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Evolution of dipolarization in the near-Earth current sheet induced by Earthward rapid flux transport
R. Nakamura1, A. Retinò1, W. Baumjohann1, M. Volwerk1, N. Erkaev2, B. Klecker3, E. A. Lucek4, I. Dandouras5, M. André6, and Y. Khotyaintsev6
1Space Research Institute, Austrian Academy of Sciences, 8042 Graz, Austria
2Institute of Computation Modelling, Russian Academy of Sciences, Siberian Branch, Krasnoyarsk, Russia
3Max-Planck-Institut für extraterrestrische Physik, P.O. Box 1312, Garching, 85741, Germany
4Imperial College, London, SW7 2BZ, UK
5CESR/CNRS, 9 Ave. du Colonel Roche, B.P. 4346, 31028 Toulouse Cedex 4, France
6Swedish Institute of Space Physics, P.O. Box 537, 75121 Uppsala, Sweden
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Abstract. We report on the evolution of dipolarization and associated
disturbances of the near-Earth current sheet during a substorm on 27
October 2007, based upon Cluster multi-point, multi-scale
observations of the night-side plasma sheet at X~−10 RE.
Three dipolarization events were observed accompanied by activations
on ground magnetograms at 09:07, 09:14, and 09:22 UT. We found that all
these events consist of two types of dipolarization signatures: (1)
Earthward moving dipolarization pulse, which is accompanied by
enhanced rapid Earthward flux transport and is followed by current
sheet disturbances with decrease in BZ and enhanced local current
density, and subsequent (2) increase in BZ toward a stable level,
which is more prominent at Earthward side and evolving tailward.
During the 09:07 event, when Cluster was located in a thin current
sheet, the dipolarization and fast Earthward flows were also
accompanied by further thinning of the current sheet down to a
half-thickness of about 1000 km and oscillation in a kink-like mode
with a period of ~15 s and propagating duskward. Probable cause
of this "flapping current sheet" is shown to be the Earthward
high-speed flow.
The oscillation ceased as the flow decreased and the field
configuration became more dipolar. The later rapid flux transport
events at 09:14 and 09:22 UT took place when the field configuration
was initially more dipolar and were also associated with BZ
disturbance and local current density enhancement, but to a lesser
degree. Hence, current sheet disturbances induced by initial
dipolarization pulses could differ, depending on the configuration
of the current sheet.
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Citation: Nakamura, R., Retinò, A., Baumjohann, W., Volwerk, M., Erkaev, N., Klecker, B., Lucek, E. A., Dandouras, I., André, M., and Khotyaintsev, Y.: Evolution of dipolarization in the near-Earth current sheet induced by Earthward rapid flux transport, Ann. Geophys., 27, 1743-1754, doi:10.5194/angeo-27-1743-2009, 2009. Bibtex EndNote Reference Manager XML
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