AGS-FIRP Track 2: Convection-Cloud Chamber Experiments to Explore Collisional Growth Processes

Collisions between cloud droplets are a primary mechanism by which clouds form precipitation, especially in clouds without ice. Despite the importance of this process, there are few experimental studies of cloud droplet collisions due to the difficulty in making these measurements in the atmosphere. In this project, a team of researchers will use an advanced laboratory instrument known as a cloud chamber to study how efficiently cloud droplets collide, especially in the turbulent conditions that mimic a cloud. This work may lead to improvements in numerical weather forecast models and will provide research training opportunities for students. The initiation of drizzle in warm clouds is a critical yet incompletely understood process in cloud microphysics, primarily governed by the transition from condensational growth to the collision-coalescence mechanism. Cloud droplets must increase to drizzle droplet sizes to initiate precipitation, but that growth is sometimes underestimated by standard cloud models. In this project, the research team will conduct a rigorous examination of collection efficiencies and how turbulence enhances collision rates between cloud droplets. Specifically, the project will focus on larger collector drops that settle through and interact with smaller cloud droplets. The research will be conducted in the Pi Convection-Cloud Chamber and incorporate techniques like fluorescence detection and Lagrangian particle tracking to observe the collection efficiency and the dynamics of droplets immediately prior to and after collisions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.