The Role of the Equatorial Currents on the Evolution of SSTA in the Eastern Pacific during Two Different Kinds of El Niño Events

Abstract

Based on the Simple Ocean Data Assimilation (SODA) from 1970 to 2001, equatorial currents and their association with the warm water propagation mechanism during two patterns of El Nio events are studied. In this study, the middle-pattern of El Nio (ME) and the eastern-pattern of El Nio (EE) events are defined as anomalous warm water originating first to the west and the east of 120°W, respectively. It is pointed out that the westerly and eastward anomalous currents in the western Pacific are stronger during the ME event than the EE event, which is conducive to the eastward migration of warm water from western Pacific by zonal advection of temperature. In contrast, the weaker westerly and the westward anomalous currents east of the dateline would be unfavorable for the eastward migration of warm water during EE events. More importantly, another propagation mechanism of the warm water is attributed to the anomalous convergence of the surface currents, as well as the anomalous divergence of the subsurface currents, which obstruct the upwelling of colder water from the deep ocean. Meanwhile, the anomalous convergence of the surface currents and the anomalous divergence of the subsurface currents maintain eastward migration, which plays an important role in the eastward migration of the warm water during ME events. Although there is anomalous convergence in the upper ocean and anomalous divergence in the subsurface ocean during EE events, they appear quasi-stationary in the western Pacific. The warm water over the eastern Pacific during EE events is caused by the local anomalous convergence of surface currents and the anomalous divergence of subsurface currents.