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Ann. Geophys., 24, 3497-3505, 2006
www.ann-geophys.net/24/3497/2006/
© European Geosciences Union 2006
Remote sensing of a near-Earth neutral line during the 5 October 2000 substorm
D. Nagata1, S. Machida1, S. Ohtani2, S. B. Mende3, Y. Saito4, and T. Mukai4
1Department of Geophysics, Kyoto University, Kyoto 606-8502, Japan
2Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA
3Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
4Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 229-8510, Japan
Abstract. In this paper we examined the continuous motions of a near-Earth neutral line
during the recovery phase of the 5 October 2000 substorm. Estimation was based
on the PSBL ion beam model proposed by Onsager (1991) and the Geotail
observations. Estimated distances from the Earth ranged from 20 to 60 RE
and retreated tailward at velocities of 250 and 300 km/s. This event
initiated with the arrival of solar wind discontinuity. Simultaneous
observations of electromagnetic field and electrons indicate the existence
of earthward propagating waves associated with field-aligned currents. Based
on these observations, we suggest that the source of the PSBL ion beams was
the retreating near-Earth neutral line formed by the compression of
the magnetosphere. Two scenarios of near-Earth neutral line motion in the tail
dynamics are also proposed. One is the formation of plural neutral lines to
create a long plasmoid. The other is the oscillation of one neutral line
between the near-Earth region and the mid-tail stagnant plasmoid.
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