Multi-instrument Investigation of the Location of Saturn's Magnetotail X-Line

Abstract

Reconnection is a fundamentally important process in planetary magnetospheres, with both local and global effects. At Saturn, observations of the magnetotail reconnection site (or x-line) are rare, with only one in situ encounter reported to date. In this work, an extensive database of plasmoids and dipolarizations (Smith et al., 2016, https://doi.org/10.1002/2015JA022005) was investigated from a multi-instrument perspective in order to probe the location and variability of the magnetotail x-line. Several clear intervals were identified in which the x-line location could be indirectly inferred to move on relatively short timescales. Two case studies are presented, the first of which concerns short-lived flows, suggesting the reconnection sites can be either short-lived (∼10 minutes) or extremely azimuthally limited (∼3RS/0.4 hr of local time). The second interval concerns the tailward motion of the reconnection site (or sites), inferred from the increasing electron temperature (and diminishing electron density) associated with the flows. This tailward motion occurs over ∼2.5 hr (approximately a quarter of a planetary rotation). The composition of the suprathermal plasma suggests that this could be an example of the gradual depletion of mass-loaded flux tubes (that must occur prior to lobe reconnection). These case studies are consistent with previous statistical work that suggested that the site of reconnection in the Kronian magnetotail can be highly dynamic.