20000714: Question

>From: "Jason Giovannettone" <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200007141622.e6EGMhT17230

>I am currently working on a project in which I have to simply plot the mean 
>sea level pressures as a beginning step.  I set the gvcord to hght and gfunc 
>to pres.  This doesn't produce any results.  Is there something else I need 
>to do?  If you have any ideas, please let me kn ow.  Thank you for your 
>time..
>
>Jason Giovannettone
>________________________________________________________________________
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>


Jason,

It would help us answer your questions in the future if you provides a 
signature 
in your email that identified yourself as a student at Purdue.

From you message above, I assume you mean that you would like to plot
the mean sea level pressure grids from a gridded data set (either a model output
or gridded surface data) using gdmap (or contour the data from gdcntr etc).

Sea level pressure in models is generally called PMSL for AVN, MRF, NGM and
EMSL for the ETA reduction and MMSL or PMSL for the RUC.

You can see all the grids that you have in a grid file by using the GDINFO
program to list out the parameters in a grid file.

Fromo GDINFO, you will see what parameters you have. Generally, for model
sea level data, GVCORD=none, GLEVEL=0. So, for ETA data for example:

GVCORD=none
GLEVEL=0
GFUNC=EMSL
GDATTIM=f000

The GDATTIM is the forecast time of the model. f000 is the analysis time. f024
would be the 24 hour forecast grid. You can use the shorthand fxxx or the 
complete
yymmdd/hhmmfxxx. If you have more than 1 initial analysis time in the grid 
file, then
you probably have to use a more complete epression for what time you want. 
Otherwise, you
will get the f000 fields from the latest time in the file.

The gdinfo output will show the GLEVEL and GVCORD associated with every 
parameter it has
in the grid file. 

When you use barnes analysis to grid surface data (using OABSFC) to create grids
from the surface observations, you will have GFUNC=PMSL and GDATTIM will
be the time of your data eg YYMMDD/HHMM rather than a forecast time as in a 
model.

If you have further questions, you ca clip out the settngs you have from the 
gdmap program
and send them to me along with any info about the type of data you are trying 
to view.

Steve Chiswell