[gradsusr] Differencing two files in GrADS

[Phil Klotzbach]

Good evening,

I am currently running OpenGRADS 2.0.1 on my Windows 7 laptop.  What I 
am attempting to do is to plot a difference between 2013 values of zonal 
wind from the long-term (1981-2010) mean values.  I have downloaded two 
separate files from the NCEP/NCAR Reanalysis off of ESRL's website 
(e.g., uwnd.2013.nc and uwnd.day.1981-2010.ltm.nc). What I am hoping to 
do is to generate a height/time cross-section of zonal wind anomalies 
during the past several months of 2013.  I am attempting to see if 
westerly wind anomalies propagating from the stratosphere have been 
impacting the circulation in the tropical Atlantic.

Before I get to a vertical cross-section, I figured I would start with a 
simpler problem of just differencing the values of 2013 zonal wind from 
the long-term mean zonal wind.  The problem that I am having is how to 
difference values of uwnd from the first file from values from the 
second file.  I have read documentation online, and it appears that you 
should be able to just generate an equation such as: uwnd_total = uwnd - 
uwnd.2 (to difference the values from the two files).  However, the 
error message that I get is as follows:

Entire grid contents are set to missing data
Grid limit of file: X = 1 144 Y = 1 73 Z = 1 17 T = 1 365 E = 1 1
Grid limit of request: X = 1 145 Y = 1 73 Z = 1 1 T = 734869 734869 E = 1 1
Warning issued for variable = uwnd.2

It looks like the problem is that GrADS does not know what the 
dimensions of the second file are.   How do you specify in the equation 
the dimensions of both variables at the same time?

Thanks for any help that you can provide.

Phil

--
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Phil Klotzbach, Ph.D.
Research Scientist
Department of Atmospheric Science
Colorado State University
Email: philk at atmos.colostate.edu
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