Juno-UVS approach observations of Jupiter's auroras

Juno ultraviolet spectrograph (UVS) observations of Jupiter's aurora obtained during approach are presented. Prior to the bow shock crossing on 24 June 2016, the Juno approach provided a rare opportunity to correlate local solar wind conditions with Jovian auroral emissions. Some of Jupiter's auroral emissions are expected to be controlled or modified by local solar wind conditions. Here we compare synoptic Juno-UVS observations of Jupiter's auroral emissions, acquired during 3-29 June 2016, with in situ solar wind observations, and related Jupiter observations from Earth. Four large auroral brightening events are evident in the synoptic data, in which the total emitted auroral power increases by a factor of 3-4 for a few hours. Only one of these brightening events correlates well with large transient increases in solar wind ram pressure. The brightening events which are not associated with the solar wind generally have a risetime of similar to 2 h and a decay time of similar to 5 h. Plain Language Summary Juno ultraviolet spectrograph (UVS) observations of Jupiter's aurora obtained during approach are presented. Jupiter's auroras are thought to be controlled in part by the solar wind, a stream of charged particles flowing outward from the Sun. The Juno approach was a rare opportunity to compare solar wind conditions near Jupiter with the Jovian ultraviolet aurora, using observations made during June 2016. Although Jupiter's aurora is always present, four brightening events were seen in the data, in which the total auroral power increased to several times the typical level for a few hours. Only one of these brightening events appears well connected with solar wind activity. The brightening events which are not associated with the solar wind all increase in brightness in about 2 h and then dim back down again in about another 5 h.