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<DIV><FONT face=Arial size=2>Perfect. Thanks. My experience with meteorological
data is quite pedestrian, so please excuse my ignorance. That is, however,
what I had suspected, but when I try to download the data using the NOMADS
GRIB server and their "Grib Filter" tool, selecting the "mean sea
level" level parameter and the "PRES" variable, the resulting file is
empty. When I retrieve the file using GrADSdap and your advice, it
plots as expected. Perhaps I am selecting incorrect
parameters/variable when using the Grib Filter tool. If you have any
insight on this, all suggestions are welcome. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Mark</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=klevey@CUSTOMWEATHER.COM href="mailto:klevey@CUSTOMWEATHER.COM">Kevin
M Levey</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=GRADSUSR@LIST.CINECA.IT
href="mailto:GRADSUSR@LIST.CINECA.IT">GRADSUSR@LIST.CINECA.IT</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, March 11, 2010 1:32
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Correcting Surface Pressure
to Sea Level</DIV>
<DIV><BR></DIV>Hi Mark,
<DIV><BR></DIV>
<DIV>If you are plotting from the GFS grib data, then use the mean sea-level
pressure variable instead of geopotential height, i.e. </DIV>
<DIV><BR></DIV>
<DIV>'define mslp = prmslmsl/100' </DIV>
<DIV><BR></DIV>
<DIV>prmslmsl is in Pascals, hence divide by 100 to get hPa (or mb).</DIV>
<DIV><BR></DIV>
<DIV><SPAN class=Apple-style-span
style="FONT-SIZE: 14px">Regards,</SPAN></DIV>
<DIV>
<DIV><SPAN class=Apple-style-span
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<DIV>
<DIV>
<DIV>
<DIV>
<DIV><BR></DIV>
<DIV>Kevin M Levey, MSc in Oceans and Atmospheric Sciences (University of Cape
Town)</DIV>
<DIV>Director of Meteorological Operations</DIV>
<DIV>CustomWeather, Inc.</DIV>
<DIV>San Francisco, California, USA</DIV>
<DIV><BR></DIV>
<DIV>"Taking the World by Storm!"</DIV>
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href="http://www.customweather.com">http://www.customweather.com</A></DIV>
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<DIV>cell: 415-794-0411</DIV>
<DIV>work: 415-777-3566</DIV>
<DIV>email: <A
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<DIV>
<DIV>On Mar 11, 2010, at 03/11/10 - 12:16 PM, Mark Hess wrote:</DIV><BR
class=Apple-interchange-newline>
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<DIV bgcolor="#ffffff">
<DIV><FONT face=Arial size=2>I tried to access the GrADS User archives for
this answer, but the page would not allow me to search.Perhaps someone can
point me in the right direction. When plotting surface pressure
(isobars) from the GFS GRIB files, my data show very low pressure
values over land. While not sure, I am guessing this is because the
data need to be corrected to sea level. Is this correct? If so, can
someone provide a resource which explains how to 'correct' the data? If I am
incorrect, Can you please explain what I am doing wrong?
Thanks.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Mark</FONT></DIV>
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