基于拉格朗日拟序结构的黑潮区域海流运输结构提取和分析

海流的拉格朗日运动对于研究物质输送有着重要意义，拉格朗日拟序结构(LCSs)作为研究海流结构的新型方法，相比于传统欧拉方法更为客观。本文提出了一种新的计算LCSs束的方法，基于25年的平均速度场，利用变分方法计算得到黑潮区域的气候态LCSs，并通过简化合并的方法得到了气候态LCSs束，该LCSs束能够突出地显示出海流特性和运输模式，其代表的平均拉格朗日环流有很强的约束作用，且具有鲁棒性。最终我们获得了气候态下12个月份的流场结构图，揭示了月周期性拉格朗日环流规律。本文还利用虚拟粒子输运、多年浮标轨迹以及气候态温盐异常3种方法进行了验证，与拉格朗日运输模式相吻合，证明了海流拉格朗日拟序结构的准确性和可靠性。     

基于拉格朗日拟序结构的吕宋海峡表层水交换研究

黑潮通过吕宋海峡入侵南海呈现明显的瞬态特征。以往的研究通常将黑潮在吕宋海峡附近的流态分为几种不同类型。本文基于表层地转流计算得到的有限时间李雅普诺夫指数场（FTLE），展示了拉格朗日视角下的吕宋海峡上层水交换特征。从FTLE场提取的拉格朗日拟序结构（LCSs）很好地识别了吕宋海峡附近的典型流态和旋涡活动。此外，这些LCSs还揭示了吕宋海峡周围复杂的输运路径和流体域，这些特征得到了卫星跟踪浮标轨迹的验证，且从流速场中是无法直接识别的。FTLE场显示，吕宋海峡附近表层水体的输运形态主要可分为四类。其中，黑潮直接向北流动的“跨越”形态和顺时针旋转的“流套”形态的发生频次明显高于直接进入南海的黑潮分支“渗入”形态和南海水流出至太平洋的“外流”形态。本文还进一步分析了黑潮在吕宋海峡处的涡旋脱落事件，突出强调了LCSs在评估涡旋输运方面的重要性。反气旋涡旋的脱落个例表明，这些涡旋主要源自黑潮“流套”，涡旋脱落之前可有效地俘获黑潮水。LCS所指示的输运通道信息有助于预测最终被反气旋涡所挟卷水体在上游的位置。而在气旋涡的形成过程中，LCS的分布特征表明，大部分气旋涡并未与黑潮水的输运路径相连通。因此，气旋涡对从太平洋到南海的上层水交换的贡献较小。     

珠江河口拉格朗日拟序结构及其在浊度锋识别中的应用

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。     

Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional Lagrangian Model

Based on theory of three-dimensional hydrodynamics,an Euler-Lagrangian particle model is established to study the transport and water exchange capability in the Jiaozhou Bay.The three-dimensional hydrodynamic model,driven by tide and wind,is used to study the effects of wetting and drying of eatuarine intertidal flats by the dry-wet grid technology based on the Estuarine,Coastal and Ocean Model (ECOM).The particle model includes the advection and the diffusion processes,of which the advection process is simulated with a certain method,and the diffusion process is simulated with the random walk method.The effect of the intertidal zone,the turbulent diffusion and the timescales of the water exchange are also discussed.The results show that a moving boundary model can simulate the transport process of the particle in the intertidal zone,where the particles are transported for a longer distance than that of the stationary result.Simulations with and without the turbulent random walk show that the effect of turbulent diffusion is very effective at spreading particles throughout the estuary and speeding up the particle movement.The spatial distribution of residence time is given to quantify the water exchange capability that has very important ramifications to water quality.The effect of wind on the water exchange is also examined and the southeasterly wind in summer tends to block the water exchange near the northeast coast,while the northerly wind in winter speeds up the transport process.These results indicate that the Lagrangian particle model is applicable and has a large potential to help understanding the water exchange capability in estuaries,which can also he useful to simulate the transport process of contaminant.     

辽东湾海蜇增殖放流模式的建立和应用

基于中国近海浪-流耦合业务化预报系统（OFS-C）和Lagrangian粒子追踪方法，本文首次建立了辽东湾海蜇增殖放流模型。模型中，海蜇用虚拟的粒子表示，具有昼夜垂直运动（DVM）特性。海蜇运动由海流和次网格参数化引起的随机运动驱动。利用航次调查数据对模型结果进行了验证，模式结果可以很好的模拟放流海蜇分布的主要结构。模型分析了物理过程对辽东湾放流海蜇的输运和分布的影响，结果显示海蜇运动主要受海流和间接的风应力的影响。放流地和捕捞地的连通性分析表明，辽东湾海蜇的主要捕捞地集中于湾顶。另外，连通性矩阵表明，瓦房店放流的部分海蜇不能到达捕捞地，因此，相对于其它放流地来说，瓦房店不是理想的放流地。敏感性实验表明了随机游走的重要性，但是对于游走格式并不敏感。海蜇栖息的深度会影响海蜇最终的分布，若海蜇栖息于海底，则在低层环流的影响下，最终分布于辽东湾中部，部分会流出辽东湾，而不能到达湾顶。     

拉格朗日拟序结构分析渤海湾岸线变化对物质输运的影响

科学评估围填海对海洋中物质输运的影响，对海洋环境保护和管理具有重要的意义。本文采用非结构网格有限体积海洋模型 （FVCOM） 模拟渤海湾 2004 年和 2018 年岸线变化前后水动力场，通过拉格朗日拟序结构的方法，评估岸线变化 对物质输运的影响。结果表明：岸线变化后，物质自近岸向湾内的扩散加强，且物质的输运通道和聚集区发生改变。曹妃甸附近原有清晰输运和聚集区域消失，物质向湾内输运；黄骅港阻碍了西部水体沿岸的南下路径，并在防沙堤顶部形成新的聚集区；渤海湾东南区域的物质输运通道向东延伸，输运能力加强，且聚集面积减小。     

Subtidal Flow Patterns in Western Florida Bay

Recent observations using moored current meters, shipboard ADCP transects, salinity mapping and drifters have been used to study the residual circulation including wind drift in western Florida Bay.Rapid, nearly synoptic surveys of salinity over a large area was an effective tracer-mapping technique, when salinity gradients were sufficiently strong, and provided qualitative information on Lagrangian water motion for the entire study area. The salinity maps indicated a general south-eastward advection, which was only subordinate to tidal mixing in a narrow zone adjacent to the Florida Keys.Drifter data collected simultaneously, allowed quantitative estimates to be added to the transport pattern suggested by salinity maps. The selectively deployed drifters yielded estimates of total drift velocities. In addition, moored current meters and shipboard current profiling were used to determine the distribution of flow across the mouth of the bay facing the Gulf of Mexico and the transport through Long Key Channel, a major connection between the bay and the Atlantic Ocean.Analysis showed that from 64 to over 92% of the drifter trajectory variances could be explained by the combination of a local wind drift, expressed in terms of a wind drift factor multiplied by the surface shear velocity, and an ambient current. For a 1 m high drifter deployed at the surface of the water column, the wind drift factor was found to be approximately 0·125m, making the drift speed roughly equal to 0·45% of wind speed. The mean drifter speeds were linearly proportional to mean transport estimates derived from the current meter observations in Long Key Channel, enhancing confidence in both data sets.The total south-eastward directed residual current varied between 100 and 5000 m day⁻¹and was weaker in summer than in winter, when southward winds associated with periodic passage of cold fronts boost the residual flow. The estimated contribution from local wind drift varied between 500 m day⁻¹in summer to 1000 m day⁻¹in winter. The remaining contribution to the observed Lagrangian residual circulation in western Florida Bay is caused by other forcing, including tidal rectification, remote wind forcing and large-scale current systems (the Gulf Stream and Florida Current systems).     

How reliable are finite-size Lyapunov exponents for the assessment of ocean dynamics?

Much of atmospheric and oceanic transport is associated with coherent structures. Lagrangian methods are emerging as optimal tools for their identification and analysis. An important Lagrangian technique which is starting to be widely used in oceanography is that of finite-size Lyapunov exponents (FSLEs). Despite this growing relevance there are still many open questions concerning the reliability of the FSLEs in order to analyse the ocean dynamics. In particular, it is still unclear how robust they are when confronted with real data. In this paper we analyze the effect on this Lagrangian technique of the two most important effects when facing real data, namely noise and dynamics of unsolved scales. Our results, using as a benchmark data from a primitive numerical model of the Mediterranean Sea, show that even when some dynamics is missed the FSLEs results still give an accurate picture of the oceanic transport properties.     

Numerical study on tidal currents and seawater exchange in the Benoa Bay, Bali, Indonesia

A three-dimensional （3-D） finite volume coastal ocean model （FVCOM） was used for the study of water cir culation and seawater exchange in the Benoa Bay, Bali Island. The M2 tidal component was forced in open boundary and discharge from six rivers was included in the numerical calculation. The M2 tidal elevation produced by the FVCOM has a good agreement with the observation data. The M2 tidal current is also suc cessfully calculated under the ebb tide and flood tide conditions. The non-linear M2 tidal residual current was produced by the coastline geometry, especially surrounding the narrow strait between the Serangan Is- land and the Benoa Peninsula. The tidal residual current also generated two small eddies within the bay and one small eddy in the bay mouth. The salinity distribution influenced by river discharge could be success- fully calculated, where the numerical calculation and the observation results have a good correlation （r2） of 0.75. Finally in order to examine the seawater exchange in the Benoa Bay, the Lagrangian particle tracking method and calculation of residence time are applied. The mechanism of particle transport to the flushing of seawater is depicted clearly by both methods.     

A modified Euler–Lagrange transformation for particle orbits in nonlinear progressive waves

This paper presents a modified Euler–Lagrange transformation method to obtain the third-order trajectory solution in a Lagrangian form for the water particles in nonlinear water waves. We impose the assumption that the Lagrangian wave frequency is a function of wave steepness and an arbitrary vertical position for each water particle. Expanding the unknown function in a small perturbation parameter and using a successive expansion in a Taylor series for the water particle path and the period of a particle motion, the third-order asymptotic expressions for the Lagrangian particle trajectories, the mass transport velocity and the period of particle motion can be derived directly in Lagrangian form. The wave frequency and mean level of the particle motion in Lagrangian form differ from those of the Eulerian. Finally, the third-order asymptotic solution obtained is uniformly valid in contrast with early works containing resonant terms presented by Wiegel [1964. Oceanographical Engineering. Prentice-Hall, New Jersey, pp. 37–40] (Eqs. (B.1) and (B.1), (B.2) in Appendix B) or Chen et al.[2006. Theoretical analysis of surface waves shoaling and breaking on a sloping bottom. Part 2 nonlinear waves. Wave motion, 43, 356–369] based on a straightforward expansion for two-dimensional progressive waves.     

Further study of synoptic variability in Wakasa Bay, Japan

Observations of synoptic variability from CTD and current meter measurements in Wakasa Bay, Japan in summer of 1980 and 1981 are compared with the results of 1979 reported by Yamagata, Umatani, Masunaga and Matsuura (1984). It is suggested that the speed and direction of propagation can basically be explained in terms of shelf wave dynamics.In the 1980 event, a dense (colder and more saline) water advanced eastward along the north coast at about 10 km day⁻¹. The lateral scale of the phenomenon was about 30 to 40 km, in agreement with the Rossby internal radius of deformation. The T-S and current data suggest that the 1980 cold event was dominated by phase propagation. In the 1981 event, a light (warmer and less saline) water area advanced eastward at the speed similar to the 1980 cold event, but the T-S and current data suggest that Lagrangian drift of water particles associated with strong eddy motions was not negligible.     

Interactions of nonlinear gravity waves and uniform current in Lagrangian system

The particle trajectory on a weakly nonlinear progressive surface wave obliquely interacting with a uniform current is studied by using an EulerLagrange transformation. The thirdorder asymptotic solution is a periodic bounded function of Lagrangian labels and time, which imply that the entire solution is uniformlyvalid. The explicit parametric solution highlights the trajectory of a water particle and mass transport associated with a particle displacement can now be obtained directly in Lagrangian form. The angular frequency and Lagrangian mean level of the particle motion in Lagrangian form differ from those of the Eulerian. The variations in the water particle orbits resulting from the oblique interaction with a steady uniform current of different magnitudes are also investigated.     

A finite-element,multi-scale model of the Scheldt tributaries,river, estuary and ROFI

We report on the development and validation of a coupled two- and one-dimensional finite-element model for the Scheldt tributaries, river, estuary and region of fresh water influence (ROFI). The hydrodynamic equations are solved on a single, unstructured, multi-scale mesh stretching from the shelf break to the Scheldt tributaries. The tide is forced on the shelf break and propagates upstream in the riverine network. Upstream boundaries lie on sluices or outside of the region of tidal dominance where daily averaged discharges are imposed. Two-dimensional, depth-averaged shallow water equations are solved by means of the discontinuous Galerkin (DG) method over the marine and estuarine parts of the computational domain. In the rivers, however, one-dimensional equations are dealt with using the DG method with the addition of a technique to cope with confluence points. Model parameters are carefully calibrated, leading to the simulation of wind- and tide-forced flows that are in excellent agreement with available data. The diffusivity in the transport equation is calibrated using time series of salinity at various locations in the estuary. Finally, the Lagrangian residual transport in the estuary and the adjacent coastal zone is investigated. This work is a major step towards an integrated model for studying the dynamics of waterborne contaminants and the water renewal timescales in the Scheldt land-sea continuum.     

Simulation of Pollutant Transport in Marmaris Bay

The circulation pattern and the pollutant transport in the Marmaris Bay are simulated by the developed three-dimensional baroclinic model. The Marmaris Bay is located at the Mediterranean Sea coast of Turkey. Since the sp ring tidal range is typically 20- 30 cm, the dominant forcing for the circulation and water exchange is due to the wind action. In the Marmaris Bay, there is sea outfall discharging directly into the bay. and that threats the bay water quality significantly. The current patterns in the vicinity of the outfall have been observed by tracking drogues which are moved by currents at different water depths. In the simulations of pollutant transport, the coliforms-counts is used as the tracer. The model provides realistic predictions for the circulation and pollutant transport in the Marmaris Bay. The transport model component predictions well agree with the results of a laboratory model study.     

Investigating transport pathways in the ocean

The ocean is a very complex medium with scales of motion that range from thousands of kilometers to the dissipation scales. Transport by ocean currents plays an important role in many practical applications ranging from climatic problems to coastal management and accident mitigation at sea. Understanding transport is challenging because of the chaotic nature of particle motion. In the last decade, new methods have been put forth to improve our understanding of transport. Powerful tools are provided by dynamical system theory, that allow the identification of the barriers to transport and their time variability for a given flow. A shortcoming of this approach, though, is that it is based on the assumption that the velocity field is known with good accuracy, which is not always the case in practical applications. Improving model performance in terms of transport can be addressed using another important methodology that has been recently developed, namely the assimilation of Lagrangian data provided by floating buoys. The two methodologies are technically different but in many ways complementary. In this paper, we review examples of applications of both methodologies performed by the authors in the last few years, considering flows at different scales and in various ocean basins. The results are among the very first examples of applications of the methodologies to the real ocean including testing with Lagrangian in-situ data. The results are discussed in the general framework of the extended fields related to these methodologies, pointing out to open questions and potential for improvements, with an outlook toward future strategies.     

厦门浔江海域污染扩散数值模拟

本文采用ＡＤＩ活动边界潮流数值模拟模拟了厦门浔江海域的潮流，计算的结果与实测数据比较吻合。文中用欧拉污染扩散数值模型计算了从同安、集美、五通口排出的污染物（ＣＯＤ）对浔江海域的影响，同时采用拉格朗日污染扩散数值模型研究在湾口、集美和在北部的湾顶污染物瞬时排放后的运移情况。     

Comparison between Eulerian diagnostics and finite-size Lyapunov exponents computed from altimetry in the Algerian basin

Transport and mixing properties of surface currents can be detected from altimetric data by both Eulerian and Lagrangian diagnostics. In contrast with Eulerian diagnostics, Lagrangian tools like the local Lyapunov exponents have the advantage of exploiting both spatial and temporal variability of the velocity field and are in principle able to unveil subgrid filaments generated by chaotic stirring. However, one may wonder whether this theoretical advantage is of practical interest in real-data, mesoscale and sub-mesoscale analysis, because of the uncertainties and resolution of altimetric products, and the non-passive nature of biogeochemical tracers. Here we compare the ability of standard Eulerian diagnostics and the finite-size Lyapunov exponent in detecting instantaneous and climatological transport and mixing properties in the south-western Mediterranean. By comparing with sea-surface temperature patterns, we find that the two approaches provide similar results for slowly evolving eddies like the first Alboran gyre. However, the Lyapunov exponent is also able to predict the (sub-)mesoscale filamentary processes occurring along the Algerian current and above the Balearic Abyssal Plain. Such filaments are also observed, with some mismatch, in sea-surface temperature patterns. Climatologies of Lyapunov exponents do not show any compact relation with other Eulerian diagnostics, unveiling a different structure even at the basin scale. We conclude that filamentation dynamics can be detected by reprocessing available altimetric data with Lagrangian tools, giving insight into (sub-)mesoscale stirring processes relevant to tracer observations and complementing traditional Eulerian diagnostics.     

Contribution of hydrodynamic conditions during shallow water stages to the sediment balance on a tidal flat: Mont-Saint-Michel Bay, Normandy, France

Field measurements were conducted in Mont-Saint-Michel Bay, a megatidal embayment (spring tidal range of 15 m), in order to monitor, over the course of a tidal cycle, sediment transport variability due to waves and tides on the upper part of a tidal flat characterised by shallow water depths. Sensors used to measure currents, water depth and turbidity were installed just above the bed (0.04 m). Two experiments were conducted under contrasting hydrodynamic conditions. The results highlight wave activity over the tidal flat even though observed wind waves were largely dissipated due to the very shallow water depths. Very high suspended sediment concentrations (up to 6 kg/m³) were recorded in the presence of wave activity at the beginning of the local flood, when significant sediment transport occurred, up to 7 times as much as under conditions of no wave activity. This influence may be attributed to the direct action of waves on bed sediments, to wave-induced liquefaction, and to the erosive action of waves on tidal channel banks. The sediment composition, comprising a clay fraction of 2-5%, may also enhance sediment transport by reducing critical shear stress through the sand lubrication effect. The results also show that antecedent meteorological conditions play an important role in suspended sediment transport on the tidal flat. Total sediment flux directions show a net transport towards the inner part of the bay that contributes to deposition over the adjacent salt marshes, and this tendency also prevails during strong wave conditions. Such sediment transport is characterised by significant variability over the course of the tidal cycle. During fair and moderate weather conditions, 83% and 71% of the total flux was observed, respectively, over only 11% and 28% of the duration of the local tidal cycle and with water depths between 0.04 and 0.3 m. These results suggest that in order to improve our understanding of sediment budgets in this type of coastal environment, it is essential to record data just at the beginning and at the end of tidal submergence close to the bed.     

洋浦经济开发区污水排海总量控制

研究建立洋浦近岸海域岸界自适应网格变动边界的潮流模型及物质输运模型。对开发区提出的多种污水排海方案进行污水质点拉格朗日追踪、污水排海的水质预测及工程投资分析 ,推荐了最佳排污口位置 ,最后计算了污水最大排放量及 8种污染物控制指标排放总量 ,为洋浦开发区的环境管理与保护提供决策依据。