枯水期珠江口冲淡水及盐度锋面的数值模拟分析

发布时间：2018-01-27 00:22

本文关键词： 河流淡水羽状流河口混合水羽状流口门外混合水羽状流三级盐度锋面 FVCOM　出处：《中山大学》2015年硕士论文　论文类型：学位论文

【摘要】：在枯水期,珠江口存在一个自表到底的沿岸分布的羽状流结构,该羽状流与外海高盐水在交界面处形成一个自表到底的羽状流锋面。河口区的羽状流及盐度锋面不仅是河口区重要的生物高生产力区,对河口的沉积过程及底部地形的发育也具有重要的作用。因此研究珠江口内盐度锋面对海洋环境的保护与治理、生物活动及生态过程的研究、河口区地形地貌的发育乃至人类的生活及生产都有重要的意义。目前对珠江口羽状流及盐度锋面的细致特征和时空变化的研究并不多,因此有必要对其开展细致且充分的研究。本文建立了基于FVCOM的珠江河网、河口和陆架海耦合的三维水动力模型。模型中将珠江三角洲河网区、河口区及外海区结合成一个整体区域,无论在水平向还是垂向上,模型网格都具有较高的分辨率。同时模型中还加入了具有高分辨率的WRF模型模拟的经观测值同化后空间和时间变化的风场。这明显改善了模型对羽状流和盐度锋面的模拟结果。模型计算的潮汐、盐度、流场及羽状流结构及其变化均与观测资料验证良好,因此该模型能较好的模拟出珠江口枯水期的水文及水动力特征。在论文中利用模型对珠江口的羽状流冲淡水团及盐度锋面特征作了较为细致和系统的分析。首先将珠江口整体冲淡水团按照其盐度性质、主要驱动力及能量输入的不同,分为从西到到东、从口门内到外的三级水团:河流淡水冲淡水团、河口混合水冲淡水团、口门外混合水冲淡水团。然后计算了模型模拟的珠江口盐度平面场的梯度,发现在三级冲淡水团相互之间及其与外海水的交界面处存在三级盐度锋面结构。并对三级冲淡水团及盐度锋面结构的时空变化特征进行了分析,结果表明珠江口三级冲淡水团及盐度锋面结构随着潮汐过程呈现周期性变化。珠江口羽状流及其盐度锋面结构主要由陆地上的径流、潮汐和风应力驱动,这三种驱动力因其时空变化而对其影响各不相同。为分析径流、潮汐和风应力对珠江口冲淡水及盐度锋面产生的动力机制,研究作了几组不同风场和潮汐条件下的数值实验。分析结果表明:1)珠江口第一级盐度锋面的形成机制较复杂,可能与径流、潮汐、风均相关,但径流对第一级盐度锋面形成产生的作用最大;2)风应力产生向岸的埃克曼输运是第二级盐度锋面形成的主要原因。3)第三级盐度锋面是冲淡水与外海高盐水的交界面,它的形成虽然与潮汐和风无关,但它对风的响应十分敏感,风应力愈强,第三级盐度锋面愈强,且向口门内推移的距离也越远。4)潮汐混合减弱了风对盐度锋面的作用,即潮汐的存在使第二、三级盐度锋面强度减弱。但潮汐作用是落潮时淇澳岛下方的局地羽状流及其锋面结构(属第一级盐度锋面)形成的关键因素。
[Abstract]:In the dry season, the Pearl River Estuary has a plume flow structure which is distributed from the surface to the end of the coast. At the interface between the plume flow and the high brine in the open sea, a plume front is formed from the surface to the bottom. The plume flow and salinity front in the estuary area are not only the important biological high productivity areas in the estuary area. It also plays an important role in the sediment process of estuaries and the development of bottom topography. Therefore, the study on the protection and management of the salt front in the Pearl River estuary to the marine environment, the study of biological activities and ecological processes. The development of topography and geomorphology, as well as the life and production of human beings, are of great significance. At present, there are few studies on the detailed characteristics and temporal and spatial changes of the plume flow and salinity front in the Pearl River Estuary. Therefore, it is necessary to carry out a detailed and full study. In this paper, a three-dimensional hydrodynamic model based on FVCOM for the coupling of Zhujiang River network, estuary and shelf sea is established. In the model, the Pearl River Delta river network is taken into account. The estuary area and the offshore area combine into a whole area, either horizontally or vertically. The model meshes have higher resolution. At the same time, the wind field simulated by WRF model with high resolution has been added to the model. The spatial and temporal variations after assimilation of observed values have been greatly improved. This obviously improves the model's response to plume flow and salt. Simulation results of the degree front. Tide calculated by the model. The salinity, flow field and plume flow structure and their variations are all well verified by the observed data. Therefore, the model can well simulate the hydrological and hydrodynamic characteristics of the Pearl River Estuary during the dry season. Firstly, the model is used to make a detailed and systematic analysis of the characteristics of the plume water mass and salinity front in the Pearl River Estuary. The whole water mass of the Pearl River Estuary is diluted according to its salinity. The main driving forces and energy input are divided into three water masses from west to east, from the inside to outside of the mouth: stream fresh water dilute water mass, estuary mixed water flushing fresh water mass. The mixed water at the entrance of the mouth is used to flush the fresh water mass. Then the gradient of the salinities plane field of the Pearl River Estuary simulated by the model is calculated. It is found that there is a third-order salt front structure between the three grade dilute water masses and the interface between them and the outer sea water, and the temporal and spatial variation characteristics of the three grade diluted water masses and the salt front structures are analyzed. The results show that the third-order diluted water mass and salinity front structure of the Pearl River Estuary change periodically with the tidal process, and the plume flow and its salinity front structure are mainly driven by the runoff, tide and wind stress on the land. These three kinds of driving forces have different influence on them because of their space-time variation. In order to analyze the dynamic mechanism of runoff, tidal and wind stress on the water and salinity front of the Pearl River Estuary. Several numerical experiments under different wind and tidal conditions have been carried out. The results show that the formation mechanism of the first salinity front in the Pearl River Estuary is complex and may be related to runoff, tide and wind. However, runoff has the greatest effect on the formation of the first salinity front. 2) the main reason for the formation of the second-order salinity front is the migration of the wind stress to the shore. 3) the third-order salinity front is the interface between the dilute water and the high brine in the open sea, although its formation is independent of the tide and the wind. However, it is very sensitive to the wind response. The stronger the wind stress, the stronger the third-order salinity front, and the farther the distance from the mouth door. 4) the tidal mixing weakens the effect of the wind on the salinity front. That is, the existence of tide weakens the intensity of the second and tertiary salinity front, but the tidal action is the key factor for the formation of the local plume and its frontal structure (which belongs to the first salinity front) under the lower tide of Qi'ao Island.
【学位授予单位】：中山大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P731

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