Abstract
An analysis of growth of a distribution of cloud drop sizes is made for different models of cumulus clouds. The temperatures at which the growing drops freeze are determined by applying Bigg's criterion. It is found that the initiation of ice occurs over a considerable depth of cloud at about the same time. At any rate, the spread of ice throughout the cloud by heterogeneous freezing is much more rapid than could be accomplished by the initiation of ice at one level and the transport of splinters by the updraft to higher levels.
