[gradsusr] mysterious bug with merra-2 data

[Jennifer M Adams]

Well, in one example, you are reading data from the edge of the time series (t=1) and in the other you are reading from the middle. Are you doing some interpolation to get your data values? You should look at the output from ‘set lat 49’ ‘set lon 4.375’, ‘set t 1’, and ‘set t 8017’ and check the ‘q dims’ output to see if you’re really reading the grid elements you are expecting. 
—Jenniferg


> On Mar 8, 2018, at 11:29 AM, Antoine Molin <amolin at plenr.fr> wrote:
> 
> Hi,
> 
> Thanks, but it doesn't change the bug.
> Antoine
> 
> -----Message d'origine-----
> De : gradsusr [mailto:gradsusr-bounces at gradsusr.org] De la part de Jennifer M Adams
> Envoyé : mardi 6 mars 2018 12:53
> À : GrADS Users Forum
> Objet : Re: [gradsusr] mysterious bug with merra-2 data
> 
> Try setting your tdef to be at 00z instead of 00:30z. 
> —Jennifer
> 
>> On Mar 2, 2018, at 9:11 AM, Antoine Molin <amolin at plenr.fr> wrote:
>> 
>> Hi,
>> 
>> I am using merra-2 data U&V wind speeds at 50m, for wind energy studies in France ; very good data…..
>> 
>> Getting « MERRA2_400.tavg1_2d_slv_Nx.%y4%m2%d2.SUB.nc4»  daily files, data are obtained with grads, using xdfopen and enclosed data descriptor files.
>> 
>> I really don’t understand why i get different values with different descriptor files, for same point and time :
>> 
>> As an example, at point (49°N ; 4.375°E) and time  2017-12-01 at 0h,  i get U50m=5.31 m/s using « merra2_dec2017.ctl »  (lat = 49, lon = 4.375, t = 1), and U50m=5.22 m/s using « merra2_2017.ctl »  (lat = 49, lon = 4.375, t=8017)…..
>> 
>> Why ????????????????
>> 
>> Thanks !
>> 
>> 
>> Antoine Molin
>> Etudes de vent PlenR
>> Tel : 03 20 47 99 76
>> 
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> --
> Jennifer Miletta Adams
> Center for Ocean-Land-Atmosphere Studies (COLA) George Mason University
> 
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--
Jennifer Miletta Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
George Mason University