A new aspect of condensation theory

The effects of the mixing of dry air into a cloud top on the droplet spectra are examined. Theoretically, the resulting cycling of air up and down in the cloud, which seems to be the essential mechanism by which cumuli are diluted to their observed liquid water mixing ratio, can double the largest drop radius and generate cloud parcels containing drops of all sizes to this maximum. These changes in the droplet distribution with size occur by a process that is influenced little by the cloud condensation nuclei or the details of droplet growth since maritime-like spectra can develop in continental-type cumuli. Large numbers of cloud condensation nuclei should have little effect in inhibiting the rain-forming process by reducing coalescence growth. On the contrary, the controlling parameters that determine precipitation efficiency and times seem to control the mixing also.