Ramparts around Lakes on Titan Impact Winds and Methane Evaporation

Understanding the lake-atmosphere interactions on Titan is crucial to answering some of Titan’s long-standing scientific questions, such as the unexpectedly high methane abundance close to the surface, or the “magic islands” that appear on one of the seas. Here we focus on specific lakes called Sharp-Edged Depressions, which are surrounded by high-elevation terrains called ramparts with unique structural and spectral properties. We aim at understanding how topography and surface properties around the lakes affect air-surface interactions. To study the effect of ramparts, we utilize the mtWRF model configured in 2D. We model a variety of lake morphologies: those surrounded by hills (300 m high, 30 km wide), those with no surrounding topography, and those at the bottom of a depression. To encapsulate the effects of surface properties, we vary the surface roughness, albedo, and thermal inertia. We also consider the effect of varying the background wind and the season. Our model indicates that the addition of topography creates weaker winds over the lake (≈ −30%) and reduces the quantity of methane evaporated (≈ −10%) compared to the no-topography case. However, topography results in deeper vertical transport of methane and deepens the marine layer (from a few meters to ≈ 50 m). Higher roughness (from 0.4 to 40 cm) of the ramparts tends to decrease the wind speed (≈ −50%) and reduces the horizontal extension of the lake breeze (≈ −20%). Albedo and thermal inertia variations have a negligible effect. Seasons have a strong effect on the evaporation of methane, with evaporation rates nearly 3 times higher in summer than in winter.