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.
Keywords auroral acceleration - Alfvén waves - Landau resonance