With the commissioning of powerful, new-generation telescopes such as the JWST and the ground-based ELTs, the first characterization of a high-molecular-weight atmosphere around a temperate rocky
exoplanet is imminent. Atmospheric simulations and synthetic observables of target exoplanets are
essential to prepare and interpret these ...
With the commissioning of powerful, new-generation telescopes such as the JWST and the ground-based ELTs, the first characterization of a high-molecular-weight atmosphere around a temperate rocky
exoplanet is imminent. Atmospheric simulations and synthetic observables of target exoplanets are
essential to prepare and interpret these observations. Here we report the results of the first part of the
THAI (TRAPPIST-1 Habitable Atmosphere Intercomparison) project, which compares 3D numerical
simulations performed with four state-of-the-art Global Climate Models (ExoCAM, LMD-Generic,
ROCKE-3D, Unified Model) for the potentially habitable target TRAPPIST-1e. In this first part, we
present the results of dry atmospheric simulations. These simulations serve as a benchmark to test
how radiative transfer, subgrid-scale mixing (dry turbulence and convection) and large-scale dynamics
impact the climate of TRAPPIST-1e and consequently the transit spectroscopy signature as seen by
JWST. To first order, the four models give results in good agreement. The inter-model spread in
the global mean surface temperature amounts to 7K (6K) for the N2-dominated (CO2-dominated,
respectively) atmosphere. The radiative fluxes are also remarkably similar (inter-model variations
less than 5%), from the surface (1bar) up to atmospheric pressures ∼5millibar. Moderate differences
between the models appear in the atmospheric circulation pattern (winds) and the (stratospheric)
thermal structure. These differences arise between the models from (1) large scale dynamics because
TRAPPIST-1e lies at the tipping point between two different circulation regimes (fast and Rhines rotators) in which the models can be alternatively trapped; and (2) parameterizations used in the
upper atmosphere such as numerical damping.