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F. Bagenal, P. A. Delamere (LASP University of Colorado)
Telescopic observations and in situ measurements of the Io plasma torus show the density, temperature and composition to vary over time, sometimes up to a factor of two. In Delamere and Bagenal (2003, JGR in press) we presented a homogeneous torus model parameterized by five variables (transport timescale, neutral source strength, ratio of oxygen to sulfur atoms in the source, fraction of superthermal electrons, temperature of these hot electrons). The model incorporates the most recent data for ionization, recombination, charge exchange and radiative energy losses for the major torus species (S, S+, S++, S+++, O, O+, O++). We solve equations of conservation of mass and energy to find equilibrium conditions for a set of input parameters. We compare model plasma conditions with those observed by Voyager 1, Voyager 2 and Cassini. Furthermore, we have investigated the variations in source conditions required to match changes in the observed plasma conditions observed over 6 months of Cassini measurements. The next step in modeling the chemistry of the torus is to extend the model to address spatial inhomogeneity. We first investigate the effect of averaging plasma conditions with latitude. We then use latitudinally-averaged conditions to model radial structure. Using longitudinally-averaged distributions of neutral atoms from models of neutral clouds we explore the effects of changing the neutral cloud distribution and the radial transport rate on torus chemistry.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.