Energy dispersed ion signatures at auroral and subauroral latitudes
Schwab, Robert Douglas
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During magnetically disturbed periods, the spatially and temporally structured electron precipitation in the auroral zone creates a significant population of thermal secondary ions. Acceleration mechanisms exist that are capable of energizing the thermal population to suprathermal energies (1 eV to 1 keV). Suprathermal ions escape into the magnetosphere and undergo "bounce" motion along magnetic field lines. These ions are bound to the magnetic flux tubes, which undergo ExB convective drift within the magnetosphere. Magnetospheric convection transports flux tubes of bouncing suprathermal ions through the auroral zone and the subauroral polarization stream (SAPS) regions. Precipitating suprathermal ions enhance ionospheric plasma density structure and constitute a possible source for the enhanced echo occurrence observed by ground-based radars in the SAPS region. Satellite energy spectrometer data often show multiple bands of suprathermal particles with enhanced number and energy flux, and with an energy increase with increasing latitude. The present work examines the hypothesis that these signatures are the result of thermal secondary ions that have been accelerated out of the auroral ionosphere over the short time scales characterizing bursts of intense auroral electron precipitation. The analysis of three events of energy-dispersed ion signatures was facilitated by three-dimensional ion tracing software developed for this thesis. The short-lived acceleration hypothesis can account for the energy-dispersed ion signatures if there exist inter-hemispheric field aligned potentials of the order of 100 V. If the source of the ions is within the auroral zone, the suprathermal ions observed in the SAPS region are most likely to be O+ ions. The long bounce period of O+ (compared to H+) allows convection to transport O+ auroral ions equatorward through a convection reversal, into the SAPS region during a single half-bounce.
DegreeMaster of Science (M.Sc.)
DepartmentPhysics and Engineering Physics
ProgramPhysics and Engineering Physics
SupervisorSofko, George J.; McWilliams, Kathryn A.
CommitteeXiao, Chijin; Smolyakov, Andrei I.; Koustov, Alexandre V. (Sasha); Johanson, Robert E.; Hussey, Glenn C.
Copyright DateApril 2007
ion tracing software