Understanding clouds across scales
Clouds are an essential part of the Earth’s climate system with significant influence on the global radiation budget. However, our understanding of clouds in the climate system is highly uncertain, in large part because of the complex network of interactions and feedbacks originating from small-scale cloud processes, such as turbulent entrainment and mixing, cloud-radiation interactions, and cloud microphysics, and the fact that these processes are usually neglected or only crudely parameterized. This is especially the case for low-level clouds such as the trade-wind shallow cumuli, which are the focus of this project “Understanding clouds across scales” (UCAS).

Entrainment and mixing have significant effects on the microphysical composition of a cloud and hence its radiative properties. These processes have been classically described by the interaction of turbulence and cloud microphysics. Recent work, however, has identified the saturation of mixed air as another crucial parameter, emphasizing the preconditioning of the mixed air by the interaction of turbulence, cloud microphysics, and radiation. We aim to investigate these processes for shallow cumuli. The project will use observations from a large upcoming observational campaign, but is based on the modeling of aforementioned processes, using a novel modeling approach that bridges the gap between direct numerical and large-eddy simulation, covering all relevant spatial scales from the entire cloud field down to the smallest lengthscales of turbulence in a single model. Resolving this wide range of scales is essential, enabling unprecedented insights on the effects of small-scale processes on entire cloud fields, without the typical restrictions of a limited domain or insufficient resolution.

All in all, this project will further process-level understanding of small-scale cloud processes and their effects on the large-scale properties of shallow cumuli, and hence their role in Earth’s climate system.