长江口湍流剖面的观测与分析

小尺度湍流过程对河口物质输运与能量交换至关重要。受传统观测方法的限制, 河口浅水区域的剖面观测资料至今较为匮乏, 进而限制了湍流过程的研究。为此, 采用新型5波束声学多普勒流速剖面仪(Nortek Signature 1 000 kHz AD2CP)在长江口开展湍流剖面观测, 获取高频、低噪的高质量湍流剖面数据, 并与声学多普勒点式流速仪(acoustic doppler velocimeters, ADV)同步观测的数据进行对比。结果表明, 通过AD2CP与ADV获得的近底部边界层摩阻流速u_*、拖曳系数C_d、雷诺应力S_R等特征参数基本一致, 底摩擦与波浪能量为河口区域湍动能的主要输入源。湍流垂向结构存在显著的非局地平衡, 即温盐等斜压作用引起的浮力通量、对流项以及强波浪作用影响的脉动压力做功、黏性输运等因素可能为长江口湍流非局地平衡的主因。     

南海北部上层海洋变化的定点观测分析

对南海季风试验(CSMEX)加密观测期(IOP)“实验3”号船在南海北部获得的CTD温盐和声学多普勒流速剖面仪(ADCP)海流等观测资料进行分析,给出东沙群岛西南部大陆坡附近IOP两个阶段定点观测的海洋分量部分结果,通过分析海水的动力、热力学结构,描述夏季风暴发、维持期间该测站上层海洋的变化,讨论近表面水的温度、盐度和海流对海面风场的响应.     

台湾海峡夏季与冬季的水体及热盐通量观测

利用在台湾海峡附近的下放式声学多普勒流速剖面仪(Lowered Acoustic Doppler Current Profiler,LADCP)观测资料和温盐观测资料,通过对连续站的两个季节观测进行正压和斜压潮流分析从而去除潮流得到准定常流,并在此基础上计算了南海和东海之间通过台湾海峡输运的水体及热盐通量。结果表明:台湾海峡大部分海域是半日潮海区(正规半日潮及不正规半日潮海区),半日潮主要分量为太阴半日分潮M2;台湾海峡的水体输运及热盐通量呈现明显的季节变化:夏季台湾海峡内表现为一支东北流向的海流,即台湾海峡暖流,存在3.3 Sv(1Sv=106 m3/s)的东北向水体输运,冬季东北季风较强,西南方向的海流加强,混合层可达到底部,存在1.8 Sv的东北向水体输运。与此对应的热盐通量分别为:夏季热通量为0.34×1015 W,盐通量为118.6×109 g/s;冬季热通量为0.14×1015 W,盐通量为72.9×109 g/s。该结果对台湾海峡通量的研究给出了一个直接观测的准确值,并为相关的数值研究提供了参考。     

现场多功能定点观测系统

现场多功能定点观测系统是为潮汐河口及沿海地区进行水文测验而研制的。它由传感器组件、压力仓、电子电路、数据采集和处理装置等组成。传感器组件有流速、流向、温度、压力、电导率和含沙量等传感器，能测量流速等６种水文参数。该系统的使用既可长期定点锚泊测量，也可短期随船测量。长期锚泊测量能适应恶劣环境。     

山东半岛北部海洋动力环境的高频地波雷达观测

利用两台高频地波雷达(ground wave radar,WERA)站对山东半岛北部雷达覆盖海区的浪、流场进行了观测,并且利用海洋-大气-波浪耦合沉积输运模型(coupled-ocean-atmosphere-wave-sediment transport modeling system,COAWST)对该区域的一个强风暴过程进行了数值模拟,对雷达观测数据、现场声学多普勒流速剖面仪(acoustic Doppler current profilers,ADCP)调查数据和数值模拟结果进行比对分析发现,模型模拟的水位变化与ADCP测量结果一致,WERA所观测到的有效波高和ADCP结果比较吻合,模型模拟的ADCP站位的流速相位、大小与雷达观测结果比较接近,与ADCP的结果有一定偏差。雷达观测的海区流场结果与模型反映趋势基本一致,但是在近岸方向上变化较大,其原因可能与ADCP的投放位置、模型的分辨率设置等因素有关。高频地波雷达系统是海岸带动力环境观测的一个有效工具,在实际应用中有着广泛的前景。     

基于新型高频声学多普勒流速剖面仪的河口近底部边界层观测初探

河口物质输运、能量交换与底边界层内的水动力过程密切相关,底边界层参数(如切应力、拖曳系数)的确定至关重要。挪威Nortek公司生产的新型声学多普勒流速剖面仪AD2CP相比传统ADCP具有高频、低噪的优点,可用于高频(16Hz)流速剖面观测,而被广泛应用于底边界层观测的ADV只能测量单点高频流速。本文采用AD2CP在长江口南槽最大浑浊带区域进行座底式观测,并与同步近底部三脚架上ADV的观测结果进行对比。结果表明,使用AD2CP测得的近底部平均流速与ADV的测量结果吻合良好;使用惯性耗散法计算了底切应力,基于ADV的单点高频流速数据计算结果为2.16×10~(-2)～5.69×10~(-1)N/m~2,基于AD2CP的结果为2.09×10~(-2)～4.26×10~(-1)N/m~2,二者范围大致相当。在此基础上,基于AD2CP数据计算出摩阻流速为4.55×10~(-3)～2.06×10~(-2)m/s、底拖曳系数范围为1.84×10~(-4)～2.49×10~(-3),与ADV的计算结果基本一致。此外,由于AD2CP可以获得高频的流速剖面数据,优于单点ADV,具备观测近底部边界层参数和边界层内湍流剖面的潜力。     

声学多普勒流速剖面仪原理及其在长江中下游的应用

介绍了声学多普勒流速剖面仪(ADP)的原理及2002年5-6月在长江中下游的应用。测量采用走航方式,获得了重庆至江阴水域和徐六泾段流速剖面大范围观测资料,对测量结果和数据处理方法做了探讨,给在复杂地形的水文条件下使用ADP技术提供了应用前景。     

长江口悬沙动力特征与输运模式

本项研究用ADCP在长江河口进行高频、高分辨率三维流速和声学浊度的定点观测,通过对定点站位潮周期内的悬沙浓度、流速和盐度的分析,计算悬沙输运率;悬沙输运机制分析表明平流作用、斯托克斯漂移效应在悬沙输运中占据主导地位.此外,从河口内向河口外,潮周期内的水动力特征与悬沙净输运具有明显的地域性差异,主要表现在悬沙输送的贡献因子、盐度的垂向混合和分布特征、垂向流速等方面.在拦门沙下游和口外地区,悬沙均向西、北方向输送,而拦门沙上游则向东、南方向输送.这种悬沙输运格局,对于长江口拦门沙及附近最大浑浊带的形成有着重要的作用.     

自由投放式声学多普勒海流剖面观测及数据处理

自由投放式声学多普勒海流剖面（FADCP）观测以“自由落体”方式进行采样,其不依赖于测船钢缆牵引即可对全深度海流进行观测,观测稳定性较下放式声学多普勒海流剖面（LADCP）大幅提升,有效减少了观测值之中的不规则运动。2021年4月与9月在南海西沙海域开展的FADCP观测实验获得了两个断面包含16个站的海流及CTD资料。基于静置期间的真实底流观测,各站全深度的海流剖面采用剪切法获得,潜标附近站位剖面与潜标观测剖面相比,平均流速偏差为3 cm/s。观测断面捕捉到了西沙海域两个时期的气旋涡,其垂直结构比HYCOM模拟更精细,表层流与绝对地转流契合。研究表明,FADCP对测船要求低、数据质量高,其后处理简便且结果良好,但无法对特定水层实施补充观测。     

船用多普勒海流计的测流原理和资料处理

多普勒海流计是根据声学多普勒效应的原理制成的测流仪。它用声波换能器取代了传统的以机械转动为基础的传感器。其量程宽,既可测弱流,又能测强流,测量呈线性,一般情况下精确度较高。多普勒海流计的种类型号很多,有的可安在平台或海底,进行定点测流,有的可装在调查船上,作锚锭浮泊或走航测流。因为它能够测量水体垂直剖面上的各层流速,因此又称它为剖面海流计我国已自行设计出 SLY1-1型声学多普勒海流计,其流向流速测量方法及仪器主要技术指标可参看文献[4]和[5]。多普勒海流计在我     

ADCP measurements of suspended sediment flux at the entrance to Jiaozhou Bay, western Yellow Sea

The purpose of the present contribution is to explore the technique to use Acoustic Doppler Current Pro- filers （ADCPs） for suspended sediment flux measurements, which may be applied to coastal embayment environments such as estuaries and tidal inlets for sediment exchange and budget studies. Based on tidal cycle measurements from the entrance of ]iaozhou Bay, Shandong Peninsula, eastern China, statistical rela- tionships between the suspended sediment concentration （SSC） and ADCP echo intensity output are estab- lished. Echo intensity data obtained during an ADCP survey along two cross-sections during a spring tidal phase were transformed into SSC data. The ADCP current velocity and SSC data were then used to calculate the flux of fine-grained sediment. The results show that net sediment transport at the entrance is directed towards the open sea, with an order of magnitude of 103 t per spring tidal cycle; hence, although Jiaozhou Bay is a low SSC environment, the tidally induced suspended sediment transport can be intense.     

Distributions of Water Masses and Currents in Tachibana Bay, West of Ari-ake Sound, Kyushu, Japan

We have investigated the water mass distribution and circulation in Tachibana Bay, which is located in the junction area between Ari-ake Sound and Amakusa-Nada in western Kyushu, Japan. This was done to clarify the mechanism by which ghost shrimp larvae, originating from a sandflat of Amakusa-Shimoshima Island, are transported. Temperature and salinity data repeatedly obtained over the area of Tachibana Bay show that relatively low salinity water lies over northern part of the bay, while high salinity water lies over southern part of the bay. The location of the low salinity water margin tends to depend on the amount of rainfall several days before the observation. A large amount of rainfall makes a clear boundary between low and high salinity waters. Current velocity data indicate an eastward mean flow just north of Tomioka, northern tip of Amakusa-Shimoshima Island, and a clockwise mean flow approaching the Tomioka Bay sandflat, which should be suitable for the on-shore transport of the ghost shrimp postlarvae. Current measurements with shipboard ADCP just west of Hayasaki Strait, at the entrance of Ari-ake Sound, show that a westward tidal residual current tends to incline to the north, with evidence of a density current in the northern part of the western Hayasaki Strait.     

ADCP application for long-term monitoring of coastal water

Three kind of application of ADCP is reported for long-term monitoring in coastal sea. (1)The routine monitoring of water qualities. The water quality and ADCP echo data (600 kHz) observed in the long-term are analgzed at MT (Marine Tower) Station of Kansai International Airport in the Osaka Bay, Japan. The correlation between the turbidity and echo intensity in the surface layer is not good because air bubbles generated by breaking wave are not detected by the turbidity meter, but detected well by ADCP. When estimating the turbidity consists ofplankrton population from echo intensity, the effect of bubbles have to be eliminated. (2) Monitoring stirring up of bottom sediment. The special observation was carried out by using following two ADCP in the Osaka Bay, One ADCP was installed upward on the sea. The other ADCP was hanged downward at the gate type stand about 3 m above from the bottom. At the spring tide, high echo intensities indicating the stirring up of bottom sediment were observed. (3) The monitoring for the boundary condition of water mixing at an estuary. In summer season, the ADCP was set at the mouth of Tanabe Bay in Wakayama Prefecture, Japan. During the observation, water temperature near the bottom showed remarkable falls with interval of about 5～7d. When the bottom temperature fell, the inflow current with low echo intensity water appears at the bottom layer in the ADCP record. It is concluded that when occasional weak northeast wind makes weak coastal upwelling at the mouth of the bay, the combination ofupwelling with internal tidal flow causes remarkable water exchange and dispels the red tide.     

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).     

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.     

Short-term and interannual variability of redox-sensitive chemical parameters in hypoxic/anoxic bottom waters of the Chesapeake Bay

A combination of CTD casts, discrete bottle sampling and in situ voltammetric microelectrode profiling was used to examine changing redox conditions in the water column at a single station south of the Bay Bridge in the upper Chesapeake Bay in late July/early August, 2002–2005. Short-term (2–4 h) fluctuations in the oxic/suboxic/anoxic interface were documented using in situ voltammetric solid-state electrodes. Profiles of dissolved oxygen and sulfide revealed tidally-driven vertical fluctuations of several meters in the depth and thickness of the suboxic zone. Bottom water concentrations of sulfide, Mn²⁺ and Fe²⁺ also varied over the tidal cycle by approximately an order of magnitude. These data indicate that redox species concentrations at this site varied more due to physical processes than biogeochemical processes. Based on analysis of ADCP data, tidal currents at this station were strongly polarized, with the principal axis of tidal currents aligned with the mainstem channel. Together with the chemical data, the ADCP analysis suggests tidal flushing of anoxic bottom waters with suboxic water from north of the site. The present study is thus unique because while most previous studies have focused on processes across relatively stable redox interfaces, our data clearly demonstrate the influence of rapidly changing physical mixing processes on water column redox chemistry.Also noted during the study were interannual differences in maximum bottom water concentrations of sulfide, Mn²⁺ and Fe²⁺. In 2003, for example, heavy spring rains resulted in severe hypoxia/anoxia in June and early July. While reported storm-induced mixing in late July/early August 2003 partially alleviated the low-oxygen conditions, bottom water concentrations of sulfide, Mn²⁺ and Fe²⁺ were still much higher than in the previous year. The latter implies that the response time of the microbial community inhabiting the suboxic/anoxic bottom waters to changing redox conditions is slow compared to the time scale of episodic mixing events. Bottom water concentrations of the redox-sensitive chemical species should thus be useful as a tracer to infer prior hypoxic/anoxic conditions not apparent from ambient oxygen levels at the time of sampling.     

不同方式的纳潮量计算比较——以胶州湾2006年秋季小潮为例

以胶州湾为例,分别通过纳潮量常用算法和走航ADCP直接测流资料计算了2006年秋季小湖期间3个不同潮对段的纳湖量.结果表明,根据纳潮量常用算法得到的纳潮量变化范围大干采用测流资料计算得到的纳潮量范围.在平均意义上,两种算法的平均值分别为6.303×108m3和6.480×108m3,仅相差O.177×108m3.这既验证了通过海流计算纳潮量的精确性,也体现了通过纳潮量算法计算纳潮量在平均意义上的有效性.     

Three-Dimensional Tidal Model and Its Application to Numerical Simulation of Water Quality in Coastal Waters

- The turbulence mechanism plays an important part in the mixing process and momentum transfer of turbulence. A three-dimensional Prandtl mixing length tidal model has been developed to simulate tidal flows and water quality. The eddy viscosities and diffusivities are computed from the Prandtl mixing length model. In order to model the water quality of an estuary or coastal area many interdependent processes need to be simulated. These may be conveniently separated into three main groups: transport and mixing processes, biochemical interaction of water quality variables and the utilization and re-cycling of nutrients by living matter. The model simulates full oxygen and nutrient balance, primary productivity and the transport, reaction mechanism and fate of pollutants over tidal time-scales. The model is applied to numerical simulation of tidal flows and water quality in Dalian Bay. The model has been calibrated against a limited data set of historical water quality observations and in general demonstra     

The role of tidal vortices in material transport around straits

The strong tidal current (tidal jet) in straits generates tidal vortices with a scale of several kilometers. The role of the vortices in material transport was investigated in the Neko Seto Sea, located in the western part of the Seto Inland Sea of Japan. A clockwise vortex with a diameter of about 0.8 km was observed in Nigata Bay (lying between two straits, the Neko Seto Strait and the Meneko Seto Strait). It was concluded that the clockwise vortex was the tidal vortex which was generated by the tidal jet in the Meneko Seto Strait. The vortex moved into the bay with the tide, but tended to stay on the sand bank in the bay. It was confirmed by current measurement with an ADCP and turbidity measurement that the secondary convergent flow was generated in the bottom layer of the vortex. This secondary flow seemed to contribute to the formation of the sand bank. It was suggested that tidal vortices may play an important role in the sediment transport and formation of topography in and around straits.     

胶州湾水交换及湾口潮余流特征的数值研究

利用基于普林斯顿海洋模式建立的胶州湾及临近海域潮汐潮流数值模型,结合胶州湾口走航式声学多普勒海流剖面仪(ADCP)测流资料,研究了胶州湾口的潮(余)流特征,并在潮流模型的基础上耦合建立了水质模块,模拟了胶州湾的水交换过程。考虑M2,S2,K1,O1,M4和MS4六个主要分潮,胶州湾口潮流场的模拟与ADCP观测数据吻合较好。外湾口水道上的潮流非常强,大潮期间观测到201 cm/s的峰值流速。团岛岬角的两侧分别存在一个流向相反的余流涡旋,两涡旋在团岛附近辐合,形成了57 cm/s的离岸强余流。整个胶州湾平均水体存留时间为71 d,平均半交换时间为25 d。胶州湾水体交换能力在空间分布上有很大差异:湾口海域最强,向湾顶逐渐减弱。湾内存在两个弱交换区,分别位于湾的西-西南部和东北端,水体存留时间多超过80 d,湾西局部水域最长达120 d,而半交换时间也大多超过40 d。潮流场的结构、强度,以及与湾口距离的远近是造成湾内水交换能力空间差异的主要原因。