Gribtonc changes

Hiya,

I'm writing to inform you about some proposed changes to the output
netCDF files produced by the gribtonc (GRIB-to-netCDF) decoder.  There
are about 35 sites that have installed the decoders package as far as I
know.  I'm currently in the process of updating the package, including
the CDLs to make them more useful and to add attributes required by
new conventions.

The original CDLs followed the NUWG conventions:

  http://www.unidata.ucar.edu/packages/netcdf/NUWG/

which haven't been modified in several years,

Lately the CF conventions

  http://www.cgd.ucar.edu/cms/eaton/cf-metadata/index.html

are becoming established as a more complete set of conventions for
model output.  Also, we are considering including spatial and temporal type
variables to make the NetCDF file more GIS compatible.  Another idea is to
enhance the metadata about the date for THREDDS servers and other NetCDF
clients.

The CDL variable names will continue to follow the NUWG conventions
for backward capability. The long_name attribute has been standardized
by concatenation of the NUWG variable name plus the NUWG level name
using the word "at" as a connector. So, the T_trop long_name is
"Temperature at tropopause" in all the CDLs.  This supports
consistency in applications such as Unidata's IDV (Integrated Data
Viewer). For similar reasons, we are adding attributes required by
other conventions such as CF, such as the standard_name attribute.  A
sample variable will look like:

        float  T_trop(record,y,x) ;
               T_trop:long_name = "Temperature at tropopause" ;
               T_trop:standard_name = "air_temperature" ;
               T_trop:units = "degK" ;
               T_trop:GRIB_parameter_number = 11 ;
               T_trop:GRIB_level_flag = 7 ;
               T_trop:_FillValue = -9999.f ;
               T_trop:navigation = "nav" ;


Some other additions to the variable attributes are the GRIB_parameter_number,
and the GRIB_level_flag attributes. These are being included so other
conventions may refer to the NCEP GRIB tables as a cross reference.  This will
permit more flexible usage for the NetCDF files.

Another variable has been added called forecast_time, a human readable
string representing the valid forecast times. To make the  data
monotonically increasing, the code sets records for all the valid times in the
netCDF file on initialization.

When netCDF GIS applications become available, the new NetCDF files
will already have the needed information for correct display. We are also
considering temporal variables so time bounding boxes can be created for the
datasets.

This is a brief summary of the kind of modifications we are making to
the decoders package.  If you have other ideas about what should be
included or omitted, please send in your comments.


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