Transient IR Phenomena Observed by Cassini/CIRS in Jupiter's Auroral Regions

Jupiter's polar aurora can be observed in several wavelength regions as bright ovals off-center from the geographical poles of the planet and co-rotating with the magnetic field (System III). Enhanced regions of auroral activity are observed at selected longitudes. The north auroral hot spot in particular is very strong and can be found between 165o}-200{o longitudes, while the less conspicuous south auroral hot spot generally is found between 330o}-90{o longitudes. Recent UV and X-ray observations of the northern aurora have shown that it varies in intensity within minutes. IR spectral line intensity changes have also been reported, but these observations have been sporadic and no periodicity has been identified. Romani et al. (see related presentation) recently observed a large decrease in C2H4 emission from the north auroral hot spot during a 48-hr period. We report observation of changes in infrared line intensities during the Cassini encounter with Jupiter. The thermal-IR spectroscopic observations were performed by the Composite Infrared Spectrometer (CIRS) at 0.3 cm-1 spectral resolution in the range 580 cm-1 - 1100 cm-1. The spectra were averaged on two-week bins during Oct. 2000 - Mar. 2001 to increase S/N and were restricted in longitude and latitude to cover both the auroral hot spot and non-hot spot regions. We observed temporal variations in the strength of the emission lines from important hydrocarbon species (C2H2, C2H6, C2H4, C6H6) on the hot spots peaking in late January 2001. Non-hot spot longitudes of the aurora saw little change during this same time interval. We compare the CIRS results with our ground-based observations from the same period. The line emission increments can be interpreted as due to temperature enhancements in the stratosphere of the planet where these spectral lines are formed. We characterize these variations and present preliminary models that address the nature of these changes and may help constrain auroral models.