A shift of El Niño onset location from eastern Pacific (EP) to western Pacific (WP) occurred around 1970. It was accompanied by a faster mean sea surface temperature (SST) warming in WP and a change of precursory SST and wind anomaly patterns. The eigenvalue analysis of a simple coupled model shows that an SST anomaly (SSTA) in WP may grow under the post-1970 mean condition but cannot under the pre-1970 mean condition. As a result, a warm SSTA appeared in WP accompanying to a preceding La Niña condition in EP after 1970, whereas such a warming was rarely seen before 1970. The preceding SSTA patterns led to distinctive zonal wind responses in EP, favoring El Niño onset in EP prior to 1970. For the post-1970 El Niño onset, an initial warming in WP was induced by anomalous downward solar radiation in association with atmospheric meridional overturning circulation or anomalous horizontal advection associated with thermocline induced eastward geostrophic currents.

1970年前后，厄尔尼诺现象发生地点从东太平洋（EP）转移到西太平洋（WP），伴随着西太平洋平均海面温度（SST）较快变暖以及前兆海表温度和风异常模式的变化。简单耦合模型的特征值分析表明，WP的海温异常（SSTA）在1970年以后的平均条件下可能增长，但在1970年之前的平均条件下不会增长。结果，1970年后，西太平洋地区出现了温暖的海温异常，并伴随着东部地区的拉尼娜现象，而这种变暖现象在1970年之前是很少见的。之前的海温异常模式导致了东部地区独特的纬向风响应，有利于厄尔尼诺现象在东部地区的爆发。 1970年之前的EP。对于1970年后厄尔尼诺现象的爆发，WP的最初变暖是由与大气经向翻转环流相关的异常向下太阳辐射或与温跃层引起的东向地转流相关的异常水平平流引起的。