[gradsusr] UKMET

[Jennifer Adams]

I grabbed a sample file: 
ftp://tgftp.nws.noaa.gov/SL.us008001/ST.opnl/MT.bmoav_CY.12/RD.20120119/PT.grid_DF.bb/fh.0006_tl.press

There are 3 different variables (grib codes 6, 7, and 102). Each variable has 8 records, each with a different grid, except for variable 102, which has 9. The ninth grid for variable 102 is a latlon grid with 1813 points, all the others are thinned grids with nxny=3447. Grib2ctl creates a pdef file for the thinned grid, presumably based on the grid specs it finds in record #1. I ran wgrib -V on this file and then grepped on 'grid=' and got this:

rec 1:00040:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=44 tropopause 6hr fcst:
rec 2:05915:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=41 tropopause 6hr fcst:
rec 3:11790:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=43 tropopause 6hr fcst:
rec 4:17233:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=37 tropopause 6hr fcst:
rec 5:23108:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=39 tropopause 6hr fcst:
rec 6:28983:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=42 tropopause 6hr fcst:
rec 7:34858:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=38 tropopause 6hr fcst:
rec 8:40733:date 2012011912 PRES kpds5=1 kpds6=7 kpds7=0 levels=(0,0) grid=40 tropopause 6hr fcst:

When checking for matches for PDEF'd grids, gribmap will check the nxny value to make sure it matches what the PDEF entry says, but doesn't go beyond that. The one latlon grid in the file does spawn an error from gribmap, "GRIB grid size does not match descriptor". Each of the 8 thinned grids will appear identical to gribmap, so they will all match, and the one that the index file will point to will be the last record in the file to match, which will not likely correspond to the information used to create the pdef file. Wesley's suggestion to break up the file and separate out the nine different grids is the only way this data can be read with GrADS. 
--Jennifer


On Dec 16, 2011, at 5:06 PM, Wesley Ebisuzaki wrote:

> Brian,
> 
> Looks like a problem with gribmap in GrADS v2.
> 
> The files have several different grids in them. GrADS should check that 
> the grid
> matches the grid in the ctl file (it does with grib1). It doesn't so all 
> the grids match
> and you can plot the wrong data. :(
> 
> Options: grib1, delete all but one of the grids.
> 
>> 18.1: lev1=101,0 var=0,3,1 MATCH
>> 19.1: lev1=101,0 var=0,3,1 MATCH
>> 20.1: lev1=101,0 var=0,3,1 MATCH
>> 21.1: lev1=101,0 var=0,3,1 MATCH
>> 22.1: lev1=101,0 var=0,3,1 MATCH
>> 23.1: lev1=101,0 var=0,3,1 MATCH
>> 24.1: lev1=101,0 var=0,3,1 MATCH
>> 25.1: lev1=101,0 var=0,3,1 MATCH
>> grib2map: Writing out the index file
> Wesley
> 
> 
> 
> Walsh, Brian J wrote:
>> 
>> Hi,
>> 
>> I’m wondering if anyone has been able to plot the UKMET grib data 
>> available on the TGFTP ftp site 
>> (ftp://tgftp.nws.noaa.gov/SL.us008001/ST.opnl/MT.bmoav_CY.12/) using 
>> GrADS. It is a thinned lat-long grid and I am able to convert it to a 
>> GRIB2 file using cnvgrib and run wgrib2 on the files, but it’s not 
>> plotting. Just wanted to see if anyone had success plotting these 
>> files and how it was accomplished.
>> 
>> Thanks
>> 
>> Brian
>> 
>> 
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--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org



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