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

[Stephen McMillan]

Senya,
I had not noticed the duplicate 164 values before, but I now see it when I
'q ctlinfo' on the LTM file.  Thanks for pointing that out, and for the CTL
file suggestion.
Stephen

On Wed, Feb 23, 2011 at 4:03 PM, Semyon Grodsky <senya at atmos.umd.edu> wrote:

> 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
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