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Effect of shoreline shape on Titan lake breezes and methane evaporation from a 3D mesoscale model

Presentation #216.02 in the session Titan III: Surface and Interior (Oral Presentation)

Published onOct 23, 2023
Effect of shoreline shape on Titan lake breezes and methane evaporation from a 3D mesoscale model

Titan, the largest moon of Saturn, has many lakes on its surface, filled in large part by liquid methane. Like water lakes on Earth, these methane lakes on Titan likely profoundly affect the local climate, which has implications for the formation of fog and/or waves. The quantification of methane evaporation from lakes is also of prime interest to understand Titan’s global methane budget. Previous studies (Rafkin and Soto 2020, Chatain et al. 2022) showed that Titan’s lakes create lake breeze circulations with characteristic dimensions similar to the ones observed on Earth. However, such studies used a model in 2D that might have induced biases in the resulting wind intensities and energy exchanges between the lake and the air. This work investigates the consequences of the addition of a third dimension to the model.

Results show that 2D simulations tend to overestimate the extension of the lake breeze over the land, and underestimate the strength of the subsidence over the lake, due to divergence/convergence geometrical effects in the mass conservation equations. In addition, 3D simulations performed with a background wind taken from a Global Climate Model show the formation of a pocket of accelerated wind behind the lake, which is not predicted in 2D simulations. An investigation of the effect of shoreline concavity on the resulting air circulation shows the formation of wind currents over peninsulas. Simulations with several lakes can either result in the formation of several individual lake breeze cells (during the day), or the emergence of a large merged cell with internal wind currents between lakes (during the night). The simulation of several real-shaped lakes located at a latitude of 74°N on Titan at the spring equinox shows that larger lakes trigger stronger winds (though not enough to form waves), and that some sections of lakes could accumulate enough methane vapor to form a thin fog. The move to 3D, along with adjustments in the parametrization of the turbulence, results in a reduction in the estimated magnitude of the average lake evaporation rate, namely to ~6 cm/Earth year.

Most of Titan’s lakes are surrounded by high topography that usually reaches 300 m altitude in less than 1 km horizontally (e.g., Mitri et al. 2019). We recently added such topographical features in the model. First results show that the lake breeze circulation is slowed down uphill and accelerated downhill on the exterior part of the rampart. We are currently investigating how topography affects the lake-air exchange of energy and methane.

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