A coupled tropical ocean-atmosphere
model that fills the gap between anomalous coupled models and fully coupled
general circulation models is described. Both the atmosphere and ocean are
represented by two and one-half layer primitive equation models, which
accentuate the physical processes in the oceanic mixed layer and atmospheric
boundary layer. The two media are coupled through both momentum and heat flux
exchanges without explicit flux correction. The coupled model, driven by solar
radiation, reproduces realistic seasonal cycles of the mixed layer temperature,
currents, and depth, and the surface winds and rainfall in the tropical
Pacific.
The model results indicate that the
equatorial westward phase propagation of the annual warming is primarily caused
by zonal temperature advection and downward solar radiation modified by clouds,
whereas the wind-evaporation-SST feedback plays a minor role. The meridional
wind component appears to have a stronger impact than the zonal wind component
on the seasonal cycle of the eastern Pacific cold tongue, because the cross
equatorial winds have stronger annual variation which is more effective in
regulation of SST through changing surface evaporation and mixed layer
entrainment. The annual variation of the solar forcing is shown to have a
significant impact on the long term mean state. Without the seasonal cycle
forcing, the western Pacific warm pool would shift eastward and the latitudinal
climate asymmetry in the eastern Pacific would be stronger.