Energetic Particles and Acceleration Regions over Jupiter’s Polar Cap and Main Aurora; a Broad Overview

Abstract:

Previous Juno mission event studies revealed powerful electron and ion acceleration, to 100’s of keV and higher, at low altitudes over Jupiter’s main aurora (MA) and polar cap (PC; poleward of the main aurora). Here we examine 30 – 1200 keV JEDI-instrument particle data from the first 16 Juno orbits to determine how common, persistent, repeatable, and ordered these processes are. For the PC regions we find: 1) Upward electron angle beams, sometimes extending to MeV energies, are persistently present in essentially all portions of the polar cap, but are generated by two distinct and spatially separable processes. 2) Particle evidence for downward acceleration via megavolt electrostatic potentials are observable for 80% of the polar cap crossings and over substantial fractions of the PC area. For the main aurora, with the orbit favoring the dusk side, we find: 1) Three distinct zones are observed that are generally arranged from lower to higher latitudes but sometimes mixed. They are designated here as the diffuse aurora (DifA), Zone-I (ZI(D)) showing primarily downward electron acceleration, and Zone-II (ZII(B)) showing bi-directional acceleration with the upward intensities often greater than downward intensities. 2) ZI(D) and ZII(B) sometimes (but not always) contain, respectively, downward electron inverted-V’s and downward proton inverted-V’s, (potentials up to 400 kV), but otherwise have broadband distributions. 3) Surprisingly, both ZI(D) and ZII(B) can generate equally powerful auroral emissions. It is suggested, but demonstrated for intense portions of only one auroral crossing, that ZI(D) and ZII(B) are associated, respectively, with upward and downward electric currents.