namelist.input: Best Practices

The following is a basic namelist.input file that is used for running the WRF model (which includes real.exe, wrf.exe, tc.exe, and ndown.exe). Click each listed variable for a description of the function, as well as best-practices for each, if applicable.

In namelist.input, multiple columns are used for multiple domains; however max_dom 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. In the descriptions below, it has been specified if a parameter is to be used for multiple domains (max_dom). If this is not shown, then you must only specify one value (in the first column), or you will receive a namelist error upon running.

&time_control
run_days = 0
run_hours = 12,
run_minutes = 0,
run_seconds = 0,
start_year = 2000, 2000, 2000,
start_month = 01, 01, 01,
start_day = 24, 24, 24,
start_hour = 12, 12, 12,
start_minute = 00, 00, 00,
start_second = 00, 00, 00,
end_year = 2000, 2000, 2000,
end_month = 01, 01, 01,
end_day = 25, 25, 25,
end_hour = 12, 12, 12,
end_minute = 00, 00, 00,
end_second = 00, 00, 00,
interval_seconds = 21600,
input_from_file = .true.,.true.,.true.,
history_interval = 180, 60, 60,
frames_per_outfile = 1000, 1000, 1000,
restart = .false.,
restart_interval = 5000,
io_form_history = 2,
io_form_restart = 2,
io_form_input = 2,
io_form_boundary = 2,
debug_level = 0,
/

&domains
time_step = 180,
time_step_fract_num = 0,
time_step_fract_den = 1,
max_dom = 1,
e_we = 74, 112, 94
e_sn = 61, 97, 91,
e_vert = 30, 30, 30,
p_top_requested = 5000,
num_metgrid_levels = 27
num_metgrid_soil_levels = 4
dx = 30000, 10000, 3333.33,
dy = 30000, 10000, 3333.33,
grid_id = 1, 2, 3,
parent_id = 0, 1, 2,
i_parent_start = 1, 31, 30,
j_parent_start = 1, 17, 30,
parent_grid_ratio = 1, 3, 3,
feedback = 1,
smooth_option = 0,
/

&physics
mp_physics = 3, 3, 3,
ra_lw_physics = 1, 1, 1,
ra_sw_physics = 1, 1, 1,
radt = 30, 30, 30,
sf_sfclay_physics = 1, 1, 1,
sf_surface_physics = 2, 2, 2,
num_soil_layers = 4,
bl_pbl_physics = 1, 1, 1,
bldt = 0, 0, 0,
cu_physics = 1, 1, 0,
cudt = 5, 5, 5,
isfflx = 1,
ifsnow = 1,
icloud = 1,
surface_input_source = 3,
num_land_cat = 21,
sf_urban_physics = 0, 0, 0,
sf_ocean_physics = 0,
/

&dynamics
w_damping = 0,
diff_opt = 1, 1, 1,
km_opt = 4, 4, 4,
diff_6th_opt = 0, 0, 0,
diff_6th_factor = 0.12, 0.12, 0.12,
base_temp = 290.,
damp_opt = 0,
z_damp = 5000., 5000., 5000.,
dampcoef = 0.2, 0.2, 0.2,
damp_opt = 0, 0, 0,
damp_opt = 0, 0, 0,
non_hydrostatic = .true., .true., .true.,
moist_adv_opt = 1, 1,1,
scalar_adv_opt = 1, 1,1,
/

&bdy_control
spec_bdy_width = 5,
spec_zone = 1,
relax_zone = 4,
specified = .true., .false., .false.,
nested = .false., .true., .true.,
/

&domains

time_step	Time step (in seconds) for integration. Best Practice It is recommended to use a value of 5-6xDX (in km) for a typical case. If you are using many vertical levels and/or with map-scale-factors much larger than 1, you will need to use a smaller time_step. If you are getting CFL errors that stop your run, this means your run has become unstable and you may need to decrease this value to about 4xDX (or perhaps even 3xDX). It makes things easier if you use a time step that evenly divides into your history_interval, so that your output times will be evenly spaced. back to top of page
max_dom	The number of domains you wish to run. The model will not read any more columns than the number specified here (so if you have 4 columns in your namelist, but have this set to 1, the model will only acknowledge the first column. back to top of page
e_we and e_sn (max_dom)	Each domain's full west-east and south-north dimensions (or grid spaces) Example: e_we = 201, 304, e_sn = 188, 289,      Best Practice These should be the same values as used when running WPS (and these values can be found in the met_em* files). See Best Practices for namelist.wps for more details about this parameter. back to top of page
e_vert (max_dom)	The number of vertical (or Eta) levels onto which real.exe will interpolate the incoming data. This number must be the same for each domain. The real.exe program will calculate reasonable levels from the number of levels requested. To see a list of these levels, use the command ncdump -v ZNW file_name To overwrite the levels calculated, you can use the eta_levels namelist parameter to specify the levels you want used (see more about this in chapter 5 of the WRF Users' Guide. Best Practice It is not recommended to have fewer than 35 levels. Typically 40-60 levels is recommended. Higher model tops require more levels for a constant dZ. back to top of page
p_top_requested	The pressure top (in Pa) to use in the model. This level must be available in the incoming WPS data. Best Practice The default and recommended value is 5000 Pa, and it is not suggested to use a level any lower (in the atmosphere) than this. back to top of page
num_metgrid_levels	The number of incoming (from WPS input data) vertical levels. This is determined by the input data you are using. Helpful Tip: If you are unsure about the number of levels your data has, you can use the following command: ncdump -h met_em.d01.<date> >& log.ncdump and look for the value near the top of the log.ncdump file. back to top of page
dx and dy (max_dom)	Grid distance (or grid resolution) in the x and y directions. Unlike in WPS (where the nest values are calculated based on the parent_grid_ratio), these values must be specified, but must still be accurate in accordance with the parent_grid_ratio. Example: max_dom = 3 parent_grid_ratio = 1, 3, 3 dx = 30000, 10000, 3333.33 dy = 30000, 10000, 3333.33 These values must also be the same as the input file (met_em.d0*) values. You can use the 'ncdump -h' command (similar to the example above) to determine this value for each domain, according to your input files. Best Practice See Best Practices for namelist.wps for more details about this parameter. back to top of page
grid_id (max_dom)	The domain number. The coarsest grid should be set to 1. In the example below, we show a more complicated example where we have 4 domains (numbered as shown - Note that we could have numbered them differently). For this example: grid_id = 1, 2, 3, 4      back to top of page
parent_id (max_dom)	The domain number of the nest's parent. The coarsest domain should be set to 1. In the example below, we show a more complicated example where we have 4 domains (numbered as shown - Note that we could have numbered them differently). For this example: grid_id = 1, 2, 3, 4 parent_id = 1, 1, 2, 1 You can see that d02 and d04 have d01 as a parent, while d03 has d02 as a parent.      back to top of page
i_parent_start and j_parent_start (max_dom)	The x and y 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. These values will be the same that you specified in WPS. Example: i_parent_start = 1, 31, j_parent_start = 1, 17,      Best Practice These values will be the same that you specified in WPS. See Best Practices for namelist.wps for more details about this parameter. back to top of page
parent_grid_ratio (max_dom)	The nesting ratio relative to the domain's parent. For the coarsest domain, parent_grid_ratio should be set to 1. These values should be the same values you used in namelist.wps. Best Practice See suggestions on the namelist.wps best practices web page. It is recommended to keep the ratios the same for each domain, unless you are very knowledgeable of the model and have a good reason to not do so. back to top of page
parent_time_step_ratio (max_dom)	This is how the model defines time step for nest domains. For the coarsest domain, this should be set to 1. Best Practice It is not mandatory to match these values to the parent_grid_ratio. If you are somewhat unfamiliar with the model, it is best to set these to a 3:1 ratio. It is also recommended to keep the ratios the same for each domain, unless you are very knowledgeable of the model and have a good reason to not do so. back to top of page
feedback	This determines whether feedback will be used when using nesting, and should be used to determine whether the run will be a one-way or two-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 fed back. If the parent_grid_ratio is even, an arbitrary choice of the southwest corner point value is used for feedback. This is the reason it is recommended to use an 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. back to top of page
smooth_option	Determines whether smoothing is to be used for the parent domain in the area of the nest if feedback is on (feedback = 1). Three options are available: 0 = no smoothing 1 = 1-2-1 smoothing 2 = smoothing-desmoothing. Best Practice It is typically recommended to keep this option set to 0. back to top of page