南海西部夏季冷涡的季节变化特征

Seasonal Variability of Cool-core Eddy in the Western South China Sea

基于美国海军的空间分辨率为0.5°×0.5°月平均的GDEM(Generalized D igital Environmen-talModel)三维温盐资料,采用P-Vector方法,计算了南海西部夏季冷涡及附近海域的三维环流,分析了此冷涡的水平结构和垂向结构及其季节变化规律。结果表明南海西部夏季冷涡所占据的海域为一上升流区,对应的是低温区和气旋式环流,其温度场具有明显的垂向层化结构,冷涡随深度增加而减弱。冷涡中心在上层靠近越南沿岸,在温跃层以下有离岸的趋势。此冷涡具有明显的季节性变化:在5、6月份冷涡开始形成,其范围达到110.75°E,最大切向流速为8 cm/s;在7、8月份冷涡达到强盛,其范围向东扩展至112.50°E,冷涡中心也向东移至(110.50°E,13.25°N),最大切向流速增加为30 cm/s;在9、10月份冷涡开始衰减。

In order to investigate the temporal and spatial features of the cool-core eddy in the Western South China sea, this paper analyzes the GDEM （ Generalized Digital Environmental Model） hydrographic data with resolution 0. 5°×0.5°. The current system in the vicinity of the cool-core eddy is determined by the P-Vector Method from the GDEM data. The results confirm the existence of the cool-core cyclonic eddy, located on the coast of South Vietnam in which upwelling occurs. The cool-core eddy shows the evident vertical layered structure （mixed layer, thermocline, and layer below the thermocline）. The horizontal temperature gradient and the maximum tangential velocity of the cool-core eddy decrease with depth. The eddy center is near the coast of the Vietnam in the upper layer, and spread offshore below thermocline. The cool-core eddy displays prominent seasonal variation： The period of May and June is its developing stage during which it reaches 110.75°E and its maximum tangential velocity is 8cm/s; the period of July and August is its strongest stage during which the eddy extends to 112.50°E and its maximum tangential velocity reaches 30 era/s, and the eddy center moves northeastward to （ 110.50° E, 13.25° N） ; during September and October, the cool-core eddy is weakening.