Do Charged Cloud Droplets Collide Faster?

Warm rain formation in clouds requires rapid coalescence of tiny droplets, a process that pure condensation-driven processes struggle to explain within the short time available in rising cloud parcels. One potential accelerator of droplet growth is electrical charging: it has long been hypothesised that charged cloud droplets might collide and coalesce more efficiently than neutral ones, especially in a turbulent airflow. To investigate this question, we developed a stochastic model tracing droplet pair trajectories at sub-Kolmogorov scales in a turbulent flow field. The model incorporates electrostatic forces, gravitational settling, and shear-induced collisions to simulate realistic encounter rates. Our simulations reveal that even moderate droplet charges can substantially increase collision frequencies under typical cloud turbulence conditions, resulting in the faster growth of droplets into raindrop sizes. These results shed new light on the microphysical mechanisms of precipitation initiation: electric charges on droplets can enhance coalescence efficiency, suggesting that natural background charging in clouds may help bridge the gap between cloud droplet populations and the onset of rain.