3D Convection-resolving Model Of Temperate, Tidally-locked Exoplanets

Screenshot of the the vertical cross section of the mixing ratio of water clouds (top)
in kg/kg of air and of the water enrichment, i.e. the relative change, in % (bottom) for the
reference case. For clarity the scale of values enrichment is limited at 500 % but it reach higher values. The vertical cross section is at y = 56 km.

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.

Maxence Lefèvre, Martin Turbet, Raymond Pierrehumbert

Comments: Accepted for publications in The Astrophysical Journal. 42 pages, 14 figures, 1 table
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2104.05559 [astro-ph.EP] (or arXiv:2104.05559v1 [astro-ph.EP] for this version)
Submission history
From: Maxence Lefèvre
[v1] Mon, 12 Apr 2021 15:24:52 UTC (1,815 KB)

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