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.
About the Author
Charles "Chief" Edward Anderson PhD '60 was the first African American to hold a PhD in meteorology, which he earned from MIT in 1960. He started the Civilian Pilot Training Program (CPTP) at the Tuskegee Institute of Alabama, responsible for training the pilots who became the famous Tuskegee Airmen. A self-taught pilot, Anderson was the first African American to receive a pilot's license, 1929, and widely acclaimed as the father of Black Aviation. In 2007, he was awarded a Congressional Medal of Honor.
Anderson, Charles E. "A Study of the Pulsating Growth of Cumulus Clouds." Dissertation. Massachusetts Institute of Technology, May 1960.