Cross-tail expansion of dipolarizing flux bundles

Abstract

Dipolarizing flux bundles (DFBs), magnetotail flux tubes with stronger, more dipolar magnetic field than the background magnetotail plasma, which are led by dipolarization fronts, typically propagate earthward within bursty bulk flows. Although DFBs are localized (typically 1-3 RE) in the cross-tail direction, many of them may combine to cause global effects, such as the substorm current wedge. Knowledge of how this local-to-global coupling happens is crucial for understanding magnetotail dynamics. We investigate how the coupling happens using multipoint observations from the Time History of Events and Macroscale Interactions during Substorms mission. Our results show that most DFBs expand in the cross-tail direction as they propagate earthward. Through such expansion, azimuthally localized DFBs can cover a wide region to cause global effects when they arrive at the inner edge of the plasma sheet.