Three-dimensional Magnetohydrodynamic Simulations of Periodic Variations of Ganymede’s Footprint

Abstract

Alfvénic power is generated through the interaction between the mini-magnetosphere of Ganymede and the corotating flow of the Jovian plasma, contributing to the formation of the Ganymede auroral footprint at Jupiter’s ionosphere. Using a three-dimensional, high-resolution global magnetohydrodynamic model of the Ganymede magnetosphere, we investigate the temporal variations of the Alfvénic power generated in the mini-magnetosphere of the moon under steady-state upstream conditions. Results show that (1) the Alfvénic power caused by the intermittent magnetic reconnections and the Kelvin-Helmholtz instabilities is quasiperiodic, varying over time with the periods about 71-333 s, which are consistent with the 100 s timescale periodicities of the Ganymede footprint's emitted power; and (2) the magnitude of the Alfvénic power is smaller when Ganymede is inside the Jovian plasma sheet where the B y component is smaller, and larger when the moon is outside the plasma sheet where the B y component is larger.