TEMPERATURE AND ABUNDANCES IN THE JOVIAN AURORAL STRATOSPHERE .1. ETHANE AS A PROBE OF THE MILLIBAR REGION

We report infrared heterodyne spectroscopy (lambda/DELTAlambda is simi lar to 10(6)) of C2H6 emission at 11.9 mum from the northern Jovian au roral region, in observations conducted over December 2-7, 1989. Accur ately measured line shapes provide information on C2H6 abundance as we ll as temperature and permit retrieval of the source pressure region. Enhanced emission was observed in the longitude range approximately 15 0-degrees-180-degrees at approximately 60-degrees north latitude, appr oximately corresponding to the CH4 7.8-mum hot spot and the region of brightest UV aurora. Significant brightness variations were observed i n the hot spot emissions on a time scale of approximately 20 hours. An alysis of the brightest hot spot spectra indicates C2H6 mole fractions of approximately (6.3-6.8) X 10(-6) at temperatures of approximately 182-184 K at 1 mbar, compared to mole fractions of (3.8 +/- 1.4) x 10( -6) averaged over spectra outside the hot spot at a temperature of app roximately 172 K at the same pressure. Fixing the mole fraction to the lower limit retrieved in the quiescent (non-hot spot) region allows t he temperature at 1 mbar to be as high as approximately 200 K within t he hot spot. These results provide upper limits to the temperature inc rease near the source of the C2H6 thermal infrared emission. Combined with results from similar measurements of ethylene emission probing th e approximately 10-mubar region (Kostiuk et al., this issue), altitude information on the thermal structure of the Jovian auroral stratosphe re can be obtained for the first time.