[gembud] GEMPAK GRIB Bug?

[Brent L Shaw]

Scott,

Thanks for looking into this and finding the problem!

Best regards,

Brent

________________________________
From: Scott Jacobs [mailto:Scott.Jacobs at noaa.gov]
Sent: Thursday, May 15, 2008 2:26 PM
To: Brent L Shaw
Cc: support-gempak at unidata.ucar.edu; gembud at unidata.ucar.edu
Subject: Re: [gembud] GEMPAK GRIB Bug?

Brent, et al.,

We fixed this problem with constant grids in 5.11.1. However, looking at the Unidata release of 5.11.1, there is a discrepancy with the function that we modified. We will work with the Unidata team to get this fixed in their copy of NAWIPS/GEMPAK so that it can be made available to the entire community.

Scott Jacobs
NCEP NAWIPS Development Team


Brent L Shaw wrote:
I have searched the GEMBUD and GEMPAK support lists and have not found this reported by anyone else, but it seems that NAWIPS/GEMPAK has an issue with GRIB records where the decoded values should be an entire grid of zeros (as sometimes happens with precipitation and hydrometeor fields in limited area mesoscale models).  I have found this problem using a Linux build of NAWIPS/GEMPAK that I have built from source using g77 and gcc.  I have found it to be a problem on both 32-bit Linux and 64-bit Linux (RedHat in both cases).  Here is a detailed description of what I did and observed:


 1.  GRIB edition 1 files (created by the NCEP-developed WRF post-processor) are decoded with dcgrib2 as follows:  dcgrib2 myfile.gem < myfile.grb
 2.  Rendered the total precipitation forecast from the resulting GEMPAK file and find a corrupted, noisy image that changes patterns each time I hit reload.  Additionally, the rendering generates the following error in the Error status window:
[DG2] Too many maxs found -- increase radius or reduce range

 1.  Ran the GEMPAK file through "gdlist" to see min/max values actually contained in the GEMPAK file.  It reports a combination of zeros, 10.0s, 20.0s, and 30.0s.
 2.  Ran the original GRIB file through wgrib and IDV and verified the original GRIB field is encoded correctly and that all grid points actually are 0.

The attached tar ball has the original GRIB record, the resulting GEMPAK file created from dcgrib2, and the sample NAWIPS image demonstrating the problem.

Thanks for your help in advance!  Please let me know if you need anything else from me.

Best regards,

Brent

Brent Shaw
Senior Meteorologist and Project Manager
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Weather Decision Technologies Inc<http://www.wdtinc.com/>.
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Norman, OK 73072
Office:  (405) 579-7675 x246
Mobile: (405) 397-9950





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