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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 2
Ann. Geophys., 24, 751–767, 2006
https://doi.org/10.5194/angeo-24-751-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 751–767, 2006
https://doi.org/10.5194/angeo-24-751-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  23 Mar 2006

23 Mar 2006

Flux closure during a substorm observed by Cluster, Double Star, IMAGE FUV, SuperDARN, and Greenland magnetometers

S. E. Milan1, J. A. Wild2,1, B. Hubert3, C. M. Carr4, E. A. Lucek4, J. M. Bosqued5, J. F. Watermann6, and J. A. Slavin7 S. E. Milan et al.
  • 1Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
  • 2Department of Communication Systems, Lancaster University, Lancaster LA1 4WA, UK
  • 3Laboratory of Planetary and Atmospheric Physics, University of Liege, Liege, B-4000 Belgium
  • 4Department of Physics, Imperial College London, London SW7 2AZ, UK
  • 5Centre d’Etude Spatiale des Rayonnements, CESR/CNRS, 31028 Toulouse Cedex, France
  • 6Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen, Denmark
  • 7Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

Abstract. We examine magnetic flux closure during an extended substorm interval on 29 August 2004 involving a two-stage onset and subsequent re-intensifications. Cluster and Double Star provide observations of magnetotail dynamics, while the corresponding auroral evolution, convection response, and substorm current wedge development are monitored by IMAGE FUV, SuperDARN, and the Greenland magnetometer chain, respectively. The first stage of onset is associated with the reconnection of closed flux in the plasma sheet; this is accompanied by a short-lived auroral intensification, a modest substorm current wedge magnetic bay, but no significant ionospheric convection enhancement. The second stage follows the progression of reconnection to the open field lines of the lobes; accompanied by prolonged auroral bulge and westward-travelling surge development, enhanced magnetic bays and convection. We find that the tail dynamics are highly influenced by ongoing dayside creation of open flux, leading to flux pile-up in the near-tail and a step-wise down-tail motion of the tail reconnection site. In all, 5 dipolarizations are observed, each associated with the closure of ~0.1 GWb of flux. Very simple calculations indicate that the X-line should progress down-tail at a speed of 20 km s-1, or 6 RE between each dipolarization.

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