Mountain torque and its influence on the atmospheric angular momentum on Titan

The impact of Titan’s large-scale topography and surface roughness on the atmospheric angular momentum budget is investigated by the Cologne Titan general circulation model that is run with and without topography constrained by Cassini. On seasonal timescales the angular momentum exchange is dominated by the friction torque, which oscillates semi-annually. Topography gives rise to a large diurnal and small seasonal mountain torque. The diurnal mountain torque is caused by surface pressure variations associated with Saturn’s tide, but has no net effect on the atmospheric angular momentum. The seasonal mountain torque is mainly contributed by low-latitude mountains that are hit by easterly surface winds. The seasonal mountain torque causes a net transfer of angular momentum from the surface to the atmosphere, which is counterbalanced by an opposite angular momentum transfer by the friction torque. The atmospheric angular momentum is larger if topography is included.