Grib2 UV winds

[Jennifer Adams]

Dear Michael --
With grib1, a record contained a single 2D grid. But with grib2, a
record can contain more then one 2D grid -- which are now referred to
as 'fields'. NCEP is packaging U and V fields into a single record;
other data providers are rumored to be putting ALL fields into a
single grib2 record. It's more economical (fields can share metadata
this way), but it makes grib2 a bit more complex than grib1. I
haven't used the degrib program, but there must be a way to specify
which field you want to extract... You could also try Wesley's wgrib2
program.
Jennifer
p.s. We are working on the direct GrADS interface to grib2. No
promises regarding a time frame, but we hope to have an alpha release
sometime this fall for early adopters to try...

On Jul 5, 2007, at 9:44 PM, Michael Purves wrote:

> We are making extensive use of GRIB2 meteorological data. I use
> degrib -c Msg# -Flt -GrADS to convert the GRIB2 data for a given
> field into a binary float file and a control file. This process
> works well with all fields, except UGRD and VGRD. In the GRIB2
> index files, these fields have a decimal value for the Message Number.
>
> 21:525022:d=2007070200:RH Relative humidity [%]:200 mb:6 hour fcst
> 22.1:546161:d=2007070200:UGRD u wind [m/s]:1000 mb:6 hour fcst
> 22.2:546161:d=2007070200:VGRD v wind [m/s]:1000 mb:6 hour fcst
>
> If I input the decimal number into degrib, the degrib program
> crashes. If I enter just the integer value, I get reasonable
> looking values for the UGRD field, but the VGRD field is identical
> to UGRD.
>
> Can anyone point me in the right direction to get both UGRD and
> VGRD from these GRIB2 files?
>
> Thank you,
>
> Michael Purves
>
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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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