[gradsusr] gradsusr Digest, Vol 126, Issue 20

[Brian Gaze]

Ivan,

Not sure if it would account for the difference but when converting from K
to C it should be -273.15.

So in your example:

 'd tmp2m-273.15'

Brian

On Sun, 23 Aug 2020 at 17:01, <gradsusr-request at gradsusr.org> wrote:

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>    1. GrADS and wgrib2 temperatures in disagreement (Ivan Toman)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sun, 23 Aug 2020 12:01:51 +0200
> From: Ivan Toman <ivtoman at inet.hr>
> To: GrADS Users Forum <gradsusr at gradsusr.org>
> Subject: [gradsusr] GrADS and wgrib2 temperatures in disagreement
> Message-ID: <80efbf07-0e18-4a6f-b073-651ffe3f0cf4 at inet.hr>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> Hello dear GrADS users,
>
> I have a problem. If I extract 2m temperature for a single lat/lon point
> using GrADS, it is in slight disagreement compared to same record
> obtained from grib2 file using wgrib2.
>
> The difference is usually around 1C but can be larger from time to time.
> I'm almost 100% sure I did not overlook anything obvious like selecting
> different time or diffrent lat/lon coordinates, but I leave something
> like that as a theoretical possibility if there is no better
> explanation. Below is an example how I extract temperatures using GrADS.
> Grib2 is WRF file, Lambert projection, and ctl/idx files are created
> using latest g2ctl and gribmap utilities. I note this because it might
> be that projection gets somehow skewed and that GrADS takes data from
> incorrect positions. Is that possible at all?
>
> It seems very important to add that wgrib2 method is in exact agreement
> to the tslist output from WRF, so for now I take that one as "correct"
> one and GrADS figures as "incorrect".
>
> Simple extraction method in GrADS:
>
> 'set lat 45.822'
> 'set lon 16.034'
> 'set string 1 bl 3 0'
> 'set t 13'
> 'd tmp2m-273'
> ans = sublin(result,2)
> temp = subwrd(ans,4)
>
>
> Is this difference normal/expected? If it is, what's the reason for
> that? If not, is there anything else where I could search for user error?
>
> Thank you,
>
> Best regards,
>
> Ivan Toman
>
>
>
>
>
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