GDOMEG computes grids of vertical motion and adds them to the
grid file.


INPUT PARAMETERS
 
    GDFILE    Grid file
    GDATTIM   Grid date/time
    GPACK     Packing type/number of bits
 
 
PROGRAM DESCRIPTION
 
    GDOMEG computes kinematic vertical motions from gridded wind
    data by vertically integrating the continuity equation in
    pressure coordinates.  An O'Brien correction is applied
    to assure zero vertical motion at the top pressure
    level.

    The O'Brien correction is based on the solution of a
    variational problem which is formulated to minimize the
    squared difference between the observed divergence and the
    adjusted divergence while simultaneously satisfying the
    isobaric continuity equation with zero vertical motion at
    the top.  The error in the divergence is assumed to increase
    linearly with decreasing pressure.  The effect of the
    correction is to adjust the OMEG values at every level by
    a fraction of the excess OMEG at the top pressure level.
    The fraction increases from nearly zero at the bottom to one
    at the top.

    The boundary condition at the surface is:

		OMEG = - G * RHO * DOT ( V, GRAD (Z) )

    where, G is the acceleration of gravity, RHO is density,
    V is either the surface wind or an estimated surface wind
    and Z is the terrain elevation.  If there is insufficient
    data, the surface OMEG is set to zero.

    The values of omega are computed on the existing pressure
    levels. A weighted average in ln p of divergence in the
    layer is used in the vertical integration.

    The computed grids are in mb/s and are named OMEG.


EXAMPLES
 
    1.  Create vertical motion grids in file obs.grd at the last
        time using GRIB packing.

        GDFILE  = obs.grd
        GDATTIM = last
        GPACK   = grib/16

    2.  Create vertical motion grids in file model.grd at the
        12-h forecast time.

        GDFILE  = model.grd
        GDATTIM = f12
        GPACK   = grib/16


ERROR MESSAGES
 
    [GDOMEG  +2]    No correction pass will be done.
    [GDOMEG  +1]    WARNING--no surface pressure grid exists.
    [GDOMEG  -1]    Fatal error initializing TAE.
    [GDOMEG  -2]    Fatal error reading TAE parameters.
    [GDOMEG  -3]    Error initializing GEMPLT.
    [GDOMEG  -4]    Requested time is not available.
    [GDOMEG  -5]    No pressure levels exist.
    [GDOMEG  -6]    The packing information is erroneous.
    [GDOMEG  -7]    Could not write output grid to the file.