Alfvénic Electron Acceleration in Aurora Occurs in Global Alfvén Resonosphere Region |
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| Authors: | Pekka Janhunen Annika Olsson Christopher T Russell Harri Laakso |
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| Institution: | (1) Department of Physical Sciences, University of Helsinki, P.O. Box 64, FIN 00014, Finland;(2) Uppsala Municipality, Office for Children, Youth and Job Market, SE, 75375 Uppsala, Sweden;(3) Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, 90024 1567, U.S.A;(4) ESA/ESTEC, Code SCI-SH, Noordwijk, 2200, AG, The Netherlands;(5) Finnish Meteorological Institute, Space Research, P.O. Box 503, FIN 00101 Helsinki, Finland;(6) Formerly at Swedish Institute of Space Physics, S-75121 Uppsala, Sweden |
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| Abstract: | Auroral emission caused by electron precipitation (Hardy et al., 1987, J. Geophys. Res. 92, 12275–12294) is powered by magnetospheric driving processes. It is not yet fully understood how the energy transfer mechanisms
are responsible for the electron precipitation. It has been proposed (Hasegawa, 1976, J. Geophys. Res. 81, 5083–5090) that Alfvén waves coming from the magnetosphere play some role in powering the aurora (Wygant et al., 2000, J. Geophys. Res. 105, 18675–18692, Keiling et al., 2003, Science
299, 383–386). Alfvén-wave-induced electron acceleration is shown to be confined in a rather narrow radial distance range of
4–5 R
E
(Earth radii) and its importance, relative to other electron acceleration mechanisms, depends strongly on the magnetic disturbance
level so that it represents 10% of all electron precipitation power during quiet conditions and increased to 40% during disturbed
conditions. Our observations suggest that an electron Landau resonance mechanism operating in the “Alfvén resonosphere” is
responsible for the energy transfer. |
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| Keywords: | auroral acceleration Alfvén waves Landau resonance |
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