北部湾东北部潮锋的观测与分析

近海潮锋的分布与温度、盐度乃至海洋生产力的分布都存在紧密联系。基于北部湾东北部的实测数据,对比分析2016—2017年北部湾东北部海域的温度、盐度、密度等分布,并利用ROMS(Regional Ocean Model System)正压与斜压模式,计算Simpson-Hunter (S-H)参数,阐述了潮锋出现位置及其与温度、盐度和密度的关系。结果表明:北部湾东北部潮锋发生的主要区域位于雷州半岛附近,潮混合区温盐密混合较为均匀。利用ROMS模式计算所得的最大垂直平均流速来计算S-H参数,认为潮锋出现位置位于S-H参数值为2处,与实测结果较为一致,且认为正压模式比斜压模式更能准确模拟潮混合区。另外,分析观测数据发现,温度、盐度、密度锋终年存在。近岸处密度锋主要受盐度锋控制,而潮混合产生的盐度锋又容易被径流掩盖。风力较大时三种锋都易向水深更深处推进,潮混合区终年垂向混合较好。

OBSERVATIONS AND ANALYSIS OF TIDAL FRONT IN NORTHEAST OF BEIBU GULF, SOUTH CHINA SEA

The distribution of coastal tidal fronts is closely related to the distribution of temperature, salinity and even marine productivity. Based on the measurement data of the northeastern Beibu Gulf, South China Sea, we analyzed and compared the temperature and salinity distributions in the gulf in 2016-2017. Using ROMS (Regional Ocean Modeling System) barotropic and baroclinic models, we calculated the Simpson-Hunter (S-H) parameters and determined the mixing areas and relationships among tidal front and temperature, salinity, and density. The results show that tidal front occurred mainly around the Leizhou Peninsula in which temperature, salinity, and density were well mixed and homogenized. With the maximum vertical average speed determined in the ROMS, the tidal fronts could be placed when the S-H parameter was set to 2, which agrees with the observation result. Therefore, we believe that the barotropic model is more accurate to simulate the tidal mixing area than the baroclinic model. The fronts of temperature, salinity, and density are there in a whole year. Nearshore density fronts depend on the salinity, while salinity fronts could be disturbed easily by runoff. In a strong wind condition, fronts of temperature, salinity, and density could be forced to deeper oceanic areas and the tidal mixing area well mixed in all seasons.