The Magnetic Mechanism for Hotspot Reversals in Hot Jupiter Atmospheres

Abstract

Magnetically-driven hotspot variations (which are tied to atmospheric wind variations) in hot Jupiters are studied using non-linear numerical simulations of a shallow-water magnetohydrodynamic (SWMHD) system and a linear analysis of equatorial SWMHD waves. In hydrodynamic models, mid-to-high latitude geostrophic circulations are known to cause a net west-to-east equatorial thermal energy transfer, which drives hotspot offsets eastward. We find that a strong toroidal magnetic field can obstruct these energy transporting circulations. This results in winds aligning with the magnetic field and generates westward Lorentz force accelerations in hotspot regions, ultimately causing westward hotspot offsets. In the subsequent linear analysis we find that this reversal mechanism has an equatorial wave analogy in terms of the planetary scale equatorial magneto-Rossby waves. We compare our findings to three-dimensional MHD simulations, both quantitively and qualitatively, identifying the link between the mechanics of magnetically-driven hotspot and wind reversals. We use the developed theory to identify physically-motivated reversal criteria, which can be used to place constraints on the magnetic fields of ultra-hot Jupiters with observed westward hotspots.

30 pages, 9 figures, 3 tables

References in corpus (18)

• The Broadband Infrared Emission Spectrum of the Exoplanet HD 189733b
• Multi-Wavelength Constraints on the Day-Night Circulation Patterns of HD 189733b
• The phase-dependent Infrared brightness of the extrasolar planet upsilon Andromedae b
• Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, With Application to HD 209458b
• Atmospheric Circulation of Hot Jupiters: A Shallow Three-Dimensional Model
• Atmospheric Dynamics of Short-period Extra Solar Gas Giant Planets I: Dependence of Night-Side Temperature on Opacity
• Hot Nights on Extrasolar Planets: Mid-IR Phase Variations of Hot Jupiters
• A New 24 micron Phase Curve for upsilon Andromedae b
• Magnetic Effects in Hot Jupiter Atmospheres
• Variability in the Atmosphere of the Hot Giant Planet HAT-P-7 b
• Rossby waves in "shallow water" magnetohydrodynamics
• 3D Structures of equatorial waves and the resulting superrotation in the atmosphere of a tidally locked hot Jupiter
• Detection of a Westward Hotspot Offset in the Atmosphere of a Hot Gas Giant CoRoT-2b
• Modeling the effects of inhomogeneous aerosols on the hot Jupiter Kepler-7b's atmospheric circulation
• TESS unveils the phase curve of WASP-33b. Characterization of the planetary atmosphere and the pulsations from the star
• Shallow-water Magnetohydrodynamics for Westward Hotspots on Hot Jupiters
• Variability in the Atmosphere of the Hot Jupiter Kepler-76b
• The Acceleration of Superrotation in Simulated Hot Jupiter Atmospheres