TEMPERATURE AND ABUNDANCES IN THE JOVIAN AURORAL STRATOSPHERE .2. ETHYLENE AS A PROBE OF THE MICROBAR REGION

Individual emission lines of ethylene (C2H4) near 10.5 mum were measur ed from the equatorial and north polar regions of Jupiter. Observation s were made at a spectral resolution of 0.00083 cm-1 using infrared he terodyne spectroscopy at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. The line shape information possible with this resolving power permitted the retrieval of quiescent ethylene abundances and the investigation of abundance and thermal structure variability in the p olar auroral region. A rough distribution of the north polar emission as a function of longitude was obtained with an instantaneous field of view (full width at half maximum) of approximately 1 arc sec on the p lanet. The greatest C2H4 emission was observed near the nominal north polar methane hot spot (60-degrees-N, 180-degrees longitude, System II I, 1965). It was found to be confined to <10-degrees longitude on the planet. Using a Voyager-derived thermal profile, retrieved ethylene mo le fractions for equatorial and north polar quiescent (non-hot spot) r egions were consistent with results from existing photochemical models . At the hot spot an 18-fold increase in abundance was required near t he 10-mubar level to reproduce the data. Alternatively varying the str atospheric thermal profile, a 67-137 K increase in temperature was req uired at the approximately 10-mubar level to satisfy the observed emis sion, if the C2H4 mole fraction is fixed to the quiescent value. These results provide the first direct probe of the upper stratosphere of J upiter and give upper limits to the temperature increase near the sour ce of the north polar thermal infrared aurora. Combined with results f rom similar measurements of auroral ethane emission (Livengood et al., this issue) probing the 1-mbar region, altitude information on the th ermal structure can be obtained for the first time. The ethylene line emission region extends to the few microbar pressure level and may ove rlap the region where the H-2 ultraviolet aurora is formed; thus it ca n be used as a probe of the coupling between the ultraviolet and therm al infrared phenomena.