Connecting the dots: A versatile model for the atmospheres of tidally locked Super-Earths

TL;DR

This paper develops a fast, adaptable 3D atmospheric model for tidally locked Super-Earths, demonstrating its application to different rotation periods and revealing dynamical regime changes related to planetary rotation.

Contribution

The authors introduce a simple, computationally efficient atmospheric model for tidally locked Super-Earths that can be easily adapted to various planetary scenarios and rotation periods.

Findings

Fast, adaptable atmospheric model for Super-Earths.

Dynamical regime shift between superrotation and divergence regimes.

Rotation period influences atmospheric circulation patterns.

Abstract

Radiative equilibrium temperatures are calculated for the troposphere of a tidally locked Super-Earth based on a simple greenhouse model, using Solar System data as a guideline. These temperatures provide in combination with a Newtonian relaxation scheme thermal forcing for a 3D atmosphere model using the dynamical core of the Massachusetts Institute of Technology global circulation model (MITgcm). Our model is of the same conceptional simplicity than the model of Held & Suarez (1994) and is thus computationally fast. Furthermore, because of the coherent, general derivation of radiative equilibrium temperatures, our model is easily adaptable for different planets and atmospheric scenarios. As a case study relevant for Super-Earths, we investigate a Gl581g-like planet with Earth-like atmosphere and irradiation and present results for two representative rotation periods of $P_{rot}$ = 10 days and $P_{rot}$ = 36.5 days. Our results provide proof of concept and highlight interesting dynamical features for the rotating regime 3 < $P_{rot}$ < 100 days, which was shown by Edson et al. (2011) to be an intermediate regime between equatorial superrotation and divergence. We confirm that the $P_{rot}$ = 10 days case is more dominated by equatorial superrotation dynamics than the $P_{rot}$ = 36.5 days case, which shows diminishing influence of standing Rossby- Kelvin waves and increasing influence of divergence at the top of the atmosphere. We argue that this dynamical regime change relates to the increase in Rossby deformation radius, in agreement with previous studies. However, we also pay attention to other features that are not or only in partial agreement with other studies, like, e.g., the number of circulation cells and their strength, the role and extent of thermal inversion layers, and the details of heat transport