海洋环流与波动重点实验室知识库

黄海冷水团环流及锋面上升流是黄海夏季环流系统中重要的组成部分之一，对黄海中的生物、化学过程及物质输运起着极其重要的作用。因此，研究黄海冷水团环流及锋面上升流的季节与天气尺度的变化特征不仅有利于提升对黄海环流结构的认识，具有显著的科学研究价值，更有助于实现对当地渔业资源的合理开发及对生态环境的有效保护。本文基于ROMS模式，对黄海冷水团环流及锋面上升流的分布特征以及季节变化特征做了系统地分析，同时通过敏感性实验，探究了锋面上升流强度的影响因素及其影响机制，得到主要结论如下：

1. 黄海冷水团环流是夏季存在于黄海次表层的气旋式环流，其于春季开始生成，夏季达到成熟，秋季逐渐减弱，冬季完全消失。黄海冷水团环流的流核位于温度锋面及温跃层的交汇区域，温度锋面及温跃层的生消过程对黄海冷水团环流结构及强度的季节变化具有重要的影响。同时，温度锋面处的斜压梯度力也是产生黄海锋面上升流的主要驱动力，并且对锋面上升流的季节变化产生重要影响。黄海的温度锋面冬弱夏强，与之对应的锋面上升流也呈现出明显的季节变化特征。

2. 黄海冷水团环流及锋面上升流的分布及强度与黄海陆架坡度密切相关，陆架坡度越陡处，与之对应的锋面越强，进而造成黄海冷水团环流及锋面上升流的强度越大，流幅越窄；反之亦然。

3. 夏季的经向风速，以及前冬、春季和夏季的大气温度能够对黄海夏季锋面上升流的强度产生显著的影响。其中，夏季的经向风速是影响锋面上升流强度的首要因素，当夏季的经向风速增加时，黄海西岸的上升流强度明显增强，而东岸的上升流强度明显减弱。

影响黄海锋面上升流强度的次要因素是夏季的大气温度，当夏季的大气温度升高时，黄海的锋面上升流显著增强。前冬及春季的大气温度也会对锋面上升流的强度产生一定的影响，当前冬及春季的大气温度升高时，黄海夏季上升流的强度普遍减弱，但减弱幅度较小。通过对大气强迫的影响机制进行分析后发现，大气温度主要通过改变黄海温度锋面处的斜压性进而影响上升流的强度，而夏季的经向风速主要通过Ekman辐合/辐散而对黄海锋面上升流的强度产生影响。

4. 除大气强迫外，大小潮过程也会对黄海上升流产生明显的影响。伴随着大小潮的变化，黄海底层的锋面上升流强度呈现出明显的半月周期的变化特征，然而，黄海各区域锋面上升流的强度对大小潮的响应存在明显的不同，在大潮期间，山东半岛沿岸及朝鲜半岛沿岸的上升流明显增强，而朝鲜湾及苏北浅滩处的上升流强度明显减弱，小潮时则完全相反。进一步的研究发现，大小潮时潮致余流的异常是引起大小潮期间黄海锋面上升流强度差异的主要原因。

5. 台风过境能够对黄海的温度及环流结构产生显著的影响，当台风过境时，黄海近岸的底层温度迅速升高，推动温度锋面向黄海内区移动。同时，台风过境时的气旋式风场会加剧黄海上层的气旋式环流，导致黄海冷水团环流的流幅及流量迅速增加。此外，台风过境能够显著减弱黄海的上升流运动，甚至在苏北浅滩、山东半岛及朝鲜半岛沿岸产生明显的下降流。台风对黄海冷水团及其环流和上升流影响的持续时间约为2~3天。

The Yellow Sea Cold Water Mass Circulation (YSCWMC) and frontal upwelling are important component of the circulation system in the Yellow Sea (YS), which play an important role in biological and chemical processes in the YS. The fishery resources of the YS is rich in species and large in quantity, which has formed many excellent fishing grounds such as Shidao, Dasha and Lusi fishery, with important ecological and economic benefits. Therefore, the study of seasonal and synoptic scale variation of the YSCWMC and frontal upwelling is not only conducive to improving the understanding of the circulation structure of the YS, but also conducive to realizing the rational development of local fishery resources and effective protection of the ecological environment. Based on the Regional Ocean Modeling System (ROMS), the distribution characteristics, the seasonal variation and the influencing factors of the YSCWMC and frontal upwellings are analyzed. The research results are as follows:

1. The YSCWMC is a cyclonic circulation which exists in the subsurface layer of the YS during warm seasons. The YSCWMC starts to generate in spring, reaches maturity in summer, gradually weakens in autumn and disappears completely in winter. The core of the YSCWMC is located at the intersection of temperature front and thermocline, which also have an important influence on the seasonal changes of the structure and intensity of the YSCWMC. Meanwhile, the baroclinic pressure gradient force at the temperature front is the main driving force of the frontal upwelling in the YS, and has great impacts on the seasonal changes of the frontal upwelling. The temperature fronts in the YS are weak in winter and strong in summer, and the corresponding frontal upwelling also shows obvious seasonal variations.

2. The distribution and intensity of the YSCWMC and frontal upwelling are closely related to the shelf slope of the YS, the steeper the shelf slope, the stronger the corresponding temperature front, which in turn causes the intensity of the YSCWMC and upwelling to be greater and the flow width to be narrower; and vice versa.

3. The air forcings, such as the meridional wind speed in summer and the air temperature in the previous winter, spring and summer can significantly influence the strength of frontal upwellings. The meridional wind speed in summer is the primary factor affecting the strength of frontal upwelling, when the southerly wind speed increases in summer, he upwelling intensifies in the western YS and weakens in the eastern YS.

The secondary factor affecting the strength of frontal upwelling in the YS is the air temperature in summer, when the air temperature in summer increases, the frontal upwelling in the Yellow Sea generally strengthens. Meanwhile, the air temperature in the preceding winter and spring can also affect the strength of frontal upwelling, when the air temperature increases in the preceding winter and spring, the strength of the upwelling in summer generally decreases, but the change magnitude is small. The mechanism analysis shows that the air temperature mainly affects the strength of the upwelling by changing the baroclinic pressure of the temperature front, while the meridional wind speed in summer mainly affects the strength of the frontal upwelling in the YS by Ekman pumping.

4. In addition to air forcings, the spring and neap tidal processes also have a significant influence on frontal upwellings in the YS. The upwelling in different regions of the YS shows different responds to spring and neap tides. During the spring tide, upwellings along the coast of Shandong Peninsula and the western coast of Korean Peninsula are significantly enhanced; however, the upwelling in the Korean Bay and Subei Bank is obviously weakened. The opposite is true during neap tides. The mechanism analysis shows that the anomaly of the tidal residual currents are the main reason for the difference in the strength of upwellings during spring and neap tides.

5. The typhoon also has obvious effects on the YSCWMC and upwellings in the YS. The cyclonic wind field during the typhoon will intensify the cyclonic circulation in the upper YS, and lead to a strengthened YSCWMC. In addition, typhoons can significantly weaken the upwelling in the bottom of the YS, and even produce significant downwelling along the coast of the YS.