Flying through a Dawn Storm : an analysis of Juno-UVS images during PJ11

Auroral dawn storms at Jupiter are spectacular brightenings of the dawn arc of the main emission. These events are relatively rare, but they account for some of the brightest aurorae ever observed at Jupiter. An event with a total power emitted by the UV aurora in excess of 8.5 TW was even observed by Hisaki and the Hubble Space Telescope on May 21st 2016, during Juno's approach of Jupiter. On February 7th 2018 (perijove 11, or PJ11), Juno's ultraviolet imaging spectrograph, called Juno-UVS, observed the development of such a dawn storm, right before Juno flew right through the magnetic field line connected to this feature. The storm started around 13:15 UT as a limited enhancement of the main emission around midnight before slowly migrating and expanding on the dusk flank. As the brightness increased, the arc began to thicken and fork into two separate arcs. Simultaneously, the signatures of methane absorption of the UV light progressively intensified, indicative of a precipitation of increasingly energetic particles. Then, around 18:15 UT, Juno entered the field lines feeding the dawn storm. The remote auroral observations thus provide extremely valuable context information for the in-situ radio waves, particle and magnetic field observations gathered at this time.