Magnetotail Reconnection at Jupiter: A Survey of Juno Magnetic Field Observations

At Jupiter, tail reconnection is thought to be driven by an internal mass loading and release process called the Vasyliunas cycle. Galileo data have shown hundreds of reconnection events occurring in Jupiter's magnetotail. Here we present a survey of reconnection events observed by Juno during its first 16 orbits of Jupiter (July 2016-October 2018). The events are identified using Juno magnetic field data, which facilitates comparison to the Vogt et al. (2010, https://doi.org/10.1029/2009JA015098) survey of reconnection events from Galileo magnetometer data, but we present data from Juno's other particle and fields instruments for context. We searched for field dipolarizations or reversals and found 232 reconnection events in the Juno data, most of which featured an increase in vertical bar B-theta vertical bar, the magnetic field meridional component, by a factor of 3 over background values. We found that most properties of the Juno reconnection events, like their spatial distribution and duration, are comparable to Galileo, including the presence of a similar to 3-day quasi-periodicity in the recurrence of Juno tail reconnection events and in Juno JEDI, JADE, and Waves data. However, unlike with Galileo we were unable to clearly define a statistical x-line separating planetward and tailward Juno events. A preliminary analysis of plasma velocities during five magnetic field reconnection events showed that the events were accompanied by fast radial flows, confirming our interpretation of these magnetic signatures as reconnection events. We anticipate that a future survey covering other Juno datasets will provide additional insight into the nature of tail reconnection at Jupiter. Plain Language Summary Magnetic reconnection is an important physical process that allows for the release of mass and energy from a planetary magnetotail. Reconnection can be observed in the magnetic field data measured by spacecraft by looking for an increase or a reversal in the north-south direction of the magnetic field. In previous work, hundreds of reconnection events have been found in Jupiter's magnetotail by analyzing magnetic field data from the Galileo mission at Jupiter. In this study we surveyed magnetometer data from the Juno mission to identify reconnection events, and we compared their properties to the Galileo events. Overall, we find that the Galileo and Juno data show similar results, including the similar to 3-day timescale for the recurrence of reconnection events and other activity in Jupiter's magnetosphere. Though here we focused on Juno magnetometer data, we hope to extend our study to other Juno datasets in the future, and we expect those results will improve our understanding of the importance of tail reconnection in Jupiter's magnetosphere.