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W. R. Pryor, A. I. F. Stewart, K. E. Simmons (LASP/University of Colorado), J. T. Clarke (University of Michigan), J. M. Ajello (JPL/Caltech), W. K. Tobiska (FDC/JPL), G. R. Gladstone (Southwest Research Institute)
Sudden increases in the brightness of Jupiter's H2 band auroral emissions (``flares") in the polar cap region on the day side have recently been reported in Hubble Space Telescope (HST) images from the Space Telescope Imaging Spectrograph (STIS). Galileo Ultraviolet Spectrometer (UVS) data also show sudden auroral brightenings in (rare) high time resolution observations at fixed wavelengths (1240 and 1611 Angstroms) from orbit C3 on November 5, 1996. These data have a 7.57 ms time resolution. Useful count levels at 1240 Angstroms were obtained in roughly 4 s. The C3 data show the 1240 Angstrom auroral brightness increasing by a factor of 4 on two occasions during a 540 s observation. The brightenings persist for about 100 s in both cases. The C3 UVS data include both the northern polar cap and the main auroral oval and do not separate the two sources. Similar high time resolution observations on orbit G8 near the southern dawn terminator did not show these brightenings.
We also studied HST STIS time-tagged FUV spectra of the Jupiter flare events. These data spatially separate the main auroral oval from the polar cap and the limb of Jupiter. In 2100 s of data from July 4, 1997 southern polar cap flares are seen on 6 occasions that each persist for about 100 s, roughly the same duration as was seen in the UVS data. The spectra cover 1190-1730 Angstroms with the G140L grating and contain short-wavelength CH4 absorption that changes the H2 band "color ratio" from values seen in the laboratory. We will derive values for the H2 color band ratios in the flares and the main auroral oval and estimates for the precipitating particle energy.
We acknowledge NASA support from the Galileo project, the Jupiter System Data Analysis Program, the Planetary Atmospheres Program, and the Hubble Space Telescope Science Institute.