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<p>Thank you Wesley for clarification!</p>
<p>Ivan<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 8/24/20 1:28 PM, Wesley Ebisuzaki -
NOAA Federal wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAMHOGenZGD9z9kw6ppA6iH-+03XfTcHbRnh-4s5N=vKnnRhhCA@mail.gmail.com">
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<div class="gmail_default" style="font-size:small">Ivan,</div>
<div class="gmail_default" style="font-size:small"><br>
</div>
<div class="gmail_default" style="font-size:small">GraDS using a
ctl file created by g2ctl is <br>
</div>
<div class="gmail_default" style="font-size:small"> (1)
bllinear interpolating from the raw grid (probably rotated
lat-lon)</div>
<div class="gmail_default" style="font-size:small"> to
the GrADS display grid as defined by XDEF and YDEF in the ctl
file.</div>
<div class="gmail_default" style="font-size:small"> (2)
bilinear interpolatiing from the GrADS display grid to the
point that you selected.<br>
</div>
<div class="gmail_default" style="font-size:small">
lat 45.822 lon 16.034</div>
<div class="gmail_default" style="font-size:small"><br>
</div>
<div class="gmail_default" style="font-size:small">Wgrib2 using
the -lon option is using a nearest neighbor interpolation</div>
<div class="gmail_default" style="font-size:small"> from the
raw grid to the point that you selected.</div>
<div class="gmail_default" style="font-size:small"><br>
</div>
<div class="gmail_default" style="font-size:small">The next
release of wgrib2 will have bilinear interpolation to a set of</div>
<div class="gmail_default" style="font-size:small">points. A
user reminded me that the interpolation library had that
facility.<br>
</div>
<div class="gmail_default" style="font-size:small"><br>
</div>
<div class="gmail_default" style="font-size:small">Wesley</div>
<div class="gmail_default" style="font-size:small"><br>
</div>
<div class="gmail_default" style="font-size:small"><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, Aug 23, 2020 at 12:57
PM Brian Gaze <<a href="mailto:brianw.gaze@googlemail.com"
moz-do-not-send="true">brianw.gaze@googlemail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div dir="ltr">Ivan,<br>
</div>
<div dir="ltr"><br>
</div>
<div>Not sure if it would account for the difference but
when converting from K to C it should be -273.15.</div>
<div><br>
</div>
<div>So in your example:</div>
<div><br>
</div>
<div> 'd tmp2m-273.15' <br>
</div>
<div><br>
</div>
<div>Brian</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, 23 Aug 2020 at
17:01, <<a
href="mailto:gradsusr-request@gradsusr.org"
target="_blank" moz-do-not-send="true">gradsusr-request@gradsusr.org</a>>
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Today's Topics:<br>
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1. GrADS and wgrib2 temperatures in disagreement
(Ivan Toman)<br>
<br>
<br>
----------------------------------------------------------------------<br>
<br>
Message: 1<br>
Date: Sun, 23 Aug 2020 12:01:51 +0200<br>
From: Ivan Toman <<a href="mailto:ivtoman@inet.hr"
target="_blank" moz-do-not-send="true">ivtoman@inet.hr</a>><br>
To: GrADS Users Forum <<a
href="mailto:gradsusr@gradsusr.org" target="_blank"
moz-do-not-send="true">gradsusr@gradsusr.org</a>><br>
Subject: [gradsusr] GrADS and wgrib2 temperatures in
disagreement<br>
Message-ID: <<a
href="mailto:80efbf07-0e18-4a6f-b073-651ffe3f0cf4@inet.hr"
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<br>
Hello dear GrADS users,<br>
<br>
I have a problem. If I extract 2m temperature for a
single lat/lon point <br>
using GrADS, it is in slight disagreement compared to
same record <br>
obtained from grib2 file using wgrib2.<br>
<br>
The difference is usually around 1C but can be larger
from time to time. <br>
I'm almost 100% sure I did not overlook anything obvious
like selecting <br>
different time or diffrent lat/lon coordinates, but I
leave something <br>
like that as a theoretical possibility if there is no
better <br>
explanation. Below is an example how I extract
temperatures using GrADS. <br>
Grib2 is WRF file, Lambert projection, and ctl/idx files
are created <br>
using latest g2ctl and gribmap utilities. I note this
because it might <br>
be that projection gets somehow skewed and that GrADS
takes data from <br>
incorrect positions. Is that possible at all?<br>
<br>
It seems very important to add that wgrib2 method is in
exact agreement <br>
to the tslist output from WRF, so for now I take that
one as "correct" <br>
one and GrADS figures as "incorrect".<br>
<br>
Simple extraction method in GrADS:<br>
<br>
'set lat 45.822'<br>
'set lon 16.034'<br>
'set string 1 bl 3 0'<br>
'set t 13'<br>
'd tmp2m-273'<br>
ans = sublin(result,2)<br>
temp = subwrd(ans,4)<br>
<br>
<br>
Is this difference normal/expected? If it is, what's the
reason for <br>
that? If not, is there anything else where I could
search for user error?<br>
<br>
Thank you,<br>
<br>
Best regards,<br>
<br>
Ivan Toman<br>
<br>
<br>
<br>
<br>
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