The Arakawa-Schubert Cumulus Parameterization

Abstract

The motivation of the paper by Arakawa and Schubert (1974) (hereafter referred to as A-S) was to present a theoretical framework that can be used for understanding the physical and logical basis for cumulus parameterization. More specifically, the paper attempted to answer the following questions:

• 1) How can cumulus clouds modify their environment while condensation takes place only inside clouds. Does the modification occur only through mixing of cloud air with the environment as clouds decay? If not, how can clouds in their mature phase modify the environment?

• 2) Since the vertical structure of that modification depends on cloud type (primarily cloud-top height) and typically more than one type of clouds coexist, a parameterization scheme should determine the spectral distribution of clouds instead of assuming a particular cloud type (or particular cloud types) a priori. What is an appropriate framework for doing this?

• 3) How does the subcloud layer control cumulus activity? What is the nature of the feedback in this link?

• 4) Finally, how can the intensity of overall cumulus activity and that of each cloud type be determined for a given large-scale condition? It is obvious that we can only parameterize cumulus activity in balance with large-scale processes. Then, how can we quantitatively define such balance?