Simultaneous UV Images and High-latitude Particle and Field Measurements Dur- ing an Auroral Dawn Storm at Jupiter

We present Juno observations between 03:00 to 06:00 UT on day-of-year 86, 2017 that link particles and fields in Jupiter’s polar magnetosphere to transient UV emissions in Jupiter’s auroral region known as dawn storms. Juno ranged between 42°N - 51°N in magnetic latitude and 5.8 - 7.8 jovian radii (1 RJ ∼ 71,400 km) during this period. These dawn storm UV emissions consist of two separate, elongated structures which extend into the nightside, rotate with the planet, have enhanced brightness (up to at least 1.4 megaRayleigh) and high color ratios. The color ratio is a proxy for the atmospheric penetration depth and energy of the electrons that produce the UV emissions. Juno observed electrons and ions on magnetic field lines mapping to these emissions. The electrons are field-aligned, bi-directional, and, at times, exhibit sudden intensity decreases below ∼10 keV coincident with intensity enhancements up to energies of ∼1000 keV, consistent with the high color ratio observations. These more energetic electron distributions have characteristic energies of ∼120 - 280 keV and downward energy fluxes (∼40 - 140 mW/m2) that are a significant fraction of those required to produce the UV emissions for this event. The ions have similar energy distributions as the electrons. Whistler mode auroral hiss waves and magnetic field perturbations up to ∼0.7% of the local magnetic field (∼1500 - 3700 nT) are also observed along Juno’s trajectory. These high latitude observations are a result of dynamic processes in the equatorial magnetosphere that trigger the generation of these dawn storm emissions.