j, is, ie, js, je, isB, ieB, jsB, jeB
+
+  is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec
+  isB = G%iscB ; ieB = G%iecB ; jsB = G%jscB ; jeB = G%jecB
+
+  tmpForSumming(:,:) = 0.
+  do J=js,je ; do i=is,ie
+    tmpForSumming(i,j) = G%areaT(i,j) * (var(i,J) * G%mask2dCv(i,J) + &
+                                         var(i,J-1) * G%mask2dCv(i,J-1)) &
+                         / max(1.e-20,G%mask2dCv(i,J)+G%mask2dCv(i,J-1))
+  enddo ; enddo
+  global_area_mean_v = reproducing_sum(tmpForSumming) * G%IareaT_global
+
+end function global_area_mean_v
+
+!> Return the global area mean of a variable on U grid. This uses reproducing sums.
+function global_area_mean_u(var, G)
+  type(ocean_grid_type),             intent(in)  :: G    !< The ocean's grid structure
+  real, dimension(SZIB_(G), SZJ_(G)), intent(in)  :: var  !< The variable to average
+
+  real, dimension(SZI_(G), SZJ_(G))              :: tmpForSumming
+  real :: global_area_mean_u
+  integer :: i, j, is, ie, js, je, isB, ieB, jsB, jeB
+
+  is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec
+  isB = G%iscB ; ieB = G%iecB ; jsB = G%jscB ; jeB = G%jecB
+
+  tmpForSumming(:,:) = 0.
+  do j=js,je ; do i=is,ie
+    tmpForSumming(i,j) = G%areaT(i,j) * (var(I,j) * G%mask2dCu(I,j) + &
+                                         var(I-1,j) * G%mask2dCu(I-1,j)) &
+                         / max(1.e-20,G%mask2dCu(I,j)+G%mask2dCu(I-1,j))
+  enddo ; enddo
+  global_area_mean_u = reproducing_sum(tmpForSumming) * G%IareaT_global
+
+end function global_area_mean_u
+
 !> Return the global area integral of a variable, by default using the masked area from the
 !! grid, but an alternate could be used instead.  This uses reproducing sums.
 function global_area_integral(var, G, scale, area)