WRF ARW User's Guide - MMM - UCAR

Default value is null (i.e., no dominant category will be computed from the fractional
categorical field).
WPS
17. DF_DX : When df_dx is assigned a character string value, the effect is to cause
geogrid to compute the directional derivative of the field in the x-direction using a central
difference along the interior of the domain, or a one-sided difference at the boundary of
the domain; the derivative field will be named according to the character string assigned
to the keyword df_dx. Default value is null (i.e., no derivative field is computed).
18. DF_DY : When df_dy is assigned a character string value, the effect is to cause
geogrid to compute the directional derivative of the field in the y-direction using a central
difference along the interior of the domain, or a one-sided difference at the boundary of
the domain; the derivative field will be named according to the character string assigned
to the keyword df_dy. Default value is null (i.e., no derivative field is computed).
19. Z_DIM_NAME : For 3-dimensional output fields, a character string giving the name
of the vertical dimension, or z-dimension. A continuous field may have multiple levels,
and thus be a 3-dimensional field, and a categorical field may take the form of a 3dimensional
field if it is written out as fractional fields for each category. No default
value.
Description of index Options
Related to the GEOGRID.TBL are the index files that are associated with each static data
set. An index file defines parameters specific to that data set, while the GEOGRID.TBL
file describes how each of the data sets should be treated by geogrid. As with the
GEOGRID.TBL file, specifications in an index file are of the form keyword=value.
Below are possible keywords and their possible values.
1. PROJECTION : A character string specifying the projection of the data, which may be
either lambert, polar, mercator, regular_ll, albers_nad83, or polar_wgs84. No
default value.
2. TYPE : A character string, either categorical or continuous, that determines
whether the data in the data files should be interpreted as a continuous field or as discrete
indices. For categorical data represented by a fractional field for each possible category,
type should be set to continuous. No default value.
3. SIGNED : Either yes or no, indicating whether the values in the data files (which are
always represented as integers) are signed in two's complement form or not. Default
value is no.
WRF-ARW V3: User’s Guide 3-45