On October 9, 2025, Lea Raillard successfully defended her PhD thesis entitled “Representation of Polar Mixed-Phase Clouds in Climate Models,” conducted under the supervision of Étienne Vignon, Gwendal Rivière, and Jean-Baptiste Madeleine.

From the Antarctic coasts to the Arctic Ocean, clouds play a central role in the climate of high latitudes. Very often mixed-phase—that is, composed of both supercooled liquid water droplets and ice crystals—they have a crucial influence on the radiative and energy balance of polar regions. However, their representation remains one of the major weaknesses of current climate models, leading to significant biases in climate change projections.

The aim of Lea’s thesis was to improve the representation of these complex clouds in the LMDZ atmospheric general circulation model. In a first step, she designed a rigorous evaluation framework based on airborne observations from the RALI-THINICE campaign, allowing for the diagnosis of model biases in representing cloud phase and the vertical structure of mixed-phase clouds. These analyses revealed an overestimation of condensates, an imperfect vertical distribution of ice and liquid phases, and an insufficient representation of solid precipitation.

To address these issues, Lea developed a new parameterization for phase partitioning between liquid and solid in stratiform mixed-phase clouds, explicitly accounting for the effect of turbulence. This new parameterization allows for more realistic spatial variability and the simulation of thin layers of supercooled liquid water, which were previously absent. She then proposed a revision of the precipitation scheme in LMDZ, incorporating new microphysical processes and a subgrid-scale treatment to better represent cloud–precipitation interactions.

This work represents an important step toward more realistic modeling of polar clouds and, more broadly, toward a better understanding of their role in the global climate system. Congratulations to Lea for her successful defense and the quality of her research!

Learn more about her work:

• Raillard, L., Vignon, É., Rivière, G., Madeleine, J.-B., Meurdesoif, Y., Delanoë, J., et al. (2024). Leveraging RALI-THINICE observations to assess how the ICOLMDZ model simulates clouds embedded in Arctic cyclones. Journal of Geophysical Research: Atmospheres, 129, e2024JD040973. https://doi.org/10.1029/2024JD040973
• Raillard, L., Vignon, É., Rivière, G., & Madeleine, J.-B. (2025). A turbulence-informed parameterization of phase partitioning in stratiform mixed-phase clouds for the ICOLMDZ model. Journal of Advances in Modeling Earth Systems, [submitted]. https://doi.org/10.22541/essoar.175096287.71557703/v1