The local effect of surface liquid methane and topography on Titan’s weather

Titan hosts quite Earth-like weather patterns. This is mainly due to the fact that its surface pressure is very close to the Earth’ (1.5 bar) and that methane is abundant and with atmospheric conditions near its triple point. It can therefore be a gas, a liquid or a solid with small variations in the temperature or pressure. We then observe similar landscapes and weather processes as on Earth: clouds, rain, rivers, lakes, seas (Hayes, 2016, Ann Rev EPS; Turtle et al., 2018, GRL)…

The Cassini-Huygens mission gave us insights on the surface conditions and topography on Titan. The future Dragonfly mission will allow an in-depth analysis of an equatorial location just after the Northern winter solstice with many meteorological sensors (Barnes et al., 2021, PSJ).

In the meantime, and to help prepare future Dragonfly operations, we can run climate models in Titan’s conditions to investigate typical weather patterns in the atmosphere. Here we focus on surface-atmosphere local interactions with an idealized mesoscale model (with a horizontal resolution of 1-4 km) based on the WRF (Weather Research and Forecasting) model developed by NCAR for Earth weather predictions. We call it mtWRF (“mesoscale Titan WRF”). This model can in particular simulate a methane lake (Rafkin & Soto, 2020, Icarus), in 3D (Chatain et al., 2024, Icarus), with topography (Moisan et al., PSJ, in review) and includes the diurnal influence of radiations (Chatain et al., 2022, PSJ). We use input atmospheric profiles from the global scale Titan Atmospheric Model (Lora et al., 2022, Icarus) at various locations and seasons. We investigate the influence of topography with idealized maps as well as synthetic topography maps based on radar data at specific locations on Titan (Bonnefoy et al., EPSC 2024).

Results show that lakes cool down by evaporating methane into the atmosphere. This induces a local cooling of the atmosphere and strong winds at the shores. We observe strong diurnal, latitudinal and seasonal variations, showing that solar heating plays a major role.

These results will help us understand the general absence of waves in lake observations, the possibility of fog in depressions, the evaporation rate of ponds after heavy rains and the intensity of winds created by local slopes.

 

References:

Barnes, J. W., Turtle, E. P., Trainer, M. G., Lorenz, R. D., MacKenzie, S. M., Brinckerhoff, W. B., Cable, M. L., Ernst, C. M., Freissinet, C., Hand, K. P., Hayes, A. G., Hörst, S. M., Johnson, J. R., Karkoschka, E., Lawrence, D. J., Gall, A. Le, Lora, J. M., McKay, C. P., Miller, R. S., … Stähler, S. C. (2021). Science goals and objectives for the Dragonfly Titan rotorcraft relocatable lander. Planetary Science Journal, 2(4), 130. https://doi.org/10.3847/PSJ/abfdcf

Bonnefoy, L. E., Lefèvre, M., Chatain, A., Spiga, A., Hayes, A. G., Rodriguez, S., & Lucas, A. (2024). Synthetic topography, roughness, albedo, and thermal inertia maps for mesoscale modeling on Titan. Europlanet Science Congress 2024, 907. https://doi.org/10.5194/epsc2024-907

Chatain, A., Rafkin, S. C. R., Soto, A., Hueso, R., & Spiga, A. (2022). Air – Sea Interactions on Titan: Effect of Radiative Transfer on the Lake Evaporation and Atmospheric Circulation. The Planetary Science Journal, 3(10), 232. https://doi.org/10.3847/PSJ/ac8d0b

Chatain, A., Rafkin, S. C. R., Soto, A., Moisan, E., Lora, J. M., Le Gall, A., Hueso, R., & Spiga, A. (2024). The impact of lake shape and size on lake breezes and air-lake exchanges on Titan. Icarus, 411(December 2023), 115925. https://doi.org/10.1016/j.icarus.2023.115925

Hayes, A. G. (2016). The Lakes and Seas of Titan. Annual Review of Earth and Planetary Sciences, 44(1), 57–83. https://doi.org/10.1146/annurev-earth-060115-012247

Lora, J. M., Battalio, J. M., Yap, M., & Baciocco, C. (2022). Topographic and orbital forcing of Titan’s hydroclimate. Icarus, 384(May), 115095. https://doi.org/10.1016/j.icarus.2022.115095

Moisan, E., Chatain, A., Rafkin, S. C. R., Soto, A., Mackenzie, S. M., & Spiga, A. (n.d.). Ramparts around lakes on Titan impact winds and methane evaporation. In Revision for the Planetary Science Journal.

Rafkin, S. C. R., & Soto, A. (2020). Air-sea interactions on Titan: Lake evaporation, atmospheric circulation, and cloud formation. Icarus, 351, 113903. https://doi.org/10.1016/j.icarus.2020.113903

Turtle, E. P., Perry, J. E., Barbara, J. M., Del Genio, A. D., Rodriguez, S., Le Mouélic, S., Sotin, C., Lora, J. M., Faulk, S., Corlies, P., Kelland, J., MacKenzie, S. M., West, R. A., McEwen, A. S., Lunine, J. I., Pitesky, J., Ray, T. L., & Roy, M. (2018). Titan’s Meteorology Over the Cassini Mission: Evidence for Extensive Subsurface Methane Reservoirs. Geophysical Research Letters, 45(11), 5320–5328. https://doi.org/10.1029/2018GL078170