Grib2 UV winds

Jennifer Adams jma at COLA.IGES.ORG
Fri Jul 6 07:35:12 EDT 2007

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
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
> Be smarter than spam. See how smart SpamGuard is at giving junk
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Jennifer M. Adams
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at

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