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P. A. Delamere, W. H. Smyth (AER, Inc.), M. L. Marconi (FPRI)
Understanding the sharply peaked radial structure of the Io plasma torus is a longstanding problem of the Io-Jupiter system. The torus structure is highlighted by the so called S+ ribbon which is the most-observed (6716Å, 6731Å) ground-based radial feature in the torus. The radial position (at east and west elongations) of the S+ emission peak as a function of System III longitude was successfully modeled by {\em Smyth and Marconi} ({\em JGR}, 103, 9091, 1998) using a transport model with a highly localized plasma source at Io's position, no plasma sinks, and an east-west electric field. The location of the ribbon inward of Io's orbit was determined by the interplay of the point source, the east-west electric field, and an outward increasing transport rate. This transport model has been improved to include spatially extended plasma sources and also plasma loss processes to understand the more detailed radial structure of S+ and S++ in the plasma torus. Ion production rates for the plasma source are determined from the AER neutral cloud model with an exobase neutral source based on a modified-sputtering flux distribution. The primary ion loss rate in the transport model is electron impact ionization, and this S+ sink is used as a source term for a complimentary S++ transport calculation. Near Io we are also considering SO charge exchange with S+ as a sink for S+. Our strategy is to steadily improve the description of plasma sources and losses before embarking on the larger problem of a more exact specification of the diffusion coefficient, DLL(L). Progress toward understanding the formation of peaks in S+ with western elongation L-shell values of Lw = 5.3 and 5.6, and the peak in S++ at Lw = 5.7 will be presented.
The author(s) of this abstract have provided an email address for comments about the abstract: pad@aer.com