Causes of Particle Precipitation along Auroral Field Lines
Quantitative theoretical results have been obtained for three basic causes of auroral particle precipitation. Pitch angle diffusion of trapped plasma sheet particles driven by resonant wave-particle interactions leads to isotropic pitch angle distributions at lower energies, with a transition to increasingly anisotropic distributions at higher energies. Diffuse auroral electron precipitation (including that associated with pulsating aurora) can be explained by such interactions. Energization of ions in the current sheet via single particle motion leads to isotropic auroral precipitation at all energies from ∿1 keV to nearly 1 MeV. Much of observed auroral ion precipitation is consistent with that expected from this current sheet energization. The electrons responsible for discrete auroral are accelerated by a field aligned potential difference V11 ∿ > 1 keV. The overall electrodynamics of this energization, and the associated currents and electric potential variations along auroral field lines an4 within the ionosphere, can be explained by single-particle motion along the field lines and current continuity in the ionosphere. The structure of the potential distribution at high-altitudes responsible for the discrete aurora has been identified but not explained.
KeywordsCurrent Sheet Pitch Angle Plasma Sheet Pitch Angle Diffusion Convection Electric Field
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