Part-2 | Configuring namelist.wps for WRF: A Step-by-Step Guide

The namelist.wps file is a crucial configuration file in the Weather Research and Forecasting (WRF) Model's Preprocessing System (WPS). It defines parameters for domain setup, geographical data processing, and meteorological data handling. Proper configuration of this file ensures that WRF simulations are accurate and tailored to specific research needs.

In this blog, we'll explore the structure of the namelist.wps file, detailing each section and its parameters, using examples for both single and multiple domains.

Structure of namelist.wps

The namelist.wps file is divided into several sections, each beginning with an ampersand (&) followed by the section name, and ending with a forward slash (/). The primary sections include:

1. &share: General settings shared across WPS components.

2. &geogrid: Settings for the geogrid program, defining the simulation domain and map projection.

3. &ungrib: Configurations for the ungrib program, handling meteorological data extraction.

4. &metgrid: Parameters for the metgrid program, which interpolates meteorological data onto the model grid.

1. &share Section

This section contains general settings applicable to multiple WPS components.

Parameters:

• wrf_core: Specifies the WRF dynamical core to use.

  • Options:

    • 'ARW': Advanced Research WRF.

    • 'NMM': Nonhydrostatic Mesoscale Model.

  • Example: wrf_core = 'ARW',

• max_dom: Defines the total number of domains, including nested domains.

  • Example: max_dom = 1,

• start_date** and *end_date: Set the start and end times for the simulation. For multiple domains, specify dates for each.

  • Format: 'YYYY-MM-DD_HH:MM:SS'

  • Example: start_date = '2025-02-01_00:00:00',

• interval_seconds: Time interval between input meteorological data files, in seconds.

  • Example: interval_seconds = 21600,

• io_form_geogrid: Specifies the format for geogrid output files.

  • Options:

    • 2: NetCDF format (recommended).

  • Example: io_form_geogrid = 2,

2. &geogrid Section

This section defines the simulation domain's parameters and map projection settings.

Parameters:

• parent_id: Specifies the parent domain ID for each domain. For the first domain, set to 1.

  • Example: parent_id = 1,

• parent_grid_ratio: Grid resolution ratio between the parent and nested domains.

  • Example: parent_grid_ratio = 1,

• i_parent_start** and *j_parent_start: Starting grid indices for nested domains within the parent domain.

  • Example: i_parent_start = 1,

• e_we** and *e_sn: Number of grid points in the west-east (e_we) and south-north (e_sn) directions.

  • Example: e_we = 689,

• geog_data_res: Specifies the resolution of geographical data for each domain.

  • Options: 'default', '10m', '5m', '2m', '30s'

  • Example: geog_data_res = 'default',

• dx** and *dy: Grid spacing in the x (west-east) and y (south-north) directions, in meters.

  • Example: dx = 10000,

• map_proj: Specifies the map projection used.

  • Options: 'lambert', 'mercator', 'polar', 'lat-lon'

  • Example: map_proj = 'lambert',

• ref_lat** and *ref_lon: Reference latitude and longitude for the domain center.

  • Example: ref_lat = 21.702,

• truelat1** and *truelat2: True latitudes for the map projection.

  • Example: truelat1 = 19.951,

• stand_lon: Standard longitude (central meridian) for the map projection.

  • Example: stand_lon = 79.805,

• geog_data_path: Path to the geographical data directory.

  • Example: geog_data_path = '/home/subha/WRF_MODEL/WPS_GEOG',

3. &ungrib Section

Configurations for extracting meteorological data from GRIB files.

Parameters:

• out_format: Specifies the output format for ungribbed data.

  • Options: 'WPS' (default format for WRF).

  • Example: out_format = 'WPS',

• prefix: Prefix used for the output files.

  • Example: prefix = 'FILE',

4. &metgrid Section

This section defines the settings for interpolating meteorological data onto the model grid.

Parameters:

• fg_name: Prefix of the input meteorological data files (same as prefix in &ungrib).

  • Example: fg_name = 'FILE',

• io_form_metgrid: Specifies the format of metgrid output files.

  • Options:

    • 2: NetCDF format (recommended for WRF input).

  • Example: io_form_metgrid = 2,

    
    

WRF Domain Wizard

WRF Domain Wizard is a web-based application designed to simplify the creation, visualization, and modification of the namelist.wps input file. It provides an intuitive graphical interface that allows users to configure their WRF domain setup without manually editing text files. This tool is particularly useful for beginners and those looking to quickly experiment with different domain configurations before running simulations.

Conclusion

The namelist.wps file is fundamental to configuring WRF simulations effectively. Each section plays a critical role in defining the domain, processing meteorological data, and ensuring smooth data flow to the WRF model. Properly setting these parameters ensures accurate and reliable weather simulations tailored to specific research needs.