Brightening of Acetylene and Ethane in the South Pole of Saturn from Ground-Based and CIRS Observations

Recent infrared imaging has shown that the southern polar stratosphere of Saturn is 15 K warmer than the equator (Flasar et al. 2005, Orton and Yanamandra-Fisher 2005). Cassini CIRS measurements show a similar effect (and also a cold north pole). The anomalously warm south pole is not purely a seasonal effect, which would predict a temperature only 5 K warmer than the equator (Bézard and Gautier 1985). We made meridional maps of C2H2 and C2H6 on Saturn during observations at Kitt Peak in April 2005. The latitudes accessible to our ground-based observations extended from the inner edge of the rings at about 15 degrees North to the south pole, with the fully insolated longitudes south of -67 degrees latitude continually in view. Our observed radiances of both species increased toward the pole, with C2H6 increasing more than C2H2. During 2004 CIRS also saw C2H6 increasing in radiance more strongly than C2H2 near the south pole. Since the contribution function for C2H6 at higher altitudes (0.01-0.2 mbar) is relatively greater than that of C2H2, the difference in brightening suggests that heat is deposited from above. This may be consistent with heating by subsiding warm air and particulates. Simulations should account for a non-uniform altitude distribution of stratospheric coolants at mid-infrared wavelengths.