Post process geogrid output to compute GWD input fields directly from source data

[islas]

These changes calculate the necessary fields in a manner that accounts for subgrid-scale orography. This in in support of subgrid orographic parameterization revisions for GWD in WRF.

Currently the gravity wave drag (GWD) input fields from WPS/geogrid are computed from averaging of the source data then performing the calculations for oa1-oa4, ol1-ol4, var, and con. This utility program instead calculates these orographic statistics directly from the source data at a subgrid-scale assuming the domain dx/dy are larger than the source data extent per value.

The code is designed to be run using the entry point ./util/compute_gwdo.py and will use ./namelist.wps if no namelist is provided.

The namelist is read to determine the geogrid domains output, source data tiles locations, and domain spacing. To avoid recalculating lat/lon positioning, the values are read from the mass staggered lat/lon locations within geo_em.d00.nc, geo_em.d01.nc, and so on. Source data is loaded as tiles are needed to compute the orographic statistics for a given domain cell based on the dx/dy extent of the cell at that lat/lon.

Once all calculations are done for all cells within a domain file, that file's original oa1-oa4, ol1-ol4, var, and con are modified with the newly calculated subgrid-scale statistics. Additionally, a MAX_EL field is created. This is repeated for all domains listed within the namelist.