Unveiling the Connection between the Alfvénic Oval and the Open-Closed Field Line Boundary at Ganymede

Abstract

<p>Alfvén waves generated by the interactions between the Ganymede magnetosphere and the fast-corotating Jovian plasma carry a significant amount of energy. This energy is partially transferred to precipitating particles, which correspond to a feature called the Alfvénic oval. However, the spatial distribution of the Alfvénic oval in the Ganymede system is unclear, and the physical correlation between the Alfvénic oval and the open-closed field line boundary (OCFB) has not been studied quantitatively. Using a high-resolution, three-dimensional global magnetohydrodynamics simulation of Ganymede's magnetosphere, we investigate the spatial distribution of the Alfvénic oval mapped on the ionosphere surface of Ganymede based on upstream measurements from Juno's PJ34 flyby. Our results show that (1) the simulated Alfvénic oval of Ganymede closely resembles the observed aurora oval, and although without kinetic physics, the magnitude of the simulated Afvénic Poynting flux is significantly lower than the estimation based on auroral luminosity; (2) the OCFB aligns closely with the poleward (equatorial) boundary of the enhanced Alfvénic power on the downstream (upstream) side; and (3) the magnetospheric flux tube convection pattern can guide the Alfvénic wave packet to propagate toward latitudes either equatorward or poleward of the OCFB on the downstream/upstream side. These results, presented for the first time in this study, provide testable predictions for both the ongoing Juno mission and future Jovian missions such as JUICE probing the minimagnetosphere system.</p>