NJ22 and WRF data

[John Caron]

Hi Robert:

If you read through NetcdfFile class, you get the raw data.

If you read through NetcdfDataset(enhance=true), you get the extra stuff. The "scientifiic data types" like Grid always use this mode.

NetcdfDataset looks for a "CoordinateSystemBuilder" that recognizes that dataset, eg ucar.nc2.dataset.conv.WRFConvention class. This is the class that adds the coordinate variables, etc, by understanding that particular files' metadata, in WRF case, I think its all in the global attributes. 

WRF continues to be a hard one to get right, there's a few flavors of it, the projection info is fishy, etc. If you send me a sample file I might be able to figure out why things aren't working out.

John


Robert B. Schmunk wrote:
> 
> John,
> 
> A user of the Weather Research & Forecast model at UCAR asked me
> for some help viewing a netCDF dataset in Panoply. In taking a
> closer look at the metadata I have been rather startled to find
> that the NJ22 libraries report some information present in the file
> that the simple CDL output of ncdump does not reveal at all.
> 
> Although I have been used to seeing this in the past for variable
> attributes, which NJ22 would prefix with an underscore (e.g.,
> ":_CoordinateAxisType"), NJ22 is reporting entire variables for a
> sample WRF dataset which ncdump does not show. Most if not all of
> these seem related to defining the coordinate system, e.g.,
> 
>    double x(west_east=93);
>      :units = "km";
>      :long_name = "synthesized GeoX coordinate from DX attribute";
>      :_CoordinateAxisType = "GeoX";
>      :_CoordinateAliasForDimension = "west_east";
>    double x_stag(west_east_stag=94);
>      :units = "km";
>      :long_name = "synthesized GeoX coordinate from DX attribute";
>      :_CoordinateAxisType = "GeoX";
>      :_CoordinateAliasForDimension = "west_east_stag";
> 
>    char Lambert;
>      :Projection_Name = "lambert_conformal_conic";
>      :latitude_of_projection_origin = 27.070636749267578; // double
>      :longitude_of_central_meridian = 120.0; // double
>      :standard_parallel = 10.0, 40.0; // double
>      :_CoordinateTransformType = "Projection";
>      :_CoordinateAxisTypes = "GeoX GeoY";
> 
> As there is not even a "Conventions" tag in the global attributes,
> I am highly curious as to exactly how NJ22 is recognizing this
> dataset and how it goes about filling in this "extra" information.
> There do seem to be some WRF classes in the API, but only WRFEta
> is in the public API.
> 
> Oddly enough, none of the quantity variables in the sample file I
> have been given are reported as being on the Lambert conformal
> conic grid, despite the Lambert information mysteriously reported.
> It's possible, of course, that the dataset's creator has omitted
> some necessary attributes.
> 
> rbs
> 
> 
> 
> 
> -- 
> Robert B. Schmunk, rschmunk at giss.nasa.gov
> NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025