Effects of tidally induced eddies on sporadic Kuroshio-water intrusion (kyucho)

The sudden intrusion of Kuroshio warm water into the Bungo Channel (kyucho) occurs mainly at neap tides during summer, suggesting that tidal mixing is one of the essential factors regulating kyucho. In order to clarify the physical mechanisms responsible for the regulation of kyucho, we carry out non-hydrostatic three-dimensional numerical experiments allowing Kuroshio warm water to intrude into a strong tidal mixing region. It is shown that the Kuroshio warm water can (or cannot) pass through the tidal mixing regions off the east coast of the Bungo Channel during neap (or spring) tides. The analysis of the dynamic balance off the east coast of the Bungo Channel shows that tidal residual currents generated by tidal flow interaction with complicated land configurations off the east coast of the Bungo Channel can also play an important role in regulating kyucho. In order to assess separately the effects of tidal mixing and tidal residual currents on kyucho, we incorporate the parameterized vertical mixing and tidal stresses into the numerical model instead of tidal currents. It is demonstrated that tidal mixing cannot by itself block the northward intrusion of Kuroshio warm water, and that an additional effect induced by tidal residual eddies equivalent to horizontal mixing is needed to regulate kyucho. This strongly suggests that the basin–ocean water exchange processes in areas with complicated land configurations can only be reproduced by taking into account the effects of tidal residual eddies on a 1-km scale in addition to tidal mixing effects evaluated by microstructure measurements.     

基于FVCOM的南海北部海域潮汐潮流数值模拟

基于非结构三角形网格的FVCOM(finite-volume coastal ocean model )数值模型, 对南海北部海域的潮汐、潮流进行了精细化数值模拟研究, 并根据模拟结果详细分析了M2, S2, K1, O1 分潮的潮汐和潮流特征。研究结果表明: 神泉港到甲子港海域表现为正规全日潮性质, 珠江口附近海区潮汐以不正规半日潮为主, 其他海域主要表现为不规则全日潮; 陆架海域和深水海域主要表现为往复流, 陆架坡折区存在较强的旋转流, 陆架坡折区为不规则半日潮流和不规则全日潮流的分界线; 东沙群岛附近海域以不规则全日潮流为主, 旋转方向为顺时针; 整个海域的最大流速分布与等深线基本平行, 东沙群岛附近速度明显变大, 最大值出现在台湾浅滩附近, 最大值超过70 cm/s; 南海潮波系统以巴士海峡传入的大洋潮波为主, 分为三支潮流, 以不同的形式进出南海北部海域; 余流在台湾浅滩附近达到最大, 超过6 cm/s, 自南向北进入台湾海峡, 近岸余流自东向西沿岸流动。本研究在东沙群岛周边的模拟结果与前人基于实测资料的分析吻合较好, 并且由于采用了高精度的三角网格, 本文对东沙群岛周边海域的潮汐潮流结构和性质的刻画和分析是迄今为止较为精细的, 同时本研究还提高了对沿岸验潮站调和常数的模拟精度。     

Bashi channel,Luzon strait: A hydraulic model experiment of the tidal current

Bottom current conditions due to tidal currents in the area of the Bashi Channel, Luzon Strait, are examined using a scaled hydraulic model in a uni-directional flow channel. The geometrical model is scaled in both the similitude of Froude's Number and the similitude of the four-thirds power law of eddy viscosity. The currents obtained from the experiment seem to be consistent in order of magnitude with the estimated currents based on observations made by Offshore Environmental System Ltd. In a quasi-steady tidal phase, formation of a strong core flow is found in the Bashi Channel. It can be explained by a simple theoretical model in which the formation of the strong current is attributed to the submarine topography of the Luzon Strait.     

中国陆架潮流沉积体系和模式

在1991年中法合作渤海潮流沉积研究的基础上,查阅了国内外有关研究成果,分析了中国陆架的水深地形、沉积地貌与潮流动力的关系,认为潮流对中国陆架的海底地貌和沉积的形成发育起了主导作用。当潮流流速大于3节时,潮流的侵蚀作用是主要的,往复潮流多形成冲刷深槽,大大刷深了海峡或水道。当潮流流速1－3节时,潮流的沉积作用是主要的,多形成浅滩,即潮流沙脊和潮流沙席。以M2分潮椭率绝对值0．4为界,大于0．久者意味着潮流旋转性强,多形成潮流沙席;小于0．4者意味着潮流往复性强,多形成潮流沙脊。提出了我国邻近陆架发育了5个现代潮流沉积地貌体系：（1）黄海东部潮流沉积体系,它由西朝鲜湾潮流沙脊和其南部的沙席两者组成;（2）渤海东部潮流沉积体系,它由老铁山水道冲刷槽,辽东浅滩沙脊和渤中浅滩沙席三者组成;（3）长江口外潮流沉积体系,它由江苏滨外潮流沙脊和长江口浅滩潮流沙席组成;（4）台湾滨外潮流沉积体系,它由台湾海峡冲刷槽、台湾浅滩沙脊、澎湖水道冲刷槽和台中浅滩沙席四者组成;（5）琼州海峡潮流沉积体系,它由琼州海峡冲刷槽、东浅滩沙脊和西浅滩沙脊三者组成。此外,在东海陆架上还有冰后期海侵早期形成的残留潮流沉积体系。全新世陆架浅海潮流沉积模式可分海峡一浅     

基于船载ADCP观测对半封闭海湾湾口断面潮流及余流的分析（英文）

基于对罗源湾可门水道的25小时连续走航ADCP观测,本文成功构建了沿走航断面共12个站位的连续海流时间序列,并对这些站位的潮流、余流以及潮通量等进行了分析。结果表明可门水道内的潮流为正规半日潮流,驻波性质明显,涨潮首先出现在水道中下层而退潮则首先发生在水道上层。水道内潮流为往复流,水道南部M2分潮流流速较大,并且其倾角自北向南逐渐增加。此外,水道两端的浅水区域内浅水分潮M4振幅较显著。可门水道内余流呈现出两层结构,20m以浅余流沿东北向流出海湾,并且出流的核心位置偏南,而20m以深的余流沿西南向流入湾内,入流的流核位于偏北的近底层区域。对潮通量的积分计算表明通过可门水道进入罗源湾的潮通量约为4.81×10^8m^3。     

基于船载ADCP观测对罗源湾湾口断面潮流及余流的分析

基于对罗源湾可门水道的25 h连续走航ADCP观测,成功构建了沿走航断面共12个站位的连续海流时间序列,并对这些站位的潮流、余流以及潮通量等进行了分析。结果表明可门水道内的潮流为正规半日潮流,驻波性质明显,涨潮首先出现在水道中下层而退潮则首先发生在水道上层。水道内的潮流为往复流,水道南部M₂分潮流流速较大,并且其倾角自北向南逐渐增加。此外,水道两端的浅水区域内浅水分潮M₄振幅较显著。可门水道内余流呈现出两层结构,20 m以浅余流沿东北向流出海湾,并且出流的核心位置偏南,而20 m以深的余流沿西南向流入湾内,入流的流核位于偏北的近底层区域。对潮通量的积分计算表明通过可门水道进入罗源湾的潮通量约为4.81×108 m3。     

Tidal bedforms in eastern part of the Bohai Sea

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象山港牛鼻山水道潮流场的高频地波雷达观测与分析

作为LORCE计划中构建高频地波雷达观测网的试点,面向象山港牛鼻山水道,在六横岛郭巨山和白马礁各设置了1台OSMAR S50高频地波雷达。在2台雷达合成表面流场有效区域的中间地带,利用Valeport旋桨式海流仪和ADCP定点开展了周日连续观测,以验证高频地波雷达合成表面流场的精度。对比定点流场和高频地波雷达对应数据发现,两者变化相关性较好,高频地波雷达在该点获得的流场有较高精度。借助SCHISM建立的区域模型结果,检验了高频地波雷达数据大面上的可用性。比较发现,观测和模拟值在大的趋势上是一致的：牛鼻山水道为规则半日潮流海域,M2是主要分潮,分潮M2和K1以往复流为主;涨潮时外海海水先通过牛鼻山水道流向象山港内,一段时间后再流向佛渡水道;落潮时象山港内海水率先经牛鼻山水道流出至外海,随后佛渡水道海水再逐渐流入牛鼻山水道。     

潮流准调和分析的软件实现

较之潮汐分析、预报的研究而言,目前关于潮流的计算还相对落后。简要论述潮流准调和分析与预报的基本原理,编程实现了潮流准调和分析、准调和预报以及潮流椭圆绘制,并具体给出了实际算例,用以说明该程序的可用性和正确性。     

黄河三角洲飞雁滩海岸的侵蚀及机理

飞雁滩海域是1964－1976年黄河刁口河流路入海区域。根据地形和断面水深监测资料，阐述了该岸段流路废弃后的岸滩侵蚀特征和地貌变化。研究结果表明，刁口河流路废弃后飞雁滩海岸向海凸出的地形特征，是造成该岸段强烈侵蚀的重要原因。进一步结合波、流动力的对应分析认为，波浪以掀沙为主，潮流以输沙为主，波浪和潮流的联合作用是飞雁滩海岸侵蚀的主要动力机制，其中潮流主要通过余流携沙外榆，造成近岸泥沙亏损。     

A BFG model for calculation of tidal current and diffusion of pollutants in nearshore areas

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象山港水交换数值研究 Ⅱ.模型应用和水交换研究

使用水平二维对流－扩散型水交换模式模拟研究了象山港的水交换,对不同区域的水交换控制机理作了初步探讨,象山港水交换状况与其控制机制的区域性变化很大。牛鼻水道至佛渡水道是一个潮流较强的潮通道;９０％水交换周期为５天左右。象山港狭湾内水交换周期较长,湾顶处９０％水交换的周期约为８０天左右。     

沙埕港湾口断面潮流及余流特征分析

基于对沙埕港湾口断面的连续走航观测资料,成功构建了沿走航断面的10个站点的连续海流序列,并分析了潮流、余流、潮通量等水文要素。分析结果表明,沙埕港湾口水道潮流类型为正规半日潮流,涨潮最先出现在中下层而落潮最先出现在上层,涨(落)潮转流相差约为30min。水道内潮流为往复流,M2和S2分潮流流速较大,倾角基本沿水道主轴方向。沙埕港湾口断面余流呈2层结构,10m以浅基本为东南向余流流出湾口,核心位于湾口断面南侧。10m以深多为西北向流入湾内,入流核心位于湾口断面中部的底层区域。对潮通量的计算表明,通过湾口进入沙埕港的潮通量约为1.63×108m3。     

Tidal and surge modelling using differential quadrature: A case study in the Bristol Channel

The Incremental Differential Quadrature Method (IDQM) was applied to a tidal and surge model of the Bristol Channel, UK. The method is considered as an alternative new numerical technique in the field of marine hydraulics and its performance was examined through this case study. For validation of the simulated results, tide gauge data along the Bristol Channel was used. Another well known 1D model (MIKE11) and a quasi-3D model (POLCOMS) provided more insight into the flow pattern of the estuary and additional validation data. Similar to MIKE11, IDQM is unconditionally stable and so time steps of around 45 min achieved good results for the Bristol Channel, whereas for methods which are restricted to the CFL criterion (e.g. explicit finite differencing schemes), the time step is limited to around 3 min. Since there is no stability constraint in IDQM, the time step must be selected with reference to accuracy rather than stability. The usefulness of IDQM was also demonstrated by using a small number of grid points (11 along the 110 km length of the Bristol Channel) to produce accurate results. Based on the results of this case study, it is concluded that IDQM can be successfully implemented for 1D modelling of tidal elevations and surges in non-prismatic irregular channels.     

Residual and tidal circulation revealed by VHF radar surface current measurements in the southern Channel Isles region (English Channel)

Two very high-frequency radars (VHFRs), operating in the southern Channel Isles region (English Channel) in February–March 2003, provided a continuous 27-day long dataset of surface currents at 2 km resolution over an area extending approximately 20 km offshore. The tidal range in the region of study is one of the highest in the world and the coastal circulation is completely dominated by tides. The radar data resolve two modes which account for 97% of the variability of the surface current velocities, with the major contribution of the first mode. This mode accounts for oscillating tidal currents whereas the second mode represents motions emerging from the interaction of tidal currents with capes and islands (eddy in the vicinity of the Point of Grouin and jet south of Chausey). A fortnightly modulation of the modal amplitudes causes the exceptional (more than 600%) variability of currents which is well captured by the VHFR observations. The radar data revealed that tidal circulation in the region is flood-dominated with a strong asymmetry of current velocity curve. Wind events and fortnightly variability affect the course of tidal cycle by modifying the magnitude and duration of ebb and flood. In addition to expected features of coastal circulation (tidally dominated flow, eddies) and high wind-current coupling, the residual currents revealed a strong cross-shore structure in the mean and a significant variability which has the same order of magnitude.     

闽江感潮河段潮汐-洪水相互作用数值模拟

本文分析了闽江感潮河段洪水、潮汐特征,利用高精度GIS数据建立了基于非结构三角网的高分辨率洪-潮耦合模型,在闽江口重点区域的网格分辨率达到50~100m。选取竹岐断面作为径流边界并基于"2006.6.6"洪水过程设计了3组数值实验,模拟结果表明:相比于只考虑洪水或者潮汐,在耦合洪水和潮汐后,各代表站的模拟值与实测值更为吻合;在30年一遇洪水的作用下,闽江感潮河段各断面的原有潮汐特征都不同程度地被洪水信号所影响,其中,文山里和解放大桥站表现出明显的洪水特征,而峡南、白岩潭和琯头站则表现出洪、潮混合特征;从峡南到琯头对应河段在高潮时段流速减小而低潮时段则流速增大,说明该河段存在很明显的洪-潮相互作用。     

基于余水位精化潮高模型的水位生成研究

研究了基于余水位精化潮高模型的水位生成方法。所提方法首先构建网格潮汐场模型,其次采用余水位提高内插模型精度。通过网格搜索策略实现了水深点所属网格的快速定位及水位生成,探索了该模型在水位改正及预报中的应用。实验表明：所提方法既可应用于水位改正又可用于水位预报,且较现有方法在精度上有所提高。     

象山港内湾潮汐应变对横向流及其余环流垂向空间结构的调控研究

横向流 (垂直于海湾主轴方向的流动) 对横向动量以及物质分布具有重要影响。已往研究表明,潮汐应变对横向流的垂向空间结构具有重要的调控作用。但这种认识仅局限于强层化海区,弱层化条件下潮汐应变对于横向流空间结构的影响仍未可知。为此,本文以象山港为例,基于实测数据阐释了弱层化条件下潮汐应变对横向流及其余环流垂向空间结构的调控作用。结果显示,象山港内湾横向流的垂向空间结构随大小潮呈现出明显的变化规律。大潮时,潮汐应变现象明显,涨潮时较强的垂向混合使得横向流在高潮阶段呈现出一层结构;落潮时垂向混合较弱,横向流在低潮时呈现两层结构。小潮时,潮汐应变受到抑制,垂向混合在涨落潮时均较弱,因此横向流在高低潮阶段均呈现出两层结构。经过潮时均进一步得到的横向余环流呈现出上层向南、下层向北的两层结构。由于潮汐应变的大小潮变化,横向余环流的反转深度反转点自大潮到小潮呈现出上升的趋势。     

Exploring conventional tidal prediction schemes for improved coastal numerical forecast modeling

This study provides a practical guide to the use of classical tidal prediction algorithms in coastal numerical forecasting models such as tide and tide-storm-surge models. Understanding tidal prediction parameter formulas and their limitations is key to successfully modifying and upgrading tidal prediction modules in order to increase the accuracy of perpetual interannual simulations and, in particular, storm-surge modeling studies for tide-dominated coastal environments. The algorithms for the fundamental prediction parameters, the five astronomical variables, used in tidal prediction are collated and tested. Comparisons between their estimation using different parameterizations shows that these methods yield essentially the same results for the period 1900–2099, revealing all are applicable for tidal forecasting simulation. Through experiments using a numerical model and a harmonic prediction program, the effects of nodal modulation correction and its update period on prediction accuracy and sensitivity are examined and discussed using a case study of the tidally-dominated coastal regime off the west coast of Korea. Results indicate that this correction needs updating within <30 days for accurate perpetual interannual tidal and mean sea-level predictions, and storm-surge model predictions requiring centimeter accuracy, for tidally-dominated coastal regimes. Otherwise, unacceptable systematic errors occur.     

Exploring German Bight coastal morphodynamics based on modelled bed shear stress

The prediction of large-scale coastal and estuarine morphodynamics requires a sound understanding of the relevant driving processes and forcing factors. Data- and process-based methods and models suffer from limitations when applied individually to investigate these systems and, therefore, a combined approach is needed. The morphodynamics of coastal environments can be assessed in terms of a mean bed elevation range (BER), which is the difference of the lowest to highest seabed elevation occurring within a defined time interval. In this study of the coastal sector of the German Bight, North Sea, the highly variable distribution of observed BER for the period 1984–2006 is correlated to local bed shear stresses based on hindcast simulations with a well-validated high-resolution (typically 1,000 m in coastal settings) process-based numerical model of the North Sea. A significant correlation of the 95th percentile of bed shear stress and BER was found, explaining between 49 % and 60 % of the observed variance of the BER under realistic forcing conditions. The model then was applied to differentiate the effects of three main hydrodynamic drivers, i.e. tides, wind-induced currents, and waves. Large-scale mapping of these model results quantify previous qualitative suggestions: tides act as main drivers of the East Frisian coast, whereas waves are more relevant for the morphodynamics of the German west coast. Tidal currents are the main driver of the very high morphological activity of the tidal channels of the Ems, Weser and Elbe estuaries, the Jade Bay, and tidal inlets between the islands. This also holds for the backbarrier tidal flats of the North Frisian Wadden Sea. The morphodynamics of the foreshore areas of the barrier island systems are mainly wave-driven; in the deeper areas tides, waves and wind-driven currents have a combined effect. The open tidal flats (outer Ems, Neuwerker Watt, Dithmarschen Bight) are affected by a combination of tides, wind-driven currents and waves. Model performance should be measurably improved by integrating the roles of other key drivers, notably sediment dynamics and salt marsh stabilisation.