namelist.wps: Best Practices

The following is a basic namelist.wps file that is used for running the WRF Preprocessing system (which includes geogrid.exe, ungrib.exe, and metgrid.exe). Click each listed variable for a description of the function, as well as best-practices for each, if applicable.

In namelist.wps, multiple columns are used for multiple domains; however max_domains determines how many columns will be used. For example, if you use 3 columns, but only set max_dom = 2, the last column will be ignored.
NOTE: Not all parameters have mulitple columns. Do not add additional columns for single column parameters, or you will receive an error.

&share
wrf_core = 'ARW'
max_dom = 2,
start_date = '2019-09-04_12:00:00','2019-09-04_12:00:00',
end_date = '2019-09-06_00:00:00','2019-09-04_12:00:00',
interval_seconds = 10800,
io_form_geogrid = 2,
active_grid = .true.,.true.,
/

&geogrid
parent_id = 1, 1,
parent_grid_ratio = 1, 3,
i_parent_start = 1, 53,
j_parent_start = 1, 25,
e_we = 150, 220,
e_sn = 130, 214,
geog_data_res = 'default','default',
dx = 15000,
dy = 15000,
map_proj = 'lambert',
ref_lat = 33.00,
ref_lon = -79.00,
truelat1 = 30.0,
truelat2 = 60.0,
stand_lon = -79.0,
geog_data_path = '/glade/work/wrfhelp/WPS_GEOG',
opt_geogrid_tbl_path = '/glade/work/wrfhelp/shared_tables/GEOGRID.TBL',
opt_output_from_geogrid_path = '/glade/work/wrfhelp/my_output/',
/

&ungrib
out_format = 'WPS',
prefix = 'FILE',
/

&metgrid
fg_name = 'FILE',
constants_name = '/glade/work/wrfhelp/input_data/constant_file',
io_form_metgrid = 2,
opt_metgrid_tbl_path = '/glade/work/wrfhelp/shared_tables/METGRID.TBL',
opt_output_from_metgrid_path = '/glade/work/wrfhelp/my_output/',
/

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&geogrid

parent_id	This is the domain number (ID) of each domain's parent. The coarsest domain (d01) should be set to 1. The example below shows a fairly complicated domain set-up to help with explanation for how to set this parameter. In this example, there are 4 domains (numbered as shown). For this particular example, the setting would be parent_id = 1, 1, 2, 1 because both d02 and d04 have d01 as a parent, while d03 has d02 as a parent.
parent_grid_ratio	The nesting ratio relative to the domain's parent. For the coarsest domain, parent_grid_ratio should be set to 1. Best Practice Recommended ratios are 3 or 5. If you are unfamiliar with the model, it is best to leave this set to 3. It is not recommended to use an even number ratio since it is best to have a center grid cell for the fine domain that corresponds with the center of the coarse domain. grid cell. cost: Assuming a 3:1 ratio and the same number of grid cells in the parent and nest domains, the fine grid will require 3x as many time steps to keep the pace of the coarse domain.
i_parent_start and j_parent_start	The x and y (or i and j) coordinates of the lower left corner of the nest in the parent domain. For the coarsest domain, a value of 1 should be specified for both i and j. Example: i_parent_start = 1, 31, j_parent_start = 1, 17,      Best Practice It is good practice to keep nest boundaries away from coarse domain boundaries, and to keep them away from steep topography. As a rough approximation, keep about 1/3 of the coarse-grid domain surrounding each side of the nest. This does not have to be exact, and the nest does not have to be centered perfectly, but this helps to prevent problems later. If the prevailing winds are westerly, and the nest will not be centered, it is better to place the nest further away from the west boundary, than the east. When using nests, start by setting up one domain, then use a program such as ncview or plotgrids.ncl to explore the nest starting and ending locations of the coarse domain. Your nest domain dimensions will be (ending index - starting index)*3+1
e_we and e_sn	Each domain's full west-east and south-north dimensions (or grid spaces) Example: e_we = 201, 304, e_sn = 188, 289      For nested domains, e_we and e_sn must be one greater than an integer multiple of the nest's parent_grid_ratio. This is to ensure that a nest always starts and ends on a parent grid point. (i.e., e_we=n*parent_grid_ratio+1 for some integer n). Best Practice Domains should not be smaller than 100x100 grid spaces. Note that there will be about 10 grid points (minimum of 5) on each side, in the boundary zone. If domains are too small, the solution will be determined by forcing data, which defeats the purpose of running a simulation. When considering the size of the coarse domain, there is no need to be economical. Doubling the size of the coarse grid domain will only result in a 25% nested forecast time increase. It is also important to consider the speed at which systems are moving through the simulated region. A multi-day forecast needs a much larger domain than a short forecast. If cost is prohibitive, consider adding an external domain.
geog_data_res	Resolution of source data to be used when interpolating static terrestrial data. The default setting uses MODIS IGBP 21-category data Notes: If you wish to use USGS static terrestrial data, instead of the default MODIS data, geog_data_res should be specified as: geog_data_res = 'usgs_30s+default', 'usgs_30s+default', Prior to V3.8, USGS was the default. If you are using a version of WPS that is prior to V3.8, and you wish to use the default USGS data, then it is only necessary to specify: geog_data_res = '10m', '2m', '30s' Prior to V3.8, if you wish to use the MODIS data, it would be necessary to specify: geog_data_res = 'modis_30s+10m', 'modis_30s+2m', 'modis_30s+30s' Possible available resolutions are 10m (~19km), 5m (~9km), 2m (~4km), and 30s (~0.9km). When there are multiple resolutions available for geographical input data, choose a resolution that is slightly better than your grid resolution. For example, if your grid resolution is 9km, using 2 minute static data would be ideal.
dx and dy	Grid distance (or grid resolution) in the x and y directions. This is given in meters for the Lambert, Polar, and Mercator projections. For the 'lat-lon' projection, this is given in degrees latitude. Only the coarse domain resolution needs to be specified, as nest domains will be calculated based on parent_grid_ratio. Best Practice It is recommended that dx and dy have the same value for Mercator, Polar, and Lambert projections. See the description for parent_grid_ratio for relevant/useful information for this parameter.
map_proj	A character string specifying the projection of the simulation domain (all domains must use the same projection). For ARW, accepted projections are 'lambert', 'polar', 'mercator', and 'lat-lon.' Best Practice lambert: well-suited for mid-latitudes; domain cannot contain poles; domain cannot be periodic in west-east direction mercator: well-suited for low-latitudes; may be used for a "channel" domain (periodic in west-east direction). polar: good for high-latitude domains, especially if the domain contains a pole lat-lon: also called cylindrical equidistant; required for global domains (but does not have to be global); can be used in its normal or rotated aspect. It is best to check the range of the map scale factor (e.g., MAPFRAC_M for the map factor in the center of a grid cell) after running geogrid.exe (this can be checked easily with the ncview program). Values should be close to 1 to ensure the projection is not causing distortion.
ref_lat and ref_lon	Real values specifying the latitude and longitude of a location whose (i,j) location in the simulation is known. For ARW, ref_lat and ref_lon give the latitude and longitude of a known location in the domain (it's recommended that these are set to the center of the coarse domain - To change this, ref_x and ref_y must also be specified - see the WPS chapter of the WRF User's Guide for more informationi).
truelat1	A real value specifying the first true latitude for the Lambert conformal conic projection, or the true latitude for the polar stereographic projection, or the Mercator projection.
truelat2	A real value specifying the second true latitude for the Lambert conformal conic projection.
stand_lon	A real value specifying the longitude that is parallel with the y-axis in conic and azimuthal projections. Best Practice If this longitude is set to the same value as ref_lon, your coarsest domain will be centered.
geog_data_path	A string that represents the location where the static geographical data is stored. Best Practice It's best to set this to the absolute path, as occasionally problems can occur when using relative paths or symbolic links.
opt_geog_tbl_path	A string that represents the location where the GEOGRID.TBL (that you wish to use) is stored. Best Practice This is an optional parameter that can be useful if you are using shared compiled code.
opt_output_from_geog_path	A string that represents the location where you would like to store your geogrid (em_geog*) files. Best Practice This is an optional parameter that can be useful if you are running in a shared directory, if you do not have permission to write to the WPS/ running directory, or if you do not have enough room to write to the WPS/ directory.

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