to the study by Yu et al. (2011), the scope of SLP anomalies may extend to the north extra-tropical Pacific.

For every two neighbouring factors among the SLP, wind, current and SST anomalies, the relationships between them are waiting for detailed investigations. In fact, the current between the wind and the SST cannot be treated trivially. On the one hand, different ocean currents have different responses to the wind, while on the other hand, SST variations caused by heat transmission rely not only on the current strength but also on the water temperature. In the present study, we focus our attention on clarifying the relationship between changes of tropical currents and anomalies of SST, where the sensitive current passages for the occurrences of El Niño and La Niña are mainly concerned. As a default, only inter-annual time scales are considered.

In general, there are four prominent zonal surface currents in the tropic Pacific: the North Equatorial Current (NEC), North Equatorial Countercurrent (NECC), South Equatorial Current (SEC), and South Equatorial Countercurrent (SECC) (Reid 1959, Wyrtki 1974). The SEC is divided further into northern and southern branches by the equator (Wang & Wu 2013), which we refer to as NSEC and SSEC, 