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Ann. Geophys., 26, 167-184, 2008
www.ann-geophys.net/26/167/2008/
© European Geosciences Union 2008
Observed tail current systems associated with bursty bulk flows and auroral streamers during a period of multiple substorms
C. Forsyth1, M. Lester1, S. W. H. Cowley1, I. Dandouras2, A. N. Fazakerley3, R. C. Fear1, H. U. Frey4, A. Grocott1, A. Kadokura5, E. Lucek6, H. Rème2, S. E. Milan1, and J. Watermann7
1Dept. Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
2CESR/CNRS, 9 Avenue du Colonel Roche, B.P. 4346, 31028, Toulouse Cedex 4, France
3Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
4Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
5National Institute of Polar Research, 9-10-1 Kaga, Itabashi, Tokyo 173-8515, Japan
6Blackett Laboratory, Imperial College, London, SW7 2BZ, UK
7Atmosphere Space Research Division, Danish Meteorological Institute, Copenhagen, Denmark
Abstract. We present a multi-instrument study of a substorm bursty bulk flow (BBF) and
auroral streamer. During a substorm on 25 August 2003, which was one of a
series of substorms that occurred between 00:00 and 05:00 UT, the Cluster
spacecraft encountered a BBF event travelling Earthwards and duskwards with a
velocity of ~500 km s−1 some nine minutes after the onset of
the substorm. Coincident with this event the IMAGE spacecraft detected an
auroral streamer in the substorm auroral bulge in the Southern Hemisphere
near the footpoints of the Cluster spacecraft. Using FluxGate Magnetometer
(FGM) data from the four Cluster spacecraft, we determine the field-aligned
currents in the BBF, using the curlometer technique, to have been
~5 mA km−2. When projected into the ionosphere, these currents
give ionospheric field-aligned currents of ~18 A km−2, which
is comparable with previously observed ionospheric field-aligned currents
associated with BBFs and auroral streamers. The observations of the BBF are
consistent with the plasma "bubble" model of Chen and Wolf (1993). Furthermore,
we show that the observations of the BBF are consistent with the creation of
the BBF by the reconnection of open field lines Earthward of a substorm
associated near-Earth neutral line.
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