Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 31, 1131-1142, 2013
http://www.ann-geophys.net/31/1131/2013/
doi: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
Cross-tail current evolution during substorm dipolarization
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.

Citation: Lui, A. T. Y.: Cross-tail current evolution during substorm dipolarization, Ann. Geophys., 31, 1131-1142, doi:10.5194/angeo-31-1131-2013, 2013.
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