[gradsusr] A problem in calculating average relative humidity in merra

Mike Bosilovich mike.bosilovich at gmail.com
Fri Jul 19 07:16:41 EDT 2013


This likely isn't a problem with grads.  Grads is returning the undef
value. If you take a look at the region around that point, at 1000mb most
land points are undef. This is because MERRA does not extrapolate to
pressure levels >  Ps.

http://gmao.gsfc.nasa.gov/research/merra/pressure_surface.php

So, check PS to see if it is < 1000mb.  It maybe a land point. If a water
point is OK to use in your work, move just a bit into the Meditterenean Sea
and you should find real values. but it is possible that there may be
undeffs over water, if the Ps becomes <1000.

If you really want data at this point, you can compute RH using surface
data, or, there is a third party routine available to perform the
extrapolation to values under the surface.

https://reanalyses.org/atmosphere/extrapolation-merra-reanalyses-obtain-continuous-fields

If you find that this is not a grads issue, feel free to contact me
offline, or use the merra-questions at lists.nasa.gov listserv.

Mike


On Fri, Jul 19, 2013 at 5:51 AM, avi kojokro <kojokroavi at gmail.com> wrote:

> I'm trying to calculate a monthly average of relative humidity, but the
> answer of Grads unreasonable.
> Is the script right? I attach it.
> I am also attaching a screenshot of Grads answer.
>
> The Script:
>
>
> 'reinit'
> 'c'
> 'set display color white'
> 'c'
> 'sdfopen http://goldsmr3.sci.gsfc.nasa.gov:80/dods/MATMCPCLD'
> 'set lev 1000'
> 'set lat 32.0'
> 'set lon 35.0'
> yr=1979
> tt=''
> while(yr<=2013)
> 'set time 1MAY'yr
> 'q time'
> say ' 'result
> *'set gxout print'
> 'd rh'
> tt1=subwrd(result,4)
> tt=tt' 'tt1
> say ' 'result
> yr=yr+1
> endwhile
> say 'apr (1979-2013) 850_hgt [m] : 'tt
>
>
>
>
>
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>
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