Impact of Wetlands on Titan's Mid-Latitude Cloudiness
Tuesday, 16 December 2014
Neish and Lorenz [Icarus 228 (2014), 27-34] suggested that Titan's lowest elevations are extensive wetlands based on crater distributions. With a Titan general circulation model (GCM), we examine whether low-lying wetlands at mid-latitudes provide sufficient surface-level moisture to trigger convective cloud formation there, as well as investigate the dynamical processes responsible for different cloud morphologies. GCMs of Titan have shown that the atmospheric circulation transports methane away from low latitudes and into the polar regions on average. Several of these models simulate moist and cloudy conditions over the summer pole, in agreement with observations of convective clouds over the south pole during its summer. However, observations of cloudiness over Titan's southern mid-latitudes that occurred around solstice and persisted until after autumnal equinox are perplexing. GCMs tend to only simulate mid-latitude clouds around equinox, and only when imposing very wet surface conditions. In GCMs where surface moisture is allowed to vary self-consistently, the mid-latitudes are dry and cloud formation is inhibited. However, these models ignore topography. The GCM in this study is three-dimensional and fully simulates Titan's methane cycle, including variable surface moisture, as well as Titan's temperatures and atmospheric superrotation. Comparison of model results to recent obsrvations of the latitudinal humidity distribution of the troposphere will help discriminate between surface distributions. These simulations can therefore begin to constrain the distribution of surface methane, beyond Titan's distinctive lakes and seas, available to the atmosphere.