Computations of Rain Formation by Coalescence

Numerical integrations were made of the statistical equations describing the evolution of droplet distributions by coalescence. The results confirmed that increasing the droplet concentration, for the same liquid water content, greatly adds to the difficulty attending rain formation by coalescence. The spread of the initial distribution was not, on the other hand, an important parameter. The computed times for rain formation were less than a half-hour when the cloud contained 50 droplets cm−3 and 1 gm m−3 liquid water. When compared with observations these times are a little too long, but rain which forms more quickly can be explained by more rapid growth in regions of higher liquid water content.