ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-24-751-2006 Flux closure during a substorm observed by Cluster, Double Star, IMAGE FUV, SuperDARN, and Greenland magnetometers Milan S. E. 1 Wild J. A. 2 1 Hubert B. 3 Carr C. M. 4 Lucek E. A. 4 Bosqued J. M. 5 Watermann J. F. 6 Slavin J. A. 7 Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK Department of Communication Systems, Lancaster University, Lancaster LA1 4WA, UK Laboratory of Planetary and Atmospheric Physics, University of Liege, Liege, B-4000 Belgium Department of Physics, Imperial College London, London SW7 2AZ, UK Centre d’Etude Spatiale des Rayonnements, CESR/CNRS, 31028 Toulouse Cedex, France Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen, Denmark Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA 23 03 2006 24 2 751 767 Copyright: © 2006 S. E. Milan et al. 2006 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/24/751/2006/angeo-24-751-2006.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/24/751/2006/angeo-24-751-2006.pdf

We examine magnetic flux closure during an extended substorm interval on 29&nbsp;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&nbsp;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<sup>-1</sup>, or 6 <i>R<sub>E</sub></i> between each dipolarization.