Re: wrf-gribs in ncl?

To add a little to the comments from Dennis and Rick, typical WRF
user-produced files have the center set to
255 because anyone can run the model and produce GRIB output. There
is no officially recognized WMO
center that is responsible for the output.

When NCL does not recognize a center it uses the standard WMO table
for the first parameters 1-127, but
because parameters 128-254 are designated "reserved for use by the
originating center", it does not attempt
to assign a name and units to parameters with these indexes.

However, in the WRF files I have looked at so far, the parameters
above 127 seem to correspond with the
parameters in the standard table provided by NCEP (US National Center
for Environmental Prediction) as
listed here:

http://www.nco.ncep.noaa.gov/pmb/docs/on388/table2.html

You can make NCL recognize these, as Dennis notes, by setting NCL up
to recognize a user-defined table.
Look at
http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/
NclFormatSupport.shtml#GRIB1-user-defined-parameter-tables

To use the NCEP table 2 values you do not have to create your own
text version of the table. You can grab it at

http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/ncep_opn.txt

You will need only to edit the line that starts with -1 to make it
universally applicable.
Change
-1 : 7 : 0 : 0
to
-1:-1:-1:-1

Then set
NCL_GRIB_PTABLE_PATH to the path of the file.

Hope this helps.
  -dave

On Jan 14, 2008, at 9:06 AM, Dennis Shea wrote:

> Hello
>
> I am sure one of the NCL developers will respond more elaborately
> later today.
>
> [1] Yes, it is possible to use WRF GRIB files.
>
> [2] *The data values and dimensionality are decoded correctly*.
> [3] NCL decodes the values but the specific parameter table
> needed
> to assign a variable name and units is not built-in to NCL.
> Hence,
> a *warning* message is issued.
>
> Please see the GRIB section of:
>
> http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/
> NclFormatSupport.shtml
>
> I believe "center=255" means missing data center identification.
>
> If you know the parameter information, you can input your own table.
>
> Regards
>
>
>
>
> There was a recent ncl-talk question regarding WRF GRIB-1
>
> [
> ern_at_student.matnat.uio.no wrote:
>> Hi all,
>> I am trying to use WRF grib1 out-files in ncl but get the
>> following error
>> message for several variables:
>>
>> warning:NclGRIB: Unknown grib parameter number detected (130,
>> center 255,
>> table version 2 grib record 1), using default variable name (VAR_130)
>>
>> Is it at all possible to use wrf gribs in ncl? and if so, does
>> anyone know
>> a way to get around this error?
>>
>> I have ncl Version 5.0.0.
>>
>> Thanks for any advice on this!
>> /Erik
>>
>> _______________________________________________
>> ncl-talk mailing list
>> ncl-talk_at_ucar.edu
>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>
>
>
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Received on Mon Jan 14 2008 - 12:23:38 MST