Radiation Parameters

Since r1551 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 (oder interface to radiation code) are modularized in module radiation_model_mod. In this context, a new Fortran NAMELIST radiation_par was added, containing all radiation-related steering parameters. The radiation module is automatically activated when a radiation_par is set in the parameter file (_p3d).

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

NAMELIST group name: radiation_par

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 (* land ice is treaded 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.	Keep the surface albedos to their initial value for the entire simulation. If set to .F., the actual albedos are calculated after Briegleb (1992).
day_init	I	172	Day of the year (1-365) at model start. The default value is 172 (June 21).
dt_radiation	R	0.0	Timestep of the radiation model (in s).
emissivity	R	0.95	Surface emissivity (0-1). At the moment only a single emissivity value can be used for each band in the atmospheric window.
lambda	R	0.0	Geographical longitude (in degrees). Note that the radiation scheme also requires information on the geographical latitude (see phi).
lw_radiation	L	.T.	Switch off longwave radiation.
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 of albedo, day_init, lambda, phi, and time_utc_init. 'rrtmg' The ​RRTMG model is used to calculate the radiative heating rates for each model column. This scheme requires setting of day_init, lambda, phi, time_utc_init. The folling 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 simualation. It is also possible to use the switches lw_radiation and sw_radiation.
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.	Switch off shortwave radiation. Note that shortwave radiation is automatically switched off during nighttime.
time_utc_init	R	43200.0	UTC time at model start in seconds starting from midnight, The default value is 43200.0 (12 p.m., noon).