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Ann. Geophys., 25, 1405-1415, 2007
www.ann-geophys.net/25/1405/2007/
© European Geosciences Union 2007
Cluster observations of a field aligned current at the dawn flank of a bursty bulk flow
K. Snekvik1, S. Haaland1,2, N. Østgaard1, H. Hasegawa3, R. Nakamura4, T. Takada3,4, L. Juusola5, O. Amm5, F. Pitout2, H. Rème6, B. Klecker2, and E. A. Lucek7
1Department of Physics and Technology, University of Bergen, Bergen, Norway
2Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany
3Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
4Space Research Institute, Austrian Academy of Sciences, Graz, Austria
5Finnish Meteorological Institute, Space Research Unit, Finland
6Centre d'Etude Spatiale des Rayonnements, Toulouse, France
7Space and Atmospheric Physics, Imperial College, London, UK
Abstract. This article describes observations of a bursty bulk flow (BBF) in the outer
central plasma sheet. The observations are made with the Cluster satellites,
located approximately 19 RE downtail, close to the midnight sector in the
Southern Hemisphere. 40–60 s after Cluster first detected the BBF, there
was a large bipolar perturbation in the magnetic field. A Grad-Shafranov
reconstruction has revealed that this is created by a field-aligned current
at the flank of the BBF. Further analysis of the plasma moments has shown
that the BBF has the properties of a depleted flux tube. Depleted flux tubes
are an important theoretical model for how plasma and magnetic flux can be
transported Earthward in the magnetotail as part of the Dungey cycle. The
field aligned current is directed Earthward and is located at the dawn side
of the BBF. Thus, it is consistent with the magnetic shear at the flank of an
Earthward moving BBF. The total current has been estimated to be about
0.1 MA.
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