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Ann. Geophys., 25, 785-799, 2007
www.ann-geophys.net/25/785/2007/
© European Geosciences Union 2007
Scattering of field-aligned beam ions upstream of Earth's bow shock
A. Kis1,*, M. Scholer1, B. Klecker1, H. Kucharek2, E. A. Lucek3, and H. Rème4
1Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
2Dept. of Physics and Institute for the Study of Earth, Oceans and Space, Univ. of New Hampshire, Durham, USA
3Imperial College, London, UK
4CESR, Toulouse, France
*now at: Geodetic and Geophysical Research Institute of HAS, Sopron, Hungary
Abstract. Field-aligned beams are known to originate from the
quasi-perpendicular side of the Earth's bow shock, while the diffuse
ion population consists of accelerated ions at the quasi-parallel
side of the bow shock. The two distinct ion populations show typical
characteristics in their velocity space distributions. By using
particle and magnetic field measurements from one Cluster spacecraft
we present a case study when the two ion populations are observed
simultaneously in the foreshock region during a high Mach number,
high solar wind velocity event. We present the spatial-temporal
evolution of the field-aligned beam ion distribution in front of the
Earth's bow shock, focusing on the processes in the deep foreshock
region, i.e. on the quasi-parallel side. Our analysis demonstrates
that the scattering of field-aligned beam (FAB) ions combined with
convection by the solar wind results in the presence of
lower-energy, toroidal gyrating ions at positions deeper in the
foreshock region which are magnetically connected to the
quasi-parallel bow shock. The gyrating ions are superposed onto a
higher energy diffuse ion population. It is suggested that the
toroidal gyrating ion population observed deep in the foreshock
region has its origins in the FAB and that its characteristics are
correlated with its distance from the FAB, but is independent on
distance to the bow shock along the magnetic field.
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