The equatorial Current in the North Pacific(NEC) is an upper layer westward ocean current, which flows to the west boundary of the ocean, east of the Philippines, and bifurcates into the northerly Kuroshio and the main body of the southerly Mindanao current. Thus, NEC is both the south branch of the Subtropical Circulation and the north branch of the Tropical Circulation. The junction of the two branches extends to the west boundary to connect the bifurcation points forming the bifurcation line. The position of the North Pacific Equatorial Current bifurcation line of the surface determines the exchange between and the distribution of subtropical and tropical circulations, thus affecting the local or global climate. A new identification method to track the line and the bifurcation channel was used in this study, focusing on the climatological characteristics of the western boundary of the North Equatorial Current bifurcation line. The long-term average NEC west boundary bifurcation line shifts northwards with depth. In terms of seasonal variation, the average position of the western boundary of the bifurcation line is southernmost in June and northernmost in December, while in terms of interannual variation, from spring to winter in the years when ENSO is developing, the position of the west boundary bifurcation line of NEC is relatively to the north(south) in EI Ni?o(La Ni?a) years as compared to normal years.
利用中国沿海台站潮位和中国近海及赤道太平洋的卫星测高、海表温度、风及气压资料，分析了中国近海海平面变化与 ENSO 的关系。分析结果表明：中国沿海海平面季节变化受 ENSO 影响明显，在厄尔尼诺事件期间，中国沿海海平面 Sa 分潮的振幅明显减小，其中年振幅的历史极小值均出现厄尔尼诺年，不同区域历史极小值出现的年份不同；另外，中国沿海 Sa 分潮的振幅对厄尔尼诺事件的响应与其强弱有关，在强事件中，响应区域和幅度较大，弱事件中，响应区域和幅度偏小。在厄尔尼诺年，中国沿海海平面多低于相邻年份，并且其年际变化存在明显的2～3 a、4～7 a、准9 a、11 a 和准19 a 的周期，其中4～7 a 的周期在冬春季节震荡最显著，其震荡幅度接近2 cm。中国近海海平面与赤道东太平洋区域的海表温度年际变化之间存在反相关关系，其相关系数为-0．42；同时与 Nio4和Nio3．4指数序列也呈现反相关关系。针对典型的1997/1998年尼诺事件发生前后的风场和气压场分析发现，尼诺发生前的冬半年，冬季风偏强，气压梯度加强，中国沿海海平面偏低；到了厄尔尼诺的盛期，出现较强的南风异常，气压梯度反向，季风转向，过渡到了厄尔尼诺事件的衰减期，为拉尼娜事件做准备，此时海平面偏高。
