Investigation of the influence of wind action upon the currents and propagation of impurities in the azov sea

The surge phenomena and currents in the Azov Sea caused by variable winds in the presence of stationary currents are studied by using a three-dimensional nonlinear mathematical model. The specific features of the transformations of impurities in the water area of the Azov Sea under the joint action of stationary and nonstationary winds are investigated. On the basis of the results of numerical calculations, we make conclusions concerning the dependence of the period of dissipation of impurities on the wind velocity and the location of the regions with impurities. It is shown that the variable wind significantly increases the deviations of the sea level and the area of distribution of the impurity as compared with the action solely of the stationary currents.     

平潭竹屿湾水交换能力和溢油风险数值模拟

应用非结构网格有限体积海洋模型对平潭竹屿湾水交换能力和溢油扩散开展了数值模拟.水交换能力计算表明,竹屿湾大部分水域水体半交换时间小于1.0 d,平均滞留时间约3.0 d左右,水体冲洗时间为15.0 d,水交换能力较强. 48 h溢油扩散计算结果表明,油粒子扫海范围及运动路径与油粒子的释放时刻及风的作用紧密相关.静风条件...     

Sources of water in the Taiwan Strait

The conveyor of the source water that feeds into the Taiwan Strait (TS), particularly from the south, is investigated using historical CTD (Conductivity-Temperature-Depth) data and a North Pacific Ocean and East Asian seas coupled model. The modeled currents and drifter trajectories suggest that the Kuroshio Branch Water (KBW) rarely flows directly into the TS from the Luzon Strait (LS) in winter; instead the massive westward movement of the Kuroshio conveys high salinity water to the southeastern TS through a loop-like route. In summer, the modeled flow fields suggest that the Kuroshio surface currents hardly intrude into the TS directly from the LS. Observations and model results show that the monsoon-driven northeastwardflowing currents in the northern South China Sea transport relatively low salinity water through the entire TS.     

Modeling of the breeze circulation of waters in the Kerch Strait

The problem of the numerical analysis of currents in the Kerch Strait is studied within the framework of a linear nonstationary two-dimensional model in the nondivergent approximation. We describe the actual situation when the motion is induced by a breeze against the background of the daily average northeast wind. The breeze is specified as acting in a narrow coastal strip and can be classified as a zonal wind. The variations of circulation near the Tuzla Island are studied in detail. It is shown that the contribution of the breeze circulation to the total circulation can be significant for the explanation of the processes running in the Kerch Strait. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 16–27, November–December, 2007.     

Tidal transport and dispersal of marine toxic microalgae in a shallow, temperate coastal lagoon

A numerical model was used to predict toxic microalgal transport and dispersion in Ria de Aveiro in Portugal. A previously developed Lagrangean particle tracking model coupled to a calibrated two-dimensional hydrodynamic model of Ria de Aveiro was used. Microalgae were regarded as passive particles and the methodology used allowed the determination of their trajectories, as induced by the tidal currents predicted by the hydrodynamic model. The model assumes Ria de Aveiro as vertically homogeneous and does not take into account the vertical distribution patterns of microalgae. Simulations were carried out during extreme spring and neap tides, with microalgal released at the mouth of the lagoon at the local flood. The maximum and minimum areas affected during the occurrence of toxic microalgal blooms were estimated to evaluate the suitability of the distribution of the sampling stations included in the local monitoring program. It was found that the tidal currents greatly determine the microalgal horizontal distribution and dispersal in the lagoon. The results confirmed that the locations of water and bivalve shellfish sampling stations, postulated by INIAP/IPIMAR, in the context of the local harmful algal bloom (HAB) program, were appropriate, although some possible refinements were identified.     

Estimation of water-vapor and ozone transport in the upper troposphere-lower stratosphere and fluxes through the tropopause during the field campaign at the Sodankyla station (Finland)

Processes of mass exchange through the tropopause at extratropical latitudes are studied. For this purpose, balloon data on ozone and water vapor obtained during the LAUTLOS field campaign were analyzed and a trajectory model was used to analyze the origin of air masses and to calculate fluxes through the tropopause. The results of observations and trajectory modeling showed that tropospheric air masses penetrated into the stratosphere by no more than ～2.5 km above the tropopause level during the campaign. Both tropospheric and stratospheric particles are present in this mixing layer. Backward trajectories showed that, at the anticyclone boundary, tropospheric air penetrates into the stratosphere in the form of fine fibrous structures (filaments). The fluxes through the tropopause were also quantitatively estimated by the Wei method with the use of forward and backward trajectories. The spatial structure of the fluxes through the tropopause coincides with the regions of the tropopause inclination and its folds. The absolute values of the fluxes calculated with the use of the Wei method decrease, depending on the length of trajectories at the expense of the filtering-out of a shallow reversible exchange. It is shown that the exchange depth can be controlled by both vertical fluxes in the troposphere and changes in the level of the tropopause itself. The use of isentropic and three-dimensional trajectories made it possible to estimate the contribution of nonadiabatic processes to the stratosphere-troposphere exchange.     

Temperature and salinity effects in modeling the trajectory of the 2011 Penglai 19-3 oil spill

In this paper, two hydrodynamic models were developed using Delft3D and were then applied to the 2011 Penglai 19-3 accident in the Chinese Bohai Sea. One model includes constant temperature and salinity, while the other model utilizes variable temperature and salinity. The two models both simulate currents fields in the Bohai Sea and utilize wind data from the National Meteorological Service of Germany (DWD) to calculate the drift of spilled oil. The hydrodynamic simulation results are consistent with the results of previous studies. We subsequently predict the surface oil trajectories of the Penglai 19-3 oil spill based on the two models, respectively. Comparing the oil-spill simulation results with remote sensing information, we show that the model with variable temperature and salinity exhibits a better fit with the actual observations. Temperature and salinity were two important factors that influenced the movement of spilled oil on the sea surface. According to the result of the variable thermohaline model, most of the oil particles spread northwest and a small portion spreads southeast to the Chinese Bohai Strait. We conclude that density currents should be considered in future oil-spill studies to generate more realistic results.     

Observations of Eddies in the Japan Basin Interior

Eddy features in the Japan Basin have been studied by combining satellite-derived sea surface temperature (SST) images and WOCE drifter tracks with recent current meter data from a deep mooring in the interior of the Basin. SST images indicate that anticyclonic eddies often appear around the Subpolar Front in cold seasons and move into the northern cold water region entraining warm water of the frontal zone. The anti-cyclonic eddies "visualized" by the entrained warm water and trajectories of some drifters are typically 30 km in radius and have rotational speeds of 0.15 to 0.3 m/s at the surface. On the other hand, the current meter data of 3-year duration show that vertically coherent eddy-like currents of the order of 0.1 m/s occur every year in cold seasons in the deep (1000 to 3000 m) layer of the Japan Basin interior. An important finding is that available time series of SST patterns are well correlated to the vertically coherent deep currents. This correlation suggests that the anticyclonic eddies indicated by both SST images and drifter tracks are actually barotropic or quasi-barotropic, extending from the surface to the bottom. It is argued that the unique current features in the deep layer of the Japan Basin can be explained in terms of barotropic eddies. A brief discussion is also made of the possible source of the eddy kinetic energy. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Lagrangian study of the near-surface intrusion of Pacific water into the South China Sea

Satellite-tracked Lagrangian drifters are used to investigate the transport pathways of near-surface water around the Luzon Strait. Particular attention is paid to the intrusion of Pacific water into the South China Sea(SCS).Results from drifter observations suggest that except for the Kuroshio water, other Pacific water that carried by zonal jets, Ekman currents or eddies, can also intrude into the SCS. Motivated by this origin problem of the intrusion water, numerous simulated trajectories are constructed by altimeter-based velocities. Quantitative estimates from simulated trajectories suggest that the contribution of other Pacific water to the total intrusion flux in the Luzon Strait is approximately 13% on average, much smaller than that of Kuroshio water. Even so, over multiple years and many individual intrusion events, the contribution from other Pacific water is quite considerable. The interannual signal in the intrusion flux of these Pacific water might be closely related to variations in a wintertime westward current and eddy activities east of the Luzon Strait. We also found that Ekman drift could significantly contribute to the intrusion of Pacific water and could affect the spreading of intrusion water in the SCS. A case study of an eddy-related intrusion is presented to show the detailed processes of the intrusion of Pacific water and the eddy-Kuroshio interaction.     

寒潮天气下高风险冰块追踪预测方法及数值模拟

为向拟建、在建和已建冰区所有冷源取水工程海域的海冰环境监测和动态风险预警提供技术支撑,本文构建了海冰–海洋耦合条件下的拉格朗日粒子追踪预测模型,并以辽东湾某核电站取水口为例,模拟并探讨了寒潮天气下高风险冰块在24 h、48 h和72 h的运移轨迹及其进入取水口的概率。结果表明,由于取水口的走向与流向和风向几乎垂直,因此在口门外随机释放的1 200个高风险冰块粒子中只有不到6%的粒子进入到取水口内。通过分区域标识粒子颜色,发现这些粒子多来自于靠近取水口300 m范围内。敏感性分析的结果表明,当释放粒子数量增至5倍时,结论不变。该项研究为冷源取水安全预警提供了一种新方法。     

胶莱人工河道水质点输运轨迹的数值模拟

利用二维水动力数学模型模拟胶莱人工河道潮流运动,并分析了胶州湾湾口设置潜堤前后胶莱人工河道水质点的运动轨迹和水位变化过程。结果表明,开通胶莱人工河道能够使黄海的胶东湾海水向渤海的莱州湾输运,但不设置潜堤时从胶州湾到莱州湾的海水输运平均流速较小;设置潜堤后胶州湾水位高于莱州湾水位的时间变长,从黄海到渤海之间的水体输运能够得到加速。计算结果还表明,潜堤顶部与平均水面距离较小时,黄、渤海之间水体输运较快。     

Assessment of water exchange between a discharge region and the open sea – A comparison of different methodological concepts

Two different methods of estimating the water exchange through the Baltic coastal region of Laxemar have been used, consisting of particle trajectories and passive tracers. Water is traced from and to a small discharge region near the coast. The discharge material in this region is treated as zero-dimensional particles or tracers with neutral buoyancy. The real discharge material could be a leakage of radio-nuclides through the sea floor from an underground repository of nuclear waste.Water exchange rates between the discharge region and the model domain are estimated using both forward and backward trajectories as well as passive tracers. The Lagrangian trajectories can account for the time evolution of the water exchange while the tracers give one average age per model grid box. Water exchange times such as residence time, age and transient times have been calculated with trajectories but only the average age (AvA) for tracers. The trajectory calculations provide a more detailed time evolution than the tracers.On the other hand the tracers are integrated “on-line” simultaneously in the sea circulation model with the same time step while the Lagrangian trajectories are integrated “off-line” from the stored model velocities with its inherent temporal resolution, presently 1 h. The sub-grid turbulence is parameterised as the Laplacian diffusion for the passive tracers and with an extra stochastic velocity for trajectories. The importance of the parameterised sub-grid turbulence for the trajectories is estimated to give an extra diffusion of the same order as the Laplacian diffusion by comparing the Lagrangian dispersions with and without parameterisation. The results of the different methods are similar but depend on the chosen diffusivity coefficient with a slightly higher correlation between trajectories and tracers when integrated with a lower diffusivity coefficient.     

Wind-wave variability in a shallow tidal sea—Spectral modelling combined with neural network methods

In this paper the wind-wave variability in the tidal basins of the German Wadden Sea is modelled with combined numerical and neural-network (NN) methods. First, the wave propagation and transformation in the study area are modelled with the state-of-the-art third-generation spectral wave model SWAN. The ability of SWAN to accurately reproduce the phenomena of interest in nonstationary conditions governed by highly variable winds, water levels and currents is shown by comparisons of the modelled and measured mean wave parameters at four stations. The principal component analysis of the SWAN results is then used to reveal the dominating spatial patterns in the data and to reduce their dimensionality, thus enabling an efficient and relatively straightforward NN modelling of mean wave parameters in the whole study area. It is shown that the data produced with the approach developed in this work have statistical properties (discrete probability distributions of the mean wave parameters etc.) very close to the properties of the data obtained with SWAN, thus proving that this approach can be used as a reliable tool for wind wave simulation in coastal areas, complementary to (often computationally demanding) spectral wave models.     

Tracing water masses with particle trajectories in an isopycnic-coordinate model of the global ocean

Offline particle trajectories are obtained for a quasi-global isopycnic-coordinate OGCM using an analytical method, adapted for use with online time-integrated isopycnal and diapycnal mass fluxes. The method is highly efficient, allowing the calculation of large ensembles of such trajectories. These ensembles can be used to establish pathways and transformations associated with the global circulation of water masses on timescales which are well in excess of any feasible model integration length. The method is here used to investigate the important, yet poorly observed, transformation of North Atlantic Deep Water (NADW) through slow spreading, upwelling and diapycnal mixing (defined when and where density decreases below a threshold value). A fundamental problem arises through unsteadiness in the thickness of NADW layers (due to various model flaws and/or intrinsic variability). Particles converge on gridboxes where layers inflate during the online time-integration period. Depending on the degree of layer inflation, only a fraction of NADW particles can be diagnosed as transformed at some point along their respective trajectories. However, the unsteadiness of layer thickness decreases during a 50-year spin-up, implying fewer converged trajectories and an increased fraction of transformed NADW. Using trajectories to trace NADW southward across the equatorial Atlantic, with mass fluxes from years 10, 30 and 50 of model spin-up, the transformed percentage (of NADW exported from the North Atlantic) increases from 17–18% (with fluxes from years 10 and 30) to 41% (using year 50 fluxes). In the latter case, about 30% of the NADW upwells south of 30°S after 500–1000 years. Most of the remaining 70% upwells in the South and North Pacific after 1000–2500 years.     

Numerical simulation of larval shrimp dispersion in the Northern Region of the Gulf of California

The trajectories of shrimp larvae in the northern part of the Gulf of California were studied from a Lagrangian point of view using a three-dimensional numerical model. The advection of particles was carried out over fortnightly periods starting at spring and neap tides. The northernmost region of the gulf has important shrimp fisheries and nursery areas have been located off the coast of Baja California at San Felipe (SF) and off the Sonora coast at Santa Clara (SC). Though the reproduction zone is believed to be south of these nursery areas, there is much that remains unknown about the zone and the routes used by shrimps to reach these areas. Passive and active simulations of shrimp larvae drift were carried out in order to study the possible areas of shrimp spawning and their migratory routes. The active migration schemes were based on assumptions that the larvae can be advected only: (1) during the day, (2) at night or (3) when the currents flow in the northward direction toward the nursery areas. It was found that the larvae in Santa Clara and San Felipe came from different production zones. No differences were found between the spring and neap tide scenarios except for the diurnal migration experiments. The distance traveled by shrimp larvae was always less than 40–50 km, except in the cases when the larvae selected the appropriate direction to the nursery areas when the larvae travel 140 km to SC and 95 km to SF.     

赤道东太平洋弯曲急流区质点轨迹及混沌运动机制

利用运动学模型 ,研究了弯曲急流控制参数为定常和发生周期扰动时的流体质点运动轨迹以及混沌现象的产生机制。发现弯曲急流控制参数为定常时 ,流体质点的运动为规则的周期运动 ;而控制参数发生扰动时 ,可以发生流体质点在不同特征区的穿行 ,流体质点的运动具有混沌特性。弯曲急流的相速、振幅发生周期扰动均可使流体质点的运动出现混沌特性。作者从运动学上对弯曲急流区的漂流浮标混沌特性给出了解释。     

长江口三维潮流数值计算及动力分析

采用三维动力学数学模型对长江口潮流场进行了计算，对长江口潮流流态在一个潮周期内逐时进行了分析，并对长江口南支盐水倒灌从动力学角度进行了初步探讨。计算结果表明：文中模型较好地重演长江口潮流场，可以用于大型复杂河口工程实际中的潮流场的计算和分析。     

南海深水井喷溢油输移扩散的数值模拟研究

文章以假设发生在南海北部深水油气勘探开发海域的1 279 m深水井喷溢油事故为例,采用深海溢油输移扩散模型,以2020年冬季(1月)和夏季(7月)三维流场和海面风场为主要环境动力,数值模拟研究未实施和实施海底消油剂处理情景下的溢油在海洋环境中的输移扩散全过程。模拟结果显示：不同深度的海流对溢油输移轨迹有着显著的影响;深水环境中,流速较小,井喷形成的浮射流能够向上输移较长距离;随着水深变浅,流速增强,流向多变,水中不同粒径的油滴以摇摆或螺旋轨迹向上浮升;在表层海流和冬季或夏季盛行风的共同作用下,海面油膜主要往下风向方向漂移扩散;实施海底消油剂处理措施后,水中油滴扩散范围较未处理时的更大,其中微小粒径油滴将在深水环境中长时间悬浮输移。结果可为今后南海深海溢油输移扩散规律的深入研究提供参考。     

The effects of chaotic advection in a three-layer ocean model

A three-layer model of an inviscid incompressible fluid is considered in a quasigeostrophic approximation within the concept of background currents. A singular topographic obstacle yields the formation of a vortical motion in the layers. It is always present in the lower layer, while in the upper and middle layers it can be observed only at certain velocities of the external flows. Three current functions describing a singular topographic flow in the lower layer and two regular flows in the upper layer are obtained. In case of a nonstationary harmonic perturbation of the external flow, chaotic particle transport is possible in these flows. This paper analyzes the chaotic properties of this model. Depending on the type of unperturbed frequency curves of the fluid particle revolution is determined by the model parameters (stratification) and the incident flow, the patterns of the chaotic transport will substantially differ. Two of the limiting dependences of the revolution frequency are determined, namely, the dependence for a singular vortex and that for a regular vortex with the smallest area. Other dependences are intermediate ones. Two limiting types of revolution frequencies determine the two different scenarios of chaotic advection.     

Dynamic processes and their influence on the transformation of the passive admixture in the sea of Azov

In this model, we apply a nonlinear three-dimensional sigma-coordinate model to study the waves and currents in the Sea of Azov generated by different fields of wind forcing: a constant wind, a quickly varying real wind obtained using the data of reanalysis applying the SKIRON model, and the wind resulting from their combined forcing. This mathematical model was also applied to study the transformation of the passive admixture appearing under the influence of wind fields in the Sea of Azov considered here. We compared the results of numerical calculations with the field data obtained under the wind forcing at a number of hydrological stations. We found the regularities of the water transport driven by onshore and offshore winds, the velocities of the currents, and the characteristics of the evolution of polluted regions at different depths as functions of the nonstationary wind intensity and the velocities of the stationary currents.