#include "cppdefs.h"
#if defined ADJOINT && !defined SOLVE3D
      SUBROUTINE ad_main2d (ng)
!
!svn $Id: ad_main2d.F 408 2009-11-04 20:36:07Z arango $
!================================================== Hernan G. Arango ===
!  Copyright (c) 2002-2009 The ROMS/TOMS Group       Andrew M. Moore   !
!    Licensed under a MIT/X style license                              !
!    See License_ROMS.txt                                              !
!=======================================================================
!                                                                      !
!  This subroutine is the main driver for adjoint  ROMS/TOMS  when     !
!  configurated as shallow water (barotropic) ocean model only. It     !
!  advances backward the vertically integrated primitive equations     !
!  for a single time step.                                             !
!                                                                      !
!=======================================================================
!
      USE mod_param
      USE mod_parallel
# ifdef MODEL_COUPLING
      USE mod_coupler
# endif
# ifdef FOUR_DVAR
      USE mod_fourdvar
# endif
      USE mod_iounits
      USE mod_scalars
      USE mod_stepping
# ifdef SO_SEMI
      USE mod_storage
# endif
!
# if defined AD_SENSITIVITY   || defined OBS_SENSITIVITY   || \
     defined OPT_OBSERVATIONS || defined SENSITIVITY_4DVAR
      USE adsen_force_mod, ONLY : adsen_force
# endif
      USE ad_diag_mod, ONLY : ad_diag
# ifdef WEAK_CONSTRAINT
      USE ad_forcing_mod, ONLY : ad_forcing
# endif
# ifdef ADJUST_WSTRESS
      USE ad_frc_adjust_mod, ONLY : ad_frc_adjust
# endif
      USE ad_ini_fields_mod, ONLY : ad_ini_fields, ad_ini_zeta
# if defined FOUR_DVAR && defined OBSERVATIONS
#  ifdef WEAK_CONSTRAINT
      USE ad_htobs_mod, ONLY : ad_htobs
#  else
      USE ad_misfit_mod, ONLY : ad_misfit
#  endif
# endif
# ifdef ADJUST_BOUNDARY
      USE ad_obc_adjust_mod, ONLY : ad_obc_adjust
# endif
# ifdef NEARSHORE_MELLOR_NOT_YET
!!    USE ad_radiation_stress_mod, ONLY : ad_radiation_stress
# endif
# ifdef AVERAGES
      USE ad_set_avg_mod, ONLY : ad_set_avg
# endif
# if defined SSH_TIDES_NOT_YET || defined UV_TIDES_NOT_YET
!!    USE ad_set_tides_mod, ONLY : ad_set_tides
# endif
      USE ad_set_vbc_mod, ONLY: ad_set_vbc
      USE ad_step2d_mod, ONLY : ad_step2d
# ifdef FLOATS_NOT_YET
!!    USE ad_step_floats_mod, ONLY : tl_step_floats
# endif
# ifdef WEAK_CONSTRAINT
      USE frc_weak_mod, ONLY : frc_ADgather, frc_clear
# endif
# ifdef AIR_OCEAN_NOT_YET
      USE ocean_coupler_mod, ONLY : atmos_coupling
# endif
# ifdef WAVES_OCEAN_NOT_YET
      USE ocean_coupler_mod, ONLY : waves_coupling
# endif
# ifdef ASSIMILATION
!!    USE oi_update_mod, ONLY : oi_update
# endif
# ifdef SO_SEMI
      USE packing_mod, ONLY : so_pack
# endif
!
      implicit none
!
!  Imported variable declarations.
!
      integer, intent(in) :: ng
!
!  Local variable declarations.
!
      logical:: backward = .TRUE.

      integer :: my_iif, next_indx1, subs, tile, thread
# ifdef SO_SEMI
      integer, save :: SOrec = 0
# endif
# ifdef FLOATS_NOT_YET
      integer :: Lend, Lstr, chunk_size
# endif
      integer :: ksav, ktmp

# ifdef FOUR_DVAR
      real(r8) :: HalfDT
# endif
!
!=======================================================================
!  Time-step adjoint vertically integrated equations.
!=======================================================================
!
!  Set time clock.
!
      time(ng)=time(ng)-dt(ng)
      tdays(ng)=time(ng)*sec2day
      CALL time_string (time(ng), time_code(ng))
!
!-----------------------------------------------------------------------
!  Read in required data, if any, from input NetCDF files.
!-----------------------------------------------------------------------
!
      CALL ad_get_data (ng)
      IF (exit_flag.ne.NoError) RETURN
!
!-----------------------------------------------------------------------
!  Process input data, if any: time interpolate between snapshots.
!  If appropriate, compute and report diagnostics.
!-----------------------------------------------------------------------
!
!$OMP PARALLEL DO PRIVATE(thread,subs,tile), SHARED(ng,numthreads)
      DO thread=0,numthreads-1
        subs=NtileX(ng)*NtileE(ng)/numthreads
        DO tile=subs*thread,subs*(thread+1)-1,+1     ! irreversible loop
          CALL ad_set_data (ng, TILE)
# ifdef AVERAGES
          CALL ad_set_avg (ng, TILE)
# endif
# ifdef DIAGNOSTICS
!!        CALL ad_set_diags (ng, TILE)
# endif
          CALL ad_diag (ng, TILE)
        END DO
      END DO
!$OMP END PARALLEL DO
      IF (exit_flag.ne.NoError) RETURN

# if (defined FOUR_DVAR && !defined OBS_SENSITIVITY) && \
      defined OBSERVATIONS
!
!-----------------------------------------------------------------------
!  If appropriate, read observation and model state at observation
!  locations.  Then, compute adjoint misfit forcing terms.
!-----------------------------------------------------------------------
!
#  ifdef SENSITIVITY_4DVAR
      IF (.not.LsenPSAS(ng)) THEN
#  endif
        HalfDT=0.5_r8*dt(ng)
        IF (((time(ng)-HalfDT).le.ObsTime(ng)).and.                     &
     &      (ObsTime(ng).lt.(time(ng)+HalfDT))) THEN
          ProcessObs(ng)=.TRUE.
          CALL obs_read (ng, iADM, backward)
          IF (exit_flag.ne.NoError) RETURN
        ELSE
          ProcessObs(ng)=.FALSE.
        END IF
!
!$OMP PARALLEL DO PRIVATE(thread,subs,tile), SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
#  ifdef WEAK_CONSTRAINT
            CALL ad_htobs (ng, TILE, iADM)
#  else
            CALL ad_misfit (ng, TILE, iADM)
#  endif
          END DO
        END DO
!$OMP END PARALLEL DO
        IF (exit_flag.ne.NoError) RETURN
#  ifdef SENSITIVITY_4DVAR
      END IF
#  endif
# endif

# ifdef WEAK_CONSTRAINT
!
!-----------------------------------------------------------------------
!  If appropriate, add representer coefficients (Beta hat) impulse
!  forcing to adjoint solution. Read next impulse record, if available.
!-----------------------------------------------------------------------
!
      IF (ProcessObs(ng)) THEN
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL ad_forcing (ng, TILE, knew(ng), nnew(ng))
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF
# endif
!
!  Avoid time-stepping if additional delayed IO time-step.
!
      IF (iic(ng).ne.ntstart(ng)) THEN

# ifdef FLOATS_NOT_YET
!
!-----------------------------------------------------------------------
!  Compute Lagrangian drifters trajectories.
!-----------------------------------------------------------------------
!
!  Shift floats time indices.
!
        IF (Lfloats(Ng)) THEN
          nfp1(ng)=MOD(nfp1(ng)+1,NFT+1)
          nf(ng)  =MOD(nf(ng)  +1,NFT+1)
          nfm1(ng)=MOD(nfm1(ng)+1,NFT+1)
          nfm2(ng)=MOD(nfm2(ng)+1,NFT+1)
          nfm3(ng)=MOD(nfm3(ng)+1,NFT+1)
!
!$OMP PARALLEL DO PRIVATE(thread,chunk_size,Lstr,Lend)                  &
!$OMP&            SHARED(ng,numthreads,Nfloats)
          DO thread=0,numthreads-1
            chunk_size=(Nfloats(ng)+numthreads-1)/numthreads
            Lstr=1+thread*chunk_size
            Lend=MIN(Nfloats(ng),Lstr+chunk_size-1)
            CALL ad_step_floats (ng, Lstr, Lend)
          END DO
!$OMP END PARALLEL DO
        END IF
# endif
!
!-----------------------------------------------------------------------
!  Solve the vertically integrated primitive equations for the
!  free-surface and momentum components.
!-----------------------------------------------------------------------
!
!  Corrector step - Apply 2D time-step corrector scheme.  Notice that
!  ==============   there is not need for a corrector step during the
!  auxiliary (nfast+1) time-step.
!
        my_iif=1
        iif(ng)=my_iif
        nfast(ng)=1
        IF (my_iif.lt.(nfast(ng)+1))then
!$OMP PARALLEL DO PRIVATE(thread,subs,tile), SHARED(ng,numthreads)
          DO thread=0,numthreads-1
            subs=NtileX(ng)*NtileE(ng)/numthreads
            DO tile=subs*thread,subs*(thread+1)-1,+1
              CALL ad_step2d (ng, TILE)
            END DO
          END DO
!$OMP END PARALLEL DO
        END IF
!
!  Set time indices for corrector step.
!
        next_indx1=3-indx1(ng)
        IF (.not.PREDICTOR_2D_STEP(ng)) THEN
          PREDICTOR_2D_STEP(ng)=.TRUE.
          ktmp=knew(ng)
          ksav=kstp(ng)
          knew(ng)=krhs(ng)
          kstp(ng)=ktmp
          krhs(ng)=ksav
        END IF
!
!  Predictor step - Advance barotropic equations using 2D time-step
!  ==============   predictor scheme.
!
!$OMP PARALLEL DO PRIVATE(thread,subs,tile), SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*(thread+1)-1,subs*thread,-1
            CALL ad_step2d (ng, TILE)
          END DO
        END DO
!$OMP END PARALLEL DO
!
!  Set time indices for predictor step. The PREDICTOR_2D_STEP switch
!  it is assumed to be false before the first time-step.
!
        IF (PREDICTOR_2D_STEP(ng).and.(iic(ng).ne.ntend(ng))) THEN
          PREDICTOR_2D_STEP(ng)=.FALSE.
          ksav=knew(ng)
          knew(ng)=krhs(ng)
          krhs(ng)=ksav
          iif(ng)=my_iif
        END IF
      END IF

# ifdef SO_SEMI
!
!-----------------------------------------------------------------------
!  If stochastic optimals with respect the seminorm of chosen
!  functional, pack adjoint state surface forcing needed by the
!  dynamical propagator.
!-----------------------------------------------------------------------
!
      IF (MOD(iic(ng)-1,nADJ(ng)).eq.0) THEN
        SOrec=SOrec+1
!$OMP PARALLEL DO PRIVATE(thread,subs,tile,SOrec)                       &
!$OMP&            SHARED(ng,numthreads,Nstr,Nend)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL so_pack (ng, TILE, Nstr(ng), Nend(ng), SOrec)
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF
# endif
!
!-----------------------------------------------------------------------
!  Set vertical boundary conditions. Process tidal forcing.
!-----------------------------------------------------------------------
!
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(numthreads)
      DO thread=0,numthreads-1
        subs=NtileX(ng)*NtileE(ng)/numthreads
        DO tile=subs*thread,subs*(thread+1)-1,+1
# if defined SSH_TIDES_NOT_YET || defined UV_TIDES_NOT_YET
          CALL ad_set_tides (ng, TILE)
# endif
          CALL ad_set_vbc (ng, TILE)
        END DO
      END DO
!$OMP END PARALLEL DO

# ifdef NEARSHORE_MELLOR_NOT_YET
!
!-----------------------------------------------------------------------
!  Compute radiation stress terms.
!-----------------------------------------------------------------------
!
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
      DO thread=0,numthreads-1
        subs=NtileX(ng)*NtileE(ng)/numthreads
        DO tile=subs*(thread+1)-1,subs*thread,-1
          CALL ad_radiation_stress (ng, TILE)
        END DO
      END DO
!$OMP END PARALLEL DO
# endif

# ifdef WAVES_OCEAN_NOT_YET
!
!-----------------------------------------------------------------------
!  Couple to waves model every CoupleSteps(Iwaves,ng) timesteps: get
!  waves/sea fluxes.
!-----------------------------------------------------------------------
!
      IF ((iic(ng).ne.ntstart(ng)).and.                                 &
     &    MOD(iic(ng)-1,CoupleSteps(Iwaves,ng)).eq.0) THEN
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL waves_coupling (ng, TILE)
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF
# endif

# ifdef AIR_OCEAN_NOT_YET
!
!-----------------------------------------------------------------------
!  Couple to atmospheric model every CoupleSteps(Iatmos) timesteps: get
!  air/sea fluxes.
!-----------------------------------------------------------------------
!
      IF ((iic(ng).ne.ntstart(ng)).and.                                 &
     &    MOD(iic(ng)-1,CoupleSteps(Iatmos,ng)).eq.0) THEN
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*(thread+1)-1,subs*thread,-1
            CALL atmos_coupling (ng, TILE)
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF
# endif
!
!-----------------------------------------------------------------------
!  If not a restart, initialize all time levels and compute other
!  initial fields.
!-----------------------------------------------------------------------
!
      IF (iic(ng).eq.ntend(ng)) THEN
!
!  Initialize other state variables.
!
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*(thread+1)-1,subs*thread,-1
            CALL ad_ini_fields (ng, TILE, iADM)
          END DO
        END DO
!$OMP END PARALLEL DO
!
!  Initialize free-surface.
!
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL ad_ini_zeta (ng, TILE, iADM)
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF

# ifdef ADJUST_WSTRESS
!
!-----------------------------------------------------------------------
!  Interpolate surface forcing increments and adjust surface forcing.
!  Skip first timestep.
!-----------------------------------------------------------------------
!
      IF (iic(ng).ne.ntstart(ng)) THEN
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL ad_frc_adjust (ng, TILE, Lfout(ng))
          END DO
        END DO
!$OMP END PARALLEL DO
      END DO
# endif

# ifdef ADJUST_BOUNDARY
!
!-----------------------------------------------------------------------
!  Interpolate open boundary increments and adjust open boundaries.
!  Skip first timestep.
!-----------------------------------------------------------------------
!
      IF (iic(ng).ne.ntstart(ng)) THEN
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL ad_obc_adjust (ng, TILE, Lbout(ng))
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF
# endif

# ifdef WEAK_CONSTRAINT
!
!-----------------------------------------------------------------------
!  Gather weak constraint forcing to storage arrays.
!-----------------------------------------------------------------------
!
      IF (iic(ng).ne.ntstart(ng)) THEN
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL frc_ADgather (ng, TILE)
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF
# endif
!
!-----------------------------------------------------------------------
!  If appropriate, write out fields into output NetCDF files.
!-----------------------------------------------------------------------
!
      CALL ad_output (ng)
      IF (exit_flag.ne.NoError) RETURN

# ifdef WEAK_CONSTRAINT
!
!-----------------------------------------------------------------------
!  Copy storage arrays index 1 into index 2, and clear index 1.
!-----------------------------------------------------------------------
!
      IF (MOD(iic(ng)-1,nADJ(ng)).eq.0) THEN
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
        DO thread=0,numthreads-1
          subs=NtileX(ng)*NtileE(ng)/numthreads
          DO tile=subs*thread,subs*(thread+1)-1,+1
            CALL frc_clear (ng, TILE)
          END DO
        END DO
!$OMP END PARALLEL DO
      END IF
# endif

# if defined AD_SENSITIVITY   || defined OBS_SENSITIVITY   || \
     defined OPT_OBSERVATIONS || defined SENSITIVITY_4DVAR
!
!-----------------------------------------------------------------------
!  Add appropriate forcing terms to the adjoint model. The form of the
!  forcing depends on the functional whose sensitivity is required.
!-----------------------------------------------------------------------
!
#  ifdef SENSITIVITY_4DVAR
      IF (LsenPSAS(ng)) THEN
#  endif
#  if !defined AD_IMPULSE
        IF ((DendS(ng).ge.tdays(ng)).and.(tdays(ng).ge.DstrS(ng))) THEN
#  endif
!$OMP PARALLEL DO PRIVATE(thread,subs,tile) SHARED(ng,numthreads)
          DO thread=0,numthreads-1
            subs=NtileX(ng)*NtileE(ng)/numthreads
            DO tile=subs*thread,subs*(thread+1)-1,+1
              CALL adsen_force (ng, TILE)
            END DO
          END DO
!$OMP END PARALLEL DO
#  if !defined AD_IMPULSE
        END IF
#  endif
#  ifdef SENSITIVITY_4DVAR
      END IF
#  endif
# endif

      RETURN
      END SUBROUTINE ad_main2d
#else
      SUBROUTINE ad_main2d
      RETURN
      END SUBROUTINE ad_main2d
#endif