Articles | Volume 27, issue 4
Ann. Geophys., 27, 1743–1754, 2009

Special issue: Ninth International Conference on Substorms (ICS9)

Ann. Geophys., 27, 1743–1754, 2009

  09 Apr 2009

09 Apr 2009

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 R. Nakamura et al.
  • 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

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.