Atmospheric Circulation of Hot Jupiters: A Shallow Three-Dimensional Model

TL;DR

This paper introduces a simple, three-dimensional atmospheric model for hot Jupiters, validated against Earth-like conditions, revealing complex flow patterns including superrotation and vortices, to improve understanding of exoplanetary atmospheres.

Contribution

It presents a novel shallow, 3D hot Jupiter atmospheric model using the IGCM solver, extending Earth-like validation to exoplanet conditions and analyzing resulting flow regimes.

Findings

Unsteady, subsonic winds with superrotation on hot Jupiters.

Presence of large-scale polar vortices in the simulated flow.

Barotropic instabilities may influence jet dynamics.

Abstract

Remote observing of exoplanetary atmospheres is now possible, offering us access to circulation regimes unlike any of the familiar Solar System cases. Atmospheric circulation models are being developed to study these new regimes but model validations and intercomparisons are needed to establish their consistency and accuracy. To this end, we present a simple Earth-like validation of the pseudo-spectral solver of meteorological equations called IGCM (Intermediate General Circulation Model), based on Newtonian relaxation to a prescribed latitudinal profile of equilibrium temperatures. We then describe a straightforward and idealized model extension to the atmospheric flow on a hot Jupiter with the same IGCM solver. This shallow, three-dimensional hot Jupiter model is based on Newtonian relaxation to a permanent day-night pattern of equilibrium temperatures and the absence of surface drag. The baroclinic regime of the Earth's lower atmosphere is contrasted with the more barotropic regime of the simulated hot Jupiter flow. For plausible conditions at the 0.1-1 bar pressure level on HD 209458b, the simulated flow is characterized by unsteadiness, subsonic wind speeds, a zonally-perturbed superrotating equatorial jet and large scale polar vortices. Violation of the Rayleigh-Kuo inflexion point criterion on the flanks of the accelerating equatorial jet indicates that barotropic (horizontal shear) instabilities may be important dynamical features of the simulated flow. Similarities and differences with previously published simulated hot Jupiter flows are briefly noted.