DPS Pasadena Meeting 2000, 23-27 October 2000
Session 35. Galilean Satellites - Atmospheres and Tori Posters
Displayed, 1:00pm, Monday - 1:00pm, Friday, Highlighted Tuesday and Thursday, 3:30-6:30pm, C101-C105, C211

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[35.10] Three-dimensional Structure of the Io Plasma Torus from Ground-based Images

J. W. Weiss, N. M. Schneider (CU/LASP)

Ground-based imaging has provided key constraints on the structure of the Io plasma torus (e.g., Schneider & Trauger, ApJ. 450, p. 450, 1995), but most analyses have not tapped the full potential of the data. In most cases, images are analyzed for peak intensities, relative intensity variations, or overall morphology. One study of longitudinal variations showed the value of detailed numerical modeling (Schneider, N. M. et al. , "On the nature of the l III brightness asymmetry in the Io torus", JGR, 102, 19823-19833, 1997.), but the fitting algorithm was not sufficiently robust or efficient to extend to other data.

We report on a comprehensive effort to derive the three-dimensional structure of the torus using an automated fitting algorithm. The image database includes the {\rm S+} images from Schneider & Trauger 1995, but additional images from other nights and other wavelengths will be added. The core of the fitting algorithm is the Colorado Io Torus Emissions Package (CITEP), a routine which simulates torus intensities based on plasma property inputs (Taylor, M.H et al. , "A comparison of the Voyager 1 ultraviolet spectrometer and plasma science measurements of the Io Plasma Torus", JGR . 100, 19541-50, 1995.). Our fitting algorithm uses IDL's down-hill simplex method to minimize a modified reduced-\chi2 goodness of fit measure, finding densities and ion temperatures over the 4.5-6.5 {\rm Rj} range. Fitting a single image provides these quantities at the torus 'ansas'; the three-dimensional structure comes from fitting a series of images spanning a complete rotation.

Our results will focus on the longitudinal variations in density and ion temperature, and changes in structure from night to night. We will also extend modeling to {\rm S++} in order to place better constraints on overall plasma properties.

This work has been supported by NASA's Planetary Astronomy Program.

If you would like more information about this abstract, please follow the link to http://ganesh.colorado.edu/CITEP. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: weiss@ganesh.colorado.edu

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