Statistics of Titan's South Polar Tropospheric Clouds

We present the first long-term study of the behavior of the sporadically observed tropospheric clouds recently discovered near Titan’s south pole. We find that one or more small individual cloud systems is present in the 70–80 south region during every night of observation. These clouds account for 0.5%–1% of Titan’s 2.0 mm flux, consistent with a global cloud cover fraction of 0.2%–0.6%. Clouds observed over multiple-night observing periods remained,nearly fixed in brightness and position with respect to Titan’s surface. The continual presence of south polar clouds is consistent with the hypothesis that surface heating during the long period of continuous polar sunlight at the time of Titan’s southern summer,solstice drives seasonal convection and cloud formation at the pole. Subject headings: infrared: solar system — planets and satellites: individual (Titan)