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

C. Forsyth, A. N. Fazakerley, I. J. Rae, C. E. J. Watt, K. Murphy, J. A. Wild, T. Karlsson, R. Mutel, C. J. Owen, R. Ergun, A. Masson, M. Berthomier, E. Donovan, H. U. Frey, Jürgen Matzka, Claudia Stolle, Y. Zhang

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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 toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100km at altitudes of 4000-7000km. 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 120-240s after Cluster 4 at 1300-2000km 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 preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven wedgelets. Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of theSCW. Key Points The substorm current wedge (SCW) has significant azimuthal structure Current sheets within the SCW are north-south aligned The substructure of the SCW raises questions for the proposed wedgelet scenario
Original languageEnglish
JournalJournal of Geophysical Research
Volume119
Issue number2
Pages (from-to)927-946
Number of pages20
ISSN2169-9380
DOIs
Publication statusPublished - 2014

Keywords

  • ASTRONOMY
  • FIELD-ALIGNED CURRENTS
  • BURSTY BULK FLOWS
  • PLASMA SHEET
  • CURRENT SYSTEMS
  • MAGNETOSPHERIC SUBSTORMS
  • AURORAL ACCELERATION
  • MAGNETOMETER ARRAY
  • MAGNETIC-FIELD
  • FINE-STRUCTURE
  • HIGH-ALTITUDE
  • Substorm current wedge
  • Field-aligned current
  • Wedgelets
  • Aurora
  • Magnetosphere
  • Earth

Cite this

Forsyth, C., Fazakerley, A. N., Rae, I. J., Watt, C. E. J., Murphy, K., Wild, J. A., Karlsson, T., Mutel, R., Owen, C. J., Ergun, R., Masson, A., Berthomier, M., Donovan, E., Frey, H. U., Matzka, J., Stolle, C., & Zhang, Y. (2014). In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge. Journal of Geophysical Research, 119(2), 927-946. https://doi.org/10.1002/2013JA019302