The data presented here were acquired with a broadband imager tuned to the [S II] 6731Å line, on the west auxiliary telescope of the McMath-Pierce Solar Telescope facility at Kitt Peak; details of the instrument were given earlier [Woodward 1999]. We have acquired 476 images of the Io plasma torus in [S II] 6731Å during 1997 and 1999 (summarized in tables I and II). This is a large amount of data, and is requiring significant manpower for acquisition and reduction, but the very size of the dataset makes it valuable. The torus is known to vary significantly and unpredictably (so far) over time. The long timebase allows us a) to observe these changes and look for patterns and explanations, and b) to remove these changes in order to produce an accurate picture of the "average" torus.
Other observations of the torus using larger telescopes give greater detail, but are necessarily limited to short timespans; thus, uncertainty always exists as to whether a particular observation is "typical" of the torus. This synoptic program can place such short observations in the context of the overall state of the torus: whether the torus was particularly bright or dim, hot or cold, extended or contracted. In particular, several HST Space Telescope Imaging Spectrograph (STIS) observations of UV emission lines near Io in October of 1997 [Roesler et al. 1999] and 1999 [Bagenal et al. 1999] are directly supported by these data, as is another long-term spectroscopic study of Io in [O I] 6300Å [Oliversen et al. 2000].
Reduction of the data has taken significantly longer than expected as a result of limited resources and difficulties in calibration, and in particular with the precise removal of scattered light from Jupiter. Reduction of the 1997 data has just been completed, using a power law model of Jupiter's scattered light; the data are shown in figure 1. This will be adequate for studies of morphological and large intensity changes; however, an improved technique for removing scattered light is being developed. The 1999 data (figure 2) is largely unprocessed. Some preliminary results are shown in figures 3 and 4.