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Gray Radiation

The two_stream_gray_rad_nml namelist only ever needs to be specified if two_stream_gray = .true. in idealized_moist_phys_nml. It contains options which specify the configuration to use to solve the two stream radiative transfer equations, as well as configuring the incoming solar radiation. It is described on Isca's website and is used in the Frierson example script.
Some of the most common options are described below:

Options

rad_scheme

string
There are 4 choices of configuration for solving the two stream radiative transfer equations in Isca:

  • FRIERSON - Semi-gray scheme with prescribed longwave and shortwave optical depths.
    Changing the \(CO_2\) concentration does not affect this scheme.

  • BYRNE - Semi-gray scheme with longwave optical depth dependent on water vapour content and \(CO_2\) concentration. Shortwave optical depth is prescribed.

    Convergence with Frierson example script

    Just running the Frierson example script but changing the rad_scheme from frierson to byrne did not converge for me - temperature kept rising. To make it converge, I had to increase the albedo_value from \(0.31\) to \(0.38\). The later being the value used in the only example script using byrne radiation.

  • GEEN - Multi-band scheme with two longwave bands and one shortwave band. One longwave band corresponds to an infrared window region (\(8-14\mu m\)) and the second corresponds to all other infrared wavelengths (\(>4\mu m\)). Longwave and shortwave optical depths depend on water vapour content and concentration.

  • SCHNEIDER - Semi-gray scheme for use in giant planet simulations. Longwave and shortwave optical depths are prescribed. Does not require a surface temperature as input, and allows specification of an interior heat flux.
    Changing the \(CO_2\) concentration does not affect this scheme.
Reference Pressure, \(P_0\)

A reference pressure, \(P_0\), is used in the FRIERSON/BYRNE/SCHNEIDER shortwave optical depth, as well as in the FRIERSON/SCHNEIDER longwave optical depth. The value of this is set to pstd_mks in the constants_nml namelist. This has a default value of \(10^5 Pa\) i.e. surface pressure on Earth.

Default: FRIERSON

Longwave Radiation

odp

float
Frierson longwave optical depth scaling parameter, \(\kappa\).
I.e. larger opd is used as a proxy for more \(CO_2\) in the FRIERSON radiation scheme.
Only ever required if rad_scheme = FRIERSON.
Default: 1.0

Incoming Solar Radiation

There is a specific section on Isca's website that explains this.

do_seasonal

bool

  • False: A diurnally and seasonally averaged insolation is selected. Incoming solar radiation takes the form:
    $$ S = \frac{S_{0}}{4}[1+\Delta_{S}P_{2}(\theta)+\Delta_{\text{sw}}\sin\theta] $$

    • \(P_{2} = (1 - 3\sin^{2}\theta)/4\) is the second legendre polynomial.
    • \(S_0\) is the solar_constant.
    • \(\Delta_s\) is del_sol.
    • \(\Delta_{sw}\) is del_sw.
    Schneider Insolation Profile

    If rad_scheme is SCHNEIDER, then the insolation with do_seasonal = False is: $$ S = \frac{S_{0}}{\pi}\cos\theta $$

  • True: The time dependent insolation has the form: $$ S = S_{0}\cos\zeta\left(\frac{a}{r}\right)^{2} $$

    • \(\zeta\) is the zenith angle.
    • \(a\) is the semi-major axis of the orbital ellipse.
    • \(r\) is the time-varying planet-star distance.

Default: False

solar_constant

float
The solar constant, \(S_0\), in the insolation equation (\(Wm^{-2}\)).
Default: 1360.0

del_sol

float
Parameter, \(\Delta_s\), in the insolation equation.
It sets the amplitude of the \(P_2\) insolation profile between the equator and the pole.
Only ever required if do_seasonal = .false. and rad_scheme is not SCHNEIDER.
Default: 1.4

del_sw

float
Parameter, \(\Delta_{sw}\), in the insolation equation.
It defines the magnitude of \(\sin \theta\) modification to the \(P_2\) insolation profile.
Only ever required if do_seasonal = .false. and rad_scheme is not SCHNEIDER.
Default: 0.0

use_time_average_coszen

bool
If True, average \(\cos\zeta\) over the period dt_rad_avg.
For example, for the Earth's diurnal period, use_time_average_coszen=True and dt_rad_avg=86400. would achieve diurnally averaged insolation.
Only ever required if do_seasonal = .true..
Default: False

dt_rad_avg

float
Averaging period (seconds) for time-dependent insolation \(\Delta t_{\text{avg}}\). If equal to -1, it sets averaging period to model timestep.
Only ever required if do_seasonal = .true..
Default: -1

solday

integer
Day of year to run time-dependent insolation perpetually.
If negative, the option to run perpetually on a specific day is not used.
Only ever required if do_seasonal = .true..
Default: -10

equinox_day

float
Fraction of year (between \(0\) and \(1\)) where Northern Hemisphere autumn equinox occurs.
A value of 0.75 would mean the end of September for 360 day year.
Only ever required if do_seasonal = .true..
Default: 0.75

\(CO_2\)

Isca give an example script using varying \(CO_2\) concentration.

do_read_co2

bool
If True, reads time-varying \(CO_2\) concentration from an input file.
The input file needs to be 4D (3 spatial dimensions and time), but no spatial variation should be defined (the code only reads in maximum value at a given time).

Compatible rad_schemes

Varying \(CO_2\) concentration can only be using if rad_scheme is byrne or geen.

Default: False

co2_file

string
Name of \(CO_2\) file to read.
The file should be in the input_dir and have a .nc appendix but that should be left out here.
File is produced using the create_time_series_file function in isca_tools which is extended from a python script provided by Isca.
Only ever required if do_read_co2 = .true..
Default: co2

co2_variable_name

string
Name of \(CO_2\) variable in \(CO_2\) file.
Only ever required if do_read_co2 = .true..
Default: co2

carbon_conc

float
Prescribed concentration (in \(ppmv\)) of \(CO_2\) which remains constant throughout the simulation.
Only ever required if do_read_co2 = .false. and rad_scheme is either byrne or geen.
For other rad_schemes, optical depth is prescribed so \(CO_2\) concentration has no effect.
Default: 360.0

Diagnostics

The diagnostics for this module can be specified using the module_name of two_stream in the diagnostic table file. The list of available diagnostics is available on Isca's website. Some of the more common ones are also given below.

co2

Carbon dioxide concentration.
Dimensions: time
Units: \(ppmv\)

Radiation

olr

Outgoing Longwave radiation. May be useful, along with swdn_toa to investigate how long experiment takes to spin up.
Dimensions: time, lat, lon
Units: \(Wm^{-2}\)

swdn_toa

Shortwave flux down at top of atmosphere. May be useful, along with olr to investigate how long experiment takes to spin up.
Dimensions: time, lat, lon
Units: \(Wm^{-2}\)

swdn_sfc

Absorbed shortwave flux at the surface.
Dimensions: time, lat, lon
Units: \(Wm^{-2}\)

lwdn_sfc

Downward longwave flux at the surface.
Dimensions: time, lat, lon
Units: \(Wm^{-2}\)

lwup_sfc

Upward longwave flux at the surface.
Dimensions: time, lat, lon
Units: \(Wm^{-2}\)