Magnetic Effects in Hot Jupiter Atmospheres

TL;DR

This study uses MHD simulations to explore magnetic effects in hot Jupiter atmospheres, finding negligible effects below 1400K and significant wind variability and Ohmic dissipation peaking around 1500-1600K, with implications for atmospheric dynamics.

Contribution

First comprehensive MHD simulations across a range of hot Jupiter temperatures, revealing the temperature-dependent significance of magnetic effects and quantifying Ohmic dissipation.

Findings

Magnetic effects negligible below 1400K.

Wind variability and westward flows at higher temperatures.

Peak Ohmic dissipation around 1500-1600K, limited by physical parameters.

Abstract

We present magnetohydrodynamic (MHD) simulations of the atmospheres of hot Jupiters ranging in temperature from 1100-1800K. Magnetic effects are negligible in atmospheres with temperatures $\lesssim$ 1400K. At higher temperatures winds are variable and in many cases, mean equatorial flows can become westward, opposite to their hydrodynamic counterparts. Ohmic dissipation peaks at temperatures $\sim$1500-1600K, depending on field strength, with maximum values $\sim 10^{18}$W at 10bar, substantially lower than previous estimates. Based on the limited parameter study done, this value can not be increased substantially with increasing winds, higher temperatures, higher field strengths, different boundary conditions or lower diffusivities. Although not resolved in these simulations there is modest evidence that a magnetic buoyancy instability may proceed in hot atmospheres.