Extract variables from GFDL FRE *.static.nc files

[tsjackson-noaa]

FRE postprocessing combines static data for a given component into a single netCDf file, eg. the 'areacello', 'deptho', etc. variables for an ocean model will all be in an ocean_monthly.static.nc file. Scripts expect one variable per netcdf file, regardless of frequency, so the framework preprocessing will need to extract these into separate files.

[jkrasting]

This could also facilitate the use of files in GFDL’s “av” time-averaged post-processing format.