New TIDAL_SAL_FLATHER option

  - This option is defaulted to False to retain previous answers,
    but should be set to True for new experiments in order to make
    the Flather OBC routine consistent with the barotropic solver

  - This option only applies for regional OBC cases with Tides and
    scalar self-attraction and loading

  + Try at fixing issue mom-ocean#476

    - Will change answers for problems with OBCs.

  - Get Matt's patch to compile again

Co-authored by: Kate Hedstrom <kshedstrom@alaska.edu>

Author: MJHarrison-GFDL

docs/zotero.bib

@@ -2747,3 +2747,16 @@ @article{Nguyen2009
 	title = {Improved modeling of the Arctic halocline with a subgrid-scale brine rejection parameterization},
 	pages = {C11014}
 }
+
+@article{Adcroft2019,
+	doi = {10.1029/2019ms001726},
+	year = 2019,
+	publisher = {American Geophysical Union ({AGU})},
+	volume = {11},
+	number = {10},
+	pages = {3167--3211},
+	author = {A. Adcroft and W. Anderson and V. Balaji and C. Blanton and M. Bushuk and C. O. Dufour and J. P. Dunne and S. M. Griffies and R. Hallberg and M. J. Harrison and I. M. Held and M. F. Jansen and J. G. John and J. P. Krasting and A. R. Langenhorst and S. Legg and Z. Liang and C. McHugh and A. Radhakrishnan and B. G. Reichl and T. Rosati and B. L. Samuels and A. Shao and R. Stouffer and M. Winton and A. T. Wittenberg and B. Xiang and N. Zadeh and R. Zhang},
+	title = {The {GFDL} Global Ocean and Sea Ice Model {OM}4.0: Model Description and Simulation Features},
+	journal = {J. Adv. Mod. Earth Sys.}
+}
+

src/core/MOM.F90

@@ -1619,6 +1619,7 @@ subroutine step_MOM_thermo(CS, G, GV, US, u, v, h, tv, fluxes, dtdia, &
           call remap_dyn_split_RK2_aux_vars(G, GV, CS%dyn_split_RK2_CSp, h, h_new, CS%ALE_CSp, CS%OBC, dzRegrid)
 
         if (associated(CS%OBC)) &
+          call pass_var(h_new, G%Domain)
           call remap_OBC_fields(G, GV, h, h_new, CS%OBC, PCM_cell=PCM_cell)
 
         call remap_vertvisc_aux_vars(G, GV, CS%visc, h, h_new, CS%ALE_CSp, CS%OBC)

src/core/MOM_barotropic.F90

@@ -279,6 +279,9 @@ module MOM_barotropic
   logical :: use_old_coriolis_bracket_bug !< If True, use an order of operations
                              !! that is not bitwise rotationally symmetric in the
                              !! meridional Coriolis term of the barotropic solver.
+  logical :: tidal_sal_flather !< Apply adjustment to external gravity wave speed
+                             !! consistent with tidal self-attraction and loading
+                             !! used within the barotropic solver
   type(time_type), pointer :: Time  => NULL() !< A pointer to the ocean models clock.
   type(diag_ctrl), pointer :: diag => NULL()  !< A structure that is used to regulate
                              !! the timing of diagnostic output.
@@ -1122,8 +1125,13 @@ subroutine btstep(U_in, V_in, eta_in, dt, bc_accel_u, bc_accel_v, forces, pbce,
 
   ! Set up fields related to the open boundary conditions.
   if (apply_OBCs) then
-    call set_up_BT_OBC(OBC, eta, CS%BT_OBC, CS%BT_Domain, G, GV, US, MS, ievf-ie, use_BT_cont, &
-                       integral_BT_cont, dt, Datu, Datv, BTCL_u, BTCL_v)
+    if (CS%TIDAL_SAL_FLATHER) then
+       call set_up_BT_OBC(OBC, eta, CS%BT_OBC, CS%BT_Domain, G, GV, US, MS, ievf-ie, use_BT_cont, &
+            integral_BT_cont, dt, Datu, Datv, BTCL_u, BTCL_v, dgeo_de)
+    else
+       call set_up_BT_OBC(OBC, eta, CS%BT_OBC, CS%BT_Domain, G, GV, US, MS, ievf-ie, use_BT_cont, &
+            integral_BT_cont, dt, Datu, Datv, BTCL_u, BTCL_v)
+    endif
   endif
 
   ! Determine the difference between the sum of the layer fluxes and the
@@ -3101,7 +3109,7 @@ end subroutine apply_velocity_OBCs
 !> This subroutine sets up the private structure used to apply the open
 !! boundary conditions, as developed by Mehmet Ilicak.
 subroutine set_up_BT_OBC(OBC, eta, BT_OBC, BT_Domain, G, GV, US, MS, halo, use_BT_cont, &
-                         integral_BT_cont, dt_baroclinic, Datu, Datv, BTCL_u, BTCL_v)
+                         integral_BT_cont, dt_baroclinic, Datu, Datv, BTCL_u, BTCL_v, dgeo_de)
   type(ocean_OBC_type), target,          intent(inout) :: OBC    !< An associated pointer to an OBC type.
   type(memory_size_type),                intent(in)    :: MS     !< A type that describes the memory sizes of the
                                                                  !! argument arrays.
@@ -3132,9 +3140,11 @@ subroutine set_up_BT_OBC(OBC, eta, BT_OBC, BT_Domain, G, GV, US, MS, halo, use_B
   type(local_BT_cont_v_type), dimension(SZIW_(MS),SZJBW_(MS)), intent(in) :: BTCL_v !< Structure of information used
                                                                  !! for a dynamic estimate of the face areas at
                                                                  !! v-points.
-
+  real,                                  intent(in), optional  :: dgeo_de  !< The constant of proportionality between
+                                                                 !! geopotential and sea surface height [nondim].
   ! Local variables
   real :: I_dt      ! The inverse of the time interval of this call [T-1 ~> s-1].
+  real :: dgeo_de_in !< The constant of proportionality between geopotential and sea surface height [nondim].
   integer :: i, j, k, is, ie, js, je, n, nz
   integer :: isd, ied, jsd, jed, IsdB, IedB, JsdB, JedB
   integer :: isdw, iedw, jsdw, jedw
@@ -3152,6 +3162,9 @@ subroutine set_up_BT_OBC(OBC, eta, BT_OBC, BT_Domain, G, GV, US, MS, halo, use_B
                            "yet fully implemented with wide barotropic halos.")
   endif
 
+  dgeo_de_in = 1.0
+  if (PRESENT(dgeo_de)) dgeo_de_in = dgeo_de
+
   if (.not. BT_OBC%is_alloced) then
     allocate(BT_OBC%Cg_u(isdw-1:iedw,jsdw:jedw), source=0.0)
     allocate(BT_OBC%H_u(isdw-1:iedw,jsdw:jedw), source=0.0)
@@ -3210,7 +3223,7 @@ subroutine set_up_BT_OBC(OBC, eta, BT_OBC, BT_Domain, G, GV, US, MS, halo, use_B
             BT_OBC%H_u(I,j) = eta(i+1,j)
           endif
         endif
-        BT_OBC%Cg_u(I,j) = SQRT(GV%g_prime(1) * GV%H_to_Z*BT_OBC%H_u(i,j))
+        BT_OBC%Cg_u(I,j) = SQRT(dgeo_de_in *  GV%g_prime(1) * GV%H_to_Z*BT_OBC%H_u(i,j))
       endif
     endif ; enddo ; enddo
     if (OBC%Flather_u_BCs_exist_globally) then
@@ -3264,7 +3277,7 @@ subroutine set_up_BT_OBC(OBC, eta, BT_OBC, BT_Domain, G, GV, US, MS, halo, use_B
             BT_OBC%H_v(i,J) = eta(i,j+1)
           endif
         endif
-        BT_OBC%Cg_v(i,J) = SQRT(GV%g_prime(1) * GV%H_to_Z*BT_OBC%H_v(i,J))
+        BT_OBC%Cg_v(i,J) = SQRT(dgeo_de_in * GV%g_prime(1) * GV%H_to_Z*BT_OBC%H_v(i,J))
       endif
     endif ; enddo ; enddo
     if (OBC%Flather_v_BCs_exist_globally) then
@@ -4520,6 +4533,14 @@ subroutine barotropic_init(u, v, h, eta, Time, G, GV, US, param_file, diag, CS,
                  "solver has the wrong sign, replicating a long-standing bug with a scalar "//&
                  "self-attraction and loading term or the SAL term from a previous simulation.", &
                  default=.false., do_not_log=(det_de==0.0))
+  call get_param(param_file, mdl, "TIDAL_SAL_FLATHER", CS%tidal_sal_flather, &
+                 "If true, then apply adjustments to the external gravity "//&
+                 "wave speed used with the Flather OBC routine consistent "//&
+                 "with the barotropic solver. This applies to cases with  "//&
+                 "tidal forcing using the scalar self-attraction approximation. "//&
+                 "The default is currently False in order to retain previous answers "//&
+                 "but should be set to True for new experiments", default=.false.)
+
   call get_param(param_file, mdl, "SADOURNY", CS%Sadourny, &
                  "If true, the Coriolis terms are discretized with the "//&
                  "Sadourny (1975) energy conserving scheme, otherwise "//&