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Journal Articles Astronomy and Astrophysics - A&A Year : 2020

Acceleration of superrotation in simulated hot Jupiter atmospheres

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Abstract

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.
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Dates and versions

insu-03673172 , version 1 (20-05-2022)

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F. Debras, N. Mayne, I. Baraffe, E. Jaupart, P. Mourier, et al.. Acceleration of superrotation in simulated hot Jupiter atmospheres. Astronomy and Astrophysics - A&A, 2020, 633, ⟨10.1051/0004-6361/201936110⟩. ⟨insu-03673172⟩
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