CUMULUS CONVECTION AND THE MADDEN-JULIAN OSCILLATION OF THE TROPICAL TROPOSPHERE

Parameterizations of cumulus convection for use in large scale numeric al models of the atmosphere are classified according to whether they a re based on an energy equilibrium principle or on a balance between th e supply of mass or moisture and its consumption by convection. Though some of the most popular cumulus parameterizations are based on mass or moisture balance, I argue that energy balance is a more appropriate governing principle. Physical consistency and the absence of spurious short wavelength instabilities are points in its favor. A simple ener gy equilibrium parameterization with a minimal representation of preci pitation processes is then described, with the objective of reducing t he convective parameterization problem to its essential elements. This model is first shown not to exhibit small scale instabilities. When w ave-related variations in the surface entropy flux are included, it is then found (in agreement with other energy balance models) to support large scale waves similar to the observed Madden-Julian oscillation o f the tropical troposphere. The characteristic period of the waves is related to the time needed for-sea-air fluxes to alter the tropospheri c profile of equivalent potential temperature, and their intensity and phase speed are sensitive to variations in the parameters controlling the formation and evaporation of precipitation.