The 10th Symposium on Global Change Studies

5A.12
SEASONAL TO INTERDECADAL VARIATIONS SIMULATED WITH AN INTERMEDIATE COUPLED TROPICAL OCEAN-ATMOSPHERE MODEL

Bin Wang, University of Hawaii, Honolulu, HI; and Z. Fang

This paper describes a coupled tropical ocean­atmosphere model which fills the gap between anomaly coupled models and fully coupled general circulation models. Both the atmosphere and ocean model are two and half layer primitive equation models. The model emphasizes essential physical processes in the oceanic mixed layer and atmospheric boundary layer with simplified dynamics for the thermocline and the free atmosphere. The ocean and atmosphere are coupled through both momentum and heat fluxes without flux correction.

A 140­year simulation reproduces realistic features of the long­term mean state, annual cycle, and El Nino­Southern Oscillation (ENSO). In particular, the distinctive annual cycle of the ITCZ/cold tongue complex and the temporal structure of ENSO anomalies (a quasi­biennial and a low­frequency component, a clear tendency of phase­lock to annual cycle, and the interdecadal modulation of the ENSO amplitude and frequency) are realistically simulated. The SST anomalies are largely standing in the eastern equatorial Pacific while propagates westward in the central Pacific. The spatial structure of the simulated ENSO is insensitive to the change of model mean state and parameters. The oscillation period depends on mean state in the equatorial eastern and central Pacific but not the western Pacific monsoon.

Two sources of climate drift are identified during the development of the coupled model which are, respectively, associated with inadequate parameterization of latent heat flux­SST feedback and cloud­SST interaction. The model's climate fluctuations were found to have substantial impacts on the formation of coupled mean states. It is a dominant source of errors for the simulated time mean climate. In contrast, the annual variation does not contribute significantly to these errors. The model's deficiencies, limitations, and future works are also discussed.

The 10th Symposium on Global Change Studies