#include "cppdefs.h"

      MODULE v2dbc_mod
!
!svn $Id$
!=======================================================================
!  Copyright (c) 2002-2020 The ROMS/TOMS Group                         !
!    Licensed under a MIT/X style license                              !
!    See License_ROMS.txt                           Hernan G. Arango   !
!========================================== Alexander F. Shchepetkin ===
!                                                                      !
!  This subroutine sets lateral boundary conditions for vertically     !
!  integrated V-velocity.                                              !
!                                                                      !
!=======================================================================
!
      implicit none
!
      PRIVATE
      PUBLIC  :: v2dbc, v2dbc_tile
!
      CONTAINS
!
!***********************************************************************
      SUBROUTINE v2dbc (ng, tile, kout)
!***********************************************************************
!
      USE mod_param
      USE mod_ocean
      USE mod_stepping
!
!  Imported variable declarations.
!
      integer, intent(in) :: ng, tile, kout
!
!  Local variable declarations.
!
#include "tile.h"
!
      CALL v2dbc_tile (ng, tile,                                        &
     &                 LBi, UBi, LBj, UBj,                              &
     &                 IminS, ImaxS, JminS, JmaxS,                      &
     &                 krhs(ng), kstp(ng), kout,                        &
     &                 OCEAN(ng) % ubar,                                &
     &                 OCEAN(ng) % vbar,                                &
     &                 OCEAN(ng) % zeta)

      RETURN
      END SUBROUTINE v2dbc
!
!***********************************************************************
      SUBROUTINE v2dbc_tile (ng, tile,                                  &
     &                       LBi, UBi, LBj, UBj,                        &
     &                       IminS, ImaxS, JminS, JmaxS,                &
     &                       krhs, kstp, kout,                          &
     &                       ubar, vbar, zeta)
!***********************************************************************
!
      USE mod_param
      USE mod_boundary
      USE mod_clima
      USE mod_forces
      USE mod_grid
      USE mod_ncparam
#ifdef NESTING
      USE mod_nesting
#endif
      USE mod_scalars
!
!  Imported variable declarations.
!
      integer, intent(in) :: ng, tile
      integer, intent(in) :: LBi, UBi, LBj, UBj
      integer, intent(in) :: IminS, ImaxS, JminS, JmaxS
      integer, intent(in) :: krhs, kstp, kout
!
#ifdef ASSUMED_SHAPE
      real(r8), intent(in) :: ubar(LBi:,LBj:,:)
      real(r8), intent(in) :: zeta(LBi:,LBj:,:)

      real(r8), intent(inout) :: vbar(LBi:,LBj:,:)
#else
      real(r8), intent(in) :: ubar(LBi:UBi,LBj:UBj,3)
      real(r8), intent(in) :: zeta(LBi:UBi,LBj:UBj,3)

      real(r8), intent(inout) :: vbar(LBi:UBi,LBj:UBj,3)
#endif
!
!  Local variable declarations.
!
      integer :: Jmin, Jmax
      integer :: i, j, know
#ifdef NESTING
      integer :: Idg, Jdg, cr, dg, m, rg, tnew, told
#endif

      real(r8), parameter :: eps = 1.0E-20_r8

      real(r8) :: Ce, Cx, Ze
      real(r8) :: bry_pgr, bry_cor, bry_str, bry_val
      real(r8) :: cff, cff1, cff2, cff3, dt2d, dVde, dVdt, dVdx
      real(r8) :: obc_in, obc_out, phi, tau
#if defined ATM_PRESS && defined PRESS_COMPENSATE
      real(r8) :: OneAtm, fac
#endif

      real(r8), dimension(IminS:ImaxS,JminS:JmaxS) :: grad

#include "set_bounds.h"
!
!-----------------------------------------------------------------------
!  Set time-indices
!-----------------------------------------------------------------------
!
      IF (FIRST_2D_STEP) THEN
        know=krhs
        dt2d=dtfast(ng)
      ELSE IF (PREDICTOR_2D_STEP(ng)) THEN
        know=krhs
        dt2d=2.0_r8*dtfast(ng)
      ELSE
        know=kstp
        dt2d=dtfast(ng)
      END IF
#if defined ATM_PRESS && defined PRESS_COMPENSATE
      OneAtm=1013.25_r8                  ! 1 atm = 1013.25 mb
      fac=100.0_r8/(g*rho0)
#endif
!
!-----------------------------------------------------------------------
!  Lateral boundary conditions at the southern edge.
!-----------------------------------------------------------------------
!
      IF (DOMAIN(ng)%Southern_Edge(tile)) THEN
!
!  Southern edge, implicit upstream radiation condition.
!
        IF (LBC(isouth,isVbar,ng)%radiation) THEN
          DO i=Istr,Iend+1
            grad(i,Jstr  )=vbar(i  ,Jstr  ,know)-                       &
     &                     vbar(i-1,Jstr  ,know)
            grad(i,Jstr+1)=vbar(i  ,Jstr+1,know)-                       &
     &                     vbar(i-1,Jstr+1,know)
          END DO
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
              dVdt=vbar(i,Jstr+1,know)-vbar(i,Jstr+1,kout)
              dVde=vbar(i,Jstr+1,kout)-vbar(i,Jstr+2,kout)

              IF (LBC(isouth,isVbar,ng)%nudging) THEN
!               IF (LnudgeM2CLM(ng)) THEN
!                 obc_out=0.5_r8*                                       &
!    &                    (CLIMA(ng)%M2nudgcof(i,Jstr-1)+               &
!    &                     CLIMA(ng)%M2nudgcof(i,Jstr  ))
!                 obc_in =obcfac(ng)*obc_out
!               ELSE
                  obc_out=M2obc_out(ng,isouth)
                  obc_in =M2obc_in (ng,isouth)
!               END IF
                IF ((dVdt*dVde).lt.0.0_r8) THEN
                  tau=obc_in
                ELSE
                  tau=obc_out
                END IF
#ifdef IMPLICIT_NUDGING
                IF (tau.gt.0.0_r8) tau=1.0_r8/tau
#else
                tau=tau*dt2d
#endif
              END IF

              IF ((dVdt*(grad(i  ,Jstr+1)+                              &
     &                   grad(i+1,Jstr+1))).gt.0.0_r8) THEN
                dVdx=grad(i  ,Jstr+1)
              ELSE
                dVdx=grad(i+1,Jstr+1)
              END IF
              cff=MAX(dVdx*dVdx+dVde*dVde,eps)
              IF ((dVdt*dVde).lt.0.0_r8) dVdt=0.0_r8
#ifdef RADIATION_2D
              Cx=MIN(cff,MAX(dVdt*dVdx,-cff))
#else
              Cx=0.0_r8
#endif
              Ce=dVdt*dVde
#if defined CELERITY_WRITE && defined FORWARD_WRITE
              BOUNDARY(ng)%vbar_south_Cx(i)=Cx
              BOUNDARY(ng)%vbar_south_Ce(i)=Ce
              BOUNDARY(ng)%vbar_south_C2(i)=cff
#endif
              vbar(i,Jstr,kout)=(cff*vbar(i,Jstr  ,know)+               &
     &                           Ce *vbar(i,Jstr+1,kout)-               &
     &                           MAX(Cx,0.0_r8)*grad(i  ,Jstr)-         &
     &                           MIN(Cx,0.0_r8)*grad(i+1,Jstr))/        &
     &                          (cff+Ce)

              IF (LBC(isouth,isVbar,ng)%nudging) THEN
#ifdef IMPLICIT_NUDGING
                phi=dt(ng)/(tau+dt(ng))
                vbar(i,Jstr,kout)=(1.0_r8-phi)*vbar(i,Jstr,kout)+       &
     &                            phi*BOUNDARY(ng)%vbar_south(i)

#else
                vbar(i,Jstr,kout)=vbar(i,Jstr,kout)+                    &
     &                            tau*(BOUNDARY(ng)%vbar_south(i)-      &
     &                                 vbar(i,Jstr,know))
#endif
              END IF
#ifdef MASKING
              vbar(i,Jstr,kout)=vbar(i,Jstr,kout)*                      &
     &                          GRID(ng)%vmask(i,Jstr)
#endif
            END IF
          END DO
!
!  Southern edge, Flather boundary condition.
!
        ELSE IF (LBC(isouth,isVbar,ng)%Flather) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
#if defined SSH_TIDES && !defined UV_TIDES
              IF (LBC(isouth,isFsur,ng)%acquire) THEN
                bry_pgr=-g*(zeta(i,Jstr,know)-                          &
     &                      BOUNDARY(ng)%zeta_south(i))*                &
     &                  0.5_r8*GRID(ng)%pn(i,Jstr)
              ELSE
                bry_pgr=-g*(zeta(i,Jstr  ,know)-                        &
     &                      zeta(i,Jstr-1,know))*                       &
     &                  0.5_r8*(GRID(ng)%pn(i,Jstr-1)+                  &
     &                          GRID(ng)%pn(i,Jstr  ))
              END IF
# ifdef UV_COR
              bry_cor=-0.125_r8*(ubar(i  ,Jstr-1,know)+                 &
     &                           ubar(i+1,Jstr-1,know)+                 &
     &                           ubar(i  ,Jstr  ,know)+                 &
     &                           ubar(i+1,Jstr  ,know))*                &
     &                          (GRID(ng)%f(i,Jstr-1)+                  &
     &                           GRID(ng)%f(i,Jstr  ))
# else
              bry_cor=0.0_r8
# endif
# ifdef ICESHELF
              cff1=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jstr-1)-                &
     &                             ABS(GRID(ng)%zice(i,Jstr-1))+        &
     &                             zeta(i,Jstr-1,know)+                 &
     &                             GRID(ng)%h(i,Jstr  )-                &
     &                             ABS(GRID(ng)%zice(i,Jstr  ))+        &
     &                             zeta(i,Jstr  ,know)))
# else
              cff1=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jstr-1)+                &
     &                             zeta(i,Jstr-1,know)+                 &
     &                             GRID(ng)%h(i,Jstr  )+                &
     &                             zeta(i,Jstr  ,know)))
# endif
              bry_str=cff1*(FORCES(ng)%svstr(i,Jstr)-                   &
     &                      FORCES(ng)%bvstr(i,Jstr))
# ifdef ICESHELF
              Ce=1.0_r8/SQRT(g*0.5_r8*(GRID(ng)%h(i,Jstr-1)-            &
     &                                 ABS(GRID(ng)%zice(i,Jstr-1))+    &
     &                                 zeta(i,Jstr-1,know)+             &
     &                                 GRID(ng)%h(i,Jstr  )-            &
     &                                 ABS(GRID(ng)%zice(i,Jstr  ))+    &
     &                                 zeta(i,Jstr  ,know)))
# else
              Ce=1.0_r8/SQRT(g*0.5_r8*(GRID(ng)%h(i,Jstr-1)+            &
     &                                 zeta(i,Jstr-1,know)+             &
     &                                 GRID(ng)%h(i,Jstr  )+            &
     &                                 zeta(i,Jstr  ,know)))
# endif
              cff2=GRID(ng)%on_v(i,Jstr)*Ce
!!            cff2=dt2d
              bry_val=vbar(i,Jstr+1,know)+                              &
     &                cff2*(bry_pgr+                                    &
     &                      bry_cor+                                    &
     &                      bry_str)
#else
              bry_val=BOUNDARY(ng)%vbar_south(i)
#endif
#ifdef ICESHELF
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jstr-1)-                 &
     &                            ABS(GRID(ng)%zice(i,Jstr-1))+         &
     &                            zeta(i,Jstr-1,know)+                  &
     &                            GRID(ng)%h(i,Jstr  )-                 &
     &                            ABS(GRID(ng)%zice(i,Jstr  ))+         &
     &                            zeta(i,Jstr  ,know)))
#else
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jstr-1)+                 &
     &                            zeta(i,Jstr-1,know)+                  &
     &                            GRID(ng)%h(i,Jstr  )+                 &
     &                            zeta(i,Jstr  ,know)))
#endif
              Ce=SQRT(g*cff)
#if defined ATM_PRESS && defined PRESS_COMPENSATE
              vbar(i,Jstr,kout)=bry_val-                                &
     &                          Ce*(0.5_r8*                             &
     &                              (zeta(i,Jstr-1,know)+               &
     &                               zeta(i,Jstr  ,know)+               &
     &                               fac*(FORCES(ng)%Pair(i,Jstr-1)+    &
     &                                    FORCES(ng)%Pair(i,Jstr  )-    &
     &                                    2.0_r8*OneAtm))-              &
     &                              BOUNDARY(ng)%zeta_south(i))
#else
              vbar(i,Jstr,kout)=bry_val-                                &
     &                          Ce*(0.5_r8*(zeta(i,Jstr-1,know)+        &
     &                                      zeta(i,Jstr  ,know))-       &
     &                              BOUNDARY(ng)%zeta_south(i))
#endif
#ifdef MASKING
              vbar(i,Jstr,kout)=vbar(i,Jstr,kout)*                      &
     &                          GRID(ng)%vmask(i,Jstr)
#endif
            END IF
          END DO
!
!  Southern edge, Shchepetkin boundary condition (Mason et al., 2010).
!
        ELSE IF (LBC(isouth,isVbar,ng)%Shchepetkin) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
#if defined SSH_TIDES && !defined UV_TIDES
              IF (LBC(isouth,isFsur,ng)%acquire) THEN
                bry_pgr=-g*(zeta(i,Jstr,know)-                          &
     &                      BOUNDARY(ng)%zeta_south(i))*                &
     &                  0.5_r8*GRID(ng)%pn(i,Jstr)
              ELSE
                bry_pgr=-g*(zeta(i,Jstr  ,know)-                        &
     &                      zeta(i,Jstr-1,know))*                       &
     &                  0.5_r8*(GRID(ng)%pn(i,Jstr-1)+                  &
     &                          GRID(ng)%pn(i,Jstr  ))
              END IF
# ifdef UV_COR
              bry_cor=-0.125_r8*(ubar(i  ,Jstr-1,know)+                 &
     &                           ubar(i+1,Jstr-1,know)+                 &
     &                           ubar(i  ,Jstr  ,know)+                 &
     &                           ubar(i+1,Jstr  ,know))*                &
     &                          (GRID(ng)%f(i,Jstr-1)+                  &
     &                           GRID(ng)%f(i,Jstr  ))
# else
              bry_cor=0.0_r8
# endif
              cff1=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jstr-1)+                &
     &                             zeta(i,Jstr-1,know)+                 &
     &                             GRID(ng)%h(i,Jstr  )+                &
     &                             zeta(i,Jstr  ,know)))
              bry_str=cff1*(FORCES(ng)%svstr(i,Jstr)-                   &
     &                      FORCES(ng)%bvstr(i,Jstr))
              Ce=1.0_r8/SQRT(g*0.5_r8*(GRID(ng)%h(i,Jstr-1)+            &
     &                                 zeta(i,Jstr-1,know)+             &
     &                                 GRID(ng)%h(i,Jstr  )+            &
     &                                 zeta(i,Jstr  ,know)))
              cff2=GRID(ng)%on_v(i,Jstr)*Ce
!!            cff2=dt2d
              bry_val=vbar(i,Jstr+1,know)+                              &
     &                cff2*(bry_pgr+                                    &
     &                      bry_cor+                                    &
     &                      bry_str)
#else
              bry_val=BOUNDARY(ng)%vbar_south(i)
#endif
#ifdef WET_DRY
              cff=0.5_r8*(GRID(ng)%h(i,Jstr-1)+                         &
     &                    zeta(i,Jstr-1,know)+                          &
     &                    GRID(ng)%h(i,Jstr  )+                         &
     &                    zeta(i,Jstr  ,know))
#else
              cff=0.5_r8*(GRID(ng)%h(i,Jstr-1)+                         &
     &                    GRID(ng)%h(i,Jstr  ))
#endif
              cff1=SQRT(g/cff)
              Ce=dt2d*cff1*cff*0.5_r8*(GRID(ng)%pn(i,Jstr-1)+           &
     &                                 GRID(ng)%pn(i,Jstr  ))
              Ze=(0.5_r8+Ce)*zeta(i,Jstr  ,know)+                       &
     &           (0.5_r8-Ce)*zeta(i,Jstr-1,know)
              IF (Ce.gt.Co) THEN
                cff2=(1.0_r8-Co/Ce)**2
                cff3=zeta(i,Jstr,kout)+                                 &
     &               Ce*zeta(i,Jstr-1,know)-                            &
     &               (1.0_r8+Ce)*zeta(i,Jstr,know)
                Ze=Ze+cff2*cff3
              END IF
              vbar(i,Jstr,kout)=0.5_r8*                                 &
     &                          ((1.0_r8-Ce)*vbar(i,Jstr,know)+         &
     &                           Ce*vbar(i,Jstr+1,know)+                &
     &                           bry_val-                               &
     &                           cff1*(Ze-BOUNDARY(ng)%zeta_south(i)))
#ifdef MASKING
              vbar(i,Jstr,kout)=vbar(i,Jstr,kout)*                      &
     &                          GRID(ng)%vmask(i,Jstr)
#endif
            END IF
          END DO
!
!  Southern edge, clamped boundary condition.
!
        ELSE IF (LBC(isouth,isVbar,ng)%clamped) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
              vbar(i,Jstr,kout)=BOUNDARY(ng)%vbar_south(i)
#ifdef MASKING
              vbar(i,Jstr,kout)=vbar(i,Jstr,kout)*                      &
     &                          GRID(ng)%vmask(i,Jstr)
#endif
            END IF
          END DO
!
!  Southern edge, gradient boundary condition.
!
        ELSE IF (LBC(isouth,isVbar,ng)%gradient) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
              vbar(i,Jstr,kout)=vbar(i,Jstr+1,kout)
#ifdef MASKING
              vbar(i,Jstr,kout)=vbar(i,Jstr,kout)*                      &
     &                          GRID(ng)%vmask(i,Jstr)
#endif
            END IF
          END DO
!
!  Southern edge, reduced-physics boundary condition.
!
        ELSE IF (LBC(isouth,isVbar,ng)%reduced) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
              IF (LBC(isouth,isFsur,ng)%acquire) THEN
                bry_pgr=-g*(zeta(i,Jstr,know)-                          &
     &                      BOUNDARY(ng)%zeta_south(i))*                &
     &                  0.5_r8*GRID(ng)%pn(i,Jstr)
              ELSE
                bry_pgr=-g*(zeta(i,Jstr  ,know)-                        &
     &                      zeta(i,Jstr-1,know))*                       &
     &                  0.5_r8*(GRID(ng)%pn(i,Jstr-1)+                  &
     &                          GRID(ng)%pn(i,Jstr  ))
              END IF
#ifdef UV_COR
              bry_cor=-0.125_r8*(ubar(i  ,Jstr-1,know)+                 &
     &                           ubar(i+1,Jstr-1,know)+                 &
     &                           ubar(i  ,Jstr  ,know)+                 &
     &                           ubar(i+1,Jstr  ,know))*                &
     &                          (GRID(ng)%f(i,Jstr-1)+                  &
     &                           GRID(ng)%f(i,Jstr  ))
#else
              bry_cor=0.0_r8
#endif
#ifdef ICESHELF
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jstr-1)-                 &
     &                            ABS(GRID(ng)%zice(i,Jstr-1))+         &
     &                            zeta(i,Jstr-1,know)+                  &
     &                            GRID(ng)%h(i,Jstr  )-                 &
     &                            ABS(GRID(ng)%zice(i,Jstr  ))+         &
     &                            zeta(i,Jstr  ,know)))
#else
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jstr-1)+                 &
     &                            zeta(i,Jstr-1,know)+                  &
     &                            GRID(ng)%h(i,Jstr  )+                 &
     &                            zeta(i,Jstr  ,know)))
#endif
              bry_str=cff*(FORCES(ng)%svstr(i,Jstr)-                    &
     &                     FORCES(ng)%bvstr(i,Jstr))
              vbar(i,Jstr,kout)=vbar(i,Jstr,know)+                      &
     &                          dt2d*(bry_pgr+                          &
     &                                bry_cor+                          &
     &                                bry_str)
#ifdef MASKING
              vbar(i,Jstr,kout)=vbar(i,Jstr,kout)*                      &
     &                          GRID(ng)%vmask(i,Jstr)
#endif
            END IF
          END DO
!
!  Southern edge, closed boundary condition.
!
        ELSE IF (LBC(isouth,isVbar,ng)%closed) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
              vbar(i,Jstr,kout)=0.0_r8
            END IF
          END DO

#ifdef NESTING
!
!  If refinement grid and southern edge, impose mass flux from donor
!  coaser grid for volume and mass conservation.
!
        ELSE IF (LBC(isouth,isVbar,ng)%nested) THEN
          DO cr=1,Ncontact
            dg=Vcontact(cr)%donor_grid
            rg=Vcontact(cr)%receiver_grid
            IF (RefinedGrid(ng).and.                                    &
     &          (rg.eq.ng).and.(DXmax(dg).gt.DXmax(rg))) THEN
              told=3-RollingIndex(cr)
              tnew=RollingIndex(cr)
              DO i=Istr,Iend
                m=BRY_CONTACT(isouth,cr)%C2Bindex(i)
                Idg=Vcontact(cr)%Idg(m)             ! for debugging
                Jdg=Vcontact(cr)%Jdg(m)             ! purposes
                cff=0.5_r8*GRID(ng)%om_v(i,Jstr)*                       &
     &              (GRID(ng)%h(i,Jstr-1)+zeta(i,Jstr-1,kout)+          &
     &               GRID(ng)%h(i,Jstr  )+zeta(i,Jstr  ,kout))
                cff1=GRID(ng)%om_v(i,Jstr)/REFINED(cr)%om_v(m)
                bry_val=cff1*REFINED(cr)%DV_avg2(1,m,tnew)/cff
# ifdef MASKING
                bry_val=bry_val*GRID(ng)%vmask(i,Jstr)
# endif
# ifdef NESTING_DEBUG
                BRY_CONTACT(isouth,cr)%Mflux(i)=cff*bry_val
# endif
                vbar(i,Jstr,kout)=bry_val
              END DO
            END IF
          END DO
#endif
        END IF
      END IF
!
!-----------------------------------------------------------------------
!  Lateral boundary conditions at the northern edge.
!-----------------------------------------------------------------------
!
      IF (DOMAIN(ng)%Northern_Edge(tile)) THEN
!
!  Northern edge, implicit upstream radiation condition.
!
        IF (LBC(inorth,isVbar,ng)%radiation) THEN
          DO i=Istr,Iend+1
            grad(i,Jend  )=vbar(i  ,Jend  ,know)-                       &
     &                     vbar(i-1,Jend  ,know)
            grad(i,Jend+1)=vbar(i  ,Jend+1,know)-                       &
     &                     vbar(i-1,Jend+1,know)
          END DO
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
              dVdt=vbar(i,Jend,know)-vbar(i,Jend  ,kout)
              dVde=vbar(i,Jend,kout)-vbar(i,Jend-1,kout)

              IF (LBC(inorth,isVbar,ng)%nudging) THEN
!               IF (LnudgeM2CLM(ng)) THEN
!                 obc_out=0.5_r8*                                       &
!    &                    (CLIMA(ng)%M2nudgcof(i,Jend  )+               &
!    &                     CLIMA(ng)%M2nudgcof(i,Jend+1))
!                 obc_in =obcfac(ng)*obc_out
!               ELSE
                  obc_out=M2obc_out(ng,inorth)
                  obc_in =M2obc_in (ng,inorth)
!               END IF
                IF ((dVdt*dVde).lt.0.0_r8) THEN
                  tau=obc_in
                ELSE
                  tau=obc_out
                END IF
#ifdef IMPLICIT_NUDGING
                IF (tau.gt.0.0_r8) tau=1.0_r8/tau
#else
                tau=tau*dt2d
#endif
              END IF

              IF ((dVdt*(grad(i  ,Jend)+                                &
     &                   grad(i+1,Jend))).gt.0.0_r8) THEN
                dVdx=grad(i  ,Jend)
              ELSE
                dVdx=grad(i+1,Jend)
              END IF
              cff=MAX(dVdx*dVdx+dVde*dVde,eps)
              IF ((dVdt*dVde).lt.0.0_r8) dVdt=0.0_r8
#ifdef RADIATION_2D
              Cx=MIN(cff,MAX(dVdt*dVdx,-cff))
#else
              Cx=0.0_r8
#endif
              Ce=dVdt*dVde
#if defined CELERITY_WRITE && defined FORWARD_WRITE
              BOUNDARY(ng)%vbar_north_Cx(i)=Cx
              BOUNDARY(ng)%vbar_north_Ce(i)=Ce
              BOUNDARY(ng)%vbar_north_C2(i)=cff
#endif
              vbar(i,Jend+1,kout)=(cff*vbar(i,Jend+1,know)+             &
     &                             Ce *vbar(i,Jend  ,kout)-             &
     &                             MAX(Cx,0.0_r8)*grad(i  ,Jend+1)-     &
     &                             MIN(Cx,0.0_r8)*grad(i+1,Jend+1))/    &
     &                            (cff+Ce)

              IF (LBC(inorth,isVbar,ng)%nudging) THEN
#ifdef IMPLICIT_NUDGING
                phi=dt(ng)/(tau+dt(ng))
                vbar(i,Jend+1,kout)=(1.0_r8-phi)*vbar(i,Jend+1,kout)+   &
     &                              phi*BOUNDARY(ng)%vbar_north(i)

#else
                vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)+                &
     &                              tau*(BOUNDARY(ng)%vbar_north(i)-    &
     &                                   vbar(i,Jend+1,know))
#endif
              END IF
#ifdef MASKING
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)*                  &
     &                            GRID(ng)%vmask(i,Jend+1)
#endif
            END IF
          END DO
!
!  Northern edge, Flather boundary condition.
!
        ELSE IF (LBC(inorth,isVbar,ng)%Flather) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
#if defined SSH_TIDES && !defined UV_TIDES
              IF (LBC(inorth,isFsur,ng)%acquire) THEN
                bry_pgr=-g*(BOUNDARY(ng)%zeta_north(i)-                 &
     &                      zeta(i,Jend,know))*                         &
     &                  0.5_r8*GRID(ng)%pn(i,Jend)
              ELSE
                bry_pgr=-g*(zeta(i,Jend+1,know)-                        &
     &                      zeta(i,Jend  ,know))*                       &
     &                  0.5_r8*(GRID(ng)%pn(i,Jend  )+                  &
     &                          GRID(ng)%pn(i,Jend+1))
              END IF
# ifdef UV_COR
              bry_cor=-0.125_r8*(ubar(i  ,Jend  ,know)+                 &
     &                           ubar(i+1,Jend  ,know)+                 &
     &                           ubar(i  ,Jend+1,know)+                 &
     &                           ubar(i+1,Jend+1,know))*                &
     &                          (GRID(ng)%f(i,Jend  )+                  &
     &                           GRID(ng)%f(i,Jend+1))
# else
              bry_cor=0.0_r8
# endif
# ifdef ICESHELF
              cff1=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jend  )-                &
     &                             ABS(GRID(ng)%zice(i,Jend  ))+        &
     &                             zeta(i,Jend  ,know)+                 &
     &                             GRID(ng)%h(i,Jend+1)-                &
     &                             ABS(GRID(ng)%zice(i,Jend+1))+        &
     &                             zeta(i,Jend+1,know)))
# else
              cff1=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jend  )+                &
     &                             zeta(i,Jend  ,know)+                 &
     &                             GRID(ng)%h(i,Jend+1)+                &
     &                             zeta(i,Jend+1,know)))
# endif
              bry_str=cff1*(FORCES(ng)%svstr(i,Jend+1)-                 &
     &                      FORCES(ng)%bvstr(i,Jend+1))
# ifdef ICESHELF
              Ce=1.0_r8/SQRT(g*0.5_r8*(GRID(ng)%h(i,Jend+1)-            &
     &                                 ABS(GRID(ng)%zice(i,Jend+1))+    &
     &                                 zeta(i,Jend+1,know)+             &
     &                                 GRID(ng)%h(i,Jend  )-            &
     &                                 ABS(GRID(ng)%zice(i,Jend  ))+    &
     &                                 zeta(i,Jend  ,know)))
# else
              Ce=1.0_r8/SQRT(g*0.5_r8*(GRID(ng)%h(i,Jend+1)+            &
     &                                 zeta(i,Jend+1,know)+             &
     &                                 GRID(ng)%h(i,Jend  )+            &
     &                                 zeta(i,Jend  ,know)))
# endif
              cff2=GRID(ng)%on_v(i,Jend+1)*Ce
!!            cff2=dt2d
              bry_val=vbar(i,Jend,know)+                                &
     &                cff2*(bry_pgr+                                    &
     &                      bry_cor+                                    &
     &                      bry_str)
#else
              bry_val=BOUNDARY(ng)%vbar_north(i)
#endif
#ifdef ICESHELF
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jend  )-                 &
     &                            ABS(GRID(ng)%zice(i,Jend  ))+         &
     &                            zeta(i,Jend  ,know)+                  &
     &                            GRID(ng)%h(i,Jend+1)-                 &
     &                            ABS(GRID(ng)%zice(i,Jend+1))+         &
     &                            zeta(i,Jend+1,know)))
#else
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jend  )+                 &
     &                            zeta(i,Jend  ,know)+                  &
     &                            GRID(ng)%h(i,Jend+1)+                 &
     &                            zeta(i,Jend+1,know)))
#endif
              Ce=SQRT(g*cff)
#if defined ATM_PRESS && defined PRESS_COMPENSATE
            vbar(i,Jend+1,kout)=bry_val+                                &
     &                          Ce*(0.5_r8*                             &
     &                              (zeta(i,Jend  ,know)+               &
     &                               zeta(i,Jend+1,know)+               &
     &                               fac*(FORCES(ng)%Pair(i,Jend  )+    &
     &                                    FORCES(ng)%Pair(i,Jend+1)-    &
     &                                    2.0_r8*OneAtm))-              &
     &                              BOUNDARY(ng)%zeta_north(i))
#else
              vbar(i,Jend+1,kout)=bry_val+                              &
     &                            Ce*(0.5_r8*(zeta(i,Jend  ,know)+      &
     &                                        zeta(i,Jend+1,know))-     &
     &                                BOUNDARY(ng)%zeta_north(i))
#endif
#ifdef MASKING
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)*                  &
     &                            GRID(ng)%vmask(i,Jend+1)
#endif
            END IF
          END DO
!
!  Northern edge, Shchepetkin boundary condition (Mason et al., 2010).
!
        ELSE IF (LBC(inorth,isVbar,ng)%Shchepetkin) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
#if defined SSH_TIDES && !defined UV_TIDES
              IF (LBC(inorth,isFsur,ng)%acquire) THEN
                bry_pgr=-g*(BOUNDARY(ng)%zeta_north(i)-                 &
     &                      zeta(i,Jend,know))*                         &
     &                  0.5_r8*GRID(ng)%pn(i,Jend)
              ELSE
                bry_pgr=-g*(zeta(i,Jend+1,know)-                        &
     &                      zeta(i,Jend  ,know))*                       &
     &                  0.5_r8*(GRID(ng)%pn(i,Jend  )+                  &
     &                          GRID(ng)%pn(i,Jend+1))
              END IF
# ifdef UV_COR
              bry_cor=-0.125_r8*(ubar(i  ,Jend  ,know)+                 &
     &                           ubar(i+1,Jend  ,know)+                 &
     &                           ubar(i  ,Jend+1,know)+                 &
     &                           ubar(i+1,Jend+1,know))*                &
     &                          (GRID(ng)%f(i,Jend  )+                  &
     &                           GRID(ng)%f(i,Jend+1))
# else
              bry_cor=0.0_r8
# endif
              cff1=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jend  )+                &
     &                             zeta(i,Jend  ,know)+                 &
     &                             GRID(ng)%h(i,Jend+1)+                &
     &                             zeta(i,Jend+1,know)))
              bry_str=cff1*(FORCES(ng)%svstr(i,Jend+1)-                 &
     &                      FORCES(ng)%bvstr(i,Jend+1))
              Ce=1.0_r8/SQRT(g*0.5_r8*(GRID(ng)%h(i,Jend+1)+            &
     &                                 zeta(i,Jend+1,know)+             &
     &                                 GRID(ng)%h(i,Jend  )+            &
     &                                 zeta(i,Jend  ,know)))
              cff2=GRID(ng)%on_v(i,Jend+1)*Ce
!!            cff2=dt2d
              bry_val=vbar(i,Jend,know)+                                &
     &                cff2*(bry_pgr+                                    &
     &                      bry_cor+                                    &
     &                      bry_str)
#else
              bry_val=BOUNDARY(ng)%vbar_north(i)
#endif
#ifdef WET_DRY
              cff=0.5_r8*(GRID(ng)%h(i,Jend  )+                         &
     &                    zeta(i,Jend  ,know)+                          &
     &                    GRID(ng)%h(i,Jend+1)+                         &
     &                    zeta(i,Jend+1,know))
#else
              cff=0.5_r8*(GRID(ng)%h(i,Jend  )+                         &
     &                    GRID(ng)%h(i,Jend+1))
#endif
              cff1=SQRT(g/cff)
              Ce=dt2d*cff1*cff*0.5_r8*(GRID(ng)%pn(i,Jend  )+           &
     &                                 GRID(ng)%pn(i,Jend+1))
              Ze=(0.5_r8+Ce)*zeta(i,Jend  ,know)+                       &
     &           (0.5_r8-Ce)*zeta(i,Jend+1,know)
              IF (Ce.gt.Co) THEN
                cff2=(1.0_r8-Co/Ce)**2
                cff3=zeta(i,Jend,kout)+                                 &
     &               Ce*zeta(i,Jend+1,know)-                            &
     &               (1.0_r8+Ce)*zeta(i,Jend,know)
                Ze=Ze+cff2*cff3
              END IF
              vbar(i,Jend+1,kout)=0.5_r8*                               &
     &                            ((1.0_r8-Ce)*vbar(i,Jend+1,know)+     &
     &                             Ce*vbar(i,Jend,know)+                &
     &                             bry_val+                             &
     &                             cff1*(Ze-BOUNDARY(ng)%zeta_north(i)))
#ifdef MASKING
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)*                  &
     &                            GRID(ng)%vmask(i,Jend+1)
#endif
            END IF
          END DO
!
!  Northern edge, clamped boundary condition.
!
        ELSE IF (LBC(inorth,isVbar,ng)%clamped) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
              vbar(i,Jend+1,kout)=BOUNDARY(ng)%vbar_north(i)
#ifdef MASKING
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)*                  &
     &                            GRID(ng)%vmask(i,Jend+1)
#endif
            END IF
          END DO
!
!  Northern edge, gradient boundary condition.
!
        ELSE IF (LBC(inorth,isVbar,ng)%gradient) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
              vbar(i,Jend+1,kout)=vbar(i,Jend,kout)
#ifdef MASKING
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)*                  &
     &                            GRID(ng)%vmask(i,Jend+1)
#endif
            END IF
          END DO
!
!  Northern edge, reduced-physics boundary condition.
!
        ELSE IF (LBC(inorth,isVbar,ng)%reduced) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
              IF (LBC(inorth,isFsur,ng)%acquire) THEN
                bry_pgr=-g*(BOUNDARY(ng)%zeta_north(i)-                 &
     &                      zeta(i,Jend,know))*                         &
     &                  0.5_r8*GRID(ng)%pn(i,Jend)
              ELSE
                bry_pgr=-g*(zeta(i,Jend+1,know)-                        &
     &                      zeta(i,Jend  ,know))*                       &
     &                  0.5_r8*(GRID(ng)%pn(i,Jend  )+                  &
     &                          GRID(ng)%pn(i,Jend+1))
              END IF
#ifdef UV_COR
              bry_cor=-0.125_r8*(ubar(i  ,Jend  ,know)+                 &
     &                           ubar(i+1,Jend  ,know)+                 &
     &                           ubar(i  ,Jend+1,know)+                 &
     &                           ubar(i+1,Jend+1,know))*                &
     &                          (GRID(ng)%f(i,Jend  )+                  &
     &                           GRID(ng)%f(i,Jend+1))
#else
              bry_cor=0.0_r8
#endif
#ifdef ICESHELF
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jend  )-                 &
     &                            ABS(GRID(ng)%zice(i,Jend  ))+         &
     &                            zeta(i,Jend  ,know)+                  &
     &                            GRID(ng)%h(i,Jend+1)-                 &
     &                            ABS(GRID(ng)%zice(i,Jend+1))+         &
     &                            zeta(i,Jend+1,know)))
#else
              cff=1.0_r8/(0.5_r8*(GRID(ng)%h(i,Jend  )+                 &
     &                            zeta(i,Jend  ,know)+                  &
     &                            GRID(ng)%h(i,Jend+1)+                 &
     &                            zeta(i,Jend+1,know)))
#endif
              bry_str=cff*(FORCES(ng)%svstr(i,Jend+1)-                  &
     &                     FORCES(ng)%bvstr(i,Jend+1))
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,know)+                  &
     &                            dt2d*(bry_pgr+                        &
     &                                  bry_cor+                        &
     &                                  bry_str)
#ifdef MASKING
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)*                  &
     &                            GRID(ng)%vmask(i,Jend+1)
#endif
            END IF
          END DO
!
!  Northern edge, closed boundary condition.
!
        ELSE IF (LBC(inorth,isVbar,ng)%closed) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
              vbar(i,Jend+1,kout)=0.0_r8
            END IF
          END DO

#ifdef NESTING
!
!  If refinement grid and northern edge, impose mass flux from donor
!  coaser grid for volume and mass conservation.
!
        ELSE IF (LBC(inorth,isVbar,ng)%nested) THEN
          DO cr=1,Ncontact
            dg=Vcontact(cr)%donor_grid
            rg=Vcontact(cr)%receiver_grid
            IF (RefinedGrid(ng).and.                                    &
     &          (rg.eq.ng).and.(DXmax(dg).gt.DXmax(rg))) THEN
              told=3-RollingIndex(cr)
              tnew=RollingIndex(cr)
              DO i=Istr,Iend
                m=BRY_CONTACT(inorth,cr)%C2Bindex(i)
                Idg=Vcontact(cr)%Idg(m)             ! for debugging
                Jdg=Vcontact(cr)%Jdg(m)             ! purposes
                cff=0.5_r8*GRID(ng)%om_v(i,Jend+1)*                     &
     &              (GRID(ng)%h(i,Jend+1)+zeta(i,Jend+1,kout)+          &
     &               GRID(ng)%h(i,Jend  )+zeta(i,Jend  ,kout))
                cff1=GRID(ng)%om_v(i,Jend+1)/REFINED(cr)%om_v(m)
                bry_val=cff1*REFINED(cr)%DV_avg2(1,m,tnew)/cff
# ifdef MASKING
                bry_val=bry_val*GRID(ng)%vmask(i,Jend+1)
# endif
# ifdef NESTING_DEBUG
                BRY_CONTACT(inorth,cr)%Mflux(i)=cff*bry_val
# endif
                vbar(i,Jend+1,kout)=bry_val
              END DO
            END IF
          END DO
#endif
        END IF
      END IF
!
!-----------------------------------------------------------------------
!  Lateral boundary conditions at the western edge.
!-----------------------------------------------------------------------
!
      IF (DOMAIN(ng)%Western_Edge(tile)) THEN
!
!  Western edge, implicit upstream radiation condition.
!
        IF (LBC(iwest,isVbar,ng)%radiation) THEN
          DO j=JstrV-1,Jend
            grad(Istr-1,j)=vbar(Istr-1,j+1,know)-                       &
     &                     vbar(Istr-1,j  ,know)
            grad(Istr  ,j)=vbar(Istr  ,j+1,know)-                       &
     &                     vbar(Istr  ,j  ,know)
          END DO
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%west(j)) THEN
              dVdt=vbar(Istr,j,know)-vbar(Istr  ,j,kout)
              dVdx=vbar(Istr,j,kout)-vbar(Istr+1,j,kout)

              IF (LBC(iwest,isVbar,ng)%nudging) THEN
!               IF (LnudgeM2CLM(ng)) THEN
!                 obc_out=0.5_r8*                                       &
!    &                    (CLIMA(ng)%M2nudgcof(Istr-1,j-1)+             &
!    &                     CLIMA(ng)%M2nudgcof(Istr-1,j  ))
!                 obc_in =obcfac(ng)*obc_out
!               ELSE
                  obc_out=M2obc_out(ng,iwest)
                  obc_in =M2obc_in (ng,iwest)
!               END IF
                IF ((dVdt*dVdx).lt.0.0_r8) THEN
                  tau=obc_in
                ELSE
                  tau=obc_out
                END IF
#ifdef IMPLICIT_NUDGING
                IF (tau.gt.0.0_r8) tau=1.0_r8/tau
#else
                tau=tau*dt2d
#endif
              END IF

              IF ((dVdt*(grad(Istr,j-1)+                                &
     &                   grad(Istr,j  ))).gt.0.0_r8) THEN
                dVde=grad(Istr,j-1)
              ELSE
                dVde=grad(Istr,j  )
              END IF
              cff=MAX(dVdx*dVdx+dVde*dVde,eps)
              IF ((dVdt*dVdx).lt.0.0_r8) dVdt=0.0_r8
              Cx=dVdt*dVdx
#ifdef RADIATION_2D
              Ce=MIN(cff,MAX(dVdt*dVde,-cff))
#else
              Ce=0.0_r8
#endif
#if defined CELERITY_WRITE && defined FORWARD_WRITE
              BOUNDARY(ng)%vbar_west_Cx(j)=Cx
              BOUNDARY(ng)%vbar_west_Ce(j)=Ce
              BOUNDARY(ng)%vbar_west_C2(j)=cff
#endif
              vbar(Istr-1,j,kout)=(cff*vbar(Istr-1,j,know)+             &
     &                             Cx *vbar(Istr  ,j,kout)-             &
     &                             MAX(Ce,0.0_r8)*grad(Istr-1,j-1)-     &
     &                             MIN(Ce,0.0_r8)*grad(Istr-1,j  ))/    &
     &                            (cff+Cx)

              IF (LBC(iwest,isVbar,ng)%nudging) THEN
#ifdef IMPLICIT_NUDGING
                phi=dt(ng)/(tau+dt(ng))
                vbar(Istr-1,j,kout)=(1.0_r8-phi)*vbar(Istr-1,j,kout)+   &
     &                              phi*BOUNDARY(ng)%vbar_west(j)
#else
                vbar(Istr-1,j,kout)=vbar(Istr-1,j,kout)+                &
     &                              tau*(BOUNDARY(ng)%vbar_west(j)-     &
     &                                   vbar(Istr-1,j,know))
#endif
              END IF
#ifdef MASKING
              vbar(Istr-1,j,kout)=vbar(Istr-1,j,kout)*                  &
     &                            GRID(ng)%vmask(Istr-1,j)
#endif
            END IF
          END DO
!
!  Western edge, Chapman boundary condition.
!
        ELSE IF (LBC(iwest,isVbar,ng)%Flather.or.                       &
     &           LBC(iwest,isVbar,ng)%reduced.or.                       &
     &           LBC(iwest,isVbar,ng)%Shchepetkin) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%west(j)) THEN
              cff=dt2d*0.5_r8*(GRID(ng)%pm(Istr,j-1)+                   &
     &                         GRID(ng)%pm(Istr,j  ))
#ifdef ICESHELF
              cff1=SQRT(g*0.5_r8*(GRID(ng)%h(Istr,j-1)-                 &
     &                            ABS(GRID(ng)%zice(Istr,j-1))+         &
     &                            zeta(Istr,j-1,know)+                  &
     &                            GRID(ng)%h(Istr,j  )-                 &
     &                            ABS(GRID(ng)%zice(Istr,j  ))+         &
     &                            zeta(Istr,j  ,know)))
#else
              cff1=SQRT(g*0.5_r8*(GRID(ng)%h(Istr,j-1)+                 &
     &                            zeta(Istr,j-1,know)+                  &
     &                            GRID(ng)%h(Istr,j  )+                 &
     &                            zeta(Istr,j  ,know)))
#endif
              Cx=cff*cff1
              cff2=1.0_r8/(1.0_r8+Cx)
              vbar(Istr-1,j,kout)=cff2*(vbar(Istr-1,j,know)+            &
     &                                  Cx*vbar(Istr,j,kout))
#ifdef MASKING
              vbar(Istr-1,j,kout)=vbar(Istr-1,j,kout)*                  &
     &                            GRID(ng)%vmask(Istr-1,j)
#endif
            END IF
          END DO
!
!  Western edge, clamped boundary condition.
!
        ELSE IF (LBC(iwest,isVbar,ng)%clamped) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%west(j)) THEN
              vbar(Istr-1,j,kout)=BOUNDARY(ng)%vbar_west(j)
#ifdef MASKING
              vbar(Istr-1,j,kout)=vbar(Istr-1,j,kout)*                  &
     &                            GRID(ng)%vmask(Istr-1,j)
#endif
            END IF
          END DO
!
!  Western edge, gradient boundary condition.
!
        ELSE IF (LBC(iwest,isVbar,ng)%gradient) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%west(j)) THEN
              vbar(Istr-1,j,kout)=vbar(Istr,j,kout)
#ifdef MASKING
              vbar(Istr-1,j,kout)=vbar(Istr-1,j,kout)*                  &
     &                            GRID(ng)%vmask(Istr-1,j)
#endif
            END IF
          END DO
!
!  Western edge, closed boundary condition: free slip (gamma2=1)  or
!                                           no   slip (gamma2=-1).
!
        ELSE IF (LBC(iwest,isVbar,ng)%closed) THEN
          IF (NSperiodic(ng)) THEN
            Jmin=JstrV
            Jmax=Jend
          ELSE
            Jmin=Jstr
            Jmax=JendR
          END IF
          DO j=Jmin,Jmax
            IF (LBC_apply(ng)%west(j)) THEN
              vbar(Istr-1,j,kout)=gamma2(ng)*vbar(Istr,j,kout)
#ifdef MASKING
              vbar(Istr-1,j,kout)=vbar(Istr-1,j,kout)*                  &
     &                            GRID(ng)%vmask(Istr-1,j)
#endif
            END IF
          END DO
        END IF
      END IF
!
!-----------------------------------------------------------------------
!  Lateral boundary conditions at the eastern edge.
!-----------------------------------------------------------------------
!
      IF (DOMAIN(ng)%Eastern_Edge(tile)) THEN
!
!  Eastern edge, implicit upstream radiation condition.
!
        IF (LBC(ieast,isVbar,ng)%radiation) THEN
          DO j=JstrV-1,Jend
            grad(Iend  ,j)=vbar(Iend  ,j+1,know)-                       &
     &                     vbar(Iend  ,j  ,know)
            grad(Iend+1,j)=vbar(Iend+1,j+1,know)-                       &
     &                     vbar(Iend+1,j  ,know)
          END DO
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%east(j)) THEN
              dVdt=vbar(Iend,j,know)-vbar(Iend  ,j,kout)
              dVdx=vbar(Iend,j,kout)-vbar(Iend-1,j,kout)

              IF (LBC(ieast,isVbar,ng)%nudging) THEN
!               IF (LnudgeM2CLM(ng)) THEN
!                 obc_out=0.5_r8*                                       &
!    &                    (CLIMA(ng)%M2nudgcof(Iend+1,j-1)+             &
!    &                     CLIMA(ng)%M2nudgcof(Iend+1,j  ))
!                 obc_in =obcfac(ng)*obc_out
!               ELSE
                  obc_out=M2obc_out(ng,ieast)
                  obc_in =M2obc_in (ng,ieast)
!               END IF
                IF ((dVdt*dVdx).lt.0.0_r8) THEN
                  tau=obc_in
                ELSE
                  tau=obc_out
                END IF
                tau=tau*dt2d
              END IF

              IF ((dVdt*(grad(Iend,j-1)+                                &
     &                   grad(Iend,j  ))).gt.0.0_r8) THEN
                dVde=grad(Iend,j-1)
              ELSE
                dVde=grad(Iend,j  )
              END IF
              cff=MAX(dVdx*dVdx+dVde*dVde,eps)
              IF ((dVdt*dVdx).lt.0.0_r8) dVdt=0.0_r8
              Cx=dVdt*dVdx
#ifdef RADIATION_2D
              Ce=MIN(cff,MAX(dVdt*dVde,-cff))
#else
              Ce=0.0_r8
#endif
#if defined CELERITY_WRITE && defined FORWARD_WRITE
              BOUNDARY(ng)%vbar_east_Cx(j)=Cx
              BOUNDARY(ng)%vbar_east_Ce(j)=Ce
              BOUNDARY(ng)%vbar_east_C2(j)=cff
#endif
              vbar(Iend+1,j,kout)=(cff*vbar(Iend+1,j,know)+             &
     &                             Cx *vbar(Iend  ,j,kout)-             &
     &                             MAX(Ce,0.0_r8)*grad(Iend+1,j-1)-     &
     &                             MIN(Ce,0.0_r8)*grad(Iend+1,j  ))/    &
     &                            (cff+Cx)

              IF (LBC(ieast,isVbar,ng)%nudging) THEN
                vbar(Iend+1,j,kout)=vbar(Iend+1,j,kout)+                &
     &                              tau*(BOUNDARY(ng)%vbar_east(j)-     &
     &                                   vbar(Iend+1,j,know))
              END IF
#ifdef MASKING
              vbar(Iend+1,j,kout)=vbar(Iend+1,j,kout)*                  &
     &                            GRID(ng)%vmask(Iend+1,j)
#endif
            END IF
          END DO
!
!  Eastern edge, Chapman boundary condition.
!
        ELSE IF (LBC(ieast,isVbar,ng)%Flather.or.                       &
     &           LBC(ieast,isVbar,ng)%reduced.or.                       &
     &           LBC(ieast,isVbar,ng)%Shchepetkin) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%east(j)) THEN
              cff=dt2d*0.5_r8*(GRID(ng)%pm(Iend,j-1)+                   &
     &                         GRID(ng)%pm(Iend,j  ))
#ifdef ICESHELF
            cff1=SQRT(g*0.5_r8*(GRID(ng)%h(Iend,j-1)-                   &
     &                          ABS(GRID(ng)%zice(Iend,j-1))+           &
     &                          zeta(Iend,j-1,know)+                    &
     &                          GRID(ng)%h(Iend,j  )-                   &
     &                          ABS(GRID(ng)%zice(Iend,j  ))+           &
     &                          zeta(Iend,j  ,know)))
#else
              cff1=SQRT(g*0.5_r8*(GRID(ng)%h(Iend,j-1)+                 &
     &                            zeta(Iend,j-1,know)+                  &
     &                            GRID(ng)%h(Iend,j  )+                 &
     &                            zeta(Iend,j  ,know)))
#endif
              Cx=cff*cff1
              cff2=1.0_r8/(1.0_r8+Cx)
              vbar(Iend+1,j,kout)=cff2*(vbar(Iend+1,j,know)+            &
     &                                  Cx*vbar(Iend,j,kout))
#ifdef MASKING
              vbar(Iend+1,j,kout)=vbar(Iend+1,j,kout)*                  &
     &                            GRID(ng)%vmask(Iend+1,j)
#endif
            END IF
          END DO
!
!  Eastern edge, clamped boundary condition.
!
        ELSE IF (LBC(ieast,isVbar,ng)%clamped) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%east(j)) THEN
              vbar(Iend+1,j,kout)=BOUNDARY(ng)%vbar_east(j)
#ifdef MASKING
              vbar(Iend+1,j,kout)=vbar(Iend+1,j,kout)*                  &
     &                            GRID(ng)%vmask(Iend+1,j)
#endif
            END IF
          END DO
!
!  Eastern edge, gradient boundary condition.
!
        ELSE IF (LBC(ieast,isVbar,ng)%gradient) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%east(j)) THEN
              vbar(Iend+1,j,kout)=vbar(Iend,j,kout)
#ifdef MASKING
              vbar(Iend+1,j,kout)=vbar(Iend+1,j,kout)*                  &
     &                            GRID(ng)%vmask(Iend+1,j)
#endif
            END IF
          END DO
!
!  Eastern edge, closed boundary condition: free slip (gamma2=1)  or
!                                           no   slip (gamma2=-1).
!
        ELSE IF (LBC(ieast,isVbar,ng)%closed) THEN
          IF (NSperiodic(ng)) THEN
            Jmin=JstrV
            Jmax=Jend
          ELSE
            Jmin=Jstr
            Jmax=JendR
          END IF
          DO j=Jmin,Jmax
            IF (LBC_apply(ng)%east(j)) THEN
              vbar(Iend+1,j,kout)=gamma2(ng)*vbar(Iend,j,kout)
#ifdef MASKING
              vbar(Iend+1,j,kout)=vbar(Iend+1,j,kout)*                  &
     &                            GRID(ng)%vmask(Iend+1,j)
#endif
            END IF
          END DO
        END IF
      END IF
!
!-----------------------------------------------------------------------
!  Boundary corners.
!-----------------------------------------------------------------------
!
      IF (.not.(EWperiodic(ng).or.NSperiodic(ng))) THEN
        IF (DOMAIN(ng)%SouthWest_Corner(tile)) THEN
          IF (LBC_apply(ng)%south(Istr-1).and.                          &
     &        LBC_apply(ng)%west (Jstr  )) THEN
            vbar(Istr-1,Jstr,kout)=0.5_r8*(vbar(Istr  ,Jstr  ,kout)+    &
     &                                     vbar(Istr-1,Jstr+1,kout))
          END IF
        END IF
        IF (DOMAIN(ng)%SouthEast_Corner(tile)) THEN
          IF (LBC_apply(ng)%south(Iend+1).and.                          &
     &        LBC_apply(ng)%east (Jstr  )) THEN
            vbar(Iend+1,Jstr,kout)=0.5_r8*(vbar(Iend  ,Jstr  ,kout)+    &
     &                                     vbar(Iend+1,Jstr+1,kout))
          END IF
        END IF
        IF (DOMAIN(ng)%NorthWest_Corner(tile)) THEN
          IF (LBC_apply(ng)%north(Istr-1).and.                          &
     &        LBC_apply(ng)%west (Jend+1)) THEN
            vbar(Istr-1,Jend+1,kout)=0.5_r8*(vbar(Istr-1,Jend  ,kout)+  &
     &                                       vbar(Istr  ,Jend+1,kout))
          END IF
        END IF
        IF (DOMAIN(ng)%NorthEast_Corner(tile)) THEN
          IF (LBC_apply(ng)%north(Iend+1).and.                          &
     &        LBC_apply(ng)%east (Jend+1)) THEN
            vbar(Iend+1,Jend+1,kout)=0.5_r8*(vbar(Iend+1,Jend  ,kout)+  &
     &                                      vbar(Iend  ,Jend+1,kout))
          END IF
        END IF
      END IF

#if defined WET_DRY
!
!-----------------------------------------------------------------------
!  Impose wetting and drying conditions.
!-----------------------------------------------------------------------
!
      IF (.not.EWperiodic(ng)) THEN
        IF (DOMAIN(ng)%Western_Edge(tile)) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%west(j)) THEN
              cff1=ABS(ABS(GRID(ng)%vmask_wet(Istr-1,j))-1.0_r8)
              cff2=0.5_r8+DSIGN(0.5_r8,vbar(Istr-1,j,kout))*            &
     &                    GRID(ng)%vmask_wet(Istr-1,j)
              cff=0.5_r8*GRID(ng)%vmask_wet(Istr-1,j)*cff1+             &
     &            cff2*(1.0_r8-cff1)
              vbar(Istr,j,kout)=vbar(Istr,j,kout)*cff
            END IF
          END DO
        END IF
        IF (DOMAIN(ng)%Eastern_Edge(tile)) THEN
          DO j=JstrV,Jend
            IF (LBC_apply(ng)%east(j)) THEN
              cff1=ABS(ABS(GRID(ng)%vmask_wet(Iend+1,j))-1.0_r8)
              cff2=0.5_r8+DSIGN(0.5_r8,vbar(Iend+1,j,kout))*            &
     &                    GRID(ng)%vmask_wet(Iend+1,j)
              cff=0.5_r8*GRID(ng)%vmask_wet(Iend+1,j)*cff1+             &
     &            cff2*(1.0_r8-cff1)
              vbar(Iend+1,j,kout)=vbar(Iend+1,j,kout)*cff
            END IF
          END DO
        END IF
      END IF

      IF (.not.NSperiodic(ng)) THEN
        IF (DOMAIN(ng)%Southern_Edge(tile)) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%south(i)) THEN
              cff1=ABS(ABS(GRID(ng)%vmask_wet(i,Jstr))-1.0_r8)
              cff2=0.5_r8+DSIGN(0.5_r8,vbar(i,Jstr,kout))*              &
     &                    GRID(ng)%vmask_wet(i,Jstr)
              cff=0.5_r8*GRID(ng)%vmask_wet(i,Jstr)*cff1+               &
     &            cff2*(1.0_r8-cff1)
              vbar(i,Jstr,kout)=vbar(i,Jstr,kout)*cff
            END IF
          END DO
        END IF
        IF (DOMAIN(ng)%Northern_Edge(tile)) THEN
          DO i=Istr,Iend
            IF (LBC_apply(ng)%north(i)) THEN
              cff1=ABS(ABS(GRID(ng)%vmask_wet(i,Jend+1))-1.0_r8)
              cff2=0.5_r8+DSIGN(0.5_r8,vbar(i,Jend+1,kout))*            &
     &                    GRID(ng)%vmask_wet(i,Jend+1)
              cff=0.5_r8*GRID(ng)%vmask_wet(i,Jend+1)*cff1+             &
     &            cff2*(1.0_r8-cff1)
              vbar(i,Jend+1,kout)=vbar(i,Jend+1,kout)*cff
            END IF
          END DO
        END IF
      END IF

      IF (.not.(EWperiodic(ng).or.NSperiodic(ng))) THEN
        IF (DOMAIN(ng)%SouthWest_Corner(tile)) THEN
          IF (LBC_apply(ng)%south(Istr-1).and.                          &
     &        LBC_apply(ng)%west (Jstr  )) THEN
            cff1=ABS(ABS(GRID(ng)%vmask_wet(Istr-1,Jstr))-1.0_r8)
            cff2=0.5_r8+DSIGN(0.5_r8,vbar(Istr-1,Jstr,kout))*           &
     &                  GRID(ng)%vmask_wet(Istr-1,Jstr)
            cff=0.5_r8*GRID(ng)%vmask_wet(Istr-1,Jstr)*cff1+            &
     &          cff2*(1.0_r8-cff1)
            vbar(Istr-1,Jstr,kout)=vbar(Istr-1,Jstr,kout)*cff
          END IF
        END IF
        IF (DOMAIN(ng)%SouthEast_Corner(tile)) THEN
          IF (LBC_apply(ng)%south(Iend+1).and.                          &
     &        LBC_apply(ng)%east (Jstr  )) THEN
            cff1=ABS(ABS(GRID(ng)%vmask_wet(Iend+1,Jstr))-1.0_r8)
            cff2=0.5_r8+DSIGN(0.5_r8,vbar(Iend+1,Jstr,kout))*           &
     &                  GRID(ng)%vmask_wet(Iend+1,Jstr)
            cff=0.5_r8*GRID(ng)%vmask_wet(Iend+1,Jstr)*cff1+            &
     &          cff2*(1.0_r8-cff1)
            vbar(Iend+1,Jstr,kout)=vbar(Iend+1,Jstr,kout)*cff
          END IF
        END IF
        IF (DOMAIN(ng)%NorthWest_Corner(tile)) THEN
          IF (LBC_apply(ng)%north(Istr-1).and.                          &
     &        LBC_apply(ng)%west (Jend+1)) THEN
            cff1=ABS(ABS(GRID(ng)%vmask_wet(Istr-1,Jend+1))-1.0_r8)
            cff2=0.5_r8+DSIGN(0.5_r8,vbar(Istr-1,Jend+1,kout))*         &
     &                  GRID(ng)%vmask_wet(Istr-1,Jend+1)
            cff=0.5_r8*GRID(ng)%vmask_wet(Istr-1,Jend+1)*cff1+          &
     &          cff2*(1.0_r8-cff1)
            vbar(Istr-1,Jend+1,kout)=vbar(Istr-1,Jend+1,kout)*cff
          END IF
        END IF
        IF (DOMAIN(ng)%NorthEast_Corner(tile)) THEN
          IF (LBC_apply(ng)%north(Iend+1).and.                          &
     &        LBC_apply(ng)%east (Jend+1)) THEN
            cff1=ABS(ABS(GRID(ng)%vmask_wet(Iend+1,Jend+1))-1.0_r8)
            cff2=0.5_r8+DSIGN(0.5_r8,vbar(Iend+1,Jend+1,kout))*         &
     &                  GRID(ng)%vmask_wet(Iend+1,Jend+1)
            cff=0.5_r8*GRID(ng)%vmask_wet(Iend+1,Jend+1)*cff1+          &
     &          cff2*(1.0_r8-cff1)
            vbar(Iend+1,Jend+1,kout)=vbar(Iend+1,Jend+1,kout)*cff
          END IF
        END IF
      END IF
#endif

      RETURN

      END SUBROUTINE v2dbc_tile
      END MODULE v2dbc_mod
