%0 Journal Article
%T Magnetic field configuration and field-aligned acceleration of energetic ions during substorm onsets
%A A. Korth
%A Z. Y. Pu
%J Annales Geophysicae (ANGEO)
%D 2003
%I Copernicus Publications
%X 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)
%U http://www.ann-geophys.net/19/1089/2001/angeo-19-1089-2001.pdf