Particle-Resolved Direct Numerical Simulation of Turbulence-Cloud-Aerosol Interactions

Clouds play a critical role in the evolution of weather and climate. They consist of numerous tiny water droplets that grow as water deposits on the background aerosol particles. The objective of the presented work is to better understand the aerosol-cloud interactions. Previous developments such as global climate models, numerical weather prediction, and large eddy simulation (LES), could not represent some of the important processes that occur at spatial scales smaller than the typical grid sizes used in these models, including the microphysics of clouds and aerosols, and the turbulent mixing between cloud droplets and environmental air. We adopt a particle-resolved direct numerical simulation (PR-DNS) approach and aim to resolve the smallest eddies in the flow, track the cloud and aerosol particles individually, and cover a domain size of practical interest. We monitor the activation of aerosol particles into cloud droplets and the deactivation of cloud droplets into aerosol particles by varying turbulence intensity and dry aerosol size distribution. A detailed analysis of atmospheric turbulence in our model is also presented. Our results indicate that dry aerosol size distribution influences the activation process. When particles are smaller, the curvature and solute effects are more pronounced. We also find that turbulence enhances the deactivation of cloud droplets.