【作者】 郭敬；

【导师】 陈显尧；

【作者基本信息】 国家海洋局第一海洋研究所 ， 物理海洋学， 2012， 硕士

【摘要】 盐度是南海物理环境的重要组成部分之一。盐度变化对南海的水动力环境有重要影响。当水动力环境改变时，南海的环流会发生相应的改变，从而对中国气候产生影响。因此，研究南海盐度变异的特征与机制，具有重要的意义。本文主要利用经验模分解方法，分析了南海混合层盐度的季节、年际变异与长期趋势。并初步分析了不同时间尺度上影响南海盐度变异的物理过程与机制。通过分析海面净淡水通量、水平平流和垂向混合等因素对南海不同区域盐度季节变化的贡献率，可以发现影响混合层盐度季节变化的主导因素在南海北部和南部存在很大差异。在南海北部，影响混合层盐度季节变化的主要因素是蒸发降水，其次是水平平流；随着逐步南移，蒸发降水对盐度季节变化的影响递减，水平平流的影响逐渐增大，而在南海南部，水平平流的作用超过蒸发降水成为影响盐度的季节变化的最主要因素。垂向混合对冬季海水盐度的上升趋势产生促进作用，而对夏季海水盐度的下降趋势产生阻碍作用，但整体上垂向混合对盐度季节变化的影响远小于蒸发降水和水平平流。利用经验模分解方法，本文分析发现南海混合层盐度、海面净淡水通量和各海峡盐通量的年际变异与ENSO之间存在较强的的相关关系。南海海面净淡水通量对混合层盐度的年际变异起主要作用。其中，厄尔尼诺期间，吕宋海峡的盐通量存在西向输送异常，导致南海北部盐度上升；而民都洛海峡和巴拉巴克海峡的盐通量存在东向输送异常，导致南海中部和南部盐度下降，因此南海混合层盐度呈现出“北强南弱”的空间形态。通过对南海混合层盐度的线性趋势分析，可以发现南海混合层盐度在1979~2008年中呈现下降趋势，下降速率为0.03psu/10年。初步分析结果表明表面淡水通量的长期变化不能完全解释混合层盐度的下降，而混合层底部水交换减弱也是导致混合层盐度下降的原因之一。后者主要由于全球变暖导致南海上层海洋温度上升，上层海洋层结变得相对稳定，从而减弱了与下层海洋的垂向交换。更多还原

【Abstract】 As a key component of the physical environment in the South China Sea (SCS),salinity variation plays a key role in modulating the hydrodynamic environment of theSCS, and will fundamentally influence the circulation and the climate of China.Therefore, it is important for deep understanding of salinity variability in the SCS atdifferent time scales. In this study, we used Empirical Mode Decomposition (EMD)method to analyze EN3salinity data in the SCS. The results show that there arenotable seasonal, interannual variability and long-term trend of salinity in the mixedlayer of SCS. Preliminary analysis and discussion for these variations were carried outin this study.Investigation of contribution of sea surface freshwater flux, advection andvertical mixing to the seasonal salinity variability in different areas shows that, thedominant factor in the northern SCS is evaporation-precipitation, and the secondaryfactor is advection; while in the southern South China Sea, the impact of advection ismore important than the evaporation-precipitation (E-P) in modulating the seasonalsalinity variability. The vertical mixing could facilitate the ascending tendency ofsalinity in wintertime, while block the descending tendency of salinity in summertime.However, its impacts are quite smaller than that of the net fresh water flux andadvection.The relationship between changing rate of salinity in the mixed layer of SCS, seasurface freshwater flux, salinity flux through different straits with the ENSO cycle inthe interannual time scales is studied. The significant correlation was revealedbetween the annual components and ENSO signals after decompose of every time series into their IMFs using EMD. The sea surface freshwater flux was found to be thekey contributor to the interannual variability of salinity, however, its influence to thespatial distribution of salinity annual variation in the mixed layer, with strong signalsin the northern part and weak ones in the southern and middle parts, is still not clear.The spatial distribution of interannual salinity variability is associated with ENSOphenomenon. During El Nino events, the westward anomaly of salinity flux in theLuzon Strait strengthen the salinity rising rate in the northern SCS, while the eastwardanomalies of salinity flux in the Mindoro and Balabac Straits weaken the ascending ofsalinity in the middle and southern SCS.The linear trend analysis of the salinity in the SCS shows the decreasing trendduring last30years from1979to2008, with decreasing rate of0.03psu/10yr. Thesalinity decreasing is very likely due to the weakening of upwelling intensity at thebottom of the mixed layer. During last30years, the warming of sea surfacetemperature (SST) increases the vertical stability of upper mixed layer, which reducesthe vertical mixing and prevent the water with high salinity from entering the mixedlayer. Further quantitative analysis is required to confirm this finding.更多还原