 
      CALL SEQUENCE...
       gpdpd  HUM TEMP ES [SP] OUTPUT \ 
              [ -kind VAL1 -c VAL2 -d VAL3 -i VAL4 -def [VAL5] ]
 
 
      DESCRIPTION...
       gpdpd  - COMPUTES DEW POINT DEPRESSION FROM T,SHUM OR RHUM
 
 
      AUTHOR  - J.D.Henderson, DEC 04/80.
      LAST REVISION: $Header: /data/armnraid1/cvs/RMNLIB/utils/rdiag/lspgm/gpdpd.ptn,v 4.21 2012/05/17 21:12:12 dugas Exp $
 
 
      PURPOSE - CONVERTS PRESSURE LEVEL GRID FILES OF TEMPERATURE AND
                SPECIFIC OR RELATIVE HUMIDITY TO DEW POINT DEPRESSION.
 
 
      INPUT FILES...
       HUM  = SPECIFIC OR RELATIVE HUMIDITY ARRAY.
       TEMP = TEMPERATURE OR VIRTUAL TEMPERATURE ARRAY.
      [SP   = SURFACE PRESSURE (MB), ONLY USED WHEN COORD .NE. 'PRES'.
              NOTE THAT ITS ACCEPTED VARIABLE NAMES ARE 'P0' OR 'PS']
 
      OUTPUT FILE...
       ES   = DEW POINT DEPRESSION ARRAYS.
 
 
      NOTES:  - 1) WATER AND ICE PHASES ARE CONSIDERED IN THE CONVERSION
                   WHEN THE COMMAND LINE PARAMETER "-def" IS SPECIFIED.
                   OTHERWISE, ONLY WATER PHASE IS CONSIDERED.
                2) CALCULATIONS ARE DONE WITH THE RPN PHYSIC'S SET
                   OF THERMODYNAMIC CONVERSION FUNCTIONS (I.E. FINTERN)
                3) IF TEMP CONTAINS VIRTUAL TEMPERATURES (I.E. 'VT'),
                   HUM MUST CONTAIN SPECIFIC HUMIDITIES.
                4) THE ASSUMED UNITS FOR 'VT' ARE EITHER CENTIGRADES
                   (FOR RPN/CMC FILES) OR KELVINS (FOR CCCma FILES).
 
 
      (COMMAND-LINE) INPUT PARAMETERS...
 
       COORD (kind) = 'SIG'/'GEM'/'GEM2'/'GEM3'/'PRES'.
       PTOIT (c)    = CONSTANT PRESSURE (PA) AT THE LID OF MODEL WHEN
                      (COORD.NE.'PRES') (DEF = pression_au_toit).
 
       The next two parametres are only used when COORD='GEM2' or 'GEM3'.
 
       PREF  (d)    = REF PRESSURE (DEF 80000 PA).
       R     (i)    = REFERENCE EXPONENT (DEF 1.0)
 
       Notes: 1) 'GEM' is the original gem eta coordinate, while 'GEM2' is
                 the first gem hybrid coordinate as implemented by Edouard
                 & Gravel in GEM/DM v2.2.0. 'GEM3' is the normalized version
                 that was implemented in the v2.3.1 GEM/DM.
              2) The default value of COORD is determined by the file type
                 and the program will also try to determine it by the
                 (internal) coding used for the coordinate itself.
              3) Specifying "-def AABB" will force the attempt to read
                 a text file called aabb.nml, containing a FORTRAN
                 namelist AABB_NML, which in turns will hold two arrays,
                 A and B such that the local pressure at level K, PL(K),
                 can be calculated as "A(K)+B(K)*PS". This then by-passes
                 all of the normal COORD-related calculations for PL(K).
 
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 UNABLE TO READ HUMIDITY FILE
        2 FOUND DATA OTHER THAN TYPE 'GRID' OR 'SUBA'
        3 HUMIDITY FILE IS NOT SHUM OR RHUM
        4 PREMATURE EOF ON HUMIDITY FILE 
        5 PREMATURE EOF ON TEMPERATURE FILE 
        6 HUMIDITY AND TEMPERATURE ARRAYS NOT THE SAME SIZE
        7 VIRTUAL TEMPERATURE NOT SUPPORTED WITH RELATIVE HUMIDITY
        8 INPUT FILE AND "COORD" MISMATCH
        9 PREMATURE EOF ON SURFACE PRESSURE FILE
       10 SURFACE PRESSURE AND TEMPERATURE ARRAYS NOT THE SAME SIZE
       11 UNSUPPORTED TYPE OF VERTICAL COORDINATE
       12 PROBLEM READING COMMAND-LINE PARAMETRE
       13 UNSUPPORTED VERTICAL COORDINATE FOUND IN GPHUM
       14 UNABLE TO READ AABB NAMELIST
       15 SP DOES NOT CONTAIN SURFACE PRESSURES FOR EARTH
