WRF-Solar® User Guide
A description of the WRF-Solar® options is herein provided. The user is referred to the WRF User’s Guide and the README.namelist file in the run directory for further details on these options.
Certain WRF-Solar® enhancements are activated by default (e.g. improved solar tracking algorithm). The rest of the available options are:
- WRF-Solar® calculates the direct and diffuse surface irradiance. The direct and diffuse irradiance are calculated directly by RRTMG (sw_physics = 4) and Goddard (sw_physics = 5) shortwave radiation parameterizations. For the rest of the shortwave parameterizations WRF-Solar parameterizes the contributions of the direct and diffuse components. The direct normal irradiance (DNI) is stored in the SWDDNI variable and the diffuse in the SWDDIF variable. RRTMG also outputs the clear sky GHI and DNI on variables SWDOWNC and SWDDNIC, respectively. By default, these variables are not in the standard output. To add them to the standard output the user needs to add a h in the IO column in the rows of the registry file containing these variables.
- Different options are available to account for the atmospheric aerosol direct and/or indirect effects.
- By setting aer_opt = 1 WRF-Solar uses a monthly climatology to represent the aerosol direct effect. This option only works with RRTMG shortwave parameterization (sw_physics = 1).
- An alternative parameterization to represent the aerosol direct effect is activated by setting aer_opt = 2. This option works for RRTMG (sw_physics = 4) and for Goddard (sw_physics = 5). In its simplest form, the user has to provide the aerosol optical depth (AOD) at 550 nm and select the predominant type of aerosol. Normally, using a rural type of aerosol is appropriate (aer_type = 1). Two options are available for setting the AOD at 550 nm: 1) constant value, and 2) variable read via auxiliary file(s) in WRF I/O API-conforming netCDF format. In addition, the user needs to indicate in the namelist how to calculate the Agnstrom exponent, single scattering albedo, and asymmetry parameter. Three options are available 1) constant values, 2) fields read from the auxiliary input, and 3) parameterize them based on the AOD at 550 nm and the predominant aerosol type. For more details on how to select these options the user is referred to the README.namelist file in the WRF run directory (the aer_opt and related variables).
- To complement the previous options that impose the aerosol optical properties, WRF-Solar allows one to explicitly model the aerosol direct and indirect effects by setting the microphysics option, mp_physics, to 28. Documentation on how to run this parameterization should be consulted before running this option. The standard way to run the parameterization is using the climatological concentrations of the water- and ice-friendly aerosols as described in the previous link. In addition, the water- and ice-friendly aerosols can be initialized with concentrations with time stamps. The concentrations of the water- and ice-friendly aerosols (QNWFA and QNIFA variables) are read in WPS intermediate format by Metgrid. Documentation to write in intermediate format is also available. These aerosol data is read by WRF-Solar setting use_rap_aero_icbc = .true. By default, this option, mp_physics = 28, only accounts for the aerosol indirect effects. Setting mp_physics = 28 and aer_opt = 3 also accounts for the aerosol direct effect in order to fully couple the cloud-aerosol-radiation system.
- To activate the effects of unresolved clouds on shortwave radiation, set shcu_physics = 5. The Cu parameterization should be turned off since the WRF-Solar shallow cumulus scheme also accounts for deep convection. This option only works with two planetary boundary layer parameterizations, bl_pbl_physics = 2 or 5. The option 5 is recommended.
- A couple of options are available to have surface irradiances updated in between calls to the shortwave parameterization.
- Setting swint_opt = 1 interpolates the irradiance in between calls to the shortwave radiation parameterization. The parameterization keeps constant the concentration of hydrometeors and estimates the clear sky irradiance.
- By setting swint_opt = 2 the Fast All-sky Radiation Model for Solar applications (FARMS) scheme is activated. FARMS calculates the surface irradiance every model time step and stores the values in SWDOWN2, SWDDNI2 and SWDDIF2 variables. It also provides clear sky irradiances (SWDOWNC2 and SWDDNIC2). This option uses the current atmospheric state, including hydrometeors, to calculate the surface irradiance and it is the recommended one.
WRF-Solar includes a solar diagnostic package (solar_diagnostic = 1). This option adds to the standard output a number of two-dimensional variables (e.g., cloud fraction, vertically integrated hydrometeor content, clearness index, etc). A complete list of the variables can be found in the README.tslist file in the run directory. If the tslist option is activated, the solar diagnostic package outputs these variables and the surface irradiances every model time step at selected locations. This requires an ascii file with the latitude and longitude of the sites to output the time series (see README.tslist file in the run directory).
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