Atmospheres & Climate

Modelling Non-Condensing Compositional Convection for Applications to Super-Earth and Sub-Neptune Atmospheres

By Keith Cowing

Status Report

astro-ph.EP

October 13, 2023

Filed under astro-ph.EP, atmosphere, modelling, sub-Neptune, super-Earth

Modelling Non-Condensing Compositional Convection for Applications to Super-Earth and Sub-Neptune Atmospheres — 2D plots showing vertical cross sections of mass mixing ratio taken in the middle of the y-domain for CM1 Case 1 and Case 4 which have an Earth Air Atmosphere. The top panel shows the qv cross sections for Case 1, isothermal Earth air atmosphere, while the bottom panel shows the qv cross section for Case 4, Earth-Air atmosphere with initial temperature and mass mixing ratio step profile. Within each panel, the top row shows the results when using only initial random perturbations to trigger convection, while the bottom row shows the results when using the initial perturbation given by Eqn. 18 in conjunction with random perturbations. The mass mixing ratio is shown for seven different time steps during the CM1 simulation. The color bar indicates the value of qv. The plots show the formation, growth, and mixing of convective plumes. Eventually, the atmosphere reaches a marginally stable state where discrete layers of varying composition form. The observed “compositional staircases” are analogous to the compositional staircases presented in compositional convection modelling for stellar atmospheres (Garaud et al. 2015). — astro-ph.EP

Compositional convection is atmospheric mixing driven by density variations caused by compositional gradients. Previous studies have suggested that compositional gradients of atmospheric trace species within planetary atmospheres can impact convection and the final atmospheric temperature profile.

In this work, we employ 3D convection resolving simulations using Cloud Model 1 (CM1) to gain a fundamental understanding of how compositional variation influences convection and the final atmospheric state of exoplanet atmospheres. We perform 3D initial value problem simulations of non-condensing compositional convection for Earth-Air, H2, and CO2 atmospheres. Conventionally, atmospheric convection is assumed to mix the atmosphere to a final, marginally stable state defined by a unique temperature profile.

However, when there is compositional variation within an atmosphere, a continuous family of stable end states is possible, differing in the final state composition profile. Our CM1 simulations are used to determine which of the family of possible compositional end states is selected. Leveraging the results from our CM1 simulations, we develop a dry convective adjustment scheme for use in General Circulation Models (GCMs).

This scheme relies on an energy analysis to determine the final adjusted atmospheric state. Our convection scheme produces results that agree with our CM1 simulations and can easily be implemented in GCMs to improve modelling of compositional convection in exoplanet atmospheres.

Namrah Habib, Raymond T. Pierrehumbert

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.08202 [astro-ph.EP] (or arXiv:2310.08202v1 [astro-ph.EP] for this version)
Submission history
From: Namrah Habib
[v1] Thu, 12 Oct 2023 10:48:35 UTC (21,017 KB)
https://arxiv.org/abs/2310.08202
Astrobiology, Astrochemistry

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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