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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 19, issue 9
Ann. Geophys., 19, 1089–1094, 2001
https://doi.org/10.5194/angeo-19-1089-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 19, 1089–1094, 2001
https://doi.org/10.5194/angeo-19-1089-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 Sep 2001

30 Sep 2001

Magnetic field configuration and field-aligned acceleration of energetic ions during substorm onsets

A. Korth1 and Z. Y. Pu2 A. Korth and Z. Y. Pu
  • 1Max-Planck-Institut für Aeronomie, D-37191 Katlenburg-Lindau, Germany
  • 2Space Weather Laboratory, Center for Space Science and Application Research, Chinese Academy of Science, Beijing, China and Department of Geophysics, Peking University, Beijing, China

Abstract. In this paper, we present an interpretation of the observed field-aligned acceleration events measured by GEOS-2 near the night-side synchronous orbit at substorm onsets (Chen et al., 2000). We show that field-aligned acceleration of ions (with pitch angle asymmetry) is closely related to strong short-lived electric fields in the Ey direction. The acceleration is associated with either rapid dipolarization or further stretching of local magnetic field lines. Theoretical analysis suggests that a centrifugal mechanism is a likely candidate for the parallel energization. Equatorward or anti-equatorward energization occurs when the tail current sheet is thinner tailward or earthward of the spacecraft, respectively. The magnetic field topology leading to anti-equatorward energization corresponds to a situation where the near-Earth tail undergoes further compression and the inner edge of the plasma sheet extends inwards as close as the night-side geosynchronous altitudes.

Key words. Magnetospheric physics (magnetospheric configuration and dynamics; plasma sheet; storms and sub-storms)

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