Energy Flux and Characteristic Energy of Electrons Over Jupiter's Main Auroral Emission

Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (~100 eV to ~1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (<10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of ~51. A refined current sheet model will likely bring this boundary closer to the expected 20–30 R_J. Outside that region, the >100-keV electrons contribute to most (>~70–80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.