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20010824: GEMPAK variables

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  • Subject: 20010824: GEMPAK variables
  • Date: Sun, 26 Aug 2001 12:46:00 -0600

Javier,

You can find the definitions that GEMPAK uses to decode GRIB parameter numbers 
to
GEMPAK variable names in $GEMTBL/grid. For the avn model, The parameter tables 
would be
wmogrib2.tbl and ncepgrib2.tbl. For example, TMPK is temperature in Kelvin, no 
scaling
(eg scales by 10**0):

% grep TMPK $GEMTBL/grid/wmogrib2.tbl
011 Temperature                       K                    TMPK             0  
-9999.00


The GRIB data provides parameter numbers, and the above tables will be used to
identify the string used as the name in GEMPAK. The vertical coordinate names 
are
defined in $GEMTBL/grid/vcrdgrib1.tbl.

More information on GEMPAK parameters can be found in the User Guide in Chapter 
3
(gparm and/or gfunc, as well as general lists in sfparm) and Appendix B for
function computations.

A parameter that has 2 levels is called a "layer" parameter. 2 levels will be 
used 
when the parameter is described in a layer, or between 2 levels, such as:

Boundary layer parameters, where the levels are the top and bottom of the layer
(eg PARM=TMPK, GLEVEL=180:0, GVCORD=PDLY is the temperature in the
layer from 0 to 180 millibars above the ground.

Stability parameters, such as the lifted index, lifted from 1000mb to 500mb; 
Helicity
using the mean storm inflor from 0 to 3000m above the ground, etc.

If you create thickness computations, such as GFUNC=ldf(hght), GLEVEL=500:1000, 
GVCORD=PRES,
you will have a thickness (aka height difference (delta Z) or depth of a layer 
in the atmosphere)
between 500mb and 1000mb for the height (HGHT) of pressure surfaces.


Steve Chiswell
Unidata User Support




>From: "Francisco Javier Soley Alfaro." <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200108241829.f7OISd116278

>Dear Steve:
>
>Jimmy Mejia succeded in configuring Gempak and the ldm and we are getting
>aviation data (*.avn) regularly. There are still problems with other type
>of data.
>
>Several weeks ago I started playing again with gempak. I have decoded some
>files using dcgrib and listed the information with gdinfo. I searched the
>gempak documentation web pages looking for information on the gempak's own
>data format. I could not find it. Where can I find the meaning of the
>parameters: TMPK, UREL, VREL, etc. When do the grids have two levels?
>I can guess to some of the meanings but I want to prepare a document in
>Spanish that explains the data format for training purposes.
>Thanks for your help.
>Javier Soley
>
>
>
>