The Role of Passive Cloud Volumes in the Transition From Shallow to Deep Atmospheric Convection

Abstract

Abstract Properly capturing the transition from shallow to deep convection remains a major shortcoming of numerical weather and climate models due to poor understanding of the physical processes controlling this transition. Although recent studies suggest shallow preconditioning and cold pool feedbacks to be important, these studies are unable to explain the initial phase of the transition. We identify an additional mechanism, namely the interaction between passive cloud volumes (PCV)—old cumulus cloud volumes in the decaying stage—and updrafts, and discuss the potential role of this mechanism in the transition from shallow to deep convection. We show that the number of updrafts interacting with PCV is very large during the transition and the updrafts better preserve their buoyancy due to entrainment of much moister air. We argue that PCV might play an important role in the transition and cumulus parameterizations could therefore benefit from including them.