詹伟康，韦 惺，叶海彬，詹海刚

(1. 热带海洋环境国家重点实验室，广东 广州 510301; 2. 中国科学院大学，北京 100049)

珠江河口拉格朗日拟序结构及其在浊度锋识别中的应用

詹伟康1,2，韦 惺1，叶海彬1，詹海刚1

(1. 热带海洋环境国家重点实验室，广东 广州 510301; 2. 中国科学院大学，北京 100049)

基于珠江河口水文实测资料和三维水动力数值模型，利用有限时间李雅普诺夫指数提取分析了流场中的拉格朗日拟序结构(LCSs)，并结合卫星遥感图像探讨珠江河口LCSs时空分布与其浊度锋的关系。结果显示，河口浊度锋与LCSs在时空上存在很好的契合，LCSs所形成的输运通道与壁垒对河口浊度锋的位置、形态及变化过程有显著影响。落潮时，泥沙随蕉门、洪奇门和横门的落潮射流注入伶仃洋，与虎门下泄的冲淡水对峙形成了一条明显的FTLE脊线，制约着浊度锋的形成和分布形态。涨潮时，来自西北三口门的淡水径流受口门外涨潮流的顶托作用，强烈的水平速度与密度梯度在此处形成LCS，阻碍径流挟带悬浮泥沙的输运而产生浊度锋。由于LCSs很好地勾画了不同动力性质的水体边界，因此可以用来对河口浊度锋进行识别、追踪和动力解释。

浊度锋；拉格朗日拟序结构(LCSs)；数值模拟；珠江河口

Abstract: Based on data measured in-situ, we extract and analyze Lagrangian Coherent Structures (LCSs) by calculating Finite Time Lyapunov Exponents of the flow field produced by a three-dimensional hydrodynamic numerical model, to study the relationship between LCSs and turbidity fronts of the Pearl River Estuary (PRE). Results show that the distribution of turbidity fronts are strongly tied to the simulated LCSs, which uncover fluid barriers that separate regions of different dynamics, and thus dominate the distribution and variation of the fronts. During the ebb tide, suspended sediment carried by the fresh water run-offs of Jiaomen, Hongqimen and Hengmen empties into the Lingding Sea through the west shoal. Meanwhile, however, the run-off of Humen from the north is much stronger than that of the other three. A prominent fluid dynamical boundary is therefore generated at the place the two kinds of run-offs meet, consequently shaping turbidity fronts. During the flood tide, significant horizontal velocity gradient and density gradient arise at the place where the freshwater run-offs of the three gates in the northwest Lingding Sea and flood current meet, leading to a remarkable LCS that impends the transport of suspended sediment, and thus a turbidity front. LCSs delineate fluid domains with quite different advective properties well. Therefore, we can locate and identify the variation of the fronts and obtain its generation mechanism by LCSs.

Keywords: turbidity front; lagrangian coherent structures(LCSs); numerical model; Pearl River Estuary

河口锋是指两种或多种具有明显不同水体之间的狭窄过渡带。其间的水平梯度可用水温、盐度、密度、叶绿素a以及悬浮泥沙等特征参数来确定。浊度锋为河口锋面现象类型之一，最初是由Kirby and Parker[1]在研究英国Severn河口的细颗粒泥沙过程中提出。……