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      SUBROUTINE gd2mvoad_1obs (cdvarname, klev) 9
*
#if defined (DOC)
*
***s/r gd2mvoad_1obs  - Adjoint of the horizontal interpolation of the model variables
*     .            in grid-point space to observation locations.
*     .           Simple multiplication by the weights of
*     .           the horizontal bilinear interpolation.
*     .           (adapted from BILINAD)
*
*
*Author  : L. Fillion *ARMA/EC 16 Jun 2010 (from gd2mvoad.ftn prior to MPI)
*
*Revision:
*
**    Purpose:  Update the estimate of GD from the gradient components
*               at the observation points which have been stored in
*               GOMOBS
*
* Arguments
*     CDVARNAME: identificator of the variable to be treated
*     KLEV     : number of levels (typically 1 for 2D-fields and NFLEV for 3D-fields)
*
*
*
#endif
      IMPLICIT NONE
*implicits
#include "pardim.cdk"
#include "comdim.cdk"
#include "comdimo.cdk"
#include "comleg.cdk"
#include "comgem.cdk"
#include "comgd0.cdk"
#include "comcst.cdk"
#include "comoahdr.cdk"
#include "comoabdy.cdk"
#include "comoba.cdk"
#include "commvo.cdk"
*
*     Arguments
*
      character*2 cdvarname
      integer klev
*
*     Local Variables
*
      INTEGER   JLEV, JGL, JLON, JOBS, IOBTYP
      INTEGER   ILON, ILOS, ILA, IMIDDLE, ISYM, IMAX
      REAL*8    DLMEAN, DLMEAS, DLLAO, DLLOO, DLDLON, DLDLOS
      REAL*8    DLDXN, DLDXS, DLDY, DLW1, DLW2, DLW3, DLW4
*
      real*8  zfield(nibeg:niend,1:klev,njbeg:njend)
     S     , zprofil(1:klev,nobtot)
*
*     Transfer Grid point field into local array (for generecity)
*
      zfield(:,:,:) = 0.
      zprofil(:,:)  = 0.
*
*
      SELECT CASE (CDVARNAME)
*
*     2D fields
*
      CASE('TG')
         ZPROFIL(1:KLEV,1:NOBTOT)= GOMTGR(1:KLEV,1:NOBTOT)
      CASE('PS')
         ZPROFIL(1:KLEV,1:NOBTOT)= GOMPS(1:KLEV,1:NOBTOT)
*
*     3D fields
*
      CASE('TT')
           ZPROFIL(1:KLEV,1:NOBTOT) = GOMT (1:KLEV,1:NOBTOT)
      CASE('Q0')
         ZPROFIL(1:KLEV,1:NOBTOT)   = GOMQ (1:KLEV,1:NOBTOT)
      CASE('O3')
         ZPROFIL(1:KLEV,1:NOBTOT)   = GOMOZ(1:KLEV,1:NOBTOT)
      CASE('TR')
         ZPROFIL(1:KLEV,1:NOBTOT)   = GOMTR(1:KLEV,1:NOBTOT)
      CASE('UU')
         ZPROFIL(1:KLEV,1:NOBTOT)   = GOMU(1:KLEV,1:NOBTOT)
      CASE('VV')
         ZPROFIL(1:KLEV,1:NOBTOT)   = GOMV(1:KLEV,1:NOBTOT)
      CASE('GZ')
         ZPROFIL(1:KLEV,1:NOBTOT)   = GOMGZ(1:KLEV,1:NOBTOT)
      END SELECT
C
C*    2. LOOP OVER ALL THE OBSERVATIONS
C     ---------------------------------
C
 200  CONTINUE
C
      Observations: DO JOBS = 1, NOBTOT
         DLLAO   = ROBHDR(NCMLAT,JOBS)
         DLLOO   = ROBHDR(NCMLON,JOBS)
         IOBTYP = MOBHDR(NCMOTP,JOBS)
C
C     *    2.1. LOCATE FIRST LATITUDE ROW NUMBER (ILA) TO THE NORTH
C     *    OF ZLAO, AND THE TWO LONGITUDE POINT NUMBERS IMMEDIATELY
C     TO THE WEST (ILON AND ILOS)
C
         ILA=MOBHDR(NCMTLA,JOBS)

C
         IF(DLLOO.LT.0.) DLLOO = DLLOO + 2.*RPI
         IF(DLLOO.GE.2.*RPI) DLLOO = DLLOO - 2.*RPI
         DLDLON = 2.*RPI/NILON(ILA)
         DLDLOS = 2.*RPI/NILON(ILA+1)
         ILON = INT(DLLOO/DLDLON) + 1
         ILOS = INT(DLLOO/DLDLOS) + 1
C
C     *    2.2 COMPUTE THE 4 WEIGHTS OF THE BILINEAR INTERPOLATION
C
         DLDXN = DLLOO/DLDLON + 1. - ILON
         DLDXS = DLLOO/DLDLOS + 1. - ILOS
         DLDY  = (RLATI(ILA)-DLLAO)/(RLATI(ILA)-RLATI(ILA+1))
         DLW1  = (1.-DLDXN)*(1.-DLDY)
         DLW2  = DLDXN*(1.-DLDY)
         DLW3  = (1.-DLDXS)*DLDY
         DLW4  = DLDXS*DLDY
C
         do jlev = 1, klev
            ZFIELD(ILON,jlev,ILA)     =   ZFIELD(ILON,jlev,ILA)
     +           + DLW1 * ZPROFIL(jlev,JOBS)
            ZFIELD(ILON+1,jlev,ILA)   =   ZFIELD(ILON+1,jlev,ILA)
     +           + DLW2 * ZPROFIL(jlev,JOBS)
            ZFIELD(ILOS,jlev,ILA+1)   =   ZFIELD(ILOS,jlev,ILA+1)
     +           + DLW3 * ZPROFIL(jlev,JOBS)
            ZFIELD(ILOS+1,jlev,ILA+1) =   ZFIELD(ILOS+1,jlev,ILA+1)
     +           + DLW4 * ZPROFIL(jlev,JOBS)
C
         end do
*
      end do OBSERVATIONS
C
C
C     1. REARRANGE GRID-POINTS ARRAYS GD0, BY CARRYING GRADIENTS
C     .  CONTRIBUTIONS OF MERIDIAN 0, NILON(JGL)+1 AND NILON(JGL+2)
C     .  INTO MERIDIANS NILON(JGL), 1, AND 2. SIMILAR TREATMENT NEAR POLES
C
C
C     1.2  EXTRA PARALLELS
C
C     TREATMENT OF GRADIENTS FOR PARALLELS -1 AND NJ + 2 (WITH SYMETRIZATION)
C
      LEVELS: DO JLEV = 1, KLEV
         IMIDDLE = NILON(1) / 2
         DO JLON = 0, IMIDDLE
            ISYM = JLON + IMIDDLE
            ZFIELD(ISYM,jlev,1) =   ZFIELD(JLON,jlev,-1)
     +           + ZFIELD(ISYM,jlev,1)
            ZFIELD(ISYM,jlev,NJ) =  ZFIELD(JLON,jlev,NJ+2)
     +           + ZFIELD(ISYM,jlev,NJ)
         END DO
*
         IMAX = NILON(1)
         DO JLON = IMIDDLE + 1, IMAX + 2
            ISYM = JLON - IMIDDLE
            ZFIELD(ISYM,JLEV,1) =   ZFIELD(JLON,JLEV,-1)
     +           + ZFIELD(ISYM,JLEV,1)
            ZFIELD(ISYM,JLEV,NJ) =  ZFIELD(JLON,JLEV,NJ+2)
     +           + ZFIELD(ISYM,JLEV,NJ)
         END DO
C
C     TREATMENT OF THE GRADIENTS AT NORTH AND SOUTH POLES.
C
         DLMEAN = 0.
         DLMEAS = 0.
         IMAX = NILON(0)
         DO JLON = 0, IMAX + 2
            DLMEAN = DLMEAN + ZFIELD(JLON,jlev,0)
            DLMEAS = DLMEAS + ZFIELD(JLON,jlev,NJ+1)
         end do
*
         DLMEAN = DLMEAN/NILON(1)
         DLMEAS = DLMEAS/NILON(NJ)
         IMAX = NILON(1)
         DO JLON = 1, IMAX
            ZFIELD(JLON,jlev,1)  = DLMEAN + ZFIELD(JLON,jlev,1)
            ZFIELD(JLON,jlev,NJ) = DLMEAS + ZFIELD(JLON,jlev,NJ)
         end do
*
      END DO LEVELS
C
C
C     1.1  EXTRA MERIDIANS
C
      DO JGL = 1, NJ
         IMAX = NILON(JGL)
         DO JLEV = 1, KLEV
            ZFIELD(IMAX,JLEV,JGL) =   ZFIELD(0,JLEV,JGL)
     +           + ZFIELD(IMAX,JLEV,JGL)
            ZFIELD(1,JLEV,JGL)    =   ZFIELD(IMAX+1,JLEV,JGL)
     +           + ZFIELD(1,JLEV,JGL)
            ZFIELD(2,JLEV,JGL)    =   ZFIELD(IMAX+2,JLEV,JGL)
     +           + ZFIELD(2,JLEV,JGL)
         END DO
      END DO
*
*     Adjoint of the identity (change of norm)
*
      DO JGL = 1, NJ
         IMAX = NILON(JGL)
         DO JLEV = 1, KLEV
            DO JLON = 1, IMAX
               ZFIELD(JLON,JLEV,JGL) = ZFIELD(JLON,JLEV,JGL) *
     +              NILON(JGL) / RWT(JGL)
            END DO
         END DO
      END DO
C
C     Transfer local results to global array
C
      select case (cdvarname)
*
*     2D fields
*
      case('TG')
         gtg0(:,1:klev,:) = zfield(:,1:klev,:)
      case('PS')
         gps0(:,1:klev,:) = zfield(:,1:klev,:)
*
*     3D fields
*
      case('TT')
         tt0(:,1:klev,:) = zfield(:,1:klev,:)
      case('Q0')
         q0 (:,1:klev,:) = zfield(:,1:klev,:)
      case('O3')
         GOZ0(:,1:klev,:) = zfield(:,1:klev,:)
      case('TR')
         GTR0(:,1:klev,:) = zfield(:,1:klev,:)
      case('UU')
         UT0(:,1:klev,:) = zfield(:,1:klev,:)
      case('VV')
         VT0(:,1:klev,:) = zfield(:,1:klev,:)
      case ('GZ')
         GZ0(:,1:klev,:) = zfield(:,1:klev,:)
      end select

      RETURN
      END