[gradsusr] Incompatible Grids in 20th Century Reanalysis (Version 2) Data

[Semyon Grodsky]

Stephen,
lon from LTM file is corrupted. It has two 164 values, one of which is 
supposed to be 166. That is why lon from LTM is set to levels instead of 
linear when opening by sdfopen.
The easiest way to avoid this problem is to write the CTL for LTM data.
--Senya


  On Wed, 23 Feb 2011, Stephen McMillan 
wrote:

> Recently I wrote the Webmaster for the 20th Century Reanalysis V2 data
> plotting pages, regarding grid incompatibility between the following two
> data files:
>
> Monthly means:
>
> ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/Monthlies/monolevel/air.sig995.mon.mean.nc
> Monthly longterm means:
>
> ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/Derived/Monthlies/monolevel/air.sig995.mon.ltm.nc
>
> I can plot the "air" variable from each without a problem, but when I
> subtract the longterm mean from the mean to create an anomaly, I get a grid
> incompatibility error.  The means file was sdfopened first, the longterm
> means file second.  For example, doing Aug1969:
>
> ga-> d air(time=aug1969)-air.2(t=8)
> Operation error:  Incompatable grids
>  Dimension ranges aren't equivalent
>  Dimension = 0
>  1st grid range = 1 181   2nd = 1 181
>  Error ocurred at column 29
> DISPLAY error:  Invalid expression
>  Expression = air(time=aug1969)-air.2(t=8)
>
> My workaround is to first regrid the longterm mean to a 2-deg linear grid,
> but it would be preferable to do a simple difference as in example above.
> The Webmaster suggests it's a GrADS bug.  His response:
>
> "The grids are identical.  This appears to be a GrADS bug.  No such
> problem obtains in NCL.  GrADS appears to insist that the longitudes
> in the LTM file don't wrap, even when they are manually set to do so.
> We have run every test we can think of, including dumping the longitudes
> from both files and comparing them.  They are the same."
>
> I have tried this with OpenGrADS versions 2.0.a7.oga.3 and 2.0.a9.oga.3 with
> equal results, but have not tried with the COLA version of either.  Can one
> of the developers or other user shed some light on this?
>
> I am using GrADS on a Windows XP.
>
> Stephen McMillan
>
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-----------------------------------------------------------
Semyon Grodsky
Computer and Space Science Building (Bldg. #224), Room 2409
Department of Atmospheric and Oceanic Science
University of Maryland
College Park, MD 20742

Phone:  301-405-5330
Fax:    301-314-9482
E-mail: senya at atmos.umd.edu