A convective wake parameterization scheme for use in general circulation models

In the atmosphere, the cold, dry, precipitation-driven downdrafts from deep convection spread laterally after striking the surface, inhibiting new convection in the disturbed wake (cold pool) area. In contrast, the leading edge of this cold air lifts unstable environmental air helping to trigger new convection. A GCM cannot resolve the disturbed and undisturbed regions explicitly, so some parameterizations of these critical mesoscale phenomena are needed. The simplest approaches are to either instantly mix downdraft air with the environment, or instantly recover the downdraft air. The instant-mixing approach tends to lead to unrealistic pulsing of convection in environments that would otherwise be able to support long-lived mesoscale convective systems while the instant recovery approach usually overestimates surface energy fluxes. By replacing these simplistic approaches with a physically based convective wake-gust front model, these problems are substantially remedied. The model produced realistic parameterized wakes that closely resemble those observed in the Global Atmospheric Research Program's Atlantic Tropical Experiment and Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment when given reasonable inputs based on observations taken during these experiments. For realistic downdraft characteristics, wake recovery time is on the order of hours, which is significantly different from the instant recovery or instant mixing assumed in previous parameterizations. A preliminary test in midlatitude continental conditions also produced reasonable wake characteristics. Sensitivity tests show the model sensitivities to variations in downdraft mass Aux, downdraft thermodynamic characteristics, and surface wind/downdraft traveling velocity. Prognostic studies using a simple coupled cloud model successfully simulated the convective termination due to stabilization of the boundary layer by precipitation-driven downdrafts, the initiation of convection after the boundary layer recovery by surface fluxes, and the phenomenon of surface flux enhancement during the convective phase.