PROJECT SUMMARY PROPOSAL ID: ATM-9312888 PRINCIPAL INVESTIGATOR: Jin, Fei-fei INSTITUTION: University of Hawaii PROGRAM: TOGA, CDP TITLE: Coupled Modeling of Annual and Interannual Tropical Ocean- Atmosphere Interaction Investigations of the tropical ocean-atmosphere interaction have focused largely on aspects of the interannual variability related to the El Nino-Southern Oscillation (ENSO) phenomenon. Coupled models of differing complexity have been developed to understand, simulate, and predict this phenomenon. However, there are increasing indications from both observational and modeling studies that the annual cycle and interannual variability are intrinsically related. This project will use a series of intermediate and hybrid coupled models, proven to be useful and economical in tropical coupled modeling, to investigate annual and interannual variability with an emphasis on the role played by the annual cycle in the interannual tropical ocean-atmosphere interaction. The goal of this research is improved understanding of the annual and interannual variabilities observed in the tropical ocean-atmosphere system. The intermediate coupled model, based on a simplified version of the 1987 Zebiak & Cane model, has been developed and extensively analyzed by Jin & Neelin. This model incorporates asymmetric components of sea surface temperature and ocean dynamics to give a realistic simulation of the climatological annual cycle and will be used to investigate the role of the annual cycle on the interannual variability. The mechanisms of frequency locking that give rise to coupled annual and sub-harmonic oscillations will be investigated. The regimes of coupled annual, quasi-biennial and low-frequency modes will be explored in an extensive range of parameter space. The intermediate coupled model will be improved with better parameterization of the physics and used fo r further studies of the coupled dynamics of the annual cycle and the interannual coupled modes. This investigation will be extended, based on the results from the research with the intermediate coupled model, to studies with a hybrid coupled model system which includes an ocean general circulation model and a quasi-steady tropical atmosphere model. The hybrid coupled model system permits a more sophisticated examination of the interaction between annual and interannual nodes and an exploration of the regime which supports the quasi-biennial and low-frequency variability with a regime diagnostic tool based on the intermediate model.
