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NCL: WRF netCDF files

WRF-ARW netCDF files do not fully conform to the common netCDF conventions: COARDS, CSM and CF.

  1. WRF variables have a named dimension "Time" but there is no corresponding coordinate variable: Time(Time).

  2. The attribute "description" is used instead of "long_name" or "standard_name". The "gsn_csm" suite of graphical interfaces will recognize the "description" attribute as a proxy for long_name (version a031).

The WRF netCDF is different from netCDF commonly produced by climate models in that the spatial coordinates (XLAT,XLONG, ZNU, ZNW) have a time dimension. However, the spatial coordinates on the sample file do not change with time. Generally, the graphic examples take advantage of this by reading only the XLAT, XLONG, ZNU and ZNW arrays at a specific time (time=0).

Another aspect of the WRF netCDF file is that the units attribute ("degree") of the XLAT and XLONG variables is not standard conforming. These attributes must be manually assigned to get the expected behavior of the gsn_csm* suite of graphical interfaces. The most commonly used standard conforming units are "degrees_north" and "degrees_east".