TRAPPIST Habitable Atmosphere Intercomparison (THAI) Workshop Report

Abstract

The era of atmospheric characterization of terrestrial exoplanets is just around the corner. Modeling prior to observations is crucial in order to predict the observational challenges and to prepare for the data interpretation. This paper presents the report of the TRAPPIST Habitable Atmosphere Intercomparison workshop (2020 September 14–16). A review of the climate models and parameterizations of the atmospheric processes on terrestrial exoplanets, model advancements, and limitations, as well as direction for future model development, was discussed. We hope that this report will be used as a roadmap for future numerical simulations of exoplanet atmospheres and maintaining strong connections to the astronomical community.

ExoCAM: A 3D Climate Model for Exoplanet Atmospheres

“…We have tested tunable parameters regarding clouds, convection, time-stepping, and sea ice and snow albedos, along with model configurations regarding the radiative transfer scheme and moist physics packages. Sensitivity tests were conducted in adherence with the THAI protocol (Fauchez et al 2020) for simulating habitable iterations of TRAPPIST-1e. Changes to primary physical schemes, for instance the radiative transfer module or the cloud microphysics package, can yield meaningful changes to cloud amounts and the global mean surface temperature.…”

“…We conduct a series of intramodel sensitivity tests with ExoCAM using the THAI protocol (Fauchez et al 2020) hab1 and hab2 cases as our starting points. We refer the reader to the core series of THAI papers for more details of the THAI protocol and also for detailed analysis of the results Turbet et al 2021).…”

“…ExoCAM has been well-received and well-used since being made public. ExoCAM, and its ancestral versions, have been employed for a wide variety of studies, including the Faint Young Sun Paradox for Earth (Wolf & Toon 2013, 2014a, high-CO 2 atmospheres (Wolf et al 2018;Zhang et al 2021), runaway and moist greenhouse thresholds for Earth (Wolf & Toon 2014b, Earth-like extrasolar planets (Wolf et al 2017;Adams et al 2019;Kang 2019aKang , 2019bKang , 2019c, habitable zone exoplanets around M-dwarf stars (Kopparapu et al 2017;Wolf 2017;Haqq-Misra et al 2018;Komacek et al , 2020aKomacek et al , 2020bWolf et al 2019;Yang et al 2019a;Hu et al 2020;Rushby et al 2020;Suissa et al 2020b;Wei et al 2020;Chen et al 2021;May et al 2021;Song & Yang 2021), planets in circumbinary systems (Wolf et al 2020), and model intercomparison studies (Yang et al 2016(Yang et al , 2019bFauchez et al 2020Turbet et al 2021). ExoCAM results have also been used off-line in projects to drive photochemistry and observability studies (Afrin Badhan et al 2019;Suissa et al 2020a).…”

“…Second, we conduct a series of intramodel climate sensitivity tests with ExoCAM. Starting from the TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI) protocol (Fauchez et al 2020), we test the model's sensitivity to a number of key tunable parameters and settings related to clouds, convection, precipitation, and sea ice to illustrate the robustness of the model's results for simulating habitable terrestrial extrasolar planets.…”

“…ExoCAM is one of the four core 3D climate models used in the THAI project (Fauchez et al 2020), alongside LMD-G, ROCKE-3D, and UM. The THAI project arose from conversations at the NASA Habitable Worlds Conference in Laramie, WY in 2017 November.…”