WRF ARW User's Guide - MMM - UCAR

MODEL
fine_input_stream: which fields from the nest input file are used in nest
initialization. The fields to be used are defined in the Registry.EM. Typically they include
static fields (such as terrain, landuse), and masked surface fields (such as skin
temperature, soil moisture and temperature). Useful for nest starting at a later time than
the coarse domain.
max_dom: the total number of domains to run. For example, if you want to have one
coarse domain and one nest, set this variable to 2.
grid_id: domain identifier that is used in the wrfout naming convention. The most
coarse grid must have grid_id of 1.
parent_id: used to indicate the parent domain of a nest. grid_id value is used.
i_parent_start/j_parent_start: lower-left corner starting indices of the nest
domain in its parent domain. These parameters should be the same as in
namelist.wps.
parent_grid_ratio: integer parent-to-nest domain grid size ratio. Typically odd
number ratio is used in real-data applications.
parent_time_step_ratio: integer time-step ratio for the nest domain. It may be
different from the parent_grid_ratio, though they are typically set the same.
feedback: this is the key setup to define a two-way nested (or one-way nested) run.
When feedback is on, the values of the coarse domain are overwritten by the values of the
variables (average of cell values for mass points, and average of the cell-face values for
horizontal momentum points) in the nest at the coincident points. For masked fields, only
the single point value at the collocating points is fedback. If the parent_grid_ratio
is even, an arbitrary choice of southwest corner point value is used for feedback. This is
the reason it is better to use odd parent_grid_ratio with this option. When
feedback is off , it is equivalent to a one-way nested run, since nest results are not
reflected in the parent domain.
smooth_option: this a smoothing option for the parent domain in area of the nest if
feedback is on. Three options are available: 0 = no smoothing; 1 = 1-2-1 smoothing; 2 =
smoothing-desmoothing.
3-D Idealized Cases
For 3-D idealized cases, no nest input files are required. The key here is the specification
of the namelist.input file. What the model does is to interpolate all variables
required in the nest from the coarse domain fields. Set
input_from_file = F, F
WRF-ARW V3: User’s Guide 5-12