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In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge

Research output: Contribution to journalJournal article

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  • C. Forsyth
  • A. N. Fazakerley
  • I.J. Rae
  • C. E. J. Watt
  • Kyle R. Murphy
  • Jim Wild
  • T. Karlsson
  • Robert Mutel
  • C. J. Owen
  • Robert Ergun
  • A. Masson
  • M. Berthomier
  • E. Donovan
  • H. U. Frey
  • Juergen Matzka
  • C. Stolle
  • Y. Zhang
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<mark>Journal publication date</mark>12/02/2014
<mark>Journal</mark>Journal of Geophysical Research: Space Physics
Issue number2
Volume119
Number of pages20
Pages (from-to)927-946
<mark>State</mark>Published
Early online date14/01/14
<mark>Original language</mark>English

Abstract

The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere towards dawn and out of the ionosphere towards dusk, linked by a westward electrojet. We use multi-spacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 Jan 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft travelled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal sub-structure on scales of 100~km at altitudes of 4,000-7,000~km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120-240~s after Cluster 4 at 1,300-2,000~km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the pre-onset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs) we conclude that the structuring of the SCW cannot solely be due to BBF driven "wedgelets". Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW.

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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.