ENSO phase-locking in an ocean-atmosphere coupled model FGCM-1.0

The mean climatology and the basic characteristics of the ENSO cycle simulated by a coupled modelFGCM-1.0 are investigated in this study. Although with some common model biases as in other directly coupledmodels, FGCM-1.0 is capable of producing the interannual variability of the tropical Pacific, such as the ENSOphenomenon. The mechanism of the ENSO events in the coupled model can be explained by ``delayed oscillator"and ``recharge-discharge" hypotheses. Compared to the observations, the simulated ENSO events show largeramplitude with two distinctive types of phase-locking: one with its peak phase-locked to boreal winter and theother to boreal summer. These two types of events have a similar frequency of occurrence, but since the secondtype of event is seldom observed, it may be related to the biases of the coupled model. Analysis show that theheat content anomalies originate from the central south Pacific in the type of events peaking in boreal summer,which can be attributed to a different background climatology from the normal events. The mechanisms of theirevolutions are also discussed.