Collaborative Research: Tropical Variability in a New Generation of Coupled Climate Simulations with Explicitly Resolved Convection

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Research is conducted on simulations performed with the superparameterized (SP) version of the Community Climate System Model (CCSM, version 3), or SP-CCSM. The atmospheric component model used in a coupled climate model typically uses a parameterization for convection, in which the effects of convection are estimated without actually resolving the convection. In superparameterization, the parameterization is replaced by a cloud resolving model at each point in the model's horizontal grid. In this way the climate model gains some of the benefits of a global cloud resolving model without the enormous computational expense of running such a high-resolution (7km or less) nonhydrostatic model over the globe. Based on a 20-year simulation performed as preliminary work, SP-CCSM produces a better tropical simulation than CCSM3, including improvements in the periodicity of El Nino/Southern Oscillation events, reduction in the classical double-ITCZ bias, and a more credible simulation of the Madden-Julian Oscillation (MJO).Two research objectives are addressed in this research: first, SP-CCSM and its component atmospheric model are used to evaluate the roles of surface fluxes, air-sea interactions, and small-scale convective processes in producing MJO events. This research also considers the mechanisms through which the MJO affects the Asian summer monsoon. Second, the work seeks to understand the effect of the MJO on El Nino/Southern Oscillation events in the equatorial Pacific.The work has broader impacts through its potential to forecasts of MJO events, which have consequences for the Asian summer monsoon and weather in the United States. Research results may also lead to improvements in the parameterization of tropical convection in weather and climate models. In addition, the project supports a postdoctoral researcher, thereby providing for the next generation of scientists in this field.