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Michael Kueppers, N. M. Schneider (LASP, University of Colorado)
While ground-based imaging observations of the Io plasma torus have produced large data sets with excellent temporal coverage, the inversion of intensities to key plasma parameters is surprisingly difficult. The intensities of optical emissions from the Io plasma torus mainly depend on the densities of electrons and ions and ion temperatures. The determination of these parameters from ground-based images is complicated by line-of-sight integration.
We report the results of optimized inversion of a large set of torus images from Catalina and Las Campanas observatories (e.g., N. Schneider and J. Trauger, ApJ 450, 450, 1995). The inversion technique combines a sophisticated ``forward model" which predicts torus emissions based on plasma conditions (CITEP, M. Taylor et al., JGR 100, 19541, 1995) with search algorithms which iteratively seek the best-fit plasma conditions.
Recently developed forward models successfully predict emission intensity and structure of ground-based images for given Io torus conditions (N. Thomas, JGR 100, 7925, 1995; M. Taylor, Dissertation, 1996; M. Küppers and N. Schneider, GRL 25, 2757, 1998). Taylor (1996) was the first first to reveal some torus structure from an inversion of a forward model. We improve on his method by using a genetic algorithm in combination with CITEP to determine the Io torus parameters that best fit ground-based images.
>From the analysis of several years of ground-based data we are investigating the threedimensional structure of the Io plasma torus and its variation with time. The results will be used to constrain models of sources and loss processes for mass and energy in the torus.
We thank D. L. Carroll for the permission to use his genetic algorithm. This work has been supported by NASA's Planetary Atmospheres and Planetary Astronomy programs.