Investigating Magnetic Field Fluctuations in Jovian Auroral Electron Beams

Abstract

The Juno spacecraft provides a unique opportunity to explore the mechanisms generating Jupiter's aurorae. Past analyses of Juno data immensely advanced our understanding of its auroral acceleration processes, however, few studies utilized multiple instruments on Juno in a joint systematic analysis. This study uses measurements from the Juno Ultraviolet Spectrograph (UVS), the Jupiter Energetic particle Detector Instrument (JEDI), and the Juno Magnetometer (MAG) from the first 20 perijoves. On magnetic field lines associated with the diffuse aurora, we consistently find small-scale magnetic field fluctuations with amplitudes of up to 100 nT on time scales of seconds to 1 min. On magnetic field lines directly linked to the main emission, the electron distribution is field-aligned, mostly broad-band in energy, and accompanied by large-scale magnetic field perturbations of several 100 nT on time scales of tens of min (except one case). These large-scale perturbations are generally associated with quasistatic field-aligned electric currents. Small-scale magnetic fields are not resolved over the main emission zone when the spacecraft is within four Jovian radii radial distance closer than radial distances four Jovian radii due to the digitization limit of the magnetometer. However, in all cases where Juno crosses the main auroral field lines beyond 4 R_J, the digitization limit is significantly reduced and we detect small-scale magnetic field fluctuations of 2–10 nT consistent with a turbulent spectrum. Associated energy fluxes projected to Jupiter can exceed 1,000 mW/m2. The general broad-band nature of the electron distributions and the consistent presence of small-scale magnetic field fluctuations over the main emission support that wave-particle interaction can dominantly contribute to power Jupiter's auroral processes.