36th DPS Meeting, 8-12 November 2004
Session 16 Jovian System
Poster I, Tuesday, November 9, 2004, 4:00-7:00pm, Exhibition Hall 1A

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[16.02] The Spatial Distribution of the Io Plasma Torus

F. Herbert (Lunar Lab, U. Arizona), N. M. Schneider (LASP), A. J. Dessler (Lunar Lab, U. Arizona)

Ground-based coronographic images of the Io plasma torus in S+~6371Å\ emission have been pseudo-tomographically deconvolved from their inherent line-of-sight integration, yielding estimates of their three-dimensional (3D) S+\ density distributions with spatial resolution of ~0.05R\mbox{\rm \scriptsize J}. By interpreting this derived time-dependent structure we can infer some of the characteristics of torus formation mechanisms.

For example, the dawn-to-dusk electric field in the torus region of Jupiter's magnetosphere causes the warm outer torus (including the ``ribbon'' feature) and the outer edge of the cold torus (which is the innermost region of the torus) to move closer to Jupiter by ~0.3R\mbox{\rm \scriptsize J}\ as the torus plasma rotates from the dawn region to dusk. Although this electric field is often approximated as spatially uniform, the initial analyses of these and other observations (Dessler and Sandel, {\em GRL 19}:2099, 1992; Schneider and Trauger, {\em ApJ 450}:450, 1995) implied a variation of the field strength with subsolar magnetic longitude. Now, preliminary results of our analyses of these observations imply differential motion between the inner and outer edges of the cold torus, indicating that the field strength varies spatially as well, appearing at times to diminish at the inner edge of the cold torus. Such behavior can result from a process known as magnetospheric ``shielding'', which has been noted in the magnetospheres of Earth and possibly Uranus, but this would be the first instance where it has been seen at Jupiter.

This and other anomalies of torus structure, such as the difference in magnetic latitudes of the warm and cold tori and the large gap between them, will be discussed at the meeting. This work was supported by NASA under grants NAG5-12944 and 9079 (Geospace Sciences Program) and NAG5-8952 (Planetary Atmospheres Program).

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.