Simultaneous Observation of an Auroral Dawn Storm with the Hubble Space Telescope and Juno

On July 13, 2016, the Hubble Space Telescope observed the onset of a dawn storm in Jupiter's northern ultraviolet aurora, while the NASA Juno spacecraft simultaneously traversed the dawnside outer magnetosphere. This represents the first concurrent auroral and in situ magnetospheric observations of the onset of a dawn storm at Jupiter. Mapping the auroral emission to the magnetosphere reveals the dawn storm corresponds to a source region at ∼60 Jupiter radii, and the eastward edge propagates toward local noon at speeds exceeding corotation. Particle observations from Jovian Auroral Distributions Experiment (JADE) and Jupiter Energetic particle Detector Instrument (JEDI) reveal the presence of enhanced hot plasma density in the outer magnetosphere during this interval, and pitch angle distributions measured with JEDI reveal pronounced field-aligned proton and heavy ion motion. Juno magnetometer (MAG) signatures reveal a reversal in the azimuthal magnetic field at the time of storm onset, suggesting acceleration of the hot plasma population above typical sub-corotational speeds. JEDI also detects a region of energetic particles which persists throughout the day following the storm, a feature which is not observed during subsequent perijoves. We interpret this dawn storm as the result of reconnection at earlier local times, possibly associated with a disruption of the azimuthal magnetodisk current.