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Coupled atmosphere-ocean response to westerly wind events (WWEs), which sometimes trigger El Ninos, was investigated using a coupled general circulation model to clarify its dependence on the timing and location of WWEs. Twelve sets of 20-member ensembles were made with an idealized single WWE imposed in different months from January to July and at different longitudes from 160 degrees E to 160 degrees W. The initial ocean states are set to be near neutral to El Nino/La Nina so that the lagged response to WWEs can be isolated. The results show that sea surface temperature (SST) in the Nino3.4 region increases largely and persistently favorable for El Nino growth when a WWE is imposed in May, whereas a WWE in March increases SST only in the easternmost Pacific. In both cases, an oceanic Kelvin wave propagates eastward to warm the eastern Pacific. When forced by the WWE in May, a positive Nino3.4 SST anomaly appears in boreal summer according to the seasonal outcrop of the equatorial thermocline, and it can strongly interact with seasonally active tropical rain belt to amplify the SST response further. A favorable combination of timing and location that maximize the impact of WWEs on El Ninos in the subsequent winter is suggested albeit its relevance to nature should severely be tested. Another experiment with initial ocean states in El Nino/La Nina years showed that the WWEs in May are efficient to amplify El Nino similar to the neutral case, but are not efficient to suppress La Nina.