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.