The Collection Efficiencies of Highly Charged Water Drops for Uncharged Cloud Droplets

Experiments have been conducted to investigate the collection efficiencies of highly charged drops with radii from 60 to 120 μm for relatively uncharged droplets of about 20 μm radius. The measurements indicate that, for drop charges approaching the Rayleigh limit value, the collection efficiencies are increased by a factor of around 20–30 over those for uncharged drops. The high collection efficiencies imply that a highly charged drop is capable of collecting uncharged droplets initially situated at distances of several drop radii from the fall trajectory of the drop. Calculations utilizing a simple numerical model for the interaction of a drop and droplet pair demonstrate that these high values of collection efficiency are due to the electrical forces of attraction arising between the drop charge and the dipole induced within the uncharged droplet. The implications of this work for the modification and dissipation of warm clouds and fogs are briefly discussed.