A STUDY OF THE PULSkTING GRW 0 TH OF CUMULUS CLOUDS by Charles Edward

The growth of five cumulus congestus clouds over the Santa Catalina Mountains near Tucson, Arizona was subjected to detailed examination by means of photogranmetric and statistical analysis. It was found that these clouds exhibited a pulsating form of cellular convection as they grew upward. Once maximum height was achieved, the circulation became a linearly increasing function of time. The pulsations were found to be related to the buoyancy restoring force of the statically stable air with frequencies near ten minutes. Higher frequencies were found near one to two minutes which could not be definitely accounted for by conventional turbulence theory. An over-all acceleration of the motion was shown to be caused by an underlying flow which responded to the mean state of the cloud column. A physical model is proposed for the circulation of a growing cumulus in which two cells are acting concurrently, yet independently, along the same vertical axis. The correct time behavior is shown to result from applying Bjerknes' circulation theorem, modified to include entrainment and mixing. Thesis Supervisor: Henry G. Houghton Title: Professor of Meteorology and Head, Department of Meteorology and Thesis Supervisor: Victor P. Starr Title: Professor of Meteorology