Volume 633, January 2020
|Number of page(s)||26|
|Section||Planets and planetary systems|
|Published online||19 December 2019|
Acceleration of superrotation in simulated hot Jupiter atmospheres
IRAP, Université de Toulouse, CNRS, UPS, Toulouse, France
2 Ecole normale supérieure de Lyon, CRAL, UMR CNRS 5574, 69364 Lyon Cedex 07, France
3 Physics and Astronomy, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK
4 Centre for Fusion, Space & Astrophysics, Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
5 Mathematics, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK
Accepted: 7 November 2019
Context. Atmospheric superrotating flows at the equator are a nearly ubiquitous result when conducting simulations of hot Jupiters. One theory explaining how this zonally-coherent flow reaches equilibrium has already been developed in the literature. This understanding, however, relies on the existence of either an initial superrotating flow or a sheared flow, coupled with a slow evolution that permits a linear steady state to be reached.
Aims. A consistent physical understanding of superrotation is needed for arbitrary drag and radiative timescales, along with the relevance of taking linear steady states into account, needs to be assessed.
Methods. We obtained an analytical expression for the structure, frequency, and decay rate of propagating waves in hot Jupiter atmospheres around a state at rest in the 2D shallow-water β-plane limit. We solved this expression numerically and confirmed the robustness of our results with a 3D linear wave algorithm. We then compared it with 3D simulations of hot Jupiter atmospheres and studied the nonlinear momentum fluxes.
Results. We show that under strong day-night heating, the dynamics do not transit through a linear steady state when starting from an initial atmosphere in solid body rotation. We further demonstrate that nonlinear effects favor the initial spin-up of superrotation and that acceleration due to the vertical component of the eddy-momentum flux is critical to the initial development of superrotation.
Conclusions. We describe the initial phases of the acceleration of superrotation, including the consideration of differing radiative and drag timescales, and we conclude that eddy-momentum-driven superrotating equatorial jets are robust, physical phenomena in simulations of hot Jupiter atmospheres.
Key words: planets and satellites: gaseous planets / planets and satellites: atmospheres / hydrodynamics / waves / methods: analytical / methods: numerical
© F. Debras et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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