5:15 PM - 7:15 PM
[PPS06-P08] The Development of a Radiation Scheme for GCMs of Planets Orbiting M-type Stars
Keywords:Terrestrial Exoplanets, Exoplanets around M-type stars, General Circulation Model, Correlated k-distribution Method
In recent years, observations of the atmospheric composition of terrestrial exoplanets have been carried out (Greene et al., 2023, Zieba et al., 2023). In order to understand the diversity of exoplanet climates and estimate habitable conditions, numerical calculation is also becoming increasingly important.
Numerical studies have been carried out on climates assuming exoplanets with General Circulation Models (GCM). In the THAI project (Fauchez et al., 2020), several GCMs have been used to calculate the climate in TRAPPIST-1e, which belongs to M-type systems, and the interpretation of observed atmospheric properties and habitability are discussed. While the habitability of real planets is being studied, calculations under idealistic configurations are also being carried out to understand the diversity of exoplanet climates. Noda et al. (2017) performed an experiment on the dependence of climates on planetary rotation rate for tidally locked planets and discussed the difference in circulation pattern and temperature distribution on planetary rotation rate. They used a radiation scheme that assumed a G-type spectrum and did not consider the case of other host star spectra.
The purpose of this study is to develop a radiation scheme for exoplanets around M-type stars with the same atmospheric composition as Earth and calculate the exoplanet climates. We aim to reveal how the circulation patterns and temperature distribution of exoplanets change with the spectral type of their host stars.
We obtained a parameter set to calculate radiation fluxes with correlated k-distribution method for atmospheres with compositions of H2O, CO2, and O3 and given TRAPPIST-1 stellar radiation (Fauchez et al., 2020) so far. Absorption line parameters for H2O, CO2, and O3 are given from HITRAN2012 (Rothman et al., 2013). We used a 1D radiative transfer model (Takahashi et al., 2023) and, at first, obtained the most suitable band setting. The radiation fields obtained from 150 cases were compared. Those cases consist of 10 combinations of the number of bands ranging from 6 to 60 in the wavenumber range of 10-50000 cm-1 and 15 combinations of the number of integral points in each band ranging from 4 to 36. We found that the band setting for 30 bands and 10 integration points in each band is a suitable band setting, which achieves both high accuracy in radiation calculations and low computational cost. Then, we decided on grid intervals of temperature and pressure used for interpolation of optical properties, such as absorption coefficient. In the future, we will obtain radiative-convective equilibrium solutions based on that parameter set and explore the diversity of exoplanet climates with DCPAM, developed by GFD-Dennou Club (Takahashi et al., 2018).
Numerical studies have been carried out on climates assuming exoplanets with General Circulation Models (GCM). In the THAI project (Fauchez et al., 2020), several GCMs have been used to calculate the climate in TRAPPIST-1e, which belongs to M-type systems, and the interpretation of observed atmospheric properties and habitability are discussed. While the habitability of real planets is being studied, calculations under idealistic configurations are also being carried out to understand the diversity of exoplanet climates. Noda et al. (2017) performed an experiment on the dependence of climates on planetary rotation rate for tidally locked planets and discussed the difference in circulation pattern and temperature distribution on planetary rotation rate. They used a radiation scheme that assumed a G-type spectrum and did not consider the case of other host star spectra.
The purpose of this study is to develop a radiation scheme for exoplanets around M-type stars with the same atmospheric composition as Earth and calculate the exoplanet climates. We aim to reveal how the circulation patterns and temperature distribution of exoplanets change with the spectral type of their host stars.
We obtained a parameter set to calculate radiation fluxes with correlated k-distribution method for atmospheres with compositions of H2O, CO2, and O3 and given TRAPPIST-1 stellar radiation (Fauchez et al., 2020) so far. Absorption line parameters for H2O, CO2, and O3 are given from HITRAN2012 (Rothman et al., 2013). We used a 1D radiative transfer model (Takahashi et al., 2023) and, at first, obtained the most suitable band setting. The radiation fields obtained from 150 cases were compared. Those cases consist of 10 combinations of the number of bands ranging from 6 to 60 in the wavenumber range of 10-50000 cm-1 and 15 combinations of the number of integral points in each band ranging from 4 to 36. We found that the band setting for 30 bands and 10 integration points in each band is a suitable band setting, which achieves both high accuracy in radiation calculations and low computational cost. Then, we decided on grid intervals of temperature and pressure used for interpolation of optical properties, such as absorption coefficient. In the future, we will obtain radiative-convective equilibrium solutions based on that parameter set and explore the diversity of exoplanet climates with DCPAM, developed by GFD-Dennou Club (Takahashi et al., 2018).