Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm34a..03g&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SM34A-03
Physics
2716 Energetic Particles, Precipitating, 2720 Energetic Particles, Trapped, 2730 Magnetosphere: Inner, 2772 Plasma Waves And Instabilities
Scientific paper
Since the discovery of earth's radiation belts researchers have sought to explain and predict the changing relativistic electron flux levels in the outer belt. This goal has proved a perplexing challenge because, surprisingly, flux levels do not always rise as energy input from the solar wind increases during active periods such as geomagnetic storms [Reeves et al., 2003;O'Brien et al., 2001]. The erratic response of the radiation belt electrons to geomagnetic activity suggests that flux levels are set by a teetering struggle between acceleration and loss. Thus, to predict flux variations, both processes must be understood. Some acceleration mechanisms have been proposed and tested resulting in incremental progress, but still little is known about how relativistic electrons are removed from the magnetosphere. We investigate how relativistic electrons are lost from the outer radiation belt using a superposed epoch analysis of electron flux decrease events identified in multi-satellite data [Onsager et al., 2002; Green et al., 2004]. More specifically, we test three mechanisms proposed to explain the flux reductions: adiabatic motion in response to a changing magnetic field topology, drift out the magnetopause boundary, and scattering into the atmosphere. The superposed study shows that the magnetic field becomes temporarily stretched at dusk suggesting that adiabatic electron motion might contribute to the initial flux reduction; however, the electron flux does not recover when the magnetic field recovers, indicating that true loss from the magnetosphere occurs. Magnetopause encounters should similarly affect both high energy protons and electrons; however, no concurrent reduction of proton flux is observed implying that this mechanism is not active. Low altitude observations show increased electron flux in the loss cone suggesting that scattering to the atmosphere is the cause the flux depletions. We investigate possible causes of the increased scattering including current sheet scattering and wave particle interactions.
Fraser Brian J.
Green James C.
O'Brien Thomas
Onsager T. G.
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