Three-dimensional numerical simulation of tides and tidal currents in the Lianzhou Bay and adjacent areas

A 3-D unstructured-grid, finite-volume coastal ocean model （FVCOM） was used to study the tides and tidal currents in the Lianzhou Bay and adjacent areas. The simulation results were in good agreement with observations. The co-tidal maps of K1 , O1 , and M2 indicated that K1 and O1 were mostly standing waves outside the Lianzhou Bay, while M2 had a largely propagating character. However, all three constituents became propagating waves when entering the Lianzhou Bay, due to the shallow waters. The tidal current ellipses showed the characters of K1 , O1 , and M2 constituents： K1 and O1 were rotating outside the bay, but rectilinear along the water channels inside the bay; M2 was mostly rectilinear over the whole area. The tidal-induced residual current shows the flow was divided into two branches by the Guantouling Peninsula： one turned to flow west; the other was blocked by the southern boundary of the peninsula, creating a clockwise circulation. In Lianzhou Bay, there were two circulation systems, a cyclonic one at the top of the bay and an anti-cyclonic at the mouth.

Three-dimensional numerical simulation for tide and tidal current in the Beibu Gulf

By means of three dimensional POM model,which computes the eddy viscosity coefficient based on two order turbulent closed model,the tide and tidal current in the Beibu Gulf are simulated with fine grid.In the computed region,six islands are considered and the bottom friction coefficients are taken to be various values from the difference of sea region.Acquired tidal harmonic constants are compared with that of 81 tidal observatories.The absolute mean error of K 1 constituent amplitude is 4 6 cm and of the lag is 9°.The absolute mean error of O 1 constituent amplitude is 5 6 cm and of the lag is 7°.The absolute mean error of M 2 constituent amplitude is 6 2 cm and of the lag is 15°.The tide,tidal current,residual water level and tide induced residual current,as well as the vertial distribution of horizontal velocity in this sea region are analysed by the simulated results.

Numerical simulation of construction project environmental impact on the tides and tidal currents in Aojiang offshore of Wenzhou

This paper have collected the measured tides and certain tidal current data in different stages of many projects during past three to five years near the Aojiang River. The harmonic method is used to analyze tide and tidal current data observed at five stations in the sea adjacent to Aojiang River. The results show that the tide is mainly regular and semidiumal in the sea near Aojiang of Wenzhou. The tidal amplitudes of M2 constituent are between 170 cm - 193 cm and the lags are between 260~ - 280~, According to the comparison of analytical results of harmonic constants of these stations in 2007, 2010 and 2011, the maximum change of tidal amplitudes and phase-lag range for the main semidiurnal tides （M2, $2, N2）, the diurnal tide （K1, O1） and the shallow water tide （M4, MS4, M6） are 1.8 cm - 4.4 cm and 3~ - 7~, respectively. After analyzing the tide and tidal current characteristics of Aojiang River, this paper uses an unstructured grid and Finite-Volume Coastal Ocean Model （FVCOM） to test the results of simulation. The simulated results agree well with the measured data. The new shoreline and depth which are produced by the construction projects closed in important major years, and the tide and tidal current field for the new shoreline and depth are constructed, which describe the superimposed influences of construction engineering in Aojiang estuary.

A method to calculate design tide levels on the basis of numerical model of tidal current and its application

In order to determine the design tide levels in the areas without measured tide level data, especially in the areas where it is difficult to measure tidal levels, a calculation method based on a numerical model of tidal current is proposed. The essentials of the method are described, and its application is illustrated with an example. The results of the application show that the design tide levels calculated by the method are close to those determined by long-time measured tide level data, and its calculation precision is high, so it is feasible to use the method to determine the design tide levels in the areas.

Numerical simulation of tides, tidal currents and residual currents in the Yellow River estuary

A 3-D Finite-Volume Coastal Ocean Model was applied in the Bohai Sea,especially near the Yellow River estuary, to simulate the tides, tidal currents, residualcurrents and shear fronts, using unstructured triangular grids. In the case of anaccurate simulation of the tides and tidal currents in the Bohai Sea, this article focuseson the Yellow River mouth. The type of tides is irregular semi-diurnal and the type oftidal currents is the reciprocating flow, mostly parallel to the coastline. The tide inducedeulerian residual currents are a couple of eddies on each side of the river mouth, withthe anticlockwise on the left side and clockwise on the other side, and both of theeddies are enhanced by the Yellow River runoff. Two patterns of shear fronts areidentified at the conversion between the flood and ebb tidal phase. The results suggestthat the shear fronts be generated in the shallow water because the tidal phase of thecoastal area is ahead of the deeper seaward area, then moves seaward and finallydisappears 1-2 hours later.

Application of adjoint assimilation technique in simulating tides and tidal currents of the Bohai Sea, the Yellow Sea and the East China Sea

Considering the interaction of different tidal waves, an adjoint numerical model is developed to simulate M2, S2, K1 and O1 tidal waves in the Bohai Sea, the Yellow Sea and the East China Sea （B-Y-E） simultaneously. Compared with previous researches, by using the adjoint assimilation technique to inverse open boundary conditions and bottom friction coefficients based on altimetric data from TOPEX/Poseidon （T/P） and tidal gauges data, the precision of the numerical simulation is significantly improved. Selecting 14 days of simulated results after the initial wanning run to conduct harmonic analysis, the results can show the characteristics of M2, S2, K1 and O1 tidal wave systems perfectly in B-Y-E. Compared with 9 current stations, the calculated harmonic constants of tidal currents for M2 and K1 are in good agreement with the observed ones.

Numerical simulation of fluctuation and undulation of the thermo-cline under tide (tidal current) action in the Bohai Sea

Besides seasonal variation, instantaneous variation of thermal layer will occur under the effects of tide, tidal current and wind disturbance. In this study the numerical simulation has been first carried out on fluctuation and undulation of thermal layer under influence of tide (simultaneous input of 8 tidal components). The study reveals the geographic distribution of thermal layer fluctuation in the entire study region and temporal and spatial variations of the undulation in tidal period superposing on the fluctuation. Especially, the wave with large amplitude simulated is consistent with observation in the channal and the sea areas with a convex coastline and complex variation of depth, internal relations of tide, tidal current, residual current as well as the factors such as geography, and the fluctuation of thermal layer is induced by residual current due to unsymmetry which occurs as a result of the tidal movement in lower layer influenced by friction and geography, meanwhile, analysis indicates that the fluctuation of thermal layer and tidal oscillation are different undulations in character.

NONLINEAR INTERACTION BETWEEN ASTRONOMICAL TIDES AND STORM SURGES AT WUSONG TIDAL STATION

There are obvious periodic oscillations in the observations of storm surges in the East China Sea . The storm surges are not only controlled by the wind stresses and isolated long wave caused by typhoons but also affected by the interaction between astronomical tides and storm surges . In the present paper we simulate the interaction between tides and storm surges by using a two dimensional numerical model. In our numerical experiments we use the data of the storm surge induced by Typhoon 8114 . The calculations tally with the measured data well. The results indicate that the periodic osculations occurring in the elevations of the surge are mainly caused by the interaction between the tide and the storm surge . The numerical experiments also indicate that the forecasting precision may be notably improved if the nonlinear interaction between tides and storm surges is taken into account.

Tidal currents in the coastal waters east of Hainan Island in winter

Using the 25-h continuing hydrographic observations at three successive stations in February 2012 and the mooring time series of current observations from January to March 2015,the tidal currents and tidal energy fluxes in the coastal waters east of Hainan Island in the northwestern South China Sea were analyzed.The diurnal and semidiurnal(using K_(1) and M_(2) as proxies,respectively)tidal currents and associated isopycnal undulations were derived with harmonic analysis.Results show that the velocities of the diurnal and semidiurnal tides derived from the 25-h observations are comparable to those from the mooring series.The semi-major axes of the tidal ellipses were O(4-7 cm/s)for barotropic tides and O(2-4 cm/s)for baroclinic tides.The directions were in NE-SW at deeper stations to N-S at the shallowest station for the diurnal tide and from NW-SE to NE-SW for the semidiurnal tide.Both the diurnal and semidiurnal isopycnal fl uctuations reached O(5 m),O(8 m),and O(10 m)at the cross-shelf stations(H03,H04,and H05)from 35 m,45 m,to 55 m,respectively,showing insignifi cant vertical variation,and the barotropic signals were predominate.The baroclinic diurnal tide showed fi rst-mode structures at H03-05,as does the semidiurnal tide at H03.The semidiurnal tide at H04 and H05 exhibited higher-mode structures.The time series of both the alongshore and cross-shore components reveal the vertically propagation features of the baroclinic tidal phase and energy.The calculated horizontal energy fl uxes of the diurnal and semidiurnal internal tides decreased from O(0.1 W/m)at H05 to O(0.01 W/m)at H03,implying a propagation and dissipation of energy from off shore to inshore.

Study on the Role of Tidal Currents in the Process of Formation and Development of the Changjiang River Delta

The Changjiang River Delta is a delta of tremendous scale which is formed under the control of tide and tidal currents. The study on the role of tide and tidal currents in the process of formation and development of the Changjiang River Delta can provide a typical example for the ocean-continent interaction process in the east area of our country. The tide and tidal currents in the Bohai Sea, Yellow Sea and East China Sea at the post-glacial transgression maximum are simulated, the sediment transport field in the Paleo-Changjiang River Estuary(PCRE) and its peripheral area at that time is calculated, and the seabed erosion/accretion pattern is obtained according to the divergence of sediment transport rate. The results show that a distinctive wave belly of standing tidal wave existed at the post-glacial transgression maximum and the wave belly lines protruded seawards from the wave belly point in the mouth of the PCRE. Under the wave belly control tidal currents converge to or diverge from the wave

Radial tidal current field in a semi-enclosed rectangular basin: formation and evolution

The radial tidal current field accounts for the formation of the radial sand ridges in the South Yellow Sea. Understanding the formation and evolution of this radial tidal current field is vital to assessing the morphodynamic features in the area. A semi-enclosed rectangular basin with and without a coastal barrier was schematized from the topography of the Bohai Sea and Yellow Sea. The 2D tidal current field in this basin was simulated using the DELFT3D-FLOW model. The concept of tidal wave refraction, which highlights the effect of the sloped or stepped submarine topography on the propagation of the tidal waves, was introduced to explain the formation of the radial tidal current field. Under the effect of tidal wave refraction, co-phase lines of the counterclockwise rotating tidal wave and incident tidal wave are transformed into clockwise and counterclockwise deflections, respectively, leading to the convergence and divergence of the flow field. Regardless of whether a coastal barrier exists or not, the outer radial tidal current field might emerge over certain topography. The responses of the radial tidal current field in this basin to the environmental variations such as coastline changes and bottom erosions were discussed. Results show that local protrusion near the focal point of the radial tidal current field will have limited effects on the location of the tidal system. However, a remarkable shift of the amphidromic point toward the entrance and central axis of this basin and a movement of the focal point of the radial tidal current field toward the entrance could be caused by the significant seaward coastline advance and submarine slope erosion.

The effect of internal tides on the vertical structure of tidal current in the North Huanghai Sea

The tidal current is generally predominant in China's offshore areas. The vertical structure of the observedtidal current is quite complicated with the presence of seasonal thermocline. The observed tidal current may be divided into two parts, an averaged barotropic tide current and a variation tide current. A method for studying the vertical structure of tidal current is developed from the constitution and distribution of energy, and the vertical structure of the observed tide current in the North Huanghai Sea is studied on the basis of the method. The result shows that the reason why the energy of the tidal current is concentrated on the neighbourhood of the thermocline mainly lies in the internal tides i under certain conditions, the fact that the direction of the internal tide current above the thermocline is opposite to the one below the thermocline will be able to cause the rotary directions of the observed tidal current above and below the thermocline to be in opposite. The interaction between the averaged barotropic and the variation tide current plays an important role in forming the vertical structure of the tidal current, and it is mainly the interaction that results in the inho-mogeneous distribution of the tide current energy in the entire water column ; the ratio between the total energies of the internal tide current above the thermocline and the variation tide current in the entire water column is greater than the ratio between the total energies of that below the thermocline and the variation's. In a strong internal tide area such as the neighbourhood of Station L4, at diurnal tide frequency, the above-mentioned corresponding ratios are about 38. 82% and 29. 88%, respectively, and the energy of the internal tide current is about 68. 70%of the energy of the variation tide current; at semidiurnal tide frequency, the above-mentioned corresponding ratios are about 26. 61 % and 19. 73% , respectively, and the total internal tide current energy is about 46. 36% of the total variation tide current energy.

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.

An Assessment of a Nowcast/Forecast System for the Straits of Florida/Florida Current Regime

The Florida Current （FC） largely fills the Straits of Florida and is variable on a broad spectrum of time and space scales. Some portions of the variability are due to variable forcing by tides, winds, heating/cooling, and throughflow; other portions are due to intrinsic instabilities of the FC. To predict, as well as to better understand this complex regime, a nowcast/forecast system （East Florida Shelf Information System （EFSIS）） has been implemented and assessed （http：//efsis. rsmas. miami. edu）. EFSIS is based on an implementation of the Princeton Ocean Model （POM） with mesoscale-admitting resolution on a curvilinear grid. It is forced by a mesoscale numerical weather prediction system （called Eta） run operationally by the National Centers for Environmental Prediction （NCEP）, eight tidal constituents from a global tidal model, and lateral boundary conditions from an operational global ocean prediction model, i.e., the Navy Coastal Ocean Model （NCOM）. Real-time observations of coastal sea level, coastal sea surface temperature, coastal HF radar-derived surface current maps, and FC volume transport are used to verify and validate EFSIS. EFSIS is part of an evolving strategy for real-time predictive coastal ocean modeling methodology, and for fostering the understanding of the variability of the regime on several time and space scales. Here, some of the verification and validation results are provided, as well as diagnostic analyses of dynamical processes. The central point is that an example is provided of a ＇scientific revolution＇ in progress that combines real-time observations and numerical circulation models to yield a credible sequence of synoptic views of coastal ocean circulation for the first time.

基于T_TIDE的江苏沿海潮汐特性分析

文中介绍了基于经典调和分析原理的潮汐预报工具———T_TIDE,利用T_TIDE对实测潮汐资料进行调和分析及预报,研究了江苏沿海吕泗验潮站(LSI站)和连云港验潮站(LYG站)的潮汐特征。结果表明,T_TIDE在江苏沿海潮汐预报中精度较高,可为沿海工程提供任意时段的潮汐预报服务,并为施工窗口期的选择提供理论支撑。M2分潮是LSI站和LYG站的主要分潮,2个站点的潮汐类型都是半日潮。1998—2012年间,LSI站的M2分潮振幅呈上升趋势。在LYG站,1995—2001年间M2分潮的振幅逐渐减小,2001—2012年间M2的振幅逐渐增大。在LSI站和LYG站,迟角都有明显的下降趋势。对2个验潮站的海平面变化进行了研究,结果表明,LSI站和LYG站的海平面分别呈现上升趋势和下降趋势。

Temperature variability caused by internal tides in the coastal waters of east coast of Peninsular Malaysia

The effects of tidal currents(i.e., barotropic and internal tides) are important in the biogeochemistry of a coastal shelf sea. The high-frequency of currents and near-bottom temperatures collected in three consecutive southwest monsoon seasons(May, June, July and August of 2013 until 2015) is presented to reveal the role of the tidal currents to the temperature variability in the coastal shelf sea of the east coast of Peninsular Malaysia(ECPM),south of the South China Sea(SCS). The results of a spectral density and harmonic analysis demonstrate that the near-bottom temperature variability and the tidal currents are influenced by diurnal(O_1 and K_1) and semidiurnal(M_2) tidal currents. The spectral density of residual currents(detided data) at 5, 10 and 16 m depth also shows significant peaks at the diurnal tidal frequency(K_1) and small peaks at the semidiurnal tidal frequency(M_2)indicating the existence of internal tides. The result of the horizontal kinetic energy(HKE) shows a strong intermittent energy of internal tides in the ECPM with the strongest energy is found at 16 m depth during a sporadic cooling event in June and July. A high horizontal cross-shore heat flux(16 m) also indicates strong intrusions of cooler water into the ECPM in June and July. During the short duration of cold pulse water observed in June and July, a cross-wavelet analysis also reveals the strong relationship between the near-bottom temperatures and the internal tidal currents at the diurnal tidal frequency. The intrusion of this cooler water is probably related to the monsoon-induced upwelling in June. It is loosely interpreted that the interaction between the strong barotropic tides and the steep slope in the central basin of the SCS under the stratified condition in southwest monsoon has generated these internal tides. The dissipation of internal tides from the slope area probably has driven the cold-upwelled water into the ECPM coastal shelf sea when the upwelling intensity is the highest in June and July.

Nonlinear tidal waves in a kind of estuary with gradually varying cross-section

-Nonlinear tidal waves in a kind of estuary are studied in the paper using one-dimensional nonlinear hydrody-namic equations with friction. The estuary has exponentially varying width B=B0 e-bx and uniform depth h. The one-dimensional hydrodynamic equations are solved by perturbation method. It was found that our solution included two special cases, Pelisenpeki's solution and Airy's solution. The former can be got by letting b=0 in our solutions, and the latter by setting 6 = 0 and f= 0 (f is linear frictional coefficient). In terms of the second-order solution, the physical mechanism of nonlinear tidal waves in estuaries with gradually varying cross-section is explored. It is shown that, under the assumption of linear friction coefficient, shallow water constituent waves consist of two parts, one is produced by shallow water nonlinear effect outside the estuary, the other is generated by shallow water nonlinear effect inside estuary. In addition, the physical mechanism of the residual tidal current and elevation are not exactly the same as that of the shallow water constituent waves. The former results from the interaction of shallow water nonlinear effect, friction and estuarine deforming effect. The latter depends chiefly on shallow water nonlinear effect. Finally, present nonlinear model is applied to the modelling of the tidal waves in the Hangzhou Bay. Seven of constituent waves (O1,K1, M2, S2, M4, S4, MS4) are taken into account. It will be found that the results modelled by incident progressive waves and their interaction agree rather well with the observations, therefore, it can be concluded that the incident progressive waves in the Hangzhou Bay are dominant.

考虑潮汐和潮流影响的台州湾台风浪数值模拟研究

为了模拟2018年14号台风“摩羯”过境台州湾时的波浪分布情况,利用Holland模式构造台风场,叠加CCMP(Cross Calibrated Multi-Platform)背景风场,由此驱动MIKE 21 SW波浪数学模型,同时也考虑了潮汐和潮流对波浪场的影响。验证结果表明:计算结果能够反映真实的波浪变化,也能够很好地反映台风对当地波浪产生的影响。受台风“摩羯”过境影响,台州湾内外波浪差异明显,整体表现为外大内小。

长江感潮河段潮汐变化特征

基于2011年长江下游大通水文站的逐日流量以及南京、镇江、江阴、天生港、徐六泾、共青圩6个潮位站的逐日高潮、低潮资料,研究海洋潮汐从河口向河段上游传播过程中的潮汐特征变化规律。结果表明,各潮位站25 h滑动平均的潮位变化与流量呈现相同的变化趋势,南京和镇江两个潮位站的水位变化最为明显,江阴、天生港、徐六泾的水位变化相对较小,共青圩潮位站的潮位基本不随径流发生相应的变化趋势;各潮位站之间均有一定的相关性,且相邻两个潮位站之间的水位相关性较高;随着潮位站之间距离的增大,水位的相关性呈现出明显的下降趋势;低水位的传播延迟时间均大于高水位的传播延迟时间;随着站点与入海口距离的增大,涨潮历时出现逐渐减小、落潮历时逐渐增大的变化趋势。

黄河口海洋动力特性与泥沙的输移扩散

本文首先对黄河口潮流、余流、风暴潮等海洋动力进行了分析，在此基础上进一步分析了黄河口泥沙的输移方向与数量，指出黄河口的泥沙在洪枯季节综合的结果是向东北方向扩散，在目前河口海洋动力条件下，有大约４０％的泥沙输往深海．本文还提出了选择最佳河口流路入海方向，充分利用河口海洋动力，提高海流输沙量。