中文摘要：

为了弄清北太平洋水入侵南海的状况，利用历史观测温-盐数据等资料对其进行了分析。结果表明：在盐度极大值层北太平洋水通过吕宋海峡的入侵整年发生，并且其入侵有很大的季节变化。冬季东北季风盛行时最强。北太平洋热带水（NPTW）入侵的季节变化与次表层地转流和南海的经向翻转环流结构有密切联系。具有盐度极小值特性的北太平洋中层水（NPIW）也通过吕宋海峡入侵南海,但其季节变化与NPTW完全反位相。冬季，由于在中层水深度北向运动的南海经向翻转环流的阻碍作用，NPIW入侵南海最弱。作者认为，北太平洋水入侵南海的机制可以基本上从南海的地转流及经向翻转环流得到解释。

英文摘要：

The intrusion of North Pacific Water into the South China Sea （SCS） through the Ltizon Strait has a great impact on the SCS circulation and water renewal. Historical in-situ data of temperature and salinity were used to analyze the intrusion. Results demonstrate that the intrusion happens all year-round through the Lüzon Strait in the salinity maximum layer and varies in season significantly, with the maximum in winter when northeastern monsoon prevails. The seasonal variation of the North Pacific Tropical Water （NPTW） has a close relationship with geostrophic current in the subsurface and with the structure of the SCS Meridional Overturning. The North Pacific Intermediate Water （NPIW）, with salinity minimum, also enters the SCS through the Ltizon Strait, but its seasonal variation is completely out of phase with that of the NPTW. The intrusion of the NPIW into the SCS is the weakest in winter due to northward movement of the SCS Meridional Overturning in intermediate depth. The intrusion mechanism of North Pacific Water into the SCS can be inter- preted mostly by the movement of the geostrophic current and Meridional Overturning in the SCS.