Atmospheric Escape by Magnetically Driven Wind from Gaseous Planets II --Effects of Magnetic Diffusion--

TL;DR

This study uses non-ideal MHD simulations to explore how magnetic diffusion affects Alfvenic wave-driven atmospheric escape in hot Jupiters, revealing wave damping impacts on mass loss and complex energy flux behaviors.

Contribution

It introduces the effects of magnetic diffusion into MHD models of hot Jupiter atmospheres, showing how it alters wave propagation and planetary wind mass-loss rates.

Findings

Magnetic diffusion significantly reduces mass-loss rates compared to ideal MHD.

Alfvenic wave energy flux exhibits nonmonotonic behavior with surface input energy.

Heating and mass loss occur only in limited zones with confined magnetic fields.

Abstract

We investigate roles of Alfvenic waves in the weakly-ionized atmosphere of hot Jupiters by carrying out non-ideal magnetohydrodynamic (MHD) simulations with Ohmic diffusion in one-dimensional magnetic flux tubes. Turbulence at the surface excites Alfven waves and they propagate upward to drive hot (~ 10^4 K) outflows. The magnetic diffusion plays an important role in the dissipation of the Alfvenic waves in the weakly ionized atmosphere of hot Jupiters. The mass-loss rate of the spontaneously driven planetary wind is considerably reduced, in comparison with that obtained from ideal MHD simulations because the Alfvenic waves are severely damped at low altitudes in the atmosphere, whereas the wave heating is still important in the heating of the upper atmosphere. Dependence on the surface temperature, planetary radius, and velocity dispersion at the surface is also investigated. We find an inversion phenomenon of the transmitted wave energy flux; the energy flux carried by Alfven waves in the upper atmosphere has a nonmonotonic correlation with the input energy flux from the surface in a certain range of the surface temperature because the resistivity is determined by the global physical properties of the atmosphere in a complicated manner. We also point out that the heating and mass loss are expected only in limited zones if the open magnetic field is confined in the limited regions.