The influence of baroclinic eddies on moisture transport in Titan's atmosphere

Using simulations with the Titan Atmospheric Model (TAM; Lora et al. 2015 [Icarus 250, 517-528]) general circulation model, we investigate the role of non-axisymmetry on the interhemispheric transport of methane moisture in Titan's atmosphere. Lakes and seas of hydrocarbons on Titan, observed only in polar regions, preferentially occur in the northern hemisphere. This asymmetry has been suggested to be the result of Milankovitch cycles in Titan's climate, where currently weaker but longer northern summers induce a buildup of surface methane. GCMs of Titan have shown that the atmospheric circulation transports methane away from low latitudes and into the polar regions on average, and paleoclimate simulations with TAM showed that changes in Titan's effective orbital parameters affect the surface methane asymmetry, in agreement with the above hypothesis. Comparison of modern-day TAM simulations run in 3D versus axisymmetric configurations reveal that an asymmetry in surface methane only forms in the former case, implicating three-dimensional eddies in its development. Similarly, only the 3D simulations, in which eddies mix moist polar air with drier equatorial air, generate low-latitude precipitation. The interface between the moist polar surface and drier mid-latitude regions intensifies baroclinicity in the lower troposphere. We examine the transport of moisture by both the seasonal mean circulation and variations therefrom, as well as the transport by baroclinic eddies, and investigate the instabilities generating them.