Shallow-water Magnetohydrodynamics for Westward Hotspots on Hot Jupiters

Abstract

Westward winds have now been inferred for two hot Jupiters (HJs): HAT-P-7b and CoRoT-2b. Such observations could be the result of a number of physical phenomena such as cloud asymmetries, asynchronous rotation, or magnetic fields. For the hotter HJs magnetic fields are an obvious candidate, though the actual mechanism remains poorly understood. Here we show that a strong toroidal magnetic field causes the planetary-scale equatorial magneto-Kelvin wave to structurally shear as it travels, resulting in westward tilting eddies, which drive a reversal of the equatorial winds from their eastward hydrodynamic counterparts. Using our simplified model we estimate that the equatorial winds of HAT-P-7b would reverse for a planetary dipole field strength $B_{\text{dip},\text{HAT-P-7b}}\gtrsim 6\mathrm{G}$, a result that is consistent with three-dimensional magnetohydrodynamic simulations and lies below typical surface dipole estimates of inflated HJs. The same analysis suggests the minimum dipole field strength required to reverse the winds of CoRoT-2b is $B_{\text{dip},\text{CoRoT-2b}}\gtrsim 3\mathrm{kG}$, which considerably exceeds estimates of the maximum surface dipole strength for HJs. We hence conclude that our magnetic wave-driven mechanism provides an explanation for wind reversals on HAT-P-7b; however, other physical phenomena provide more plausible explanations for wind reversals on CoRoT-2b.

References in corpus (20)

• Atmospheric Circulation and Tides of "51Peg b-like" Planets
• Equatorial superrotation on tidally locked exoplanets
• Transitions in the cloud composition of hot Jupiters
• Inference of Inhomogeneous Clouds in an Exoplanet Atmosphere
• Multi-Wavelength Constraints on the Day-Night Circulation Patterns of HD 189733b
• Dynamic Meteorology at the Photosphere of HD 209458b
• Magnetic Drag on Hot Jupiter Atmospheric Winds
• Atmospheric Heat Redistribution on Hot Jupiters
• Atmospheric Dynamics of Short-period Extra Solar Gas Giant Planets I: Dependence of Night-Side Temperature on Opacity
• Dynamic mineral clouds on HD 189733b I. 3D RHD with kinetic, non-equilibrium cloud formation
• 3.6 and 4.5 $\mu$m $Spitzer$ Phase Curves of the Highly-Irradiated Hot Jupiters WASP-19b and HAT-P-7b
• Magnetic Scaling Laws for the Atmospheres of Hot Giant Exoplanets
• Magnetic Effects in Hot Jupiter Atmospheres
• Variability in the Atmosphere of the Hot Giant Planet HAT-P-7 b
• Estimating the magnetic field strength in hot Jupiters
• Detection of a Westward Hotspot Offset in the Atmosphere of a Hot Gas Giant CoRoT-2b
• The Atmospheric Circulation and Observable Properties of Non-Synchronously Rotating Hot Jupiters
• Modeling the effects of inhomogeneous aerosols on the hot Jupiter Kepler-7b's atmospheric circulation
• Observational Consequences of Hydrodynamic Flows on Hot Jupiters
• Equatorial magnetohydrodynamic shallow water waves in the solar tachocline

Cited by in corpus (29)

• The Atmospheric Circulation of Ultra-hot Jupiters
• Hot Jupiters: Origins, Structure, Atmospheres
• Climate of an Ultra hot Jupiter: Spectroscopic phase curve of WASP-18b with HST/WFC3
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Exploring the Effects of Active Magnetic Drag in a GCM of the Ultra-Hot Jupiter WASP-76b
• Evidence for H${}_2$ Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b
• Equatorial anti-rotating day side wind flow in WASP-43b elicited by deep wind jets?
• Understanding the atmospheric properties and chemical composition of the ultra-hot Jupiter HAT-P-7b: I. Cloud and chemistry mapping
• No umbrella needed: Confronting the hypothesis of iron rain on WASP-76b with post-processed general circulation models
• Temporal Variability in Hot Jupiter Atmospheres
• Variability in the Atmosphere of the Hot Jupiter Kepler-76b
• The Impact of Mixing Treatments on Cloud Modelling in 3D Simulations of Hot Jupiters
• The Acceleration of Superrotation in Simulated Hot Jupiter Atmospheres
• A Lack of Variability Between Repeated Spitzer Phase Curves of WASP-43b
• Smaller than expected bright-spot offsets in Spitzer phase curves of the hot Jupiter Qatar-1b
• Dynamics and Clouds in Planetary Atmospheres from Telescopic Observations
• Observational Consequences of Shallow-water Magnetohydrodynamics on Hot Jupiters
• Shallowness of circulation in hot Jupiters -- Advancing the Ohmic dissipation model
• Spitzer thermal phase curve of WASP-121 b
• Signatures of Obliquity in Thermal Phase Curves of Hot Jupiters
• Variability from thermo-resistive instability in the atmospheres of hot jupiters
• Examining NHD vs QHD in the GCM THOR with non-grey radiative transfer for the hot Jupiter regime
• Westward hotspot offset explained by subcritical dynamo action in an ultra-hot Jupiter atmosphere
• Spitzer phase curve observations and circulation models of the inflated ultra-hot Jupiter WASP-76b
• Symmetries and conservation laws of the one-dimensional shallow water magnetohydrodynamics equations in Lagrangian coordinates
• The Magnetic Mechanism for Hotspot Reversals in Hot Jupiter Atmospheres
• Effective drag in rotating, poorly conducting plasma turbulence
• Patchy nightside clouds on ultra-hot Jupiters: General Circulation Model simulations with radiatively active cloud tracers
• Unraveling the Mystery of the Peculiar and Young Hot Jupiter CoRoT-2b. I. H${}_2$O and CO Detection from Dayside Observations with Gemini-S/IGRINS