TITLE: Application of a cloud-resolving model to the climate-change problem

ABSTRACT:
Convection contributes significantly to the uncertainty of the climate feedbacks to the forcing due to increasing presence of anthropogenic green-house gases as simulated by the contemporary global climate models (GCMs). In nature, convection tends to self-organize on larger scales, from squall-lines to tropical cyclones (TCs), or even planetary-scale systems associated with the Madden-Julian Oscillation. The general effects of convection on the scales resolved by the GCMs have been represented by semi-empirical parameterizations; however, the effects of self-organization of convection have been generally missing in the conventional GCMs. Idealized theoretical model of self-organization has indicated that effects on climate feedbacks can be significant.

Cloud-resolving models (CRMs) have been used to gain some insight into these important issues. In this talk, the results of application of a particular CRM, the System for Atmospheric Modeling, or SAM, to several problems involving self-organized tropical convection will be presented. For example, in idealized radiative-convective equilibrium (RCE) experiments using large 3D domains, sea surface temperature (SST) increase can lead to an abrupt transition ("on-off switch") from uniform to aggregated convection. In the case of RCE with f-plane rotation over a period of several hundred days, self-aggregation's dependence on SST manifests itself as quasi-periodically developing and dying tropical cyclones (TCs) above certain SST threshold. It is demonstrated that in the RCE with rotation and interactive slab-ocean, in a computational domain large enough to pertain the development of TCs, the SST warming due to CO2-doubling can be notably reduced compared to the RCE using domains that are too small to contain the TCs. The results of direct comparison of the RCE with prescribed climatological large-scale rising motion to the observations of similar regime in the Tropics will also be reported.

SPEAKER WEBSITE: http://rossby.msrc.sunysb.edu/~marat/index.html