Temperature and abundances in the Jovian auroral stratosphere: 1. Ethane as a probe of the millibar region

Abstract

We report infrared heterodyne spectroscopy (λ/Δλ ∼ 106) of C2H6 emission at 11.9 μm from the northern Jovian auroral region, in observations conducted over December 2–7, 1989. Accurately measured line shapes provide information on C2H6 abundance as well as temperature and permit retrieval of the source pressure region. Enhanced emission was observed in the longitude range ∼150°–180° at ∼60° north latitude, approximately corresponding to the CH4 7.8‐μm hot spot and the region of brightest UV aurora. Significant brightness variations were observed in the hot spot emissions on a time scale of ∼20 hours. Analysis of the brightest hot spot spectra indicates C2H6 mole fractions of ∼(6.3–6.8) × 10−6 at temperatures of ∼182–184 K at 1 mbar, compared to mole fractions of (3.8 ± 1.4) × 10−6 averaged over spectra outside the hot spot at a temperature of ∼172 K at the same pressure. Fixing the mole fraction to the lower limit retrieved in the quiescent (non‐hot spot) region allows the temperature at 1 mbar to be as high as ∼200 K within the hot spot. These results provide upper limits to the temperature increase near the source of the C2H6 thermal infrared emission. Combined with results from similar measurements of ethylene emission probing the ∼10‐μbar region (Kostiuk et al., this issue), altitude information on the thermal structure of the Jovian auroral stratosphere can be obtained for the first time.