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Re: vertical velocity

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  • Subject: Re: vertical velocity
  • Date: Wed, 31 Jan 2007 15:11:49 -0700
Frank,

You sent your message to my email account rather than the gempak
support, so it wound up burried.

The standard units that the OMEG data are transmitted in (for GRIB) is
"Pa s-1",
which is SI, but somewhat clunky to use. You will see that the decoders
in GEMPAK scale these to mb s-1 (eg the -2 scale factor you will find in
the entries under $GEMTBL/grid/*).

If you set SCALE=0 in the gempak programs, and plot OMEG, you are seeing
mb s-1.

In GARP, the fdf files control the scaling. For the NAM 40km grid (#212)
for example, the fdf file
$GARPHOME/fdf/scalar/eta212/general/Omega_mbs-1
sets the SCALE parameter to "3", which then means that these are
microbars per second. So, the answer to your question is that the FDF
file
is scaling the data for ease of display/interpretation.

Steve Chiswell
Unidata User Support

On Wed, 2007-01-31 at 15:42 -0500, Frank J. Marsik wrote:
> Steve:
> 
> Any suggestions regarding my previous question about GARP's use
> of pressure velocity (mb/sec)?  What simply conversion am I missing
> here, given that most atmospheric vertical motions are on the order
> of cm/sec (or microbars/sec)?
> 
> thanks...
> 
> frank
> 
> ============================================================================
> 
> Frank J. Marsik
> U-M Air Quality Laboratory            "We must remember that intelligence
> Space Research Building, Rm 2109       is not enough.  Intelligence  -
> 2455 Hayward Ave                       plus character - that is the goal
> Ann Arbor, MI  48109-2143              of true education."
> 
> Phone: 734-763-5369                           - Martin Luther King
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> URL: http://www.umich.edu/~marsik/
> 
> ============================================================================
>  
> 
-- 
Steve Chiswell <address@hidden>
Unidata