A New Framework to Explain Changes in Io's Footprint Tail Electron Fluxes

Abstract

We analyze precipitating electron fluxes connected to 18 crossings of Io's footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). The strength of precipitating electron fluxes is dominantly organized by “Io-Alfvén tail distance,” the angle along Io's orbit between Io and an Alfvén wave trajectory connected to the tail aurora. These fluxes best fit an exponential as a function of down-tail extent with an e-folding distance of 21°. The acceleration region altitude likely increases down-tail, and the majority of parallel electron acceleration sustaining the tail aurora occurs above 1 RJ in altitude. We do not find a correlation between the tail fluxes and the power of the initial Alfvén wave launched from Io. Finally, Juno has likely transited Io's Main Alfvén Wing fluxtube, observing a characteristically distinct signature with precipitating electron fluxes ~600 mW/m2 and an acceleration region extending as low as 0.4 RJ in altitude.