EXPERIMENTS WITH A SPECTRAL CUMULUS PARAMETERIZATION THEORY

The thermodynamic equation and the water vapor equation, with the effects of cumulus convection parameterized according to the Arakawa-Schubert theory, are integrated during a short time interval and the resultant temperature and moisture tendencies are then studied. The quasi-equilibrium assumption is formulated as an optimization problem in which the objective is to minimize the changes in the cloud work function. The feedback loop consists of temperature and moisture changes due to large-scale vertical motion, radiative cooling and surface fluxes. The response of the model to different patterns of the above three types of forcing is compared to observations. The model suggests a suppressive effect of deep convection on shallow convection, which is shown to be strongly coupled to boundary layer forcing through surface fluxes of heat and moisture. The dis-tribution of clouds is shown to be sensitive to the choice of the radiative cooling profile when the dynamical forcing is small. In the static control a lateral detrainment coefficient is introduced as well as a cloud type dependent autoconversion coefficient in the parameteri-zation of rain. i