Bistability of the atmospheric circulation on TRAPPIST-1e

Abstract

Using a 3D general circulation model, we demonstrate that a confirmed rocky exoplanet and a primary observational target, TRAPPIST-1e presents an interesting case of climate bistability. We find that the atmospheric circulation on TRAPPIST-1e can exist in two distinct regimes for a 1 bar nitrogen-dominated atmosphere. One is characterized by a single strong equatorial prograde jet and a large day-night temperature difference; the other is characterized by a pair of mid-latitude prograde jets and a relatively small day-night contrast. The circulation regime appears to be highly sensitive to the model setup, including initial and surface boundary conditions, as well as physical parameterizations of convection and cloud radiative effects. We focus on the emergence of the atmospheric circulation during the early stages of simulations and show that the regime bistability is associated with a delicate balance between the zonally asymmetric heating, mean overturning circulation, and mid-latitude baroclinic instability. The relative strength of these processes places the GCM simulations on different branches of the evolution of atmospheric dynamics. The resulting steady states of the two regimes have consistent differences in the amount of water content and clouds, affecting the water absorption bands as well as the continuum level in the transmission spectrum, although they are too small to be detected with current technology. Nevertheless, this regime bistability affects the surface temperature, especially on the night side of the planet, and presents an interesting case for understanding atmospheric dynamics and highlights uncertainty in 3D GCM results, motivating more multi-model studies.

Sporadic Spin-orbit Variations in Compact Multiplanet Systems and Their Influence on Exoplanet Climate

“…Because of the small orbital separation (semi-major axes) of worlds around M-dwarfs, theory suggests that they will be locked in a synchronized state due to strong tidal forces from the host star. As such, the majority of previous work using three-dimensional (3D) general circulation models (GCMs) M-dwarf planets assumed 1:1 spin orbit rotation ratios for planets with short ( 50 days) orbital periods (e.g., Way et al 2016;Kopparapu et al 2017;Yang et al 2019;Chen et al 2019;Joshi et al 2020;Guzewich et al 2020;Lefèvre et al 2021;Cohen et al 2021;Hammond & Lewis 2021;Wolf et al 2022;Sergeev et al 2022;Braam et al 2022). This assumption is acceptable due to the computational expense and time-consuming nature of many state-of-the-science GCMs.…”