Auroral Precipitation and Quasi-Trapped electrons

Details Auroral Precipitation and Quasi-Trapped electrons Auroral Precipitation and Quasi-Trapped electrons

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm72d..03s&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SM72D-03

Physics

2407 Auroral Ionosphere (2704), 2455 Particle Precipitation, 2716 Energetic Particles, Precipitating, 2720 Energetic Particles, Trapped, 7867 Wave/Particle Interactions

Scientific paper

The visual auroral takes on a bewildering variety of forms ranging from the discrete, highly structured to the diffuse glow. There is a similarly large variety of electron distribution functions associated with aurora precipitation ranging from the field-aligned monoenergetic to the broad spectrum, nearly isotropic. An enormous conceptual simplification can be obtained by assuming that auroral electrons are accelerated as spatially narrow, field-aligned beams, which are immediately scattered. The scattering leaves the bulk of electrons in quasi-trapped orbits. The trapped electrons are subject to a rapid pitch-angle scattering process that maintains pitch-angle isotropy and continued auroral luminosity after the acceleration event has passed. Gradient and curvature drift of electrons acts to spatially diffuse the forms. A radiation transport code is used to test this hypothesis. Auroral imagery from the Polar Satellite is used to define an initial radiation distribution, assuming pitch angle isotropy. The radiation transport code, is used to compute subsequent precipitation patterns, due to rapid pitch angle diffusion between a prescribed set of altitudes. These precipitation patterns can be compared with subsequent Polar images. It is found for a particular isolated substorm event that the luminosity decay time of about a half hour can be accounted for with the radiation transport code, assuming rapid pitch angle scattering occurs between the altitudes of 6,000 and 30,000 km. Eventually, the trapped electron population will fall to the point that it will no longer sustain the instability responsible for rapid pitch-angle diffusion. This will leave a residual population more permanently trapped. The role of the aurora in replenishing the radiation belts will be discussed.

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