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T. Kostiuk (NASA GSFC), T. Livengood (Challenger Center/GSFC), K. Fast, T. Hewagama (U MD/GSFC), D. Buhl (NASA GSFC), F. Schmuelling (NRC at NASA GSFC), J. Goldstein (Challenger Center)
Thermal infrared auroral spectra from Jupiter's North polar region have been collected from 1979 to 1999 in a continuing study of long-term variability in the northern thermal IR aurora, using C_2H_6 emission lines near 12\,\mum as a probe. Data from Voyager 1 and 2 IRIS measurements and ground based spectral measurements were analyzed using the same model atmosphere to provide a consistent relative comparison. A retrieved equivalent mole fraction was used to compare the observed integrated emission. Short term (days), medium term (months) and long term (years) variability in the ethane emission was observed. The variability of C_2H_6 emission intensities was compared to Jupiter's seasonal cycle and the solar activity cycle. A positive correlation appears to exist, with significantly greater emission and short term variability during solar maxima. Observations on 60\circ\,N latitude during increased solar activity in 1979, 1989, 1998 and most recently in 1999 show up to 5 times brighter integrated line emission of C_2H_6 near the north polar ``hot spot'' (150--210\circ latitude) than from the north quiescent region. Significantly lower enhancement was observed during periods of lower solar activity in 1982, 1983, 1993, and 1995. Planned observations in coordination with CIRS measurements during the Cassini flyby of Jupiter in December 2000 and possible sources and mechanisms for the enhancement and variability will be discussed.