Multiple equilibria in a cloud-resolving model using the weak temperature gradient approximation

Multiple equilibria corresponding to either a state with persistent, precipitating deep convection or a nonprecipitating 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 nonprecipitating 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.