Do Earth’s auroral substorms and Jupiter’s dawn storms arise from the same processes?

For the first time, Juno has granted views of the night side aurora at Jupiter during several hours long observation sequences. Among the most spectacular events captured by Juno-UVS (the UltraViolet imaging Spectrograph on board Juno) are dawn storms. The images of these events show a striking resemblance to the sequence of events forming auroral substorms at Earth. They often start with transient north-south aligned features located poleward of the main oval. A few hours later, the post-midnight portion of the main arc brightens and forms a bead-like pattern. A few tens of minutes later, it then broadens both in latitude and in longitude, ultimately forming two separate arcs, one migrating poleward and one moving equatorward. At the same time, the whole feature, which first appeared fixed in local time, progressively accelerates towards co-rotation with the magnetic field. Finally, the equatorward part of the dawn storm transforms into large injection signatures. During this presentation, we will show in parallel similar sequences of terrestrial substorms and interpret these events in similar ways. Indeed, our thesis is that the two auroral events are the signatures of similar collapses of the magnetotail, even if the two systems did not accrue mass and energy through similar processes.

Juno did more than observe the dawn storms from their initiation to their dissipation, the spacecraft also flew through the field lines connected to the auroral events. We will discuss the particle distributions and the enhancements of Alfvén wave activity that arose as Juno entered the heart of the storm.