Radiation Parameters

For revision r1551 onwards, an interface for use of radiation models is available in PALM. Currently, PALM offers one built-in radiation model for clear-sky conditions, calculating the net radiation at the surface.

All parts of the radiation code (and the interface of the radiation code) are modularized in module radiation_model_mod. In this context, a new Fortran NAMELIST radiation_parameters was added, containing all radiation-related steering parameters. The radiation module is automatically activated if a radiation_parameters is set in the parameter file (_p3d).

When using the RRTMG radiation model, it is required to compile the radiation code first as a library. Moreover, the use of netCDF is mandatory.

NAMELIST group name: radiation_parameters

Parameter Name	FORTRAN Type	Default Value	Explanation
albedo	R	0.2	Surface albedo (value of 0-1).
albedo_type	I	5	This parameter controls the choice of the surface albedos for direct/diffuse/broadband albedo for a solar angle of 80° according to the following list of predefined land surfaces. For radiation_scheme = 'rrtmg' the shortwave and longwave albedo values are used and the actual albedos are then calculated based on the current solar angle after Briegleb (1992). Setting on or more of the parameters albedo_lw_dif, albedo_lw_dir, albedo_sw_dif, albedo_sw_dir will overwrite the respective values set by albedo_type. By default, albedo_lw_dif = albedo_lw_dir and albedo_sw_dif = albedo_sw_dir. Moreover, constant_albedo = .T. will keep the albedos constant during the simulation. For radiation_scheme = 'clear-sky' the broadband albedo is used and does not vary in the course of the simulation. albedo_type Description shortwave longwave broadband 0 user defined - - - 1 ocean 0.06 0.06 0.06 2 mixed farming, tall grassland 0.09 0.28 0.19 3 tall/medium grassland 0.11 0.33 0.23 4 evergreen shrubland 0.11 0.33 0.23 5 short grassland/meadow/shrubland 0.14 0.34 0.25 6 evergreen needleleaf forest 0.06 0.22 0.14 7 mixed deciduous forest 0.06 0.27 0.17 8 deciduous forest 0.06 0.31 0.19 9 tropical evergreen broadleaved forest 0.06 0.22 0.14 10 medium/tall grassland/woodland 0.06 0.28 0.18 11 desert, sandy 0.35 0.51 0.43 12 desert, rocky 0.24 0.40 0.32 13 tundra 0.10 0.27 0.19 14 land ice* 0.90 0.65 0.77 15 sea ice 0.90 0.65 0.77 16 snow 0.95 0.70 0.82 17 pavement/roads 0.08 0.08 0.08 (* land ice is treated differently than sea ice)
albedo_lw_dif	R	depending on albedo_type	Surface albedo for longwave diffuse radiation for a solar angle of 60°.
albedo_lw_dir	R	depending on albedo_type	Surface albedo for longwave direct radiation for a solar angle of 60°.
albedo_sw_dif	R	depending on albedo_type	Surface albedo for shortwave diffuse radiation for a solar angle of 60°.
albedo_sw_dir	R	depending on albedo_type	Surface albedo for shortwave direct radiation for a solar angle of 60°.
constant_albedo	L	.F.	Parameter to fix the surface albedos. When constant_albedo = .T., the surface albedos are kept constant during the entire simulation If set to .F., the actual albedos are calculated after Briegleb et al. (1986) and Briegleb (1992).
dt_radiation	R	0.0	Time step of the radiation model (in s).
emissivity	R	0.95	Surface emissivity (0-1) for user-defined grid points. Please note, by default emissivity is determined by the prescribed vegetation-, pavement-, water-, or building type at the given surface element. Setting this parameter has only an effect if vegetation-, pavement-, water-, or building type is set to zero, i.e. a user-defined value. At the moment, only a single emissivity value can be used for each band in the atmospheric window.
lw_radiation	L	.T.	Parameter to switch off longwave radiation. When using RRTMG, longwave radiation calls can be switched off by setting lw_radiation = .F..
net_radiation	R	0.0	Net radiation at the surface in W/m². This parameter is only used in case of radiation scheme= 'constant'.
radiation_scheme	C*10	'clear-sky'	Radiation scheme to be used. The user can choose between the following schemes: 'constant' A constant net radiation at the surface is prescribed (see #net_radiation). 'clear-sky' A simple clear sky model is used to calculate the radiation fluxes at the surface (shortwave incoming, shortwave outgoing, longwave incoming, longwave outgoing) and consequently the net radiation at the surface. This scheme requires setting albedo, day_of_year_init, longitude, latitude, and time_utc_init. 'rrtmg' The ​RRTMG model is used to calculate the radiative heating rates for each model column. This scheme requires setting day_of_year_init, longitude, latitude, time_utc_init. The following parameters can be set optionally: albedo_type (and/or albedo_lw_dif, albedo_lw_dir, albedo_sw_dif, albedo_sw_dir). constant_albedo can be used to fix the albedo during the simulation. It is also possible to use the switches lw_radiation and sw_radiation. Please note that the use of RRTMG requires to compile PALM with __rrtmg preprocessor directive. By the same token it is not possible to switch the radiation scheme to 'clear-sky' or 'constant' for such a compiled PALM executable.
skip_time_do_radiation	R	0.0	Time after which the radiation model is switched on. This parameter can be used to allow the LES model to develop turbulence before it is affected by radiation.
sw_radiation	L	.T.	Parameter to switch of shortwave radiation. When using RRTMG, shortwave radiation calls can be switched off by setting sw_radiation = .F.. Note that shortwave radiation is automatically switched off during nighttime.