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<p>Hello,</p>
<p>No the 273.15 is not factor because I use same conversion in both
methods and also difference is not constant.</p>
<p>My lat/lon points do not correspond to the exact grid point
locations. However, I am aware that GrADS will select nearest grid
point, but, doesn't wgrib2 also do the same? Do you think that
wgrib2 (and tslist output) does interpolation automatically?</p>
<p>My wgrib2 method is this:</p>
<p>wgrib2 $gribfile -rpn "273:-" -match "(TMP:2 m)" -lola "$lon:1:1"
"$lat:1:1" grid.grb grib >/dev/null</p>
<p>wgrib2 grid.grb -csv grid.csv >/dev/null<br>
</p>
<p>where $lon and $lat are exactly same figures as are used in GrADS
script.</p>
<p>Thank you for your idea of interpolation with gr2stn, I will try
it and see what do I get in that case.</p>
<p> Ivan<br>
</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 8/24/20 3:14 PM, Stephen McMillan
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CA+exxN1zt7UhBQD1BdhVOXN+6kyiWbbxqgXdZWN=4r+eSQsffw@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Ivan,
<div><br>
</div>
<div>In addition to Brian's response, which would account for a
difference of 0.15 deg only, please consider this...</div>
<div><br>
</div>
<div>You said nothing about your grid data resolution so, in the
example you provided, did you set the lat and lon to a precise
grid point or to a point in between grid points? When setting
lat or lon, GrADS will automatically set to the nearest grid
point, which may be different than what you intended.</div>
<div><br>
</div>
<div>Have you considered interpolating instead to your desired
point? E.g., using gr2stn or lterp. Here's an example using
gr2stn:</div>
<div><br>
</div>
<div>'d gr2stn(tmp2m-273.15,16.034,45.822)'</div>
<div><br>
</div>
<div>Stephen Mc</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, Aug 23, 2020 at 6:08
AM Ivan Toman <<a href="mailto:ivtoman@inet.hr"
moz-do-not-send="true">ivtoman@inet.hr</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">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>
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