Part-3 | Understanding the namelist.input File in WRF: A Complete Guide
- Subhadip Datta
- Feb 11
- 3 min read
Updated: Mar 11
The namelist.input file is the main configuration file for running the Weather Research and Forecasting (WRF) Model. It controls physics schemes, numerical integration, output frequency, domain nesting, and boundary conditions.
This blog provides a detailed breakdown of the namelist.input file, explaining all components, their significance, and when to modify them for different simulations.
1. Structure of namelist.input
The namelist.input file consists of several sections, including:
&time_control – Defines simulation time, input/output frequency, and restart settings.
&domains – Configures the model grid, nesting, and timestep.
&physics – Specifies physical parameterizations (radiation, convection, microphysics).
&dynamics – Controls numerical integration and advection schemes.
&bdy_control – Manages lateral boundary conditions.
&namelist_quilt – Optimizes parallel processing.
2. Detailed Explanation of namelist.input Components
2.1 &time_control Section: Simulation Time & Output Settings
This section defines the start and end times, data output frequency, and restart options.
&time_control
run_days = 0,
run_hours = 24,
start_year = 2025, 2025,
start_month = 02, 02,
start_day = 10, 10,
start_hour = 00, 00,
end_year = 2025, 2025,
end_month = 02, 02,
end_day = 11, 11,
end_hour = 00, 00,
interval_seconds = 21600,
input_from_file = .true., .true.,
history_interval = 180, 60,
frames_per_outfile = 1, 1,
restart = .false.,
restart_interval = 3600,
io_form_history = 2,
io_form_restart = 2,
io_form_input = 2,
io_form_boundary = 2,
/Key Parameters:
run_days, run_hours → Defines the total simulation duration.
start_*, end_* → Sets simulation start and end times (YYYY-MM-DD HH:MM:SS).
interval_seconds → Time interval for input meteorological data (e.g., 6-hourly GFS = 21600 sec).
history_interval → Model output frequency (in minutes per domain, e.g., 180 min for domain 1, 60 min for domain 2).
restart → Enables/disables restart runs (.true. for long simulations).
restart_interval → Defines how often restart files are saved (e.g., every 1 hour = 3600 sec).
io_form_* → Defines the format for input, output, restart, and boundary files (typically 2 for NetCDF).
When to Modify:
Adjust history_interval for higher/lower temporal resolution of output.
Set restart = .true. for long simulations (if running for multiple days).
Increase restart_interval to reduce frequent saving (if disk space is an issue).
2.2 &domains Section: Grid Configuration & Nesting
This section controls grid resolution, nesting, and time-stepping.
&domains
time_step = 90,
time_step_fract_num = 0,
max_dom = 1,
e_we = 100,
e_sn = 100,
dx = 3000,
dy = 3000,
parent_id = 1,
parent_grid_ratio = 1,
i_parent_start = 1,
j_parent_start = 1,
smooth_option = 0,
/Key Parameters:
time_step → Time step in seconds (suggested: dx * 6 rule; e.g., dx = 3km, so time_step = 18s).
max_dom → Number of nested domains.
e_we, e_sn → Grid size in west-east and south-north directions.
dx, dy → Grid spacing in meters.
parent_id → Domain nesting structure (1 for main domain, 2 for child domain, etc.).
parent_grid_ratio → Nesting ratio (e.g., 3 means child domain has 3x finer resolution).
i_parent_start, j_parent_start → Location of child domains within the parent grid.
When to Modify:
Adjust time_step based on grid resolution (keep dx / 6 rule).
Increase e_we, e_sn to expand domain size.
Modify dx, dy for higher/lower resolution simulations.
2.3 &physics Section: Physical Parameterizations
This section defines the physics schemes for microphysics, radiation, convection, and land surface interactions.
&physics
mp_physics = 6,
ra_lw_physics = 4,
ra_sw_physics = 4,
bl_pbl_physics = 1,
cu_physics = 3,
sf_surface_physics = 2,
sf_sfclay_physics = 1,
/Key Parameters:
mp_physics → Microphysics scheme (6 for WSM6, 8 for Thompson, 2 for Lin).
ra_lw_physics, ra_sw_physics → Longwave and shortwave radiation schemes (4 for RRTMG).
bl_pbl_physics → Planetary boundary layer scheme (1 for YSU, 2 for MYJ).
cu_physics → Cumulus parameterization (use 0 for explicit convection in high-resolution grids).
sf_surface_physics → Land surface model (2 for NOAH, 1 for simple slab).
When to Modify:
Higher resolution (<4 km): Set cu_physics = 0 (convection resolved explicitly).
Tropical studies: Use mp_physics = 8 (Thompson scheme).
Urban modeling: Use sf_surface_physics = 2 (NOAH LSM).
2.4 &dynamics Section: Numerical Methods
This section controls advection, diffusion, and numerical stability settings.
&dynamics
w_damping = 0,
diff_opt = 1,
km_opt = 4,
damp_opt = 0,
/Key Parameters:
w_damping → Controls vertical velocity damping (set 1 to reduce instability).
diff_opt → Diffusion option (1 for default, 2 for second-order Smagorinsky).
km_opt → Turbulence model (4 for 3D TKE).
When to Modify:
Use w_damping = 1 for high-resolution urban runs.
Set diff_opt = 2 for LES-type turbulence modeling.
2.5 &bdy_control Section: Boundary Conditions
This section handles lateral boundary conditions.
&bdy_control
spec_bdy_width = 5,
spec_zone = 1,
relax_zone = 4,
/Key Parameters:
spec_bdy_width → Number of grid points for boundary relaxation.
relax_zone → Width of relaxation zone (use 4 for smoother transitions).
3. Summary Table: Key Parameters & When to Modify
Section | Parameter | When to Modify |
&time_control | history_interval | Increase for frequent outputs |
&domains | dx, dy | Change for different resolutions |
&physics | cu_physics | Set 0 for high-resolution runs |
&dynamics | w_damping | Enable for urban studies |
&bdy_control | spec_bdy_width | Increase for smoother boundary transition |
Conclusion
The namelist.input file is essential for configuring WRF simulations. Understanding its sections allows you to fine-tune physics schemes, nesting, numerical settings, and output controls to suit your research needs.
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