长江口邻近海域近岸水舌向外海的短期扩展过程分析

A short-term extension process of coastal water tongue adjacent to the Changjiang River Estuary

通过线性回归合成3颗卫星的遥感反射率，得到2006年7月27日-2006年8月8日期间有效数据量较多且时间连续的遥感反射率资料，并据此对长江口邻近海域近岸水舌向外海的扩展过程进行了分析。结果表明：在此期间存在一次明显的扩展过程，水舌的遥感反射率随离岸距离增加而降低，水舌主要沿纬度方向扩展，而在南、北方向摆动范围不大。该扩展过程分为伸展和消退两个阶段，7月27日-8月2日期间，水舌逐天向东伸展，最远处到达124．4。E附近；在向东伸展途中，水舌宽度逐渐变窄但变化幅度较小；水舌内部遥感反射率的不同等值线均向东伸展，但向东伸展的程度不同，水舌边界的伸展速度变化较大（17．6～33．4km／d），平均为每天24．5km。从8月3日起水舌开始消退，至8月8日已完全消失；在消退过程中，水舌的范围缩小，遥感反射率下降，水舌轴线方向基本保持不变。结合相关资料对该过程的生消机理进行初步分析认为，在水舌扩展过程中，潮流的主要作用是阻碍沿岸水沿岸线方向运动，持续而强劲的南风对水舌的产生和伸展起重要作用，而东风则促使水舌消退。

In order to establish a sufficient available data both for the spatial coverage and temporal duration, the reflectance data of three satellites of Aqua, Terra and SeaWiFS from July 27 to August 8, 2006 were merged by linear regression. A coastal water extension process was analyzed with the established data in the area adjacent to the Changjiang River Estuary. The results show that there is an obvious extension process from July 27 to August 8, 2006. During the extension process, the remote sensing reflectance of the coastal water decreases with the increase of distance from shore, the coastal water tongue extends almost in the east- west direction. According to the spatial coverage of reflectance and its concentration, the whole process is further divided into two stages, i. e. , an eastward growing period from July 23 to August 2, and a westward extinction period from August 3 to August 8. During the eastward growing period, the coastal water tongue extends gradually to the east along the latitude of 32.4°N, and reaches the east-most longitude of 124.4°E. On the way to east, the coastal water tongue gradually narrows its shape and decreases its concentration. The moving speed of the tip of coastal water tongue boundary changes from 17.6 km/d to 33.4 kin/d, with an average speed of 24.5 km/d. During the westward extinction period from August 3 to August 8, the coastal water tongue is getting narrow as well as decreasing concentration as a whole, but remains the spatial position unchanged. Based on the preliminary analysis of the mechanism of such process, it is believed that the tidal current would constrain the movement of coastal current along the coastal during the eastward growing period. The southerly wind during the eastward growing period and the easterly wind during the westward extinction period are found most-likely to be the cause of the coastal water extension process.