[Met_help] Met questions
John Halley Gotway
johnhg at rap.ucar.edu
Wed Nov 19 16:13:49 MST 2008
Sounds good to me. As long as you can get your output into GRIB version 1 format, you should be fine. MET does not currently support GRIB version 2, but I'd bet your PostProcessor is writing GRIB
version 1 anyway. GRIB version 1 is a VERY rigid format. As long as your data is in GRIBv1, I'm confident that you'll be able to run it through MET.
And you're correct, here's what we require:
- the data must be on a regular grid (lat/lon, polar stereographic, mercator, or lambert conformal) and on pressure levels.
- the GRIB file must contain a GDS section (i.e. grid-description-section). I'm not sure if a GDS is "required" in GRIB, but I've never seen a GRIB file without one.
- in MET, when comparing a gridded forecast to a gridded observation, they must be on the same grid. The copygb tool may be used to regrid a GRIB file.
I can't say with 100% certainty that you won't run into problems, but I'm very hopeful. In the past, we've found some minor bugs in reading GRIB files. But if you run into one, we'll fix it.
If you'd like a lot of detail about how GRIB files are structured, here's a document from NCEP that I refer to a lot:
Ed Tollerud wrote:
> We have expanded the list of models that we seek to verify using MET
> with point data to include RUC, GFS, and others (!!!!) in addition to
> our WRF ensemble (ARW, NMM, ARW with different versions of
> microphysics). Since processing so far has been performed using LFMPost
> (our local postprocessor), our plan now is to create MET-compatible GRIB
> versions for all these using LFMPost instead of WPP. My understanding is
> that 'compatible' means in pressure coordinates on a regular
> (non-staggered) grid. Are there other GRIB-related factors that we also
> need to consider? Do output fields need to have a certain name or units
> (to match WRFpost maybe) or that always designated in the MET command
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