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Ann. Geophys., 22, 2213-2227, 2004
www.ann-geophys.net/22/2213/2004/
© European Geosciences Union 2004
Different Alfvén wave acceleration processes of electrons in substorms at ~4-5 RE and 2-3 RE radial distance
P. Janhunen, A. Olsson, J. Hanasz, C. T. Russell, H. Laakso, and J. C. Samson
Finnish Meterological Institute, Department of Geophysics, P.O. Box 503, 00101 Helsinki, Finland
Abstract. Recent statistical studies show the existence of an island of cavities
and enhanced electric field structures at 4-5RE radial
distance in the evening and midnight magnetic local time (MLT) sectors
in the auroral region during disturbed conditions, as well as ion beam
occurrence frequency changes at the same altitude. We study the
possibility that the mechanism involved is electron Landau resonance with incoming Alfvén
waves and study the feasibility of the idea further with Polar
electric field, magnetic field, spacecraft potential and electron data
in an event where Polar maps to a substorm over the CANOPUS
magnetometer array. Recently, a new type of auroral kilometric
radiation (AKR) emission originating from ~2-3RE radial
distance, the so-called dot-AKR emission, has been reported to occur
during substorm onsets and
suggested to also be an effect of Alfvénic wave acceleration in a
pre-existing auroral cavity. We improve the analysis of the dot-AKR, giving it
a unified theoretical handling with the high-altitude
Landau resonance phenomena. The purpose of the paper is to study the two types of Alfvénic
electron acceleration, acknowledging that they have different physical mechanisms, altitudes and
roles in substorm-related auroral processes.
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