Shallow-water Magnetohydrodynamics for Westward Hotspots on Hot Jupiters

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 t...

Full description

Saved in:
Bibliographic Details
Published in:Astrophysical journal. Letters 2019-02, Vol.872 (2), p.L27
Main Authors: Hindle, A. W., Bushby, P. J., Rogers, T. M.
Format: Article
Language:English
Subjects:
Computational fluid dynamics
Computer simulation
Dipoles
Eddies
Equatorial winds
Extrasolar planets
Field strength
Fluid flow
Gas giant planets
Kelvin waves
Magnetic fields
Magnetohydrodynamic simulation
Magnetohydrodynamics
magnetohydrodynamics (MHD)
planets and satellites: atmospheres
planets and satellites: individual (CoRoT-2b, HAT-P-7b, HD 189733b)
Wind
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary: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 , 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 , 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.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/ab05dd