Collective dynamics of bursty particle precipitation initiating in the inner and outer plasma sheet

Abstract

Using multiscale spatiotemporal analysis of bursty precipitation events in the nighttime aurora as seen by the POLAR UVI instrument, we report a set of new statistical signatures of high- and low-latitude auroral activity, signaling a strongly non-uniform distribution of dissipation mechanism in the plasma sheet. We show that small-scale electron emission events that initiate in the equatorward portion of the nighttime auroral oval (scaling mode A1) have systematically steeper power-law slopes of energy, power, area, and lifetime probability distributions compared to the events that initiate at higher latitudes (mode B). The low-latitude group of events also contain a small but energetically important subpopulation of substorm-scale disturbances (mode A2) described by anomalously low distribution exponents characteristic of barely stable thermodynamic systems that are prone to large-scale sporadic reorganization. The high latitude events (mode ) can be accurately described by a single set of distributions exponents over the entire range of studied scales, with the exponent values consistent with globally stable self-organized critical (SOC) behavior. The low- and high latitude events have distinct inter-trigger time statistics, and are characterized by significantly different MLT distributions. Based on these results we conjecture that the inner and outer portions of the plasma sheet are associated with two (or more) mechanisms of collective dynamics that may represent an interplay between current disruption and magnetic reconnection scenarios of bursty energy conversion in the magnetotail.