The Growth Characteristics of Small Cumulus Clouds

Abstract

The vertical growth, diameters and trajectories of cumulus clouds observed over the San Francisco Peaks near Flagstaff, Ariz., were determined from photogrammetric measurements. New clouds formed in a small, well defined area. Their trajectories indicate the complex nature of orographic effects on the wind field. Active cloud elements were found to have growth characteristics similar to thermals observed in laboratory experiments. In particular, thermals broadened with height along a cone whose interior angle was about 30°, increasing their volumes by an order of magnitude prior to destructive erosion. Computed values of buoyancy decreased from a maximum initially, approaching zero or becoming negative near the erosion level, depending on the form of the momentum equation used.