EOS: Atmospheric Radiative Transfer in Habitable Worlds with HELIOS

Abstract

We present EOS, a procedure for determining the outgoing longwave radiation (OLR) and top-of-atmosphere (TOA) albedo for a wide range of conditions expected to be present in the atmospheres of rocky planets with temperate conditions. EOS is based on HELIOS and HELIOS-K, which are novel and publicly available atmospheric radiative transfer (RT) codes optimized for fast calculations with GPU processors. These codes were originally developed for the study of giant planets. In this paper we present an adaptation for applications to terrestrial-type, habitable planets, adding specific physical recipes for the gas opacity and vertical structure of the atmosphere. To test the reliability of the procedure, we assessed the impact of changing line opacity profile, continuum opacity model, atmospheric lapse rate, and tropopause position prescriptions on the OLR and the TOA albedo. The results obtained with EOS are in line with those of other RT codes running on traditional CPU processors, while being at least one order of magnitude faster. The adoption of OLR and TOA albedo data generated with EOS in a zonal and seasonal climate model correctly reproduces the fluxes of the present-day Earth measured by the CERES spacecraft. The results of this study disclose the possibility to incorporate fast RT calculations in climate models aimed at characterizing the atmospheres of habitable exoplanets.

EOS-ESTM: a flexible climate model for habitable exoplanets

“…• The atmospheric radiative transfer is calculated using EOS (Simonetti et al 2022), a procedure tailored for atmospheres of terrestrial-type planets, based on the opacity calculator HELIOS-K (Grimm & Heng 2015;Grimm et al 2021) and the radiative transfer code HELIOS (Malik et al 2017(Malik et al , 2019. Thanks to EOS, the ESTM radiative transfer can be now calculated for a variety of atmospheres with different bulk and greenhouse compositions, illuminated by stars with different SEDs.…”

“…We believe that this behaviour can be associated to the temperature dependence of the OLR and TOA albedo. In fact, for temperatures above ∼300 K, the CAM3 model features the largest value of OLR (Simonetti et al 2022, Fig. 10a therein) and, at the same time, a slightly higher TOA albedo compared to other models (Simonetti et al 2022, Fig. 10b therein).…”

“…As such, the concentrations of greenhouse gases can only be varied in trace abundances, the list of greenhouse gases cannot be expanded, and it is not possible to model stellar spectra different from the solar one. To overcome these limitations and to use an updated repository of spectroscopic data, the new version of ESTM uses the EOS radiative transfer procedure (Simonetti et al 2022) to calculate the terms 𝐼 and 𝐴. EOS is a line-by-line procedure based on the publicly available opacity calculator HELIOS-K (Grimm & Heng 2015;Grimm et al 2021) and the radiative transfer code HELIOS (Malik et al 2017(Malik et al , 2019. Line absorption from N 2 , O 2 , H 2 O, CO 2 and CH 4 are calculated using data from the HITRAN 2016 (Gordon et al 2017) repository.…”

“…In this paper, we present a new release of the ESTM model, which we call EOS-ESTM. EOS is our new procedure for calculating RT in rocky planetary atmospheres with any pressure, chemical composition, and stellar spectral type (Simonetti et al 2022). In our previous version we were limited to Earth-like systems.…”

Climate and atmospheric models of rocky planets: habitability and observational properties

“…Thanks to its extremely low computational cost, it can be used to explore the parameter space unconstrained by observations of individual rocky (exo)planets, or to perform statistical studies of climate properties whenever many runs for different parameter configurations are needed. The model has been recently upgraded and its most recent version, EOS-ESTM (Biasiotti et al 2022), includes a new code, EOS, (Simonetti et al 2022;Simonetti 2022) for the treatment of the radiative transfer, as well as a number of parametrizations to simulate the climate impact of oceans, land, ice, and clouds as a function of temperature and host star zenith distance. EOS-ESTM can be applied to a large variety of rocky planets, with terrestrial and non-terrestrial atmospheric compositions illuminated by solar-and nonsolar-type stars.…”