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Re: status africa data

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  • Subject: Re: status africa data
  • Date: Fri, 5 Jun 2009 14:01:15 -0600 (MDT)
On Fri, 5 Jun 2009, Ethan Davis wrote:


Robb Kambic wrote:

There is also a problem with the TOM_REALFORECASTS.20080112_v1_pf.grb grib
that has ~50 perturbations in the file. The variables look the same to
the our grib reader because ECMWF uses local additions to the PDS
section to distinguish the variables. Using the ECMWF decoder gribex,
the following local use information was displayed.

ECMWF local usage identifier.               30
 Class.                                       1
 Type.                                       11
 Stream.                                   1035
 Version number or Experiment identifier.  0001

I don't know what this means but it probably identifies the variables so
they aren't treated the same. According to the WMO documentation it states:

29-40    Reserved: need not be present
41-nn    Reserved for originating center use

So ECMWF is complying with the Grib1 specfications.


I'm not sure I understand how this is in compliance. Since 29-40 are
reserved, shouldn't they be using 41 or above for the local usage
identifier?


Ethan,

They do, look at:

http://www.ecmwf.int/publications/manuals/libraries/gribex/localDefinition1.html
The problem I see is that it describes the ensemble information but so far I haven't found out how they distinguishing the perturbations. The PDS is 106 bytes long, the ensemble information stops at byte 52. The information in bytes 53-106 appears to be the same for every record. So that doesn't help. I'll have to create a support message about this problem. 

Robb...






Ethan



===============================================================================
Robb Kambic                                Unidata Program Center
Software Engineer III                      Univ. Corp for Atmospheric Research
address@hidden             WWW: http://www.unidata.ucar.edu/
===============================================================================