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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 8
Ann. Geophys., 16, 940-947, 1998
https://doi.org/10.1007/s00585-998-0940-x
© European Geosciences Union 1998
Ann. Geophys., 16, 940-947, 1998
https://doi.org/10.1007/s00585-998-0940-x
© European Geosciences Union 1998

  31 Aug 1998

31 Aug 1998

A statistical study of field-aligned electron beams associated with ion conics events

W. Miyake1, T. Mukai2, and N. Kaya3 W. Miyake et al.
  • 1Communications Research Laboratory, 4-2-1 Koganei, Tokyo 184, Japan Fax: +81 423 27 6657; e-mail: miyake@crl go.jp
  • 2The Institute of Space and Astronautical Science, Yoshinodai, Sagamihara 229 , Japan
  • 3Kobe University, 1-1, Rokkodai, Nada, Kobe 657, Japan

Abstract. A statistical study of field-aligned electron beams associated with upflowing ion conics is presented from Exos-D (Akebono) observations below 10 000 km. The electron beams are narrowly collimated along the field line and generally have energies of several tens of eV. They are divided in the analysis into three types: upflowing, downflowing, and counterstreaming. All the types of electron beams are almost equivalent in their energy and pitch angle characteristics and their association rate with upflowing ion events. About 50% of ion conics are found to be coincident with field-aligned electron beams. There is also a correlation in energy between the field-aligned electrons and ion conics. These show that the association is not a mere coincidence but rather that the field-aligned acceleration of electrons is related to the perpendicular energization of ions. The association rate of upflowing electrons is high on the nightside, while that of downflowing electrons is high on the dayside. The association rate of downflowing electrons is high at low altitudes, and the rates of the three types of electron beams become equivalent at high altitudes. Data indicate that the height of the electron acceleration region is lower on the nightside. It is suggested that the average height of the electron acceleration region is around the satellite apogee (–10000 km), and the average thickness of the region is about thousands km.

Key words. Ionosphere-magnetosphere interactions · Particle acceleration · Auroral phenomena

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