Idealised 3D simulations of diabatically-forced Ledoux convection. Application to the atmosphere of hot rocky exoplanets

Abstract

We investigate the impact on convective numerical simulations of thermo-compositional diabatic processes. We focus our study on simulations with a stabilizing temperature gradient and a destabilizing mean-molecular weight gradient. We aim to establish the possibility for a reduced temperature-gradient in such setups. A suite of 3D simulations were conducted using a numerical hydrodynamic code. We used as a simplified test case, a sample region of the secondary atmosphere of a hot rocky exoplanet within which the chemical transition CO+O $\leftrightarrow$ CO${}_2$ could occur. Newtonian cooling and a chemical source term was used to maintain a negative mean molecular weight gradient. Our results demonstrate that this setup can reduce the temperature gradient, a result which does not converge away with resolution or over time. We also show that the presence of the reduced temperature gradient is a function of the forcing timescales. The above transition leads to a bifurcation of the temperature profile when the chemical forcing is fast, reminiscent of the bifurcation seen in the boiling crisis for steam/liquid convection. With the reduced temperature gradient in these idealized setups, there exists the possibility for an analogy of the reddening (currently observed in the spectra of brown dwarfs) in the spectra of rocky exoplanet atmospheres. Detailed 1D modelling is needed, in order to characterize the equilibrium thermal and compositional gradients, the timescales, and the impact of a realistic equation of state, in order to assess if the regime identified here will develop in realistic situations. This possibility cannot, however, be excluded a priori. This prediction is new for terrestrial atmospheres and represents strong motivation for the use of diabatic models when analysing atmospheric spectra of rocky exoplanets that will be observed with e.g. the James Webb Space Telescope.

13 pages, 10 figures

References in corpus (11)

• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• A chemical model for the atmosphere of hot Jupiters
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Theoretical Emission Spectra of Atmospheres of Hot Rocky Super-Earths
• Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics
• Thermo-compositional diabatic convection in the atmospheres of brown dwarfs and in Earth's atmosphere and oceans
• Cloudless atmospheres for young low-gravity substellar objects
• A high performance and portable all-Mach regime flow solver code with well-balanced gravity. Application to compressible convection
• The interaction between shear and fingering (thermohaline) convection

Cited by in corpus (2)

• A 3D picture of moist-convection inhibition in hydrogen-rich atmospheres: Implications for K2-18 b
• Modelling Non-Condensing Compositional Convection for Applications to Super-Earth and Sub-Neptune Atmospheres