台风影响下长江口羽流的响应与淡水输运机制

河口区域冲淡水锋面及物质输运会对台风产生快速而复杂的响应，并产生显著的生态效应及沉积过程，且不同类型的台风会对水动力及物质输运产生不同影响。本文以长江河口为研究区域，利用盐度锋面附近的浮标站点观测数据，发现在登陆型超强台风“利奇马”的影响下，旋转流特征消失，站点全水深出现持续近两天的北向流；而在转向型强台风“巴威”的影响下，出现持续约三天的全水深南向流。应用覆盖长江口及邻近海域的有限体积海洋模型（FVCOM）对两次台风过程进行模拟，实验对比台风过境前后流场、盐度场并且计算淡水通量，发现台风过境时通过破坏夏季典型的向海扩张的表层平流型羽流结构，从而促进盐度垂向混合，导致大量淡水堆积在靠岸一侧，加强了沿岸的淡水输运，进而形成底部捕获型羽流。对于登陆型台风“利奇马”的影响，淡水输运主要沿苏北海岸向北，而在转向型台风“巴威”偏北风的影响下，淡水则显著沿岸向浙闽海域流动。这两种台风过后，表层淡水开始向海扩展，垂向盐度分层再一次呈现，在2～3天内完全恢复为表层平流型羽流结构。

Dynamical response of Changjiang River plume and freshwater transport to typhoon impacts

The plume front and mass transport in estuaries have complex dynamical response under the impacts of typhoon events, which have significant influence on ecological effects and sedimentary processes in coastal and offshore regions. However, different types of typhoon events will have great differences on hydrodynamics and affected physical transport. Based on the observational data of buoys near the front of the Changjiang River plume, it is found that under the influence of landing-type Super Typhoon Lekima, the rotational tidal flow at buoy site was re-shaped into a continuous northward flow in whole water column with the duration of nearly two days. Under the influence of the passing-by-type Typhoon Bavi, it also produced a unidirectional flow, but with southward direction for three days. The Finite-Volume Community Ocean Model was applied to investigate the dynamic response of river plume to the typhoon impact. Series of model experiments reveal that the typical surface-advected plume of the Changjiang River in summer can be strongly changed under typhoon attack. With increased vertical mixing, the salinity stratification is decreased, and consequently produces a bottom-advected plume feature. It results in a large amount of freshwater accumulated on the coastal region, and the alongshore freshwater transport can be strengthened. Under the influence of Typhoon Lekima, the freshwater transport mainly flows northward along the Jiangsu coast. However, under Typhoon Bavi with northerly wind, freshwater transport mainly has southward direction along Zhejiang and Fujian coasts. After the typhoon impacts, the plume structure can be quickly restored to the surface-advected plume in two or three days. The strong vertical salinity stratification reinstated in the water column.