A simple model of convection with memory

Abstract

There are at least three distinct time scales that are relevant for the evolution of atmospheric convection. These are the time scale of the forcing mechanism, the time scale governing the response to a steady forcing, and the time scale of the response to variations in the forcing. The last of these, t mem, is associated with convective life cycles, which provide an element of memory in the system. A highly simplified model of convection is introduced, which allows for investigation of the character of convection as a function of the three time scales. For short t mem, the convective response is strongly tied to the forcing as in conventional equilibrium parameterization. For long t mem, the convection responds only to the slowly evolving component of forcing, and any fluctuations in the forcing are essentially suppressed. At intermediate t mem, convection becomes less predictable: conventional equilibrium closure breaks down and current levels of convection modify the subsequent response. Copyright 2009 by the American Geophysical Union.