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20010619: GEMPAK: barnes analysis and first guess

>From: Christian Page <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200106190945.f5J9jTp17390

>
>Hi,
>
>I would like to use the first-guess option in oabsfc (and oabsnd), but found n
> o
>information in the mailing lists or the GEMPAK documentation.



Here is a topic of similar interest using the first guess with model data:
http://www.unidata.ucar.edu/projects/coohl/mhonarc/MailArchives/gempak/msg01439.html


>
>Here are my questions:
>
>- Must the guess field be in the same grid as the grid created by oagrid?

Yes, the guess file must be on the same grid.

>- If so, is there an easy way to process an ETA gempak file, by example, and
>extract PMSL and put it on the same grid as the gridfile created by oagrid?

You can use the GDBIINT program I provided. You can interpolate individual
grids to the new projection.


>- Will the guess file help a lot to get a better analysis, and/or fill area th
> at is without METAR data?

The first guess field can help the analysis converge quicker, as well
as provide an analysis basis when data is sparse.


>- Is it better to use analysis and forecast data, or just analysis data from
>models?

The models often have several additional data sources, so they can often
reveal detail where just one data set will not. Of course, the model
will also smooth out features and throw out "bad" data.


>- Is there a regional model that covers more than CONUS that is available on
>UNIDATA feed and that contains geopotential and PMSL? Or must I use global
>models?

The AVN and MRF data sets have several grids which provide coverage areas
greater than CONUS (such as the north america and northern hemisphere grids),
however, the model run is the "global" run, so essentially you are 
at that scale. Both the AVN and UKMET thinned grids on NOAAPORT provide the 
global
coverage, as does the NOGAPS data from IDD.



>
>Thanks a lot again,
>
>Christian Page
>Universite du Quebec a Montreal
>
>


Steve CHiswell