An intermediate coupled model (ICM) based on an ocean model with three vertical modes and a statistical atmosphere model was used to investigate the relationship between the dominant modes of variability in the ocean and the atmosphere in the Tropical Pacific. Tests on sensitivity to the oceanic vertical structure of the ocean show that the time scale of variability in the sea surface temperature anomaly (SSTA) mainly depends on the relative contribution of the baroclinic modes. The first two atmospheric modes, i.e. the central and 'off-equatorial' modes, play different roles in modulating the impact of oceanic baroclinic modes on SST changes through coupled processes. In the model, the central mode excites the second oceanic mode which drives the observations-like interannual variability in the model. The atmospheric off-equatorial mode, on the other hand, favors the gravest baroclinic mode through the forcing of Rossby waves and consequently shortens the frequency of SSTA variability in the tropical Pacific. This suggests a possible mechanism governing time modulation of the El Ni¿o events characteristics in the tropical Pacific. ¿ 2001 American Geophysical Union