Olson 2001 Landmap NetCDF update:

Olson_2001_Land_Map.025x025.generic.GCHP.nc is a copy of
Olson_2001_Land_Map.025x025.generic.nc with minor updates applied for
compatibility with GCHP. While the Olson landmap is regridded internally
from quarter-deg resolution in GEOS-Chem classic, it is regridded on-the-fly
by ExtData when using GCHP. The regridding scheme is conservative fractional
regridding, and currently requires input as floating point values. However,
the Olson Land Map file read by GEOS-Chem classic contains integers. Reading
in variables as integers causes ExtData to exit with an error.

To make the data compatible with GCHP, the Olson 2001 landmap netcdf for GCHP
stores the OLSON variable as 32-bit floating point rather than int32.
Additionally, the long_name is updated to not include parentheses so as to
enable compatibility with the isCoards script that checks for compliance with
the COARDS standards.

~ Lizzie Lundgren, 2 Nov 2016

Olson_2001_Land_Type_Masks.025x025.generic.nc contains Olson 2001 land type
data as binary masks (one mask variable per land type). The script to generate
the file is ./scripts/make_OLSONXX_land_masks.ncl. This work was done so that
the Olson land map could be read in and regridded by HEMCO.

~ Lizzie Lundgren, 4 Jan 2018