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

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.