Inferences from Simple Models of Tropical Convection

Understanding and modeling of the tropical atmosphere has been impeded in part because of the immense complexity of moist convection. This complexity has led to the development over the past half century of parameterizations of increasing sophistication, yet models that employ these parameterizations continue to struggle to account for phenomena like the Madden-Julian Oscillation. Disappointment stemming from such failures has led, more recently, to the abandonment of parameterizations in favor of models that explicitly, albeit crudely, resolve moist convective clouds. Such models have spawned revelations about such phenomena as the instability of radiative-convective equilibrium states and the ensuing self-organization of moist convection.

Yet the migration to models of increasing resolution and sophistication threatens to favor simulation over understanding. Yet this need not be the case since such models can serve as test beds for conceptual understanding and simple models. In this talk I will show that the marriage of three simple and elegant ideas: boundary layer quasi-equilibrium, the weak temperature approximation, and gross moist stability can explain the essence of such features of the tropical atmosphere as its mean relative humidity, the Walker Circulation, the strong observed correlation of precipitation and column humidity, self-aggregation, and the diurnal cycle of convection. These simple models can serve as vehicles for understanding the real tropical atmosphere as well as the behavior of sophisticated models.