HR: 1340h
AN: SM13B-0337    [Abstracts]
TI: Modeling the Temporal and Azimuthal Variability of the Io Plasma Torus Observed by Cassini UVIS
AU: * Steffl, A J
EM: steffl@boulder.swri.edu
AF: Southwest Research Institute, Department of Space Studies, 1050 Walnut St., Suite 400, Boulder, CO 80027 United States
AU: Delamere, P A
EM: peter.delamere@lasp.colorado.edu
AF: Laboratory for Atmospheric and Space Physics, University of Colorado Campus Box 392, Boulder, CO 80309-0392 United States
AU: Bagenal, F
EM: fran.bagenal@lasp.colorado.edu
AF: Laboratory for Atmospheric and Space Physics, University of Colorado Campus Box 392, Boulder, CO 80309-0392 United States
AB: Observations by the Cassini Ultraviolet Imaging Spectrograph (UVIS) showed remarkable temporal and azimuthal variability in the composition of the Io plasma torus. Among the observed variations are a factor of ~2 decrease in the amount of S II (and corresponding increase in the amount of S IV) present in the torus over a 45-day period and a nearly sinusoidal azimuthal variation in composition with a period some 1.5% longer than the System III rotation period of Jupiter. Unexpectedly, the amplitude of this azimuthal variation in composition is modulated by its phase relative to System III longitude. Here, we present results from our efforts to model the observed compositional variability of the Io torus using a neutral cloud theory model with additional heating supplied to the torus plasma by a small fraction (0.2%) of hot (~50 eV) electrons. The long-term variation in composition is found to be caused by a factor of ~3 increase in the amount of neutral material supplied to the torus, perhaps resulting from increased volcanic activity on Io. Superimposed on this temporal variation, the observed azimuthal variability and its modulation with System III longitude can be reproduced by introducing two azimuthally-varying sources of hot electrons: a primary source that slips 12.2°/day relative to System III longitude and a secondary source that remains fixed in System III longitude.
DE: 2732 Magnetosphere interactions with satellites and rings
DE: 5719 Interactions with particles and fields
DE: 5737 Magnetospheres (2756)
DE: 5780 Tori and exospheres
DE: 6219 Io
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005