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 optional O'Brien correction may be 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. Do the adjustment pass. GDFILE = obs.grd GDATTIM = last GPACK = grib/16 NPASS = 2 2. Create vertical motion grids in file model.grd at the 12-h forecast time. Do no adjustment. GDFILE = model.grd GDATTIM = f12 GPACK = grib/16 NPASS = 1 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.