Cloud formation along mountain ridges on Titan

Abstract

Cassini radar passes have shown a number of mountain ranges on Titan. Radar data covering approximately one quarter of Titan's surface places mountains in primarily equatorial regions with the mean height of about 900 m. The flow of air over topographic features can both trigger and enhance cloud formation. Orographically induced clouds near terrestrial mountain ranges include shallow wave clouds produced from upslope flow as well as precipitating stratus and cumulus type clouds; mountains can provide the perturbations needed to trigger convective clouds. The Titan regional atmospheric modeling system (TRAMS) has been used to explore a number of convective cloud properties and is now used to report on clouds formed when a mountain peak is placed within the model domain. Using a range of heights and surface winds compatible with Cassini/Huygens data, constraints can be placed on the scenarios in which clouds can be expected to form. Given sufficiently humid conditions (at least 50% humidity), convection is triggered. For drier environments similar to the Huygens landing site, short-lived, optically thin clouds form from air rising upslope. Precipitation is also seen in the cases of the convective clouds, which could have implications for the eroded appearance of Titan's mountains.