C $Header: /home/ubuntu/mnt/e9_copy/MITgcm/model/src/diags_phi_rlow.F,v 1.2 2003/02/18 15:30:47 jmc Exp $
C $Name: checkpoint48g_post $

#include "CPP_OPTIONS.h"

CBOP
C     !ROUTINE: DIAGS_PHI_RLOW
C     !INTERFACE:
      SUBROUTINE DIAGS_PHI_RLOW( 
     I                       k, bi, bj, iMin,iMax, jMin,jMax,
     I                       phiHydF, phiHydC, alphRho, tFld, sFld,
     I                       myTime, myIter, myThid)
C     !DESCRIPTION: \bv
C     *==========================================================*
C     | S/R DIAGS_PHI_RLOW                                    
C     | o Diagnose Phi-Hydrostatic at r-lower boundary
C     |   = bottom pressure (ocean in z-coord) ; 
C     |   = sea surface elevation (ocean in p-coord) ;
C     |   = height at the top of atmosphere (in p-coord) ;
C     *==========================================================*
C     \ev

C     !USES:
      IMPLICIT NONE
C     == Global variables ==
#include "SIZE.h"
#include "EEPARAMS.h"
#include "PARAMS.h"
#include "GRID.h"
#include "SURFACE.h"
#include "DYNVARS.h"

C     !INPUT/OUTPUT PARAMETERS:
C     == Routine Arguments ==
C     bi,bj      :: tile index            
C     iMin,iMax,jMin,jMax :: Loop counters
C     phiHydF    :: hydrostatic potential anomaly at middle between 
C                   2 centers k & k+1 (interface k+1)
C     phiHydC    :: hydrostatic potential anomaly at cell center
C                  (atmos: =Geopotential ; ocean-z: =Pressure/rho)
C     alphRho    :: Density (z-coord) or specific volume (p-coord)
C     tFld       :: Potential temp.
C     sFld       :: Salinity 
C     myTime :: Current time
C     myIter :: Current iteration number
C     myThid :: Instance number for this call of the routine.
      INTEGER k, bi,bj, iMin,iMax, jMin,jMax
      _RL phiHydF(1-OLx:sNx+OLx,1-OLy:sNy+OLy)
      _RL phiHydC(1-OLx:sNx+OLx,1-OLy:sNy+OLy)
      _RL alphRho(1-OLx:sNx+OLx,1-OLy:sNy+OLy)
      _RL tFld(1-OLx:sNx+OLx,1-OLy:sNy+OLy,Nr,nSx,nSy)
      _RL sFld(1-OLx:sNx+OLx,1-OLy:sNy+OLy,Nr,nSx,nSy)
      _RL myTime
      INTEGER myIter, myThid

#ifdef INCLUDE_PHIHYD_CALCULATION_CODE

C     !LOCAL VARIABLES:
C     == Local variables ==
C     i,j :: Loop counters
      INTEGER i,j
      _RL zero, one, half
      _RL ddRloc, ratioRm, ratioRp
      PARAMETER ( zero= 0. _d 0 , one= 1. _d 0 , half= .5 _d 0 )
CEOP

      IF ( buoyancyRelation .EQ. 'OCEANIC' ) THEN

C----- Compute bottom pressure deviation from gravity*rho0*H
C      Start from phiHyd at the (bottom) tracer point and add Del_h*g*rho' 
C      with Del_h = distance from the bottom up to tracer point

       IF (integr_GeoPot.EQ.1) THEN
C  --  Finite Volume Form

         DO j=jMin,jMax
          DO i=iMin,iMax
           IF ( k .EQ. kLowC(i,j,bi,bj) ) THEN
             ddRloc = rC(k)-R_low(i,j,bi,bj)
             phiHydLow(i,j,bi,bj) = phiHydC(i,j)
     &            + ddRloc*gravity*alphRho(i,j)*recip_rhoConst
           ENDIF
          ENDDO
         ENDDO

       ELSE
C  --  Finite Difference Form

         ratioRm = one
         ratioRp = one
         IF (k.GT.1 ) ratioRm = half*drC(k)/(rF(k)-rC(k))
         IF (k.LT.Nr) ratioRp = half*drC(k+1)/(rC(k)-rF(k+1))

         DO j=jMin,jMax
          DO i=iMin,iMax
           IF ( k .EQ. kLowC(i,j,bi,bj) ) THEN
             ddRloc = rC(k)-R_low(i,j,bi,bj)
             phiHydLow(i,j,bi,bj) = phiHydC(i,j)
     &                  +( MIN(zero,ddRloc)*ratioRm
     &                    +MAX(zero,ddRloc)*ratioRp
     &                   )*gravity*alphRho(i,j)*recip_rhoConst
           ENDIF
          ENDDO
         ENDDO

C  --  end if integr_GeoPot = ...
       ENDIF
        
C  -- end buoyancyR = Oceanic (z)
      ENDIF

      IF (k.EQ.Nr) THEN
C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|
C  --  last level (bottom): rescale (r*) and add surface contribution

       IF ( buoyancyRelation .EQ. 'OCEANICP' .OR.
     &      buoyancyRelation .EQ. 'ATMOSPHERIC' ) THEN
C  -- P coordinate : Phi(R_low) is simply at the top :
        DO j=jMin,jMax
         DO i=iMin,iMax
           phiHydLow(i,j,bi,bj) = phiHydF(i,j)
         ENDDO
        ENDDO
       ENDIF

        DO j=jMin,jMax
         DO i=iMin,iMax
           phiHydLow(i,j,bi,bj) = phiHydLow(i,j,bi,bj)
     &            + Bo_surf(i,j,bi,bj)*etaN(i,j,bi,bj)
     &            + phi0surf(i,j,bi,bj) 
         ENDDO
        ENDDO

C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|
C  -- end if k=Nr.
      ENDIF

#endif /* INCLUDE_PHIHYD_CALCULATION_CODE */

      RETURN
      END