Simulation of auroral electron acceleration by inertial Alfvén waves

摘要

A two-dimensional particle code, similar to that used in the work of Swift (2007), is used to model the acceleration of auroral electrons by inertial Alfvén waves. The simulation domain is 20,000 km parallel to the magnetic field and some tens of kilometers across. Effects of a variable magnetic field and magnetic mirror force are included. The Alfvén wave is launched by a moving bipolar potential waveform with peak amplitudes of ±200 V imposed at the top of the simulation domain. Electrons are accelerated to 3 keV energy. Two types of acceleration processes are seen: one is impulsive acceleration from shock structures, and the other is from weaker parallel electric fields extending over several thousand kilometers. The shock structures are very small, and electrons accelerated by these structures can produce auroral forms with thicknesses considerably smaller than an electron inertial length. Electrons also tend to undergo multiple acceleration events. Electrons are more strongly accelerated upward. Half of these are destined to precipitate in the opposite hemisphere, and half are destined to become trapped. This implies that much of the aurora seen in the Northern Hemisphere is due to electrons accelerated in the Southern Hemisphere. The simulations also suggest that auroral acceleration processes provide a likely source for radiation belt particles.