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20021002: convert ccm netcdf file to gempak

Wuyin,

If you are creating grib messages, then you do have to
create the necessary parameter tables for the model center
for the grib decoders to correctly identify the parameters.
Typically, you would define the projection in the GDS block
which is the convention by which the decoder will determine
the grid projection for the GEMPAK file.

As for the netcdf file, writing a decoder for a specific CDL is
possible, which is what I did for the NCAP/NCEP reanalysis NetCDF files
with the dcreanal and dcreanal2 decoders. These netcdf files
used the COARDS convention. If yoru files are similar,
then the dcreanal decoder would be a good strarting point.

It is not generally possible to write a single NetCDF decoder 
for all possible NetCDF grid files since the flexibility in the 
CDL convention used prohibits a generic solution.

One typical problem you may confront is that GEMPAK requires
even spacing between grid rows, while some climate model output uses
a gaussian grid where the grid row spacing varies with latitude.
You would have to interpolate to evenly spaced grid rows in that case
in order to use the data within GEMPAK.

Steve Chiswell


>From: Wuyin Lin <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200210021446.g92Ekp105849

>Dear GEMPAK support team,
>
>   I would like to display ccm output using gempak.
>The ccm output are in netcdf format. I do find some
>old messages on the unidata archive discussing 
>the conversion from netcdf to gempak. (e.g.,
>http://www.unidata.ucar.edu/projects/coohl/mhonarc/MailArchives/gempak/msg0068
> 9.html)
>but still clueless how to apply it.
>
>   Indirectly, I attempted to use dcgrib/dcgrib2. 
>First, a sample netcdf file is converted to GRIB using
>gradsnc/lats4d. But there is not much documentation
>for lats4d and the generated GRIB file can't be
>recogized by the decoders dcgrib/dcgrib2 for various
>reason (e.g, projection, grib compression table, etc.)
>causing the creation of gempak to fail.
>
>   Advices on how to proceed with this conversion and
>guidelines for any existing resources are greatly appreciated.
>
>   thank you very much,
>
>Wuyin Lin
>address@hidden
>
>
>From address@hidden Tue Oct  1 14:14:33 2002
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> EDT)
>Date: Tue, 1 Oct 2002 16:16:57 -0400 (EDT)
>From: Wuyin Lin <address@hidden>
>To: address@hidden
>Subject: convert ccm netcdf tape to gempak
>Message-ID: <address@hidden>
>MIME-Version: 1.0
>Content-Type: TEXT/PLAIN; charset=US-ASCII
>
>Dear GEMPAK support team,
>
>   I would like to display ccm output using gempak.
>The ccm output are in netcdf format. I do find some
>old messages on the unidata archive discussing 
>the conversion from netcdf to gempak. (e.g.,
>http://www.unidata.ucar.edu/projects/coohl/mhonarc/MailArchives/gempak/msg0068
> 9.html)
>but still clueless how to apply it.
>
>   Indirectly, I attempted to use dcgrib/dcgrib2. 
>First, a sample netcdf file is converted to GRIB using
>gradsnc/lats4d. But there is not much documentation
>for lats4d and the generated GRIB file can't be
>recogized by the decoders dcgrib/dcgrib2 for various
>reason (e.g, projection, grib compression table, etc.)
>causing the creation of gempak to fail.
>
>   Advices on how to proceed with this conversion and
>guidelines for any existing resources are greatly appreciated.
>
>   thank you very much,
>
>Wuyin Lin
>address@hidden
>