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Ann. Geophys., 24, 751-767, 2006
www.ann-geophys.net/24/751/2006/
© European Geosciences Union 2006
Flux closure during a substorm observed by Cluster, Double Star, IMAGE FUV, SuperDARN, and Greenland magnetometers
S. E. Milan1, J. A. Wild1,2, B. Hubert3, C. M. Carr4, E. A. Lucek4, J. M. Bosqued5, J. F. Watermann6, and J. A. Slavin7
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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