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Ann. Geophys., 24, 2667-2684, 2006
www.ann-geophys.net/24/2667/2006/
© European Geosciences Union 2006
Longitudinal drift of substorm electrons as the reason of impulsive precipitation events and VLF emissions
A. A. Lubchich1, A. G. Yahnin1, E. E. Titova1, A. G. Demekhov2, V. Yu. Trakhtengerts2, J. Manninen3, and T. Turunen3
1Polar Geophysical Institute, Apatity, Russia
2Institute of Applied Physics, Nizhny Novgorod, Russia
3Geophysical Observatory, FIN-99600 Sodankylä, Finland
Abstract. Using the data from satellite CRRES and three
geostationary LANL spacecraft, the propagation of an electron cloud from
midnight to the evening sector is investigated. An electron cloud was
injected during a weak isolated substorm that developed on a quiet
geomagnetic background. It is found that within the local time sector from
03:00 until at least 08:00 MLT, the propagation of electrons at perpendicular
pitch-angles is well described by a simple model of drift in the dipole
magnetic field. The flux levels in the field-aligned electrons increase
simultaneously with the flux at perpendicular pitch angles, which is
attributed to the pitch angle diffusion by the whistler mode. This pitch-angle
diffusion leads to precipitation of electrons from a drifting cloud and an
increase in the ionospheric electron density, simultaneously observed above
Tromsø, Norway, by the EISCAT UHF radar in the morning sector
(04:40–05:25 MLT). The precipitation develops as quasi-periodic pulses with a period of
about 100 s. We discuss the models of pulsating precipitation due to the
whistler cyclotron instability and show that our observations can be
explained by such a model.
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