In this project we developed a mesoscale climate model of Titan and focused on the evaporation of lakes, which is the first major step in the atmospheric methane cycle. We started from a version of the WRF model adapted to Titan by the U.S. host (SwRI, Rafkin & Soto 2020) and progressively developed its capacities.
1) In a first study, we added a radiative transfer module to WRF modelling solar and infrared fluxes. Although Titan is 9.5 times farther away from the Sun than the Earth and has a thick hazy atmosphere, radiation has a major impact on the atmospheric circulation. We found that the breeze flowing from the cold air above the lake to the warmer air above the land shows strong diurnal variations driven by radiative processes (Chatain et al, PSJ, 2022; presented at LPSC 2022, EGU 2022, the French PNP 2022, EGU 2023).
2) In a second study, we improved the model to run in 3 dimensions instead of 2. The results (Chatain et al, Icarus 2024; presented at DPS 2022, OPAG 2022, Titan Through Time 2023, the Spanish CPESS 2023, AOGS 2023) show that the divergence/convergence of winds and vapour mixing in 3D strongly impact the atmospheric circulation above the lake, the methane evaporation budget and the lake equilibrium temperature. We also observed that the turbulent kinetic energy (TKE) computed by the 2D model and based on studies of Earth atmosphere was strongly overestimated. We therefore corrected this effect to adapt the TKE to Titan’s sluggish atmosphere.
3) In a third study, we investigated the abundant small lakes on Titan that are surrounded by ramparts. Our results show that surface roughness on the ramparts has a very significant effect in the dynamics, as it slows down the surface wind, affecting evaporation rates, temperatures and the overall climate above lakes. Simulations with topography show that high ramparts deform the local lake breeze created by the lake, but do not stop it (Moisan, Chatain et al, submitted to PSJ in Feb. 2024; presented at Titan Through Time 2023, the Spanish CPESS 2023, DPS 2023, the French conference Elbereth 2024).
4) The fourth study investigated how the implementation of realistic topography in 3D simulations of lakes affects the methane budget and could lead to the formation of methane fog (Chatain et al, to be submitted to JGR: Planets in 2024; presented at DPS 2023 and FAIRPLAY workshop 2023).
5) With a fifth study we investigated cloud dynamics on Titan from image analysis. The analysis of a cloud system observed over few hours by the Cassini spacecraft allowed us to quantify the very slow evolution of a polar cloud, giving insights on its physics (presented at the Spanish CPESS 2023). In parallel, we submitted proposals to observe cloud systems in the coming years with the JWST to investigate on the frequency of such events. This investigation is continued after the end of the TLALOC project in the framework of a 2023-2026 PhD thesis at LMD co-supervised by the TLALOC researcher.
6) Finally, we started to develop a model that includes microphysics to study the formation and evolution of clouds in the lakes region. This investigation will also be continued with the PhD thesis at LMD.