19990608: GEMPAK GDCROSS with layer functions

>From: "John H.E. Clark" <address@hidden>
>Organization: Penn State University
>Keywords: 199906081528.JAA26160

>Could you help with a GEMPAK problem? I have been trying to run the
>following code in GDCROSS. It cannot evaluate GFUNC, which is horizontal
>potential vorticity advection. I have successfully contoured potential
>vorticity. Also I have successfully displayed GRAD(pvor(thes,geo)) in
>GVECT.
>
>Thanks for your consideration,
>John Clark
>
>CXSTNS   = 43.3;-81.0>38.9;-74.9
> GDATTIM  = f15
> GVCORD   = pres
> GFUNC    = adv(pvor(thes,geo),geo)
> GVECT    = wnd
> GDFILE   = /home/clark/models/gemmm5_971230_00-06
> WIND     = bm1
> REFVEC   =
> PTYPE    = LOG
> YAXIS    = 1000/300
> CINT     = 2
> SCALE    =
> LINE     = 2/-2/1
> BORDER   = 1
> TITLE    = 1/-3/ |
> CLEAR    = yes
> DEVICE   = XW
> TEXT     = 0.5
> PANEL    = ul
> CLRBAR   =
> CONTUR   = 2 / 2
> FINT     =
> FLINE    = 10-20
> CTYPE    = C
>


John,

The trouble you are having is that PVOR is a layer quantity, while GEO
is calculated at a single level. The result is an error message
stating GEO can not be found for a layer.

In order to do the above calculation, you can use the advection of PVOR
by the layer average geostrophic wind, eg:

gfunc = adv(pvor(thes,geo),vlav(geo))

Now the vertical cooordinate and levels for both terms of the advection
will match.

Steve Chiswell