ENSO CYCLE IN A COUPLED OCEAN-ATMOSPHERE MODEL AND ITS NEGATIVE FEEDBACK MECHANISM

A coupled ocean-atmosphere anomaly model has been developed for simula ting ENSO cycle and its mechanism-study in this paper. After a long mo del run, the coupled model is successful in demonstrating ENSO-like ir regular interannual variability and corresponding horizontal spatial s tructures. Based on the simulated results, the dynamics and the thermo dynamics of the model ENSO cycle have been investigated, and in partic ular the negative feedback mechanisms that act to oppose instability o f air-sea interaction, inducing termination of warm and cold events, h ave been examined. A derailed analysis of the oceanic wave dynamical p roperties and heat budget of the SST changes in. representative cycle suggests that the negative feedback mechanism to check the unstable gr owth of a warm event obviously differs from that of a cold event. The mechanism that induces decay and termination of a cold event is closel y related to the negative, delayed feedback effect produced by the oce anic dynamical wave reflection at the western boundary. However, indep endent of the wave reflection effect: the negative feedback mechanism by which the coupled system returns from a warm event is associated wi th a slowly eastward-propagating coupling mode. Accompanied with the s trong unstable development of the equatorial positive SST anomaly the anomalous upwelling of cold water generated off the equator and the no nlinear anomalous meridional advection generated in the equator west o f instability area jointly restrain the instability and finally plunge the system from a mature warm phase into a weak cold phase. A compari son between the results from the present model and the previous works is also discussed in this paper.