Distribution of the tropical Pacific surface zonal wind anomaly and its relation with two types of El Niño

El Niño events with an eastern Pacific pattern (EP) and central Pacific pattern (CP) were first separated using rotated empirical orthogonal functions (REOF). Lead/lag regression and rotated singular value decomposition (RSVD) analyses were then carried out to study the relation between the surface zonal wind (SZW) anomalies and sea surface temperature (SST) anomalies in the tropical Pacific. A possible physical process for the CP El Niño was proposed. For the EP El Niño, strong westerly anomalies that spread eastward continuously produce an anomalous ocean zonal convergence zone (ZCZ) centered on about 165°W. This SZW anomaly pattern favors poleward and eastward Sverdrup transport at the equator. For the CP El Niño, westerly anomalies and the ZCZ are mainly confined to the western Pacific, and easterly anomalies blow in the eastern Pacific. This SZW anomaly pattern restrains poleward and eastward Sverdrup transport at the equator; however, there is an eastward Sverdrup transport at about 5°N, which favors the warming of the north-eastern tropical Pacific. It is found that the slowness of eastward propagation of subsurface warm water (partly from the downwelling caused by Ekman convergence and the ZCZ) is due to the slowdown of the undercurrent in the central basin, and vertical advection in the central Pacific may be important in the formation and disappearance of the CP El Niño.