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19990630: gempak assistance

>From: Matt Fearon <address@hidden>
>Organization: .
>Keywords: 199906302250.QAA24636

>I am a fairly new user of gempak software, but I know how to tinker
>around
>pretty well.
>
>I am trying to extract stab(tmpc) for layers above ground level to
>achieve a temperature lapse rate at individual grid points (from the
>surface
>to about 5km). I have been using the gdlist program, however the region
>I am
>concerned with is California. Therefore I have to deal with elevation
>issues.
>I have been trying to use hagl instead of pres for the vertical
>coordinates, but I
>have been unsuccessful.
>
>If someone knows a good method for extracting stab(tmpc) to establish a
>lapse rate
>at individual grid points considering elevation, I would greatly
>appreciate all advice.
>
>Thank you,
>Matt Fearon
>address@hidden
>

Matt,

From your question, you apparently want to calculate:

T(~5km) - T(surface) 
-------------------
Z(~5km) - Z(surface)

If you are using the ETA 211 grid from the IDD for instance,
you have  T@2m, T@500mb, Z@surface, Z@500mb.

So, assuming that either 500mb or 550mb is adequate in approximating 
~5km, you can do:

gvcord = pres
glevel = 500
gfunc = quo(sub(tmpc,tmpc@2%hagl),sub(hght,hght@0%none^f000))

The Height grid is only given at F000 (since the ground doesn't advect with 
time),
hence the ^f000 specification).

Actually, since the above temperature is at 2m, while the height is at 0m HAGL,
you could add 2m to the height subtraction around the last "sub"
to get something like: quo(sub(,),sub(hght,add(hght@0%none^f000,2)))

The point is, depending on what model grid you have, you may have to 
determine if you have temp at 2m , and height at 0m etc.
The best way to do this is to use gdinfo to inspect your grids
to determine what parameters they give you to work with.
Steve Chiswell
Unidata User Support