SOCRATES Radiation Scheme Interface

Summary

SOCRATES (Suite Of Community RAdiative Transfer codes based on Edwards and Slingo) is the radiation scheme used by UK Met Office for Earth and planetary science [MannersEtAl2015], which has many significant advantages over RRTM, notably its flexibility in terms of atmospheric composition and the spectral properties of the radiation scheme (e.g. number of bands, etc).

• The code used to integrate Socrates into Isca is contained within the folder src/atmos_params/socrates/interface.

• The Socrates source code itself is NOT packed within this Isca repository, and NEW users will need to download it from the Met Office Science Repository. Users can then either choose to put the Socrates code within the directory src/atmos_params/socrates/src/trunk, or can set the bash environment variable GFDL_SOC equal to the location of the source code for Socrates. Detailed instructions on how to do this are included in the README.md for the Socrates test-case: exp/test_cases/socrates_test/README.md.

• The basis of socrates_interface was coded by Mark Hammond (Univ. of Oxford) and James Manners (Met Office) and modified by Stephen Thomson (Univ. of Exeter) [Thomson_and_Vallis2019]. Features added include seasonality in the radiation based on Isca’s astronomy package, and the ability to use a radiation timestep != atmospheric timestep.

• Socrates radiation scheme requires mass mixing ratios for all quantities (e.g. CO2, water vapor etc). This contrasts with RRTM, which wants volume mixing ratios.

Namelist options

The Socrates namelist socrates_rad_nml can be found at src/atmos_param/socrates/interface/socrates_config_mod.f90.

Radiation options

Here are some options to set incoming radiation:

Name	Default	Description
solday	0	If solday>0, do perpetual run corresponding to day of the year = solday in [0, days per year]
do_rad_time_avg	True	Average coszen for shortwave radiation over dt_rad
equinox_day	0.75	Fraction of the year defining NH autumn equinox in [0, 1]
stellar_constant	1368.22	solar constant (units: Wm \(^{-2}\)), consistent with RRTM default
tidally_locked	False	Tidally locked or not
frierson_solar_rad	False	Options for annual-mean incoming solar, as prescribed in Frierson’s grey scheme
del_sol	1.4	Latitudinal variation of shortwave radiation, as prescribed in Frierson’s grey scheme
del_sw	0	Latitudinal variation of shortwave radiation, as prescribed in Frierson’s grey scheme
input_planet_emissivity	1.0	Emissivity of surface. Defined as constant all over surface.

The following namelist variables set radiation time stepping and spatial sampling:

Name	Default	Description
dt_rad	0	Radiation timestep - every step if dt_rad<dt_atmos
store_intermediate_rad	True	Keep rad constant over entire dt_rad? (recommended)
dt_rad_avg	-1	If averaging, over what time? dt_rad_avg=dt_rad if dt_rad_avg<=0
chunk_size	16	Number of gridpoints to pass to Socrates at a time (see README.md)

Spectral files

Socrates reads external input spectral files that tell it the number of spectral bands to use, with one file setting the shortwave options, and another file setting the longwave options. Some spectral files have lots of bands, which will make the model run slowly. The default files used in the Met Office’s Unified Model-GA7, and also in Isca, can be found within the data/spectra directory of Socrates source code. For example, it can be here if you put the Socrates source code within the trunk directory:

src/atmos_param/socrates/src/trunk/data/spectra/ga7/sp_lw_ga7 for the longwave
src/atmos_param/socrates/src/trunk/data/spectra/ga7/sp_sw_ga7 for the shortwave

or here if you have set GFDL_SOC as an environment variable:

$GFDL_SOC/data/spectra/ga7/sp_lw_ga7 for the longwave
$GFDL_SOC/data/spectra/ga7/sp_sw_ga7 for the shortwave

Name	Default	Description
socrates_hires_mode	False	If False then run in ‘GCM mode’, and if True then use high-res spectral file
lw_spectral_filename	‘unset’	Longwave spectral file, which can be found at Socrates source code data directory (e.g. data/spectra/ga7/sp_lw_ga7) or self-generated
sw_spectral_filename	‘unset’	Shortwave spectral file, which can be found at Socrates source code data directory (e.g. data/spectra/ga7/sp_sw_ga7) or self-generated
lw_hires_spectral_filename	‘unset’	High-res longwave spectral file if socrates_hires_mode is True
sw_hires_spectral_filename	‘unset’	High-res shortwave spectral file if socrates_hires_mode is True

CO2, ozone and other gases

To include radiative effects of water vapor, CO2 and ozone, the following switches should be True:

Name	Default	Description
inc_h2o	True	To include radiative effects of water vapor
inc_co2	True	To include radiative effects of CO2
inc_o3	True	To include radiative effects of ozone

In addition, you need to set their concentrations by specifing them directly or reading from the external files (close attention should be paid to the concentration units):

Name	Default	Description
account_for_effect_of_water	True	False: radiation is fed water mixing ratios = 0 True: radiation is fed mixing ratios based on model specific humidity
account_for_effect_of_ozone	True	False: radiation is fed ozone mixing ratios = 0 True: radiation is fed mixing ratios based on model ozone field
do_read_co2	False	Read CO2 from an external file? If True, needs to specify CO2 file and variable names
co2_file_name	‘co2’	Name of file containing CO2 field - n.b. don’t need to include '.nc'
co2_field_name	‘co2’	Name of CO2 variable in CO2 file (specified by co2_file_name)
input_co2_mmr	False	True if the input file contain values as mass mixing ratio False if the input file contain values as volume mixing ratio
co2_ppmv	300	Default CO2 concentration in ppmv
do_read_ozone	False	Read ozone from an external file? If True, needs to specify ozone file and variable names
ozone_file_name	‘ozone’	Name of file containing ozone field - n.b. don’t need to include '.nc'
ozone_field_name	‘ozone’	Name of ozone variable in ozone file (specified by ozone_file_name)
input_o3_file_is_mmr	True	True if the input file contain values as mass mixing ratio False if the input file contain values as volume mixing ratio

To include the radiative effects of other gases, such as CO, CH4, O2, SO2, CFC, etc, first you need to turn on the switches starting with inc_ (default False), then specify the corresponding concentrations through variables ending with _mix_ratio in the namelist.

Diagnostics

Diagnostics from Socrates are under module name socrates. The outputs include the temperature tendencies due to LW/SW radiation, LW/SW radiation fluxes at each level, and the fluxes at surface and the top of the atmosphere (TOA).

Name	Description	Units	Dimension (not including time)
soc_tdt_lw	Socrates temperature tendency due to LW radiation	Ks \(^{-1}\)	(pfull, lat, lon)
soc_tdt_sw	Socrates temperature tendency due to SW radiation	Ks \(^{-1}\)	(pfull, lat, lon)
soc_tdt_rad	Socrates temperature tendency due to radiation	Ks \(^{-1}\)	(pfull, lat, lon)
soc_flux_lw	Socrates net LW flux (positive up)	Wm \(^{-2}\)	(phalf, lat, lon)
soc_flux_sw	Socrates net SW flux (positive up)	Wm \(^{-2}\)	(phalf, lat, lon)
soc_surf_flux_lw	Socrates net LW surface flux (positive up)	Wm \(^{-2}\)	(lat, lon)
soc_surf_flux_lw_down	Socrates LW surface flux down	Wm \(^{-2}\)	(lat, lon)
soc_surf_flux_sw	Socrates net SW surface flux (positive down)	Wm \(^{-2}\)	(lat, lon)
soc_surf_flux_sw_down	Socrates SW surface flux down	Wm \(^{-2}\)	(lat, lon)
soc_olr	Socrates TOA LW flux (positive up)	Wm \(^{-2}\)	(lat, lon)
soc_toa_sw	Socrates net TOA SW flux (positive down)	Wm \(^{-2}\)	(lat, lon)
soc_toa_sw_down	Socrates net TOA SW flux down	Wm \(^{-2}\)	(lat, lon)
soc_coszen	Socrates cosine (zenith_angle)	None	(lat, lon)
soc_co2	Socrates CO2 concentration (mass mixing ratio)	kg kg \(^{-1}\)	(pfull, lat, lon)
soc_ozone	Socrates ozone concentration (mass mixing ratio)	kg kg \(^{-1}\)	(pfull, lat, lon)
soc_spectral_olr	Socrates substellar OLR spectrum	Wm \(^{-2}\)	(socrates_lw_bins, lat, lon)

Relevant modules and subroutines

The Socrates radiation scheme is initiatized and called by src/atmos_spectral/driver/solo/idealized_moist_phys.F90.

The major modules/files under src/atmos_param/socrates/interface/ are:

• socrates_interface.F90 and socrates_calc.F90: The Socrates interfaces that initialize/finalize the Socrates, call subroutines to get inputs, set options for radiation and run core radiaiton code, and output the diagnostics.

• socrates_config_mod.f90: module to set the namelist, including the solar radiation options, time-step, and concentrations of CO2, ozone and other well-mixed gases

• read_control.F90 and set_control.F90: The Socrates use the StrCtrl structure to control the switches for core radiaiton code. For example, if you want to include the effects of CO2, you not only need to provide the value of CO2 concentration, but also need to turn on the switch to tell Socrates to calculate its effect: set control%l_co2 = .true., where control is a StrCtrl structure. Basically, all the logical switches are set in these two files.

• set_bound.F90 and set_dimen.F90: modules to set the boundary fields and dimensions for the radiation code

• set_atm.F90, set_aer.F90, and set_cld.F90: set the input atmospheric profiles, aerosol fields and clouds fields for the core radiation code (currently the aerosol and clouds are not activated)

Other radiation schemes employed in Isca can be found at:

• RRTM: see src/atmos_param/rrtm_radiation

• Two-stream gray radiation: see src/atmos_param/two_stream_gray_rad

References

[MannersEtAl2015] [Thomson_and_Vallis2019]

Authors

This documentation was written by Qun Liu (thanks to Stephen’s PR of Socrates), peer reviewed by Stephen Thomson, and quality controlled by Ruth Geen.