Modeling convective methane clouds on Titan with a kilometer-scale regional model

    Titan, the largest moon of Saturn, is four times smaller than Earth but has a slightly higher surface pressure (1.5 bar), due to its very extended atmosphere. Titan's atmosphere is mainly composed of nitrogen, with a few percents of methane. The pressure and temperature (~94 K at the surface) conditions there enable a full "hydrological" cycle of methane, with lakes stable on the surface, evaporation, clouds, rain, and rivers.
    In this work, we focus on the methane clouds in Titan's troposphere, and in particular on the convective ones.
    Titan's methane clouds are monitored from Earth-based telescopes since the end on the 1990's, and have been observed from close by the Cassini spacecraft during half a Titan year (2004 - 2017). Some of the methane clouds in Titan's troposphere are thought to exhibit convective dynamics (e.g. Griffith 2005, 2009, Schaller 2009, Lemmon 2019, Rannou 2021). To understand the processes driving the clouds formation and evolution, modeling is also used, from global scale to regional scale models.

    Here we use a regional scale model (160x160 km), with kilometric horizontal resolution. The model is a coupling between the physics of the Titan Planetary Climate Model (Titan PCM, de Batz de Trenquelléon et al. 2025 a,b) and the dynamics of the Weather Research and Forecast model (WRFv4, Skamarock et al. 2019).
    We perform idealized simulations with several initial perturbations, at several seasons and locations, in order to constrain in which conditions methane convection appears on Titan.

    We obtain condensation for a diversity of setups, with in some cases the triggering of deep convection. We discuss the environments where we find deep convection in our model, and compare them to what has been observed on Titan. We also study convective ascents and the convective available potential energy (CAPE) obtained in our simulations, and compare it to Earth's storms.

References

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