Tropical convection tends to self-organize on scales much larger than individual updrafts, from squall-lines to tropical cyclones (TCs), and ultimately to phenomenon as big as the Madden-Julian Oscillation (MJO). Most climate models, employed for the future climate-change projections, use semi-empirical parameterizations of convection; however, they, in general, do not represent the effects of aggregated convection, even as big as the MJO. The current consensus is that the clouds represent the biggest uncertainty of the climate feedbacks to the anthropogenic forcing; therefore, it is important to understand the role the organized convection plays in regulating the tropical climate.

In my talk, some recent results of modeling self-organization of tropical convection using a cloud-resolving model (CRM) will be presented. Among them are the cloud-resolving simulations of the radiative-convective equilibrium (RCE) over large domains with f-plane rotation. As generally accepted, the RCE is a good idealization of the tropical atmosphere. It is demonstrated that the size and strength of the simulated co-existing TCs generally increases with the increasing sea-surface temperature (SST). It is also shown that while the presence of TCs at colder SSTs tends to decrease the implied climate sensitivity (defined as potential SST change in response to the given external forcing) as compared to the sensitivity of RCE without rotation, the TCs could substantially amplify the climate feedback at warmer SSTs. Some preliminary results of recent idealized cloud-resolving RCE over the equatorial beta-plane with the goal to simulate explicitly the self-organization of tropical convection into the MJO will be presented. The simulated MJO sensitivities on an aqua-planet as simulated by the GCM with the CRM used as the super-parameterization of convection will also be discussed.


Speaker's Website: http://rossby.msrc.sunysb.edu/~marat/index.html

Faculty Host: Kerry Emanuel