The coalescence of large and small water drops : its effect on rainfall intensity

Coalescence of raindrops and cloud droplets has been studied in collaboration with W. Hitschfeld, by allowing drops of 3 mm diameter to fall through a three metre column of cloud. The observed drop growth is expressed in terms of a collection efficiency, the fraction of the cloud water in the path of the drop, which is actually picked up. Collection efficiencies, using three clouds of different droplet-size distributions, are found to be in good agreement with aerodynamic collision efficiencies, calculated from a theory by Langmuir. His assumption that collision always leads to coalescence is thus confirmed