[gradsusr] Difference two files in GrADS continued

[Phil Klotzbach]

Hi everyone,

Thanks so much for your help!  In order to zero in on the problem 
further, I've tried to simplify the problem by opening two files with 
the exact same dimensions (latitude/longitude/time/levels) (uwnd.2009.nc 
and uwnd.2010.nc).  Basically, what I want to obtain is a height/time 
cross-section of the difference between the two years (e.g., zonal wind 
in 2010 minus zonal wind in 2009).  Let's say in this case, I've opened 
up uwnd.2010.nc first and then uwnd.2009.nc second - using the sdfopen 
command.  Since I want to create a height/time cross-section, I need to 
set the following dimensions before starting the calculation:

set dfile 1
set t 152 258
set z 1 16
set x 1
set y 1

Then, I want to create an average over a specific area:

uave = aave(uwnd, lon=-70, lon=-20, lat=0, lat=30)

When I display the uave field, it looks perfect - a height/time 
cross-section for zonal wind in 2010.   But, if I then switch to the 
second file (e.g., set dfile 2) (zonal wind in 2009) and try to change 
the dimensions on that file, it instantly tells me that uave (the 
variable that had the height/time cross-section for 2010) has all 
undefined values.  For example:

set dfile 2
set t 152 258
display uave - Gives message saying cannot contour grid - all undefined 
values

I'm not sure how to get around this issue.  I tried this with two files 
that have the exact same dimensions (e.g., uwnd.2009.nc and 
uwnd.2010.nc) - in order to make sure that it wasn't a time dimension 
mismatch that was causing the original problem.

Is there any way to specify the dimensions in both files at the same 
time?  Thanks for any additional help.

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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