XDFOPEN For Nonstandard NetCDF File

[daved]

Hi Jennifer,
Thanks, that worked fine. Can you tell me how such an xdf descriptor
file could be opened remotely
via GDS? My confusion is the use of open versus xdfopen. Is it possible
to use the open
command in GDS?

Dave

Jennifer M. Adams wrote:

> Dave,
> The simplest option is to use the Z dimension as a proxy for M, since
> your variable doesn't appear to vary in Z. Using the Z dimension
> makes it easier to slice and dice (and average) through your ensemble
> dimension, but you should document in the descriptor file (with
> comments and perhaps in the title too) that Z is ensemble member
> instead of a vertical axis such as depth or millibars. You can still
> use xdfopen if you do it this way, just give the name of the ensemble
> dimension with your ZDEF entry.
>
> The second option is to list each ensemble member as a separate
> variable, with declarations like this:
> t2m=>t2m0 0 t,0,y,x 2m Temperature Ensemble 0
> t2m=>t2m1 0 t,1,y,x 2m Temperature Ensemble 1
> t2m=>t2m2 0 t,2,y,x 2m Temperature Ensemble 2
> ...
> With this option you have to use the 'open' command with a full
> 'dtype netcdf' descriptor. This reminds me of a question from Vincent
> Moron (a colleague of yours at IRI) who asked about reading a netcdf
> with 5 dims. I believe the 2nd option would work in his case ...
>
> A variable that looked like this (with ncdump)
> float u(T,M,Z,Y,X)
> could be described this way (assuming Z dimension has 5 elements):
> u=>u0 5 t,0,z,y,x U-Wind Ensemble 0
> u=>u1 5 t,1,z,y,x U-Wind Ensemble 1
> ...
>
> This option didn't occur to me at the time when he asked his
> question, but I do think that will work, although I haven't tested it
> (yet)!
>
> Jennifer
>
>
>
> On Mar 16, 2006, at 1:19 PM, David G DeWitt wrote:
>
>> Hi Folks,
>> I am trying to open a netcdf file that has an extra dimension, i.e.
>> ensemble
>> member. Reading the documentation it appears that GrADS can handle
>> this
>> with a comma delimited list for the units parameter, i.e.
>>
>> VAR=>hist0 0 0,y,x First historgram interval for VAR
>>
>> is the example given in the documentation. For a variable with the
>> following ncdump what would this syntax look like:
>>
>> float t2m(T, M, Y, X)
>>
>> where:
>> T is time
>> M is ensemble member (the non-standard dimension)
>> Y is latitude
>> X is longitude
>>
>> Thanks for any advice you can give me on this. I have tried what I
>> thought
>> this would be and I clearly do not understand the example.
>>
>> Dave
>>
>
> Jennifer M. Adams
> IGES/COLA
> 4041 Powder Mill Road, Suite 302
> Beltsville, MD 20705
> jma at cola.iges.org



--
Dr. David G. DeWitt
223 Monell Building
IRI - International Research Institute for Climate Prediction (IRI)
Lamont-Doherty Earth Observatory
Columbia University
61 Route 9W
Palisades, NY 10964-8000
United States
Phone: (845) 680-4415
Fax: (845) 680-4865
daved at iri.columbia.edu