Behavior of Cumulus Activity and the Structures of Circulations in an "Aqua Planet" Model

Part I: The Structure of the Super Clusters

Abstract

As an extension of the 'aqua planet' experiments by Hayashi and Sumi (1986, HS86), GCM experiments with various SST distributions and cumulus parameterizations are performed in order to examine the structure of cumulus activity and its parameter dependence. In part I, the results of the analyses concentrating on the super clusters are described.
The super clusters, which were named by HS86, are expressed in the model as continuously moving precipitating areas of the grid scale. The associated circulation structure can be explained in terms of the wave-CISK dynamics of Kelvin waves. The super clusters become more active when a warmer SST is used. On the other hand, the 30 day oscillation, that is an eastward-moving planetary scale structure, is more distinct when a colder SST is used.
The behavior of cumulus activity is highly sensitive to the choice of cumulus parameterization. When the moist convective adjustment scheme is used instead of Kuo's (1974) scheme, the eastward-moving structure of the grid scale is no longer observed at the equator. However, the planetary scale structure still clearly appears in the experiment with the moist convective adjustment scheme.