Vertical structure of the tidal currents on the continental shelf of the East China Sea

The available data on tidal currents spanning periods greater than six months for the continental shelf of the East China Sea (26°30.052′N, 122°35.998′E) were analyzed using several methods. Tidal Current Harmonic Analysis results demonstrated that semi-diurnal tides dominated the current movement. The tidal currents of the principal diurnal and semidiurnal rotated clockwise with depth, with the deflection of the major semi-axes to the right in the upper layer and to the left in the lower layer. The vertical structures of two principal semi-diurnal constituents-M2 and S2-were similar, which indicates that the tidal currents are mainly barotropic in this area. The main features of the variation of the four principal tidal constituents with depth demonstrate that the currents in this region are influenced by the upper and lower boundary layers. Therefore, the tidal constituents of the shallow water are similar. Different vertical modes were calculated based on the Empirical Orthogonal Function (EOF) analysis of the Eastern and Northern components of the tidal currents, with a variance contribution for the zero-order model of at least 90%. The variance contribution of the baroclinic model is minimal, which further reveals a strong barotropic character for the tidal currents of this region.     

THE EXTRACTION OF HARMONIC TIDAL CONSTANTS FROM HIGH AND LOW WATERS

With the application of electronic computers, the extraction of harmonic constants from high and low waters becomes an extremely simple process as compared with Doodson's technique. The phenomenon of aliasing is examined by supposing the samples are taken .at intervals of exactly 6 lunar hours. The constituents with frequencies satisfying the relation (σ1+σ2) =2σM2,are inseparable and the coefficient determinant of the normal equations will be singular if the heights only are used. When the values of the first derivatives and the irregularity of the sampling are taken into consideration the condition of the determinant is improved. Large diurnal tides can cause irregularity of sampling and so we are in favour of the separation of the aliased constituents. For tidal current data, if the slack times are available, the results of analysis can be much improved. The results for major constituents derived from the observed high and low waters agree satisfactorily with those from hourly data.     

THE FRONTS OF THE HUANGHAI COLD WATER MASS (HCWM) INDUCED BY TIDAL MIXING

Since Simpson and Hunter proposed in 1974 the idea that shallow water frouts were induced by tidal mixing, many authors have investigated the tide induced shallow water fronts in various areas. It was generally assumed that a critical value of the stratified parameter K =log 10(H/U3) may be used to identify the location of these fronts. Here,H means the depth of sea water. U denotes the characteristie velocity of tidal current, and the critical value of K is generally taken as 1.8-2.0.In this paper. Simpson-Hunter's stratified parameter K was calculated by using quasi-maximum current velocity (which consists of the. six main tidal constituents. i.e. M2,S2, O1. K1, M4, M S4) in the H anghai Sea (Yellow Sea) and in the northern Donghai Sea (East China Sea) as well. Calculated results show that the areas of the Subei (the northern part of Jiangsu) Shoal, the area off the mouth area of the Changjiang(the Yangze) River, along the coast of Shandong Peninsula. and along the western coast of Korea, the tidal mi     

Tide and current observations in the central Chukchi Sea during the summer of 2012

Current data from a moored Acoustic Doppler Current Profiler(ADCP) deployed at 69?30.155′N,169?00.654′W in the central Chukchi Sea during 2012 summertime is analyzed in the present paper.Characteristics of tidal and residual currents are ob-tained with Cosine-Lanczos filter and cross-spectral analyses.The main achievements are as follows:1) Along with the local inertial frequency of 12.8 h,two other peaks at ~12-h and ~10-d dominate the time series of raw velocity;2) The M_2 dominates the 6 resolved tide constituents with significant amplitude variations over depth and the ratios of current speed of this constituent to that of the total tidal current are 54% and 47% for u and v components,respectively.All the resolved tidal constituents rotate clockwise at depth with the exception of MM and O1.The constituents of M_2 and S_2 with the largest major semi-axes are similar in eccentricity and orientation at deeper levels;3) The maximum of residual currents varies in a range of 20–30 cms~(-1) over depth and the current with lower velocities flow more true north with smaller magnitudes compared to the current in surface layer.The ~10 d fluctuation of residual current is found throughout the water column and attributed to the response of current to the local wind forcing,with an approximate 1.4 d lag-time at the surface level and occurring several hours later in the lower layer;4) Mean residual currents flow toward the north with the magnitudes smaller than 7 cms~(-1) in a general agreement with previous studies,which suggests a relatively weaker but stable northward flow indeed exists in the central Chukchi Sea.     

MODELLING THE HYDRODYNAMICS OF THE BOHAI SEA IN CHINA

The effects of tides, wind and river discharges on the flow patterns in Bohai Sea are investigated. The Finite Element Method is used to cast the vertically integrated, long wave equations into a system of nonlinear ordinary equations in time. For simplicity we adopted linear triangular elements which are easily integrated exactly and lead to matrices of relatively small bandwidth. The system of ordinary differential equations is solved using a simple finite difference scheme.Because of the small contribution from three partial tides S2, K1 and O1, we take only the M2 tide into account. In this study the computations show Liaodong Bay in the north to be the locale of both the maximum flood and ebb strengths; tidal currents in Laizhou Bay in the south are of less importance in the tidal circulation of Bohai Sea. The discharges of four major rivers and wind speed of 7.0 m/s blowing from the north are used for examining the change in the M2 tidal current field. The simulations show that the influence of wi     

The Impact of Large-Scale Reclamation on Hydro-Dynamic Environment——A Case Study of Xinghua Bay

A hydro-dynamic model is established on basis of MIKE21 FM to simulate the hydro-dynamic characteristics of Xinghua Bay and investigate the influence of reclamation project on the tidal elevation and tidal currents. Tidal elevation data was obtained at the six tide gauge stations around the Xinghua Bay, and another six current stations were established to observe the tidal current velocity and direction. Validation shows that the model-simulated tidal elevation and tidal currents agree well with observations made at different stations. Predictions are made according to the reclamation project proposed in the regional marine planning of Hanjiang Industrial Park around the port in Putian City. The variations of hydro-dynamic factors, such as tide, current velocity and direction and tidal influx are obtained, and the adverse effect of reclamation on marine environment is discussed. It is shown that the tidal level inside the Xinghua Bay during high tide decreases after the reclamation project is completed. The tidal currents during flooding tide generally decrease in the southeast of the reclamation region, with the maximum decreasing amplitude reaching 0.44 m s^-1. On the other hand, the tidal currents during flooding tide increase around the southeast and southwest corners of the reclamation region. The tidal currents during ebb tide increase around the southeast and southwest corners of the reclamation region, with the maximum increasing amplitude attaining 0.18 m s^-1. The results in this paper can give some guidance for the marine environment management and the effective utilization of land in Putian.     

ON THE VERTICAL STRUCTURE OF TIDAL CURRENTS IN SHALLOWWATER NEAR THE CHANGJIANG RIVER ESTUARY

This research on the vertical structure of tidal current in shallow water near the Changjiang River estuary is based on a great deal of observation data of current obtained recently, and a simple mathematic model. The essential features of the structure are: (1) the maximum velocity decreases with depth, the shallower the water, the lower the velocity; (2) the orientation of maximum velocity continuously deviates from the surface to the bottom to the left at the western side of the mouth bar and to the right at the eastern side; (3) the time of maximum velocity leads steadily with depth; (4) in general, tidal currents rotate clockwise, the nearer the sea-bed, the narrower the ellipse of the tidal current; (5) the ratio W1/W2 varies non-linearly with depth, and is smaller in the middle layer than at the surface and bottom. Bottom friction is the main cause of the vertical structure.     

The Characteristics of Near-surface Velocity During the Upwelling Season on the Northern Portugal Shelf

Observations made on the northern Portugal mid-shelf between May 13 and June 15,2002 were used to characterise the near-surface velocity during one upwelling season. It was found that in the surface mixed layer,the 'tidal current' was diurnal,but the tidal elevation was semi-diurnal. Both the residual current and the major axes of all tidal constituents were nearly perpendicular to the isobaths and the tidal current ellipses rotated clockwise;the major axis of the major tidal ellipse was about 3 cm s-1. The extremely strong diurnal current in the surface layer was probably due to diurnal heating,cooling,and wind mixing that induced diurnal oscillations,including the diurnal oscillation of wind stress. This is a case different from the results measured in the other layers in this area. The near-inertial spectral peaks occurred with periods ranging from 1 047 min to 1 170 min,the longest periods being observed in deeper layers,and the shortest in the surface layer. Weak inertial events appeared during strong upwelling events,while strong inertial events appeared during downwelling or weak subinertial events. The near-inertial currents were out of phase between 5 m and 35 m layers for almost the entire measurement period,but such relationship was very weak during periods of irregular weak wind. Strong persistent southerly wind blew from May 12 to 17 and forced a significant water transport onshore and established a strong barotropic poleward jet with a surface speed exceeding 20 cm s-1. The subinertial current was related to wind variation,especially in the middle layers of 15 m and 35 m,the maximum correlation between alongshore current and alongshore wind was about 0.5 at the 5 m layer and 0.8 at the 35 m layer. The alongshore current reacted more rapidly than the cross-shore current. The strongest correlation was found at a time lag of 20 h in the upper layer and of 30 h in the deeper layer. The wind-driven surface velocity obtained from the PWP model had maximum amplitude of about 7 cm s-1,corresponding to a wind stress at 0.1 Pa,and the horizontal velocity shear due to thermal wind balance had the order of 3 cm s-1. So the local wind and thermal wind would only explain a part of the strong surface velocity variations.     

The observed currents in summer in the Bohai Sea

A harmonic method was used to analyze the tidal currents observed in summer at 11 stations made from 1996 to 2001 in the Bohai Sea, China. Data was compared among different instruments and intervals. Elliptic elements were calculated based on harmonic constants, of which vertical distributions of the maximum speed and rotation direction were discussed for understanding the characteristics of diurnal and semi-diurnal tidal current components. The results indicate that the maximum speed of M2 tidal current component is much larger than that of K1; the rotation direction of M2 tidal current constituent is clockwise in the central part of the Bohai Sea and in the Laizhou Bay, but anticlockwise in the Liaodong Bay and Bohai Bay. For K1 tidal current constituent, it is clockwise in the central Bohai Sea but anti-clockwise in the Laizhou Bay and Liaodong Bay. The tidal currents in most stations in the Bohai Sea were regular semidiurnal except for those in the central Bohai Sea, being irregular semidiurnal.     

基于ERS-2和Envisat测高卫星提取西太平洋潮汐信息

对两颗太阳同步轨道测高卫星ERS-2和Envisat 1995～2010年169个重复周期（共近15 a）的数据进行沿轨正交响应分析，得到中国海及西太平洋地区的海洋潮汐调和常数，并利用交叉点位置上升轨迹与下降轨迹提取的潮汐信息和验潮站数据分析了结果的准确度。结果表明，除S2、K1分潮外，基于ERS-2和Envisat测高卫星能够提取出可靠和分布合理的潮汐调和常数，结合交叉轨迹与邻近地面轨迹将有效改善采样规律和观测样本数量，进一步提高潮汐参数的准确度。     

青岛台站重力固体潮和海潮负荷特征研究

选取青岛台站2012-01~2013-02 gPhone重力仪连续观测资料进行预处理和调和分析，获得其重力潮汐参数，并选取8个全球海潮模型对O1、K1和M2潮波进行海潮负荷改正。结果表明：1）8个主要潮波调和分析的振幅因子标准差均在2.6%之内，与理论潮汐模型值的差异也在3.0%之内；2）利用海潮模型对O1、K1和M2潮波进行改正能有效地降低残差矢量，观测残差负荷改正的有效性大致分布在30%~75%，全球海潮模型对青岛台站主要潮波的海潮负荷改正差别不大。     

Tidal Analysis of High and Low Water Data

1　Introduction　Itisverycommontousetidalconstantsinoceanen gineering .Ingeneral,tidalconstantscanbeobtainedfromtidalharmonicanalysisbasedonthehourlydata .However ,thereisamassofhistoricaltidaldatamere lyonthetimeandmagnitudesofsuccessivehighandlowwaterlevels .Moreover ,sometimeswemayhavetidaltableswhichonly givethepredictedvaluesofhighandlowwatersforsomeports,withoutinforma tionontidalconstants .Inthesetablesthetimeinter valsbetweensuccessivetidalextremaareirregular .Therefore ,mostofthestan…     

Tidal analysis in the venturi-shaped area between Zhenhai and Shenjiamen in the East China Sea

In order to better understand the general tidal features in the venturi-shaped area between Zhenhai and Shenjiamen in the northern coastal region of Zhejiang Province in the East China Sea, the tidal data were obtained from both the three permanent tide stations of Zhenhai, Dinghai and Shenjiamen, and four temporary tide stations of Mamu, Chuanshan, Guoju and Liuheng, along with the current speed being observed at Luotou Waterway. Results from harmonic analysis show that: (1) The area was dominated by shallow water tides with irregular semi-diurnal features, and the smallest tidal range occurred in the area near a crossing line between Zhenhai and Dinghai stations, indicating that a tidal node existed in the southern Hangzhou Bay; (2) Formulae, HS2/HM2 >0.4 and gM2-(gK1+gO1)=270° (where H and g are harmonic constants), could be used as judging criteria for high and low tidal level diurnal inequalities; (3) The duration difference between ebb and flood tides could be roughly assessed by the ratio of HM4 vs. HM2; and the larger the ratio is, the bigger the duration difference is. At the same time, the duration period could be assessed by 2gM2-gM4, the epoch difference between M2 and M4 tidal constituents. If 2gM2-gM4 <180°, then the ebb duration is longer than the flood duration; if 180°< 2gM2-gM4 <360°, the result is reversed; (4) Taking Dinghai station as a center point, the highest tidal levels and the average high tidal levels, as well as the average tidal ranges at all stations became higher and larger both southeastwards and northwestwards, while the lowest tidal levels and the average low tidal levels appeared to be lower both southeastwards and northwestwards; and (5) The tidal patterns were not all in line with the tidal current patterns. As a conclusion, the smallest tidal range occurred in the narrow part of the venturi-shaped area. Along the both sides of the area, the highest tidal level and tidal range became higher and larger, while the lowest tidal level became lower with the increase of the distance from the narrow throat area. This is somehow different from the theory that the tidal level increases gradually when it moves towards the top narrow area of a V-shaped bay or estuary.     

TYPES AND DISTRIBUTION PATTERNS OF MODERN TIDAL CHANNELS ALONG THE HUANGHE RIVER DELTA COAST

INTRODUCTIONTidalchannelsareimportantgeomorphologicunitsalongsiltcoasts.Theyhaveanevidentfunc tionfortidalflatbecausetheyareassociatedwithitsrapidbayheadwarderosionandlateralswing ing.Thetidalchannelsdevelopalongthecoastandplayanimportantroleinseaandlandinterac tion .Manyscientistsresearchedthetidalchannels (Bayliss Smith ,1 978;Shao ,1 988;Zhang ,1 995) .TheScientificandTechnicalCommitteeofShandongProvince (1 991 )investigatedthecoastoftheHuanghe (Yellow)RiverDeltaandresearchedtheti…     

深圳湾潮流动力特征研究

应用短期资料的潮流准调和分析方法,对深圳湾4测站两周日海流观测获得的表、中、底层海流资料进行分析,计算了4测站O_1、K_1、M_2、S_2、M_4、MS_4 6个主要分潮的潮流调和常数,并给出各测站在各层的潮流椭圆要素。计算结果表明:深圳湾主要为不规则半日潮流海区,浅水分潮流在总海流中的影响较大;站位1、2和4主要分潮流的北分量大于东分量,而站位3主要分潮流的北分量小于东分量。观测期间余流的流向主要呈北和东北向;最小余流速度出现在站位3;余流流速表层最大,中层次之,底层最小。整个海区潮流的可能最大流速表层在76～102cm/s之间;中层在80～106cm/s之间;底层在56～88cm/s之间。整个海区潮流表现出往复流的性质。     

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Spatial distribution characteristics of surface tidal currents in the southwest of Taiwan Strait

This study was conducted on the spatial distribution characteristics of surface tidal currents in the southwestern Taiwan Strait based on the quasi-harmonic analysis of current data obtained by two high frequency surface wave radar (HFSWR) systems. The analysis shows that the tidal current pattern in the southwestern Taiwan Strait is primarily semi-diurnal and influenced significantly by shallow water constituents. The spatial distribution of tidal current ellipses of M₂ is probably affected by the interaction between two different systems of tide wave, one from the northern mouth of Taiwan Strait and the other from the Bashi Channel. The directions of the major axes of M₂ tidal current ellipses coincide roughly with the axis of the Taiwan Strait. The spatial distribution of the magnitudes of the probable maximum current velocity (PMCS) shows gradual increase of the velocity from northeast to southwest, which is in accordance with the spatial distribution of the measured maximum current velocity (MMCS). The directions of the residual currents are in accordance with the direction of the prevailing monsoon wind at the Taiwan Strait and the direction of the Taiwan warm current during summer. The bathymetry also shows a significant effect on the spatial distribution characteristics of tidal currents.     

中国台湾地区海洋负荷潮汐对重力、位移、倾斜和应变固体潮观测的影响

利用最新的由卫星测高数据解算获得的Csr4.0全球海潮模型，中国近海海潮资料和标准地球模型负荷格林函数，采用积分格林函数方法研究了台湾地区10个台站的重力，位移，倾斜和应变固体潮观测中的海潮负荷效应。给出了4个主要潮波（O1，K1，M2，S2）的负荷振幅和相位，研究了负荷应变花分布特征，构制了台北站的负荷时变特征，数值结果说明，台湾地区各台站受海潮影响十分明显，因此在实施重力，位移，倾斜和应变固体潮观测中心必须考虑海潮负荷效应。