Periodic shearing motions in the Jovian magnetosphere causing a localized peak in the main auroral emission close to noon

TL;DR

This study uses 3D MHD simulations to explain a localized brightness peak in Jupiter's aurora near noon, caused by periodic shearing motions in the magnetodisk driven by flux-tube dynamics.

Contribution

It provides a novel simulation-based explanation for the transient auroral brightness enhancement observed near noon on Jupiter.

Findings

Periodic shearing motions cause localized auroral brightness peaks.

Flux-tube dynamics drive the shearing motions and associated currents.

Simulation results match observed transient auroral features.

Abstract

Recently, a transient localized brightness enhancement has been observed in Jupiter's main auroral emission close to noon by Palmaerts et al. (2014). We use results from three-dimensional global MHD simulations to understand what is causing this localized peak in the main emission. In the simulations, the peak occurs every rotation period and is due to shearing motions in the magnetodisk. These shearing motions are caused by heavy flux-tubes being accelerated to large azimuthal speeds at dawn. The centrifugal force acting on these flux-tubes is then so high that they rapidly move away from the planet. When they reach noon, their azimuthal velocity decreases, thus reducing the centrifugal force, and allowing the flux-tubes to move back closer to Jupiter. The shearing motions associated with this periodic phenomenon locally increase the field aligned currents in the simulations, thus causing a transient brightness enhancement in the main auroral emission, similar to the one observed by Palmaerts et al. (2014).