Air–Sea Interactions on Titan: Effect of Radiative Transfer on the Lake Evaporation and Atmospheric Circulation

Abstract

Titan’s northern high latitudes host many large hydrocarbon lakes. Like water lakes on Earth, Titan’s lakes are constantly subject to evaporation. This process strongly affects the atmospheric methane abundance, the atmospheric temperature, the lake mixed layer temperature, and the local wind circulation. In this work we use a 2D atmospheric mesoscale model coupled to a slab lake model to investigate the effect of solar and infrared radiation on the exchange of energy and methane between Titan’s lakes and atmosphere. The magnitude of solar radiation reaching the surface of Titan through its thick atmosphere is only a few watts per square meter. However, we find that this small energy input is important and is comparable in absolute magnitude to the latent and sensible heat fluxes, as suggested in a study by Rafkin & Soto (2020). The implementation of a gray radiative scheme in the model confirms the importance of radiation when studying lakes at the surface of Titan. Solar and infrared radiation change the energy balance of the system leading to an enhancement of the methane evaporation rate, an increase of the equilibrium lake temperature almost completely determined by its environment (humidity, insolation, and background wind), and a strengthening of the local sea breeze, which undergoes diurnal variations. The sea breeze efficiently transports methane vapor horizontally, from the lake to the land, and vertically due to rising motion along the sea breeze front and due to radiation-induced turbulence over the land.

Taking Titan’s Boreal Pole Temperature: Evidence for Evaporative Cooling in Ligeia Mare

“…Indeed, we only used the temperature profiles modeled for the middle of Ligeia Mare, while there may exist differences due to exchange processes between the center and the border of the sea. For instance, the temperature difference between the (colder) sea and the (warmer) surrounding lands may generate sea breeze and therefore stronger winds and evaporative cooling at the shores (Chatain et al 2022).…”

Turbulent Fluxes and Evaporation/Sublimation Rates on Earth, Mars, Titan, and Exoplanets

“…Subsequent modeling efforts made improvements, by either incorporating stability effects (Lora et al, 2015;Tokano, 2009Tokano, , 2023 or calculating z 0m , z 0v and z 0h separately (Mitri et al, 2007), but neither groups of models included both effects together. Models based on WRF (e.g., Chatain et al, 2022;Newman et al, 2016;Rafkin & Soto, 2020) include both stability and roughness length (z 0m ≠ z 0v ≠ z 0h ) effects, but were based on older versions of WRF and therefore contain the stability approximations and limits described in Section 3.1.2. Lastly, all the models described above except for Mitri et al (2007) and those based on WRF do not explicitly calculate transfer across the interfacial layer.…”