Speaker: Professor Dennis L. Hartmann University of Washington 

Title: "Tropical Convection and Climate: Some Recent Work on Anvil Clouds"

Abstract: Clouds associated with tropical convection over the warm tropical ocean have a substantial effect on the absorption of solar radiation and the emission of terrestrial radiation to space, but their net effect on the energy balance of Earth is remarkably small. Observations show that this balance of shortwave and longwave cloud radiative effects results from the particular distribution of optical depth of the ice clouds that extend over a very large area compared to the actual area of precipitation. Using a simplified modeling framework we explore the physical processes that are likely needed to predict how such clouds will change in a warmed Earth. We find that the interactions among radiation, cloud physics and turbulent motions within the extended ice cloud are likely extremely important for determining the distribution of albedo observed. The lifecycle of tropical convective clouds from active convection to decaying anvil ice clouds is critical to the radiative neutrality of the cloud systems. While global climate models can produce some of the cancellation observed, the observed pdf of convective cloud albedo is not produced. If time allows we will review some recent analyses of the Fixed Anvil Temperature hypothesis and discuss recent insights using climate models in global radiative convective mode.