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F. Scherb (U Wisc), R.J. Oliversen (NASA/GSFC), M.E. Freed (Raytheon), J. Corliss, R.C. Woodward (U Wisc), W.H. Smyth (AER), J.P. Morgenthaler (U Wisc), O.L. Lupie (CSC), K.D. Retherford (JHU)
Since 1990, almost 1500 spectra of [O\,I]\,6300Å\ emission from Io with good signal-to-noise have been obtained for all System~III longitudes and all available Io orbital positions. When adjusted for long-term intensity variations, the data show a correlation with System~III longitude, peaking where Io crosses the plasma torus centrifugal equator. We have also found a correlation between the flux and the Doppler width of the emission line.
Included in this dataset are spectra of Io acquired during the October 14, 1997 HST/STIS FUV observations of Io's FUV neutral oxygen and sulfur emissions [Roesler et al.\ 1999]. The [O\,I]\,6300Å\ emission increased in intensity simultaneously with the FUV O and S multiplets observed by STIS, but by a larger factor. The groundbased observations further show that, after the end of the HST observations, there was a sharp drop in intensity as Io crossed the torus centrifugal equator.