平直斜坡上破波带内质量输移流对污染物输移影响的数值研究

破波带内外都有质量输移流存在,其对破波带内污染物输移有怎样的影响,需要进一步深入研究。本文基于实验以及考虑质量输移流的对流扩散数学模型研究了平直斜坡上破波带内质量输移流对污染物输移影响。数学模型包括波浪模型、近岸流模型以及对流扩散模型。首先建立了破波带内污染物输移数学模型,其中波浪场基于波能守恒方程来计算,波导流场基于Longuet-Higgins提出的辐射应力模拟,污染物对流扩散方程中考虑了质量输移流的影响,并利用算例验证该数学模型。其次简要介绍了平直斜坡上破波带内污染物输移实验,并分析了污染物输移特性。连续投放污染物会形成污染带,本文分析了两种波况下不同时刻污染带与岸线夹角的变化,以及污染物在垂直岸线和沿岸线方向的输移速度,结果表明对两种波况来说在初始10-40s污染团向岸线方向输移速度分别约为0.05m/s、0.017m/s,之后速度分别减小为0.001m/s、0.011m/s。数值模拟结果与实验结果比较表明：考虑质量输移流的模拟结果与实验更为吻合。因而,通过实验以及数模研究表明破波带内质量输移流对破波带内污染物在垂直岸线方向的输移有重要影响,而对沿岸方向的输移则影响较小。     

A two-dimensional numerical model of tidal motions on the shelf of Guinea

The general statement of a non-linear problem in modelling a barotropic tide for the limited part of a real shelf and the problems related to artificial division of the computation area in the ocean by a liquid boundary are considered. Linear combinations of various types of boundary conditions and analytical expressions are used to describe the tidal wave structure at the liquid boundaries. The results of test computations for basins with the simplest outlines are given. The model is used to reconstruct the spatial distribution of characteristics of theM ₂ tide on the shelf of Guinea. The methods of computation and specification of unambiguously determined model parameters are described. Joint analysis of the modelling results and the field data has been carried out. The tidal map of theM ₂ wave is plotted for the area under investigation.Translated by Mikhail M. Trufanov.     

Reliability of ADCP data detided with a numerical model on the East China Sea shelf

The reliability of a numerical tide model for detiding acoustic Doppler current profiler (ADCP) data is examined on the East China Sea shelf. The process is adopted for the ADCP data obtained on 12–13 May 2003. The ocean model accompanied by the most precise harmonic constants available to public is used to compute external tides. The root mean square difference is less than 10 cm/s between the detided currents and those using the least squares method, and so the detiding process using the numerical model is available to detect the East China Sea shelf circulation faster than this speed.     

潮流、风暴潮耦合模型推算珠江口海域极值流速

分别采用模式气压场及模式台风场计算气压分布及风速分布,采用地形拟合的sigma坐标水动力方程组及紊流方程建立了潮流、风暴潮耦合模型。三维水动力方程组通过分裂算子法与Casulli半隐式差分格式直接求解。在珠江口的极值流速计算中,先进行了南海北部的潮流、风暴潮耦合模拟,模拟水位与实测值符合较好。以六区域模拟结果为边界,采用嵌套网格方法,在珠江口进行了高分辨率的潮流、风暴潮耦合模拟。选用1968～1999年共65个影响工程区域的台风过程,计算出珠江口的海域年极值流速序列,分析了该海域多年一遇的极值流速分布。     

Three-dimensional tidal current numerical model of the Oujiang Estuary

The characteristics of three-dimensional (3-D) tidal current in the Oujiang Estuary are investigated according to in situ observations. The Oujiang Estuary has features of irregular coastline, complex topography, many islands, moveable boundary, and submerged dyke, therefore, a 3-D numerical model on an unstructured triangular grid has been developed. The σ coordinate transformation, the moveable boundary and submerged dyke treatment techniques were employed in the model so it is suitable for the tidal simu...     

A numerical experiment on computations of the Black Sea density fields and current velocities during summer

A near-bottom pressure equation consistent with the original set of difference equations is derived in the framework of a numerical energetically-balanced model. The model is used to simulate numerically three-dimensional density and current velocity fields and in the Black Sea for a specific season. The climatic values of temperature, salinity, and tangential wind stress during summer are applied as the original conditions. Analysis of the hydrophysical fields at the final moment of integrating is performed. The difference between new data and data derived earlier is demonstrated.Translated by V. Puchkin.     

A hybrid forecasting model for depth-averaged current velocities of underwater gliders

In this paper, we propose a hybrid forecasting model to improve the forecasting accuracy for depth-averaged current velocities (DACVs) of underwater gliders. The hybrid model is based on a discrete wavelet transform (DWT), a deep belief network (DBN), and a least squares support vector machine (LSSVM). The original DACV series are first decomposed into several high- and one low-frequency subseries by DWT. Then, DBN is used for high-frequency component forecasting, and the LSSVM model is adopted for low-frequency subseries. The effectiveness of the proposed model is verified by two groups of DACV data from sea trials in the South China Sea. Based on four general error criteria, the forecast performance of the proposed model is demonstrated. The comparison models include some well-recognized single models and some related hybrid models. The performance of the proposed model outperformed those of the other methods indicated above.     

Using a lowered acoustic Doppler current profiler for measuring current velocities in the Black Sea

The results obtained with the use of a lowered acoustic Doppler current profiler (LADCP) are presented. The use of the LADCP from a vessel was the first in the history of the study of the Black Sea. The measurements were carried out in the northeastern Black Sea under the auspices of the Black Sea Ecosystem Recovery Program (BSERP) in May 2004. The effect of the computation parameters on the quality and accuracy of the calculations of velocity profiles was studied. It was shown that the use of optimal parameters and reliable navigation data and setting the instrument as close to the bottom as possible could essentially enhance the accuracy of the measurements. The current velocity calculations from the LADCP data were compared with the data on the vessel drift under calm weather. The accuracy of the calculations reached 6–8 cm/s. Recommendations on the choice of the optimal parameters for processing the data on the current velocity are presented.     

Estimates of extreme conditions of tide and surge using a numerical model of the north-west European continental shelf

Estimates of extreme currents and water levels due to tides, storm surges and their combination are required for the design of offshore structures, and other purposes. Techniques are described which provide such estimates for the north-west European continental shelf. The techniques employ spatial distributions of tide and surge from an established numerical sea model and existing statistical analyses of coastal sea level data. The assumptions embodied in the method are discussed and an indication given of the probable magnitude of the associated errors. The few observational estimates available provide limited verification of the results.     

Potential vorticity estimates of absolute velocities on the Ross Sea shelf

We analyze absolute velocities on the continental shelf off Cape Adare, in the western sector of the Ross Sea (Antarctica). Such a velocity field is here inferred by using a novel inverse method of absolute velocity determination, namely the tracer PV method, related to potential vorticities of temperature and salinity. This theoretical choice allows us to directly use in situ temperature and salinity data. Moreover, it avoids high-order derivatives, which can give large uncertainties that affect estimates made using previous approaches. The tracer PV method also allows us to separately estimate the steady and non-diffusive component and the unsteady and diffusive components of the flow. The western sector of the Ross Sea is characterized by a surface layer of Antarctic Surface Water over layers of Low Salinity Shelf Water and High Salinity Shelf Water, flowing northward with average velocities ～6–7 cm/s. At ～200 m depth an intrusion of warmer and saltier Circumpolar Deep Water is also evident in our data. The steady absolute velocities are in good agreement with those obtained from the classical Margules equation, in particular regarding the northward flux of the High Salinity Shelf Water. Furthermore, velocities due to diffusive processes and mesoscale activity are discussed. Finally, a steady “thermal” approximation is discussed; it allows for a qualitative check of the results by means of temperature horizontal sections only.     

Three-dimensional numerical model study of the residual current in the South China Sea

A three-dimensional baroclinic shelf sea model is employed to simulate the tidal and non-tidal residual current in the South China Sea. The four most significant constituents, M₂, S₂, K₁ and O₁, are included in the experiments with tidal effect. At most stations, the computed harmonic constants agree well with the observed ones. The circulations of the South China Sea in summer (August) and winter (December) are mainly discussed. It is shown that the barotropic tidal residual current is too weak to affect the South China Sea circulation, whilst the contribution of the baroclinic tidal residual current to the South China Sea circulation would be important in the continental shelf sea areas, especially in the Gulf of Thailand and Gulf of Tonkin. In the deep-sea areas, the upper barotropic or baroclinic tidal residual current is relatively very weak, however, the speed order of the deep baroclinic tidal residual current can be the same as that of the mean current without tidal effect. Moreover, the baroclinic tidal residual current seems to be related to the different seasonal stratification of ocean.     

二维情况下波浪对潮流场作用的数值分析

波浪和潮流是近岸地区主要的动力因素,两者之间存在着复杂的相互作用.波浪与潮流在时间尺度、空间尺度上都有很大的差别,因此现阶段对于波流相互作用的研究主要采用两种不同的概化方法.第一种方法是把周期变化的潮流概化成具有某一特征的海流叠加到波浪运动方程中去,用来模拟波流运动结构在短时间内所发生的变化.对于波浪来说,海流的作用既有动力学影响又有运动学的影响,在运动学方面,包括水深和海流对波浪频散关系的影响,另外还有由于顺流或逆流引起的波长的变化;在动力学方面,海流会引起波浪波高的变化;另一种方法是把波浪过程概化为在潮周期中具有平均意义的波浪要素叠加到潮流运动方程中,用来计算波浪对流的运动状态的影响,主要着眼于波浪和潮流对于泥沙的输运研究.     

Measurement of the current and spectral analysis on the continental shelf in the East China Sea

Direct measurements of current velocity and water temperature were undertaken at the mooring Sta. M (125°29.38' N, 31°49.70' E) on the continental shelf area in the East China Sea in June 1999 by R/V Xiangyanghong 14. The relationship between various time series of oceanic fluctuations is calculated by spectral analysis. The major results are as follows: (1) an average (u,v) of (6.9,-3.0 cm/s) at the 30 m depth is obtained during the 9-day observation, and that at the 45 m depth is (3.7,-1.1 cm/s), i. e., the mean flows are southeastward at both the 30 and 45 m depths;the currents become stronger gradually during the observation period; this may be mainly attributed to the transition of the tidal currents from neap to spring; (2)semidiurnal fluctuation is the most dominant in the current fluctuations, and rotates mainly clockwise; in the next place, there is also diurnal fluctuation;the local inertial period is close to the period of diurnal fluctuation, and an inertial motion is clockwise; thus, loca     

Measurement of the current and spectral analysis on the continental shelf in the East China Sea

Direct measurements of current velocity and water temperature were undertaken at the mooring Sta. M (125°29.38' N,31°49.70'E) on the continental shelf area in the East China Sea in June 1999 by R/V Xiangyanghong 14. The relationship between various time series of oceanic fluctuations is calculated by spectral analysis. The major results are as follows: (1) an average (u,v) of (6.9,-3.0 cm/s) at the 30 m depth is obtained during the 9-day observation, and that at the 45 m depth is (3.7,-1.1 cm/s), I. E., the mean flows are southeastward at both the 30 and 45 m depths;the currents become stronger gradually during the observation period; this may be mainly attributed to the transition of the tidal currents from neap to spring; (2)semidiurnal fluctuation is the most dominant in the current fluctuations, and rotates mainly clockwise; in the next place, there is also diurnal fluctuation;the local inertial period is close to the period of diurnal fluctuation, and an inertial motion is clockwise; thus, local inertial motion combines with diurnal fluctuation, and makes the spectral peaks in clockwise components much higher than those in counterclockwise ones;except for the fluctuations of above main periods, there is also the peak at 3 d period for counterclockwise components in the upper and lower layers; (3) the calculation of cross spectra between two time series of current velocities at the 30 and 45 m depths shows that both the current fluctuations at the 30 and 45 m depths are much alike, I. E.,they are synchro; this shows that the flow field here is rather vertically homogeneous; (4)power spectra of temperature time series at both the 30 and 45 m depths show that the semidiurnal peak is the most predominant, and the second highest peak is the diurnal period; besides spectral peaks at above periods, there are also obvious spectral peaks at 6.8 h and 2 d; (5)plots of temperature time series at 16,30,35,45 and 50 m depths show that the temporal variations of temperature at these depths are synchro, which are like those in the velocity field; temperature records also show a gradual rise in temperature, which are also like those in the velocity field.     

Insights into the structure of the Wyville Thomson Ridge overflow current from a fine-scale numerical model

One of the major pathways in the northern part of the Meridional Overturning Circulation (MOC) is that of the deep water in the Nordic Seas that runs through the Faroe-Shetland Channel (FSC) and Faroe Bank Channel (FBC), as well as crossing the Wyville Thomson Ridge (WTR), on its way into the Atlantic Ocean. The WTR overflow cascades down the southern side of the ridge via the narrow Ellett Gully to the Cirolana Deep (CD) which, at 1700 m, is the deepest hole in the extreme north of the Rockall Trough. The overflow accounts for nearly 1/10th of the total Faroe-Shetland Channel Bottom Water (FSCBW) discharged through the Faroese channels and is an important intermediate water mass in the Rockall Trough. Over a period of only seven days in April 2003 bottom water temperatures cooled dramatically, from 4.46 to 3.03 °C in the CD and from 3.93 to 2.54 °C in the Ymir Trough (YT). A numerical general circulation model (MITgcm) has been applied in order to reproduce the details of this dense water overflow event. Model results were consistent with the observed cooling and total water transport. It was found that the descending gravity current forms a pair of mesoscale eddies with cyclonic and anticyclonic vorticity at the exit to the CD. Analysis of mixing processes were obtained when a passive tracer was included in the model. It was found that downstream flow is characterized by an explosive detrainment regime in the CD. The model sensitivity runs revealed that the final depth to which the overflow descends depends on the initial upstream velocity of the overflow, as well as the buoyancy difference. It is argued that models of overflows need to have realistic representations of the density structure of the overflow, and sufficiently fine vertical resolution, for the subsequent fate of the overflow to be accurately represented.     

宁波,舟山内海域实测海流分析及潮流场的数值模拟

本文根据８０年代中后期所进行的潮位、现场测流资料分析宁波、舟山内海域的潮运动及海流特征，并进行了潮流场的数值模拟计算。     

河口最大浑浊带形成的动力模式和数值试验

应用改进的ECOM模式,耦合泥沙输运模型,研究理想河口最大浑浊带形成的动力机制。河口最大浑浊带位于滞流点处,上下游余流均向该处输运泥沙,造成该处泥沙汇合,而由流场辐合产生的上升流又使该处的泥沙不易落淤。南岸(河口东向)的泥沙浓度比北岸高,最大浑浊带位于南岸,这是由于盐水入侵带来的高盐水位于北岸的底层,其斜压效应使底层的环流由北向南流动,把底层高浓度的泥沙向南岸平流,聚集于南岸底层。除上游河流泥沙来源外,强大的涨落潮流冲刷床面,使沉降于床面的泥沙再次悬浮,成为余流输运泥沙的来源之一。     

Formation of a circulation in the quasiisopycnic model of the Black Sea taking into account the stochastic nature of the wind stress

We discuss the results of numerical experiments carried out within the framework of a new version of the quasiisopycnic model of the Black Sea [1, 2]. We take into account the stochasticity of the wind stress, vertical shift of the flow velocity in the upper quasihomogeneous layer, and diapycnic mixing. We generalize the procedure of “convective adjustment,” which enables us to consider the propagation and transformation of waters of the Sea of Marmara. It is shown that the consideration of these factors enables one to determine the structure and seasonal variability of hydrothermodynamic fields in the sea more correctly. Translated by Peter V. Malyshev and Dmitry V. Malyshev