[Met_help] Re: Applying grid_stat to custom fields

[John Halley Gotway]

Jan,

I understand your frustration.  There's always a desire to support more data formats.  The reason we chose to begin by supporting GRIB is that our original statement of work required us to replicate 
and extend the existing capabilities of a verification package from NCEP.  Their package only reads GRIB data, so that's where we had to start.

I would like to support a more generalized NetCDF format for gridded data in the future.  However, we will need the grid information encoded into the NetCDF file for MET to read.  The output of 
PCP-Combine is gridded NetCDF, and we do encode the grid definitions into the header.

As for a workaround... since PCP-Combine writes out gridded NetCDF data that Grid-Stat can read, I'd suggest reformatting your NetCDF files to look like the output of PCP-Combine.  However, rather 
than working with METv1.0, I'll give you a beta release of METv1.1 to work with.  We've generalized the output of PCP-Combine a bit for METv1.1.  I haven't done this myself, but I do know of other 
users who have.  So hopefully it'll work alright.

In your NetCDF file, you'll need to name the field "WIND" since that's the GRIB abbreviation for wind speed (http://www.nco.ncep.noaa.gov/pmb/docs/on388/table2.html), and you'll need to add the grid 
information to the header.  Take a look at the example NetCDF output from PCP-Combine for the beta version of METv1.1 for an example.  If you need help figuring out how to define the grid info, let me 
know.

Also, I should mention that we will be supporting additional NetCDF formats in the future.  Specifically, the WRF-ARW folks have come up with a PostProcessor that reads WRF-ARW output and writes 
NetCDF.  It's meant as an alternative to the WRF-PostProcessor (don't ask me why).  We plan to support their NetCDF output in coming releases.

Hope that helps.

You can access the latest beta release of METv1.1 at: ftp://ftp.rap.ucar.edu/incoming/irap/johnhg/METv1.1beta6.20080613.tar.gz

While the code is in good shape and we don't anticipate making many more changes before the release, let me caution you that the MET User's Guide included in there has not yet been updated to reflect 
the additions/fixes.  We're still working on that.

Thanks,
John

Jan Ploski wrote:
> John,
> 
> If I understand correctly, grid_stat can only process GRIB files as input, 
> but not arbitrary NetCDF files. We would like to apply MET to verifying 
> custom fields (for example: scalar wind speed at 80m geometric height), 
> which are neither standardized by GRIB nor output by the WRF 
> postprocessor. It seems to me that the need to go through GRIB 
> unnecessarily restricts MET's applicability. In my understanding MET 
> generally operates on grids, and GRIB files are a rather restrictive way 
> to represent gridded data (even though well-established in meteorology). 
> One can always convert a GRIB file to NetCDF, but not every NetCDF file's 
> content conforms with GRIB. Would you agree or is there something in the 
> GRIB format that makes it essential for some important MET functionality 
> to work? Also, could you please suggest a workaround that could make MET 
> applicable to our case?... Thanks!
> 
> Regards,
> Jan Ploski
> 
> --
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