[Met_help] MET point stat problem with wind projection

[John Halley Gotway]

Marlous,

Did you also apply the updated version of "point_stat.cc" I sent you?  I'm guessing not because that's the error message you'd get if you didn't.  So I'm resending that patch to point_stat.cc.  You'll
need to use both.

Thanks,
John

Marlous Jonker wrote:
> Hi John,
> 
> Thanks for the help. I copied the new read_grib.cc file into the right
> directory and recompiled MET like you said. The previous error is not
> there anymore, so that's good. However, there is a new one:
> 
> "ERROR: read_grib_record() -> can't find matching VGRD record when
> trying to rotate the UGRD field to grid-relative coordinates"
> 
> In the attachment is the grib file I used. According to me, both the
> UGRD and VGRD records are in the grib file. The file is a product of the
> WRF post processor and is interpolated by copygb, so there should be no
> problem, yet there is.
> 
> I am a bit confused where this error originates from. Hope you can help
> me out.
> 
> Cheers,
> Marlous
> 
> -----Oorspronkelijk bericht-----
> Van: John Halley Gotway [mailto:johnhg at ucar.edu] 
> Verzonden: vrijdag 7 mei 2010 23:21
> Aan: Marlous Jonker; met_help
> Onderwerp: Re: [Met_help] MET point stat problem with wind projection
> 
> Marlous,
> 
> OK, upon further review, I see that that check we're doing for lat/lon
> grids is totally unnecessary.  There's no wind rotation required for
> lat/lon grids since grid-relative and earth-relative winds are the same!
> I'm sending you an additional file from which I've removed that
> unnecessary check.  Please copy the attached version of "read_grib.cc"
> into METv2.0/lib/vx_met_util/. and recompile MET.
> 
> It appears that I sent you a previous version of read_grib.cc on April
> 16, 2010.  I've made this change on top of that other file I sent you.
> So the attached file contains both.
> 
> You should now be able to verify UGRD and VGRD using Point-Stat.  Again,
> I'll be sure to add this change to the development version so it shows
> up in the upcoming release.
> 
> Please let me know if you run into any problems.
> 
> Thanks,
> John
> 
> John Halley Gotway wrote:
>> Marlous,
>>
>> OK, I see what's going on here.  There are two main issues - one
> that's easy to address and one that will take more time.
>> First, the easy one.  The GRIB file you sent me contains 4 records: 
>> UGRD, VGRD, TMP, DPT.  The records are defined on a lat/lon 
>> projection, and the winds fields are defined relative to the grid.  In
> 
>> Point-Stat, the "process_grid()" subroutine is called to extract the 
>> grid definition from the file and setup masking regions and what not.
> That "process_grid()" routine just reads the first record from the GRIB
> file to extract that grid definition.  However, the first record in the
> file you sent is for UGRD.  And since your UGRD records are on a lat/lon
> grid and the winds are defined relative to the grid, that's the problem.
> When winds are defined to be grid relative, MET first rotates them to be
> earth relative before verifying them.  And for some reason, we haven't
> implemented that grid rotation for lat/lon projections.
>> My fix for this first problem is, rather than reading the first record
> 
>> from the GRIB file, just use the first verification field requested in
> 
>> the config file to define the grid.  That's what we do in the other 
>> MET tools anyway.  I'm not sure why the logic was different in
> Point-Stat.  The attached version of "point_stat.cc" does just that and
> should enable you to read these GRIB files with Point-Stat.  I'll
> include this change in the development version of Point-Stat so it gets
> included in the next official release of MET.  But I won't post the
> change as a bug fix unless I get more complaints about it.
>> So copy the attached version of "point_stat.cc" into
> METv2.0/src/point_stat/. and recompile MET.
>> Second, the harder issue.  We need to add support for rotating winds 
>> from grid relative to earth relative for lat/lon grids.  I'll talk to
> another developer here about this issue next week.  Until we add that
> functionality, you won't be able to verify these wind fields using MET.
>> Hope that helps.
>>
>> Thanks,
>> John Halley Gotway
>> met_help at ucar.edu
>>
>> Marlous Jonker wrote:
>>> Hi John!
>>>
>>>  
>>>
>>> How are you doing? Since your last help with MET I've been able to 
>>> produce PointStat statistics for temperature and dew point 
>>> temperature using WRF output and it looks pretty good, so thanks 
>>> again for your previous help! Next thing coming up is 10m wind
> verification.
>>> Implementing it in the config file, I encounter this error:
>>>
>>>  
>>>
>>> "ERROR: read_grib_record() -> rotation of non-conformal Plate Carree 
>>> projection not yet implemented"
>>>
>>>  
>>>
>>> I even get this error when removing the wind from the config file as 
>>> verification parameter. It's only when the U GRD and V GRD variables 
>>> are removed from the grib file that I could get rid of this error.
>>>
>>>  
>>>
>>> I wonder what the meaning of this error is (something with the wind
>>> projection?) and whether there is something wrong with the grib file 
>>> or some other reason I cannot think of.
>>>
>>>  
>>>
>>> In the attachments are the config file, MET ascii observation file 
>>> and 2 grib files: one _orig with the wind and one without the wind
> variables.
>>>  
>>>
>>> I hope you can help me with this problem too.
>>>
>>>  
>>>
>>> Cheers and thanks in advance,
>>>
>>> Marlous
>>>
>>>  
>>>
>>> -------------------------------------------------------------------
>>>
>>>   Marlous Jonker
>>>
>>>   Meteorological Researcher
>>>
>>>   Meteo Consult BV, Wageningen, the Netherlands
>>>
>>>   Tel: +31 (0)317 399872
>>>
>>>   Email: M.Jonker at weer.nl
>>>
>>>   www: research.meteogroup.com
>>>
>>> -------------------------------------------------------------------
>>>
>>>  
>>>
>>>
>>>
>>>
>>>
>>> ---------------------------------------------------------------------
>>> ---
>>>
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> 
> 
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