Observations and modeling of the transition from shallow to deep convection

Dr. Joseph Zehnder, Arizona State University

The transition from shallow to deep convection is a complex process and depends on details of the environment in which the convection is occuring.  Thunderstorms that occur over the mountains in central and southern Arizona during the summer monsoon season develop in stages, with shallow turrets eroding and followed by deeper convection. One possibility is that the shallow convection moistens the column, consuming some of the CAPE but allowing subsequent convection to use the remaining CAPE more effectively.

Observations of orographic cumulus development over the Santa Catalina Mountains in southern Arizona have been made using a digital camera for the last two summers. Some preliminary results and plans for further studies are outlined.   In second part of the talk, a simple dynamical model consisting of three coupled shallow water layers with an accompanying convection scheme is described. Allowing a transition from shallow to deep convection that depends on the shallow convection conditioning the atmosphere results in an excitation of Matsuno type normal modes with steady, periodic or chaotic behavior.