Planetary Waves on Titan

In April 2008 we observed tropospheric clouds on Titan located at near equatorial latitudes (30S-10S). These clouds were first detected on 13 April 2008 by our Titan IRTF spectral monitoring program (Schaller et al. 2008) and were subsequently observed in Gemini adaptive optics images until May 2008. In subsequent observations, cloud activity across the southern hemisphere of the moon resumed its previous low levels (Schaller et al. 2006b). During part of this ~4-week period of cloud activity near the equator and southern midlatidues, clouds were also observed near the south pole. These observations show that a large atmospheric perturbation at one latitude can trigger planetary waves capable of inducing cloud activity at latitudes otherwise stable against convection during the present season. South polar tropospheric cloud activity has been essentially non existent as seen from ground-based observations since 2005. The south pole is not predicted by general circulation models to be able to support convective cloud formation at the present season (e.g. Mitchell et al. 2006). Understanding Titan's methane-based meteorological cycle, including the causes and frequencies of these large cloud events and their subsequent evolution across the moon, holds the key for interpreting the fluvial surface features seen on Titan's surface by the Cassini Spacecraft.