GEMPAK Manual | Programs

GDVINT performs interpolation between vertical coordinates.

INPUT PARAMETERS
 
    GDFILE    Grid file
    GDOUTF    Output grid file
    GDATTIM   Grid date/time
    GVCORD    Grid vertical coordinate
    GLEVEL    Grid level
    MAXGRD    Maximum number of grids
    GAREA     Graphics area
    VCOORD    Vertical coordinate type
 
 

PROGRAM DESCRIPTION
 
     This program performs vertical interpolations from one
     input vertical coordinate to another.  The output grid
     file may be the same as the input file or be a separate
     file.  If areal subsetting is specified, output must be
     to another GEMPAK file.

     The input file is specified in GDFILE and the output file
     in GDOUTF.  If GDOUTF does not exist, then a new file
     will be created with the maximum number of grids given
     in MAXGRD.  GDATTIM specifies the time at which to
     perform the interpolation.

     GVCORD specifies the input and output vertical
     coordinates separated by a slash.  The coordinates
     supported are:

	PRES	--	pressure
	THTA	--	potential temperature
	HGHT 	--	height above sea level
	SGMA	--	sigma p
	ETA	--	eta
	ZAGL	--	height above ground level

     When SGMA is specified, the pressure on SGMA=0 is
     given following a semicolon.  For example, if the
     pressure at SGMA=0 is 50 mb, the specification in
     GVCORD is

		SGMA:50

     GLEVEL specifies the vertical coordinate levels to
     interpolate.  This may be a single level, a list of
     levels separated by semicolons or a range with an
     increment separated by dashes.

     GAREA specifies areal subsetting.  It can be specified
     as either lower-left and upper-right grid
     coordinates, separated by semicolons and preceded by
     a single @, or as lower-left and upper-right latitude
     and longitude coordinates separated by semicolons.
     In the latter case, the locations are rounded to the
     nearest grid points.  The navigation projection and its
     parameters are used along with the specified corner
     points to set the navigation in the output grid file.
     If areal subsetting is used, the output file must be
     different from the input file.

     VCOORD specifies a list of GEMPAK coordinate names.
     All grids at the specified time having one of these
     coordinate names will be transfered to the output
     file.  This allows surface grids with vertical
     coordinate types NONE or ESFC to be transfered into
     the output file.  It also allows subsetting of
     grids in other vertical coordinates to be put into
     the output file.  VCOORD is also used to specify
     the Lorenz condition for interpolation into THTA
     coordinate.  To specify the Lorenz condition,
     conclude the VCOORD input with /L.

     If the output vertical coordinate is THTA and
     the Lorenz condition is specified, underground
     isentropic surfaces are assigned surface values,
     and PSYM is built down hydrostatically using the
     surface pressure in the Exner function.  In all
     other cases, underground surfaces are assigned
     missing values.

     If the output vertical coordinate is PRES, underground
     pressure levels are assigned a height value computed
     by extrapolating downward using the surface values
     of pressure, temperature, and height.  A constant
     lapse rate atmosphere with the standard lapse rate of
     6.5 K / 1000 m is assumed.

     If surface values of the interpolated parameters
     are not available, GDVINT extrapolates values to the
     surface from two levels above the surface.  These
     values are used in the interpolation and are placed
     in the output file where they are assigned the
     output vertical coordinate and GLEVEL=0.

     If heights are not available in the input grid file,
     a hydrostatic integration is done in the input coordinate
     to generate values for the interpolation.


EXAMPLES
 
     1.  Interpolate from sigma, with P(SGMA=0) = 0 to
         theta over a subgrid defined by the latitude
         and longitude bounds.  The actual subgrid will
         be defined by the grid points closest to the
         latitude longitude bounds.  Also transfer all
         grids with vertical coordinates NONE, MSLV and
         ESFC into the output file.  Apply the Lorenz
         condition for underground surfaces.

         GDFILE  = z00jun16.ngmsgm
         GDOUTF  = z00jun16.ngmtht
         GDATTIM = f24
         GLEVEL  = 256-412-4
         GVCORD  = sgma:0/thta
         MAXGRD  = 2000
         GAREA   = 30;-100;45;-70
         VCOORD  = none;mslv;esfc/L

     2.  Interpolate from pressure to the height above
         ground coordinate over a subset of the grid
         specified by grid index bounds.

         GDFILE  = z00jun16.ngmprs
         GDOUTF  = z00jun16.ngmzag
         GDATTIM = f36
         GLEVEL  = 500-15000-500
         GVCORD  = pres/zagl
         MAXGRD  = 3200
         GAREA   = @12;23;34;78
         VCOORD  = mslv;esfc

     3.  Interpolate from isentropic coordinates to sigma
         (ptop=50) over the entire grid.  Put the output
         in the same file as the input.  Note that sigma
         values are scaled by 10000.  In this example,
         maxgrd is ignored.

         GDFILE   = z00jun16.ngm
         GDOUTF   = z00jun16.ngm
         GDATTIM  = f48
         GLEVEL   = 9500-500-500
         GVCORD   = thta/sgma:50
         MAXGRD   = 3200
         GAREA    = grid
         VCOORD   = none;esfc

ERROR MESSAGES
 
    [GDVINT  +4]    Warning--no surface elevation grid exists.
    [GDVINT  +3]    No pressure on this level.
    [GDVINT  +2]    No output vertical coordinate value on this level.
    [GDVINT  +1]    All values are missing.
    [GDVINT  -1]    Fatal error initializing TAE.
    [GDVINT  -2]    Fatal error reading TAE parameters.
    [GDVINT  -3]    Fatal error initializing GEMPLT.
    [GDVINT  -4]    No thermodynamic data in the input file.
    [GDVINT  -5]    Navigation blocks are different.
    [GDVINT  -6]    Required surface pressure is absent.
    [GDVINT  -7]    Required surface elevation is absent.
    [GDVINT  -8]    Too few levels to interpolate this parameter.
    [GDVINT  -9]    No parameters to interpolate -- check GVCORD, GDATTIM.
    [GDVINT -10]    Top pressure for SGMA or ETA missing.
    [GDVINT -11]    Subset region is invalid.
    [GDVINT -12]    File ... cannot be opened.
    [GDVINT -13]    User specified coordinates are invalid.
    [GDVINT -14]    Levels not correctly specified.
    [GDVINT -15]    Grid size is too large.