Seasonal and interannual variations of surface currents in the southern Taiwan Strait to the west of Taiwan Shoals were investigated by using measurements of high frequency(HF)ground wave radars from January 2006 to April 2009.The results demonstrate that surface currents in the water channel to the west of Taiwan Shoals are composed of a significant,seasonally fluctuating component and a relatively stable northward component.Forced by the East Asia monsoon,the annual variation of the surface longshore current is linearly correlated with the longshore wind.Behind the seasonal signal is a stable northward flow with speeds of O(10 cm/s).The observations also show that surface currents in the area are subject to distinct interannual variation,and the southward surface flow was more profound in winter 2007/2008 than in other winters.Observations from bottom-mounted ADCP also indicated that,in that winter,longshore currents in the west side of the Taiwan Strait are very different from the previous winter.The northward flow appeared much weaker,the currents were southward in most layers,and the interannual differences were observed throughout the water column.Hydrographic observations in the same period suggest that the large-scale southward intrusion of the Zhe-Min coastal water is the direct cause of the interannual difference.The enhancement of the East Asian monsoon during the 2007/2008 La Ni a event is considered as the main reason for the winter current anomalies in the study area.
利用2006年1月～2009年4月间的高频地波雷达观测分析了台湾海峡南部浅滩以西区域表层海流的季节与年际变化特征.结果表明,台湾浅滩西侧水道的表层海流主要由明显的季节波动分量和相对稳定的北向常流两部分组成.受季风的影响,表层顺岸流速的周年变化与风速之间存在明显的线性关系.在季节信号的背后则存在一支大约10 cm/s量级的稳定的北向常流.观测还表明,研究海域表层海流有明显的年际差异,2007/2008年冬季表层南向流明显比其他年份增强.锚系海床基ADCP海流剖面观测亦表明该年冬季台湾海峡西侧顺岸流与2006/2007年冬季不同,北向流明显减弱,各观测水层多为南向流,年际差异贯穿整个水柱.同期的水文观测表明闽浙沿岸水的大规模南侵是造成上述年际差异的直接原因.2007/2008年La Ni a事件导致东亚冬季风增强应是造成研究海域冬季流场异常的主因.
