Quasi-equilibrium

Quasi-equilibrium of the cloud work function was proposed by Arakawa and Schubert (AS) as a closure assumption to determine the intensity of convective activity. Their idea is that convective and non-convective processes nearly balance, so that the cloud work function is quasi-invariant. Quasiequilibrium has been tested using both tropical and midlatitude observations, and has held up well. Some conceptual problems arise, however, when we attempt to specify which processes are in fact non-convective. One solution to these problems is to adopt a prognostic closure as an alternative to quasiequilibrium closure. To illustrate both the quasi-equilibrium and prognostic closures at work, we present some numerical results from a general circulation model. Finally, it is pointed out that because quasi-equilibrium closure is an approximation, its adoption forces us to give up the ability to forecast or simulate some phenomena that may be of interest.