Towards understanding the role of turbulence on droplets in clouds: In situ and laboratory measurements

The role of turbulence in droplet growth in clouds is controversial, in part because of the difficulty of studying underlying processes in the cloud environment, and in part because of the difficulty of achieving real cloud conditions in controlled laboratory or computational studies. This paper is a synthesis of research on turbulence effects on cloud droplets that includes field and laboratory studies. Results from cloud measurements show that the turbulence exhibits similar internal intermittency to that observed in the laboratory, and in direct numerical simulations. We explore the consequences of this by relating measurements of droplet accelerations in the laboratory, to conditions observed in the clouds. We show that there is a strong likelihood of droplet accelerations in clouds exceeding the acceleration due to gravity. We discuss these observations in terms of the dynamics of droplets, including velocity statistics and clustering, and their influence on droplet growth.