Journal of Geophysical Research, submitted 10/09.

Multiple equilibria in a cloud-resolving model

Sharon L. Sessions, Satomi Sugaya, David J. Raymond
Department of Physics, New Mexico Institute of Mining and Technology, Socorro, NM.

Adam H. Sobel
Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY.

Abstract

Multiple equilibria corresponding to either a state with persistent, precipitating deep convection or a non-precipitating state are shown to exist in a cloud resolving model employing the weak temperature gradient (WTG) approximation. WTG is important for the existence of both equilibria; numerical experiments show that a weak enforcement of WTG eliminates the dry non-precipitating state. In situations which support both equilibria, we find that the dry equilibrium has a small or negative gross moist stability, while larger positive values of gross moist stability correspond to the precipitating equilibrium. Our simulations also show that the gross moist stability tends to become negative during times of rapid change in the atmospheric moisture, as occurs in the transient stages of convection.