WRF ARW User's Guide - MMM - UCAR

that the MODIS-based categories should only be used with the Noah land surface model
in WRF.
WPS
The 20-category MODIS-based land use data may be selected instead of the USGS data
at run-time through the geog_data_res variable in the “geogrid” namelist record. This is
accomplished by prefixing each resolution of static data with the string “modis_30s+”.
For example, in a three-domain configuration, where the geog_data_res variable would
ordinarily be specified as
geog_data_res = ‘10m’, ‘2m’, ‘30s’
the user should instead specify
geog_data_res = ‘modis_30s+10m’, ‘modis_30s+2m’, ‘modis_30s+30s’
The effect of this change is to instruct the geogrid program to look, in each entry of the
GEOGRID.TBL file, for a resolution of static data with a resolution denoted by
‘modis_30s’, and if such a resolution is not available, to instead look for a resolution
denoted by the string following the ‘+’. Thus, for the GEOGRID.TBL entry for the
LANDUSEF field, the MODIS-based land use data, which is identified with the string
‘modis_30s’, would be used instead of the ‘10m’, ‘2m’, and ‘30s’ resolutions of USGS
data in the example above; for all other fields, the ‘10m’, ‘2m’, and ‘30s’ resolutions
would be used for the first, second, and third domains, respectively. As an aside, when
none of the resolutions specified for a domain in geog_data_res are found in a
GEOGRID.TBL entry, the resolution denoted by ‘default’ will be used.
Selecting Static Data for the Gravity Wave Drag Scheme
The gravity wave drag by orography (GWDO) scheme in the ARW requires ten static
fields from the WPS. In fact, these fields will be interpolated by the geogrid program
regardless of whether the GWDO scheme will be used in the model. When the GWDO
scheme will not be used, the fields will simply be ignored in WRF, and the user need not
be concerned with the resolution of data from which the fields are interpolated. However,
it is recommended that these fields be interpolated from a resolution of source data that is
slightly lower (i.e., coarser) in resolution than the model grid; consequently, if the
GWDO scheme will be used, care should be taken to select an appropriate resolution of
GWDO static data. Currently, five resolutions of GWDO static data are available: 2degree,
1-degree, 30-minute, 20-minute, and 10-minute, denoted by the strings ‘2deg’,
‘1deg’, ‘30m’, ‘20m’, and ‘10m’, respectively. To select the resolution to interpolate
from, the user should prefix the resolution specified for the geog_data_res variable in
the “geogrid” namelist record by the string “XXX+”, where XXX is one of the five
available resolutions of GWDO static data. For example, in a model configuration with a
48-km grid spacing, the geog_data_res variable might typically be specified as
geog_data_res = ‘10m’,
WRF-ARW V3: User’s Guide 3-21