WRF ARW User's Guide - MMM - UCAR

WPS
given by the parent_grid_ratio variable; this ratio determines the nominal grid
spacing for a nest in relation to the grid spacing of the its parent.
Next, the lower-left corner of a nest is specified as an (i, j) location in the nest’s parent
domain; this is done through the i_parent_start and j_parent_start variables, and
the specified location is given with respect to the unstaggered grid. Finally, the
dimensions of each nest, in grid points, are given for each nest using the s_we, e_we,
s_sn, and e_sn variables. The nesting setup in our example namelist is illustrated in the
figure above, where it may be seen how each of the above-mentioned variables is
determined. Currently, the starting grid point values in the south-north (s_sn) and westeast
(s_we) directions must be specified as 1, and the ending grid point values (e_sn and
e_we) determine, essentially, the full dimensions of the nest; to ensure that the upperright
corner of the nest's grid is coincident with an unstaggered grid point in the parent
domain, both e_we and e_sn must be one greater than some integer multiple of the
nesting ratio. Also, for each nest, the resolution (or list or resolutions; see the description
of namelist variables) of source data to interpolate from is specified with the
geog_data_res variable. For a complete description of these namelist variables, the user
is referred to the description of namelist variables.
Selecting Between USGS and MODIS-based Land Use Classifications
By default, the geogrid program will interpolate land use categories from USGS 24category
data. However, the user may select an alternative set of land use categories
based on the MODIS land-cover classification of the International Geosphere-Biosphere
Programme and modified for the Noah land surface model. Although the MODIS-based
data contain 20 categories of land use, these categories are not a subset of the 24 USGS
categories; users interested in the specific categories in either data set can find a listing of
the land use classes in the section on land use and soil categories. It must be emphasized
WRF-ARW V3: User’s Guide 3-20