The effect of revised collision efficiencies on the growth of cloud droplets by coalescence

Abstract

Abstract The collection efficiencies of water drops falling in still air have been recalculated by Hocking and Jonas (1970). In this paper these revised values have been used to estimate the rate of production of large droplets ( r > 30 μm) by coalescence. It is found that there is an increase in the rate of production of droplets with radii of about 20 to 25 μm compared with the rate calculated using Hocking's earlier (1959) values, but generally a decrease in the rate of production of droplets with radii 20 to 25 μm. It is also shown that neglecting the small, but finite, collection efficiencies predicted for droplets with radii less than about 15 μm has negligible effect on the rate of production of larger droplets.