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OBC Restarts Failing Fix #437

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OBC Restarts Failing Fix #437

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f2eabe0
Reconstruct OBC-exterior h halo for exact restart
manishvenu Jun 2, 2026
0055ce3
Simplify OBC-exterior h reconstruction to a single in-place zero-grad…
manishvenu Jun 3, 2026
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37 changes: 37 additions & 0 deletions src/core/MOM_dynamics_split_RK2.F90
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,8 @@ module MOM_dynamics_split_RK2
use MOM_lateral_mixing_coeffs, only : VarMix_CS
use MOM_MEKE_types, only : MEKE_type
use MOM_open_boundary, only : ocean_OBC_type, radiation_open_bdry_conds
use MOM_open_boundary, only : OBC_segment_type, OBC_DIRECTION_E, OBC_DIRECTION_W
use MOM_open_boundary, only : OBC_DIRECTION_N, OBC_DIRECTION_S
use MOM_open_boundary, only : open_boundary_zero_normal_flow, open_boundary_query
use MOM_open_boundary, only : open_boundary_test_extern_h, update_OBC_ramp
use MOM_open_boundary, only : copy_thickness_reservoirs
Expand Down Expand Up @@ -419,6 +421,8 @@ subroutine step_MOM_dyn_split_RK2(u_inst, v_inst, h, tv, visc, Time_local, dt, f
integer :: i, j, k, is, ie, js, je, Isq, Ieq, Jsq, Jeq, nz
integer :: cont_stencil, obc_stencil, vel_stencil
integer :: cor_stencil
integer :: n ! OBC segment loop index (OBC-exterior h fix)
type(OBC_segment_type), pointer :: segment => NULL() ! OBC segment (OBC-exterior h fix)

is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec ; nz = GV%ke
Isq = G%IscB ; Ieq = G%IecB ; Jsq = G%JscB ; Jeq = G%JecB
Expand Down Expand Up @@ -465,6 +469,39 @@ subroutine step_MOM_dyn_split_RK2(u_inst, v_inst, h, tv, visc, Time_local, dt, f
! Update OBC ramp value as function of time
call update_OBC_ramp(Time_local, CS%OBC, US)

! === OBC-exterior h fix (minimal): the OBC-exterior h halo is not reconstructed
! bit-for-bit across an exact restart, and vertvisc_coef reads it (zero-gradient
! projection across OBCs), seeding a last-bit velocity divergence. Rebuild it here with a
! single in-place zero-gradient fill over all segments: copy the first interior thickness
! into the exterior ghost cell. u-points (E/W) and v-points (N/S) only read same-row /
! same-column neighbours, never the diagonal corner, so no corner handling is needed.
if (associated(CS%OBC)) then
do n=1,CS%OBC%number_of_segments
segment => CS%OBC%segment(n)
if (.not. segment%on_pe) cycle
if (segment%is_E_or_W) then
I = segment%HI%IsdB
do k=1,nz ; do j=segment%HI%jsd,segment%HI%jed
if (segment%direction == OBC_DIRECTION_W) then
h(I,j,k) = h(I+1,j,k)
elseif (segment%direction == OBC_DIRECTION_E) then
h(I+1,j,k) = h(I,j,k)
endif
enddo ; enddo
elseif (segment%is_N_or_S) then
J = segment%HI%JsdB
do k=1,nz ; do i=segment%HI%isd,segment%HI%ied
if (segment%direction == OBC_DIRECTION_S) then
h(i,J,k) = h(i,J+1,k)
elseif (segment%direction == OBC_DIRECTION_N) then
h(i,J+1,k) = h(i,J,k)
endif
enddo ; enddo
endif
enddo
endif
! === end OBC-exterior h fix ===

do k=1,nz ; do j=G%jsd,G%jed ; do I=G%IsdB,G%IedB
u_old_rad_OBC(I,j,k) = u_av(I,j,k)
enddo ; enddo ; enddo
Expand Down
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