== Radiation Parameters ==
[[TracNav(doc/app/partoc|nocollapse)]]

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 [/browser/palm/trunk/SOURCE/radiation_model.f90 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 if a {{{radiation_par}}} is set in the parameter file ({{{_p3d}}}).

When using the RRTMG radiation model, it is required to [wiki:doc/tec/radiation#Installation compile the radiation code] first as a library. Moreover, the use of netCDF is mandatory.

\\
'''NAMELIST group name: radiation_par''' \\\\

||='''Parameter Name'''  =||='''[../fortrantypes FORTRAN Type]'''  =||='''Default Value'''  =||='''Explanation'''  =||
|----------------
{{{#!td style="vertical-align:top"
[=#albedo '''albedo''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
0.2
}}}
{{{#!td
Surface albedo (value of 0-1).
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#albedo_type '''albedo_type''']
}}}
{{{#!td style="vertical-align:top"
I
}}}
{{{#!td style="vertical-align:top"
5
}}}
{{{#!td
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_dif], [#albedo_lw_dir albedo_lw_dir], [#albedo_sw_dif albedo_sw_dif], [#albedo_sw_dir albedo_sw_dir] will overwrite the respective values set by albedo_type. By default, [#albedo_lw_dif albedo_lw_dif] = [#albedo_lw_dir albedo_lw_dir] and [#albedo_sw_dif albedo_sw_dif] = [#albedo_sw_dir albedo_sw_dir]. Moreover, [#constant_albedo 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)
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#albedo_lw_dif '''albedo_lw_dif''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
depending on [#albedo_type albedo_type]
}}}
{{{#!td
Surface albedo for longwave diffuse radiation for a solar angle of 60°.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#albedo_lw_dir '''albedo_lw_dir''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
depending on [#albedo_type albedo_type]
}}}
{{{#!td
Surface albedo for longwave direct radiation for a solar angle of 60°.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#albedo_sw_dif '''albedo_sw_dif''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
depending on [#albedo_type albedo_type]
}}}
{{{#!td
Surface albedo for shortwave diffuse radiation for a solar angle of 60°.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#albedo_sw_dir '''albedo_sw_dir''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
depending on [#albedo_type albedo_type]
}}}
{{{#!td
Surface albedo for shortwave direct radiation for a solar angle of 60°.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#constant_albedo '''constant_albedo''']
}}}
{{{#!td style="vertical-align:top"
L
}}}
{{{#!td style="vertical-align:top"
.F.
}}}
{{{#!td
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).
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#day_init '''day_init''']
}}}
{{{#!td style="vertical-align:top"
I
}}}
{{{#!td style="vertical-align:top"
172
}}}
{{{#!td
Day of the year (1-365) at model start. The default value is 172 (June 21).
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#dt_radiation '''dt_radiation''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
0.0
}}}
{{{#!td
Time step of the radiation model (in s).
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#emissivity '''emissivity''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
0.95
}}}
{{{#!td
Surface emissivity (0-1). 

At the moment, only a single emissivity value can be used for each band in the atmospheric window.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#lambda '''lambda''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
0.0
}}}
{{{#!td
Geographical longitude (in degrees). 

Note that the radiation scheme also requires information on the geographical latitude (see [wiki:doc/app/inipar#phi phi]).
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#lw_radiation '''lw_radiation''']
}}}
{{{#!td style="vertical-align:top"
L
}}}
{{{#!td style="vertical-align:top"
.T.
}}}
{{{#!td
Parameter to switch off longwave radiation.

When using RRTMG, longwave radiation calls can be switched off by setting {{{lw_radiation = .F.}}}.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#net_radiation '''net_radiation''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
0.0
}}}
{{{#!td
Net radiation at the surface in W/m². This parameter is only used in case of [#radiation_scheme radiation scheme]{{{= 'constant'}}}.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#radiation_scheme '''radiation_scheme''']
}}}
{{{#!td style="vertical-align:top"
C*10
}}}
{{{#!td style="vertical-align:top"
'clear-sky'
}}}
{{{#!td
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 albedo], [#day_init day_init], [#lambda lambda], [wiki:doc/app/inipar#phi phi], and [#time_utc_init time_utc_init].


'' 'rrtmg' ''

The [http://rtweb.aer.com/rrtm_frame.html RRTMG model] is used to calculate the radiative heating rates for each model column. This scheme requires setting [#day_init day_init], [#lambda lambda], [wiki:doc/app/inipar#phi phi], [#time_utc_init time_utc_init]. The following parameters can be set optionally: [#albedo_type albedo_type] (and/or [#albedo_lw_dif albedo_lw_dif], [#albedo_lw_dir albedo_lw_dir], [#albedo_sw_dif albedo_sw_dif], [#albedo_sw_dir albedo_sw_dir]). [#constant_albedo constant_albedo] can be used to fix the albedo during the simulation. It is also possible to use the switches [#lw_radiation lw_radiation] and [#sw_radiation sw_radiation].

}}}
|----------------
{{{#!td style="vertical-align:top"
[=#skip_time_do_radiation '''skip_time_do_radiation''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
0.0
}}}
{{{#!td
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.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#sw_radiation '''sw_radiation''']
}}}
{{{#!td style="vertical-align:top"
L
}}}
{{{#!td style="vertical-align:top"
.T.
}}}
{{{#!td
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.
}}}
|----------------
{{{#!td style="vertical-align:top"
[=#time_utc_init '''time_utc_init''']
}}}
{{{#!td style="vertical-align:top"
R
}}}
{{{#!td style="vertical-align:top"
43200.0
}}}
{{{#!td
UTC time at model start in seconds starting from midnight, The default value is {{{43200.0}}} (12 p.m., noon).
}}}