CALL SEQUENCE...
      gsomgah  SSLNSP SSTEMP SSVORT SSDIV GSOMEG INPUT OUTPUT \ 
      [ -lon VAL1 -lat VAL2 -npg VAL3 -kind VAL4 -lv1 VAL5 -l VAL6 ]
 
 
      DESCRIPTION...
      gsomgah - CONVERTS ETA (SIGMA/HYBRID) LEVEL Q,D FILES TO VERTICAL MOTION
 
 
      AUTHORS - M.LAZARE AND F.MAJAESS.
      LAST REVISION: $Header: /home/cvs/RMNLIB/utils/rdiag/lspgm/gsomgah.ptn,v 4.10 2014/10/16 11:34:06 dugas Exp $
 
 
      PURPOSE - COMPUTES A GRID FILE OF VERTICAL MOTION (DP/DT) FROM
                ETA (SIGMA/HYBRID) LEVEL SPECTRAL FILES OF VORTICITY
                AND DIVERGENCE.
 
      NOTE    - INPUT IS SPECTRAL, OUTPUT IS GAUSSIAN GRIDS,
                ALL GLOBAL.
 
 
      INPUT FILES...
       SSLNSP = SPECTRAL LN(SF PRES) ON ETA (SIGMA/HYBRID) LEVELS
       SSTEMP = SPECTRAL TEMPERATURE ON ETA (SIGMA/HYBRID) LEVELS
       SSVORT = SPECTRAL VORTICITY   ON ETA (SIGMA/HYBRID) LEVELS
       SSDIV  = SPECTRAL DIVERGENCE  ON ETA (SIGMA/HYBRID) LEVELS
 
      OUTPUT FILE...
       GSOMEG = GRIDS OF VERTICAL MOTION OMEGA (DP/DT) AT MID-LAYER
                POSITIONS. UNITS ARE NEWTONS/M**2/SEC.
 
 
      INPUT PARAMETERS...
 
       ILG   (lon)  = LENGTH OF A GAUSSIAN GRID ROW.
       ILAT  (lat)  = NUMBER OF GAUSSIAN LATITUDES.
       KPACK (npg)  = OUTPUT PACKING DENSITY (0 DEFAULT TO 4)
       COORD (kind) = 'SIG'/'ETA' FOR SIGMA/ETA VERTICAL COORDINATE
       PTOIT (lv1)  = PRESSURE (PA) OF THE RIGID LID OF THE MODEL.
                      AS OF NOW, HAS TO BE GREATER THAN 0.01 PA.
       LAY   (l)    = ARRANGEMENT TYPE OF INTERFACES
                      WITH RESPECT TO MID_LAYERS =
                    0    , AS LAY=2 FOR MOMENTUM AND LAY=4 FOR THERMODYNAMICS,
                           (UPWARD COMPATIBILTY WITH EARLIER VERSIONS OF GCM)
              OR    1 / 2, LAYER INTERFACE PLACED AT AN EQUAL SIGMA/GEOMETRIC
                           DISTANCE FROM THE MIDDLE OF THE ADJACENT LAYERS
              OR    3 / 4, BASE LAYERS EXTRAPOLATED SO THAT THE MIDDLE OF THE
                           LAYERS ARE AT THE CENTRE OF THE SIGMA/GEOMETRIC LAYERS
 
       READ(5,5010) ILG,ILAT,KPACK,COORD,PTOIT,LAY
 5010  FORMAT(10X,3I5,1X,A4,E10.0,I5)
 
 
      EXAMPLE OF INPUT CARD...
 
 * GSOMGAH   64   52    0  SIG        0.    0
 
         0123456789012345678901234567890123456789012345678901234567890
         1         2         3         4         5         6         7
 
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 ERROR RETREIVING FULL LEVELS FROM SSVORT
        2 ERROR RETREIVING HALF LEVELS FROM SSTEMP
        3 FIRST SSVORT AND SSTEMP NOT THE SAME TYPE/SIZE
        4 TOO MANY ZONAL WAVENUMBERS IN SPECTRAL FILES
        5 PREMATURE EOF ON SSLNSP
        6 MORE THAN ONE SIZE IN INPUT FILES
        7 PREMATURE EOF ON SSVORT
        8 PREMATURE EOF ON SSDIV
        9 ABORT READING INPUT
     20+L LEVEL L NOT THE SAME IN SSVORT AND SSDIV