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Oliversen et al. 2001
Oliversen, R.J., Scherb, F., Smyth, W.H., Freed, M.E., Woodward, R.C., Marconi, M.L., Retherford, K.D., Lupie, O.L. and Morgenthaler, J.P. (2001). Sunlit Io atmospheric [O I] 6300 Å emission and the plasma torus. Journal of Geophysical Research 106: doi: 10.1029/2000JA002507. issn: 0148-0227.

A large database of sunlit Io [O I> 6300 ¿ emission, acquired over the period 1990--1999, with extensive coverage of Io orbital phase angle ϕ and System III longitude &lgr;III, exhibits significant long-term and short-term variations in [O I> 6300 ¿ emission intensities. The long-term average intensity shows a clear dependence on &lgr;III, which establishes conclusively that the emission is produced by the interaction between Io's atmosphere and the plasma torus. Two prominent average intensity maxima, 70¿ to 90¿ wide, are centered at &lgr;III≈130¿ and &lgr;III≈295¿. A comparison of data from October 1998 with a three-dimensional plasma torus model, based upon electron impact excitation of atomic oxygen, suggests a basis for study of the torus interaction with Io's atmosphere. The observed short-term, erratic [O I> 6300 ¿ intensity variations fluctuate ~20--50% on a timescale of tens of minutes with less frequent fluctuations of a factor of ~2. The most likely candidate to produce these fluctuations is a time-variable energy flux of field-aligned nonthermal electrons identified recently in Galileo plasma science data. If true, the short-term [O I> intensity fluctuations may be related to variable field-aligned currents driven by inward and outward torus plasma transport and/or transient high-latitude, field-aligned potential drops. A correlation between the intensity and emission line width indicates molecular dissociation may contribute significantly to the [O I> 6300 ¿ emission. The nonthermal electron energy flux may produce O(1D) by electron impact dissociation of SO2 and SO, with the excess energy going into excitation of O and its kinetic energy. The [O I> 6300 ¿ emission database establishes Io as a valuable probe of the torus, responding to local conditions at Io's position. ¿ 2001 American Geophysical Union

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Abstract

Keywords
Magnetospheric Physics, Magnetosphere interactions with satellites and rings, Planetology, Fluid Planets, Interactions with particles and fields, Planetology, Fluid Planets, Tori and exospheres, Planetology, Solar System Objects, Jovian satellites
Journal
Journal of Geophysical Research
http://www.agu.org/journals/jb/
Publisher
American Geophysical Union
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