Shallow-water Magnetohydrodynamics for Westward Hotspots on Hot Jupiters

A. W. Hindle, P. J. Bushby, Tamara Rogers

Research output: Contribution to journalArticle

7 Scopus citations

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--Rfpag-7b would reverse for a planetary dipole field strength B dip ,HAT P 7b 6 ≥, 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 dip ,CoRoT 2b ≥ 3 k, 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.

Original languageEnglish (US)
Article numberL27
JournalAstrophysical Journal Letters
Volume872
Issue number2
DOIs
StatePublished - Jan 1 2019
Externally publishedYes

Keywords

  • magnetohydrodynamics (MHD)
  • planets and satellites: atmospheres
  • planets and satellites: individual (CoRoT-2b, HAT-P-7b, HD 189733b)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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