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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 31, issue 6 | Copyright

Special issue: Dynamical processes in space plasmas II

Ann. Geophys., 31, 1131-1142, 2013
https://doi.org/10.5194/angeo-31-1131-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 27 Jun 2013

Regular paper | 27 Jun 2013

Cross-tail current evolution during substorm dipolarization

A. T. Y. Lui A. T. Y. Lui
  • Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA

Abstract. We examine evolution of the cross-tail current during substorm current disruption/dipolarization using observations from two satellites in the near-Earth magnetotail at the downtail distances of 8–9 RE. By choosing times when these two satellites are separated, mainly in the north–south distance in the tail current sheet, precise determination of current density in the layer embedded between these satellites can be obtained with Ampère's law. Two such events are examined and several common features are found. The current densities in the layer embedded by the two satellites were reduced by ~ 40–70% during substorm dipolarization. The changes in current densities have the fast kinetic timescale, i.e., in seconds, implying a kinetic process for current disruption/dipolarization. The estimated power within the current layer was mainly dissipative in the dawn–dusk direction and mainly dynamo in the Sun–tail direction that is needed to drive the north–south substorm current system in the ionosphere. Remote sensing of the energization site with the ion sounding technique shows that the energization site was initially earthward of the satellite and moved down the tail at later times. Breakdown of the frozen-in condition occurred intermittently during the disturbance interval. These features provide important clues to the substorm onset process.

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