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Ann. Geophys., 25, 1709-1720, 2007
www.ann-geophys.net/25/1709/2007/
© European Geosciences Union 2007
Multi-scale observations of magnetotail flux transport during IMF-northward non-substorm intervals
A. Grocott1, T. K. Yeoman1, S. E. Milan1, O. Amm2, H. U. Frey3, L. Juusola2, R. Nakamura4, C. J. Owen5, H. Rème6, and T. Takada4,*
1Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
2Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
3Space Sciences Lab, University of California, Berkeley, CA 94720-7450, USA
4Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, Graz, 8042, Austria
5Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
6CESR, 9 avenue du colonel Roche, Toulouse, 31028, France
*now at: Solar-Terrestrial Physics Group, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Yoshinodai 3-1-1, Sagamihara 229-8510, Japan
Abstract. Simultaneous observations by the Cluster spacecraft and
SuperDARN radars are presented of magnetotail flux transport during
northward, but BY-dominated IMF. Two events are discussed, which
occurred on 14 August 2004 and 17 September 2005, during intervals of
negative and positive IMF BY, respectively. During both intervals the
Cluster spacecraft observed isolated bursts of Earthward plasma convection
in the central plasma sheet. During the first event, the flows observed by
Cluster also had a significant V⊥Y component in the duskward
direction, consistent with westward azimuthal flows observed in the midnight
sector by the Northern Hemisphere SuperDARN radars. During the second event,
Cluster 4 observed a significant dawnward V⊥Y component, again
consistent with the Northern Hemisphere SuperDARN observations which
revealed eastward azimuthal flow. In this instance, however, Cluster 3
observed a duskward V⊥Y component which was more consistent with
the duskward sense of the convection observed by the Southern Hemisphere
SuperDARN radars. This implies that Cluster 3 and Cluster 4 were located on
different field lines which experienced opposite net azimuthal forces and
hence observed oppositely directed convection. These observations are
consistent with previous SuperDARN studies of nightside flows under
northward IMF and, more importantly, provide the first simultaneous in-situ
evidence for a mode of tail reconnection occurring during non-substorm
intervals in an asymmetric tail.
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