3D convection-resolving model of temperate, tidally-locked exoplanets

TL;DR

This paper introduces a high-resolution convection-resolving model for tidally-locked exoplanets, revealing that cloud feedback is weaker than GCM predictions due to transient convection aggregation.

Contribution

It develops a coupled CRM-WRF and LMD-Generic model to better simulate convection and clouds on tidally-locked exoplanets, focusing on Proxima b.

Findings

Cloud albedo increases with stellar flux as predicted by GCMs.

Cloud feedback is weaker due to transient convection aggregation.

Low partial cloud cover reduces overall cloud feedback.

Abstract

A large fraction of known terrestrial-size exoplanets located in the Habitable Zone of M-dwarfs are expected to be tidally-locked. Numerous efforts have been conducted to study the climate of such planets, using in particular 3-D Global Climate Models (GCM). One of the biggest challenges in simulating such an extreme environment is to properly represent the effects of sub-grid convection. Most GCMs use either a simplistic convective-adjustment parametrization or sophisticated (e.g., mass flux scheme) Earth-tuned parametrizations. One way to improve the representation of convection is to study convection using Convection Resolving numerical Models (CRMs), with an fine spatial resolution . In this study, we developed a CRM coupling the non-hydrostatic dynamical core WRF with the radiative transfer and cloud/precipitation models of the LMD-Generic climate model to study convection and clouds on tidally-locked planets, with a focus on Proxima b. Simulations were performed for a set of 3 surface temperatures (corresponding to three different incident fluxes) and 2 rotation rates, assuming an Earth-like atmosphere. The main result of our study is that while we recover the prediction of GCMs that (low-altitude) cloud albedo increases with increasing stellar flux, the cloud feedback is much weaker due to transient aggregation of convection leading to low partial cloud cover.