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1.
The low salinity water lenses(LSWLes) in the expansion area of the Changjiang diluted water(CDW) exist in a certain period of time in some years. The impact of realistic river runoff, ocean currents and weather conditions need to be taken into account in the dynamical analysis of LSWL, which is in need of research. In this paper, the POM-σ-z model is used to set up the numerical model for the expansion of the CDW. Then LSWL in summer 1977 is simulated, and its dynamic mechanism driven by wind, tide, river runoff and the Taiwan Warm Current is also analyzed. The simulated results indicate that the isolated LSWL detaches itself from the CDW near the river mouth, and then moves towards the northeast region outside the Changjiang Estuary. Its maintaining period is from July 26 to August 11. Its formation and development is mainly driven by two factors. One is the strong southeasterly wind lasting for ten days. The other is the vertical tidal mixing during the transition from neap tide to spring tide.  相似文献   

2.
A vertical (laterally averaged) two-dimensional hydrodynamic model is developed for tides, tidal current, and salinity in a branched estuarine system. The goveming equations are solved with the hydrostatic pressure distribution assumption and the Boussinesq approximation. An explicit scheme is employed to solve the continuity equations. The momentum and mass balance equations are solved implicitly in the Cartesian coordinate system. The tributaries are govemed by the same dynamic equations. A control volume at the junctions is designed to conserve mass and volume transport in the finite difference schemes, based on the physical principle of continuum medium of fluid. Predictions by the developed model are compared with the analytic solutions of steady wind-driven circulatory flow and tidal flow. The model results for the velocities and water surface elevations coincide with analytic results. The model is then applied to the Tanshui River estuarine system. Detailed model calibration and verification have been conducted with measured water surface elevations,tidal current, and salinity distributions. The overall performance of the model is in qualitative agreement with the available field data. The calibrated and verified numerical model has been used to quantify the tidal prism and flushing rate in the Tanshui River-Tahan Stream, Hsintien Stream, and Keelung River.  相似文献   

3.
A 3-D numerical model is set up in a large domain covering the Hang zhou Bay and the Changjiang Estuary based on the ECOM model in orthogonal curvilinear coordinates.The numerical schemes for baroclinic pressure gradient (BPG) terms and convective terms are improved in the paper according to the characteristics of velocity field and mass transport in the area.The model is validated by the simulations of residual current and salinity transport in the Hangzhou Bay and the Changjiang Estuary.  相似文献   

4.
By coupling the three-dimensional hydrodynamic model with the wave model, numerical simulations of the three-dimensional wave-induced current are carried out in this study. The wave model is based on the numerical solution of the modified wave action equation and eikonal equation, which can describe the wave refraction and diffraction. The hydrodynamic model is driven by the wave-induced radiation stresses and affected by the wave turbulence. The numerical implementation of the module has used the finite-volume schemes on unstructured grid, which provides great flexibility for modeling the waves and currents in the complex actual nearshore, and ensures the conservation of energy propagation. The applicability of the proposed model is evaluated in calculating the cases of wave set-up, longshore currents, undertow on a sloping beach, rip currents and meandering longshore currents on a tri-cuspate beach. The results indicate that it is necessary to introduce the depth-dependent radiation stresses into the numerical simulation of wave-induced currents, and comparisons show that the present model makes better prediction on the wave procedure as well as both horizontal and vertical structures in the wave-induced current field.  相似文献   

5.
New Eulerian-Lagrangian Method for Salinity Calculation   总被引：4，自引：0，他引：4  
A difference scheme in curvilinear coordinates is put forward for calculation of salinity in estuaries and coastal waters, which is based on Eulerian-Lagrangian method. It combines first-order and second-order Lagrangian interpolation to reduce numerical dispersion and oscillation. And the length of the curvilinear grid is also considered in the interpolation. Then the scheme is used in estuary, coast and ocean model, and several numerical experiments for the Yangtze Estuary and the Hangzhou Bay are conducted to test it. These experiments show that it is suitable for simulations of salinity in estuaries and coastal waters with the models using curvilinear coordinates.  相似文献   

6.
This paper proposes a new method to retrieve salinity profiles from the sea surface salinity(SSS) observed by the Soil Moisture and Ocean Salinity(SMOS) satellite. The main vertical patterns of the salinity profiles are firstly extracted from the salinity profiles measured by Argo using the empirical orthogonal function. To determine the time coefficients for each vertical pattern, two statistical models are developed. In the linear model, a transfer function is proposed to relate the SSS observed by SMOS(SMOS_SSS) with that measured by Argo, and then a linear relationship between the SMOS_SSS and the time coefficient is established. In the nonlinear model, the neural network is utilized to estimate the time coefficients from SMOS_SSS, months and positions of the salinity profiles. The two models are validated by comparing the salinity profiles retrieved from SMOS with those measured by Argo and the climatological salinities. The root-mean-square error(RMSE) of the linear and nonlinear model are 0.08–0.16 and 0.08–0.14 for the upper 400 m, which are 0.01–0.07 and 0.01–0.09 smaller than the RMSE of climatology. The error sources of the method are also discussed.  相似文献   

7.
A numerical simulation and an experimental study on vortex-induced motion(VIM) of a new type of deep draft multi-columns floating drilling production, storage and offloading(FDPSO) are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform's sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ V_r ≤ 8.9. The typical ‘8' shape trajectory does not appear in the platform's motion trajectories.  相似文献   

8.
Cruise observations with CTD (conductivity-temperature-depth) profiler were carried out in the southern Taiwan Strait in the summer of 2005. Using the cruise data, two-dimensional maps of salinity and temperature distributions at depths of 5, 10, 15, 20, and 30 m were generated. The maps show a low salinity tongue sandwiched by low temperature and high salinity waters on the shallow water side and high temperature and high salinity waters on the deep water side. The further analysis indicates that the low salinity water has a nature of river-diluted water. A possible source of the diluted water is the Zhujiang (Pearl) Estuary. Meanwhile, the summer monsoon is judged as a possible driving force for this northeastward jet-like current. The coastal upwelling and the South China Sea Warm Current confine the low salinity water to flow along the central line of the strait. Previous investigations and a numerical model are used to verify that the upstream of the low salinity current is the Zhujiang Estuary. Thus, the low salinity tongue is produced by four major elements:Zhujinag Estuary diluted water, monsoon wind driving, coastal upwelling and South China Sea Warm Current modifications.  相似文献   

9.
A 3D,time-dependent,baroclinic,hydrodynamic and salinity model was implemented and applied to the Oujiang River estuarine system in the East China Sea.The model was driven by the forcing of tidal elevations along the open boundaries and freshwater inflows from the Oujiang River.The bottom friction coefficient and vertical eddy viscosity were adjusted to complete model calibration and verification in simulations.It is demonstrated that the model is capable of reproducing observed temporal variability in the water surface elevation and longitudinal velocity,presenting skill coefficient higher than 0.82.This model was then used to investigate the influence of freshwater discharge on residual current and salinity intrusion under different freshwater inflow conditions in the Oujiang River estuary.The model results reveal that the river channel presents a two-layer structure with flood currents near the bottom and ebb currents at the top layer in the region of seawater influenced on north shore under high river flow condition.The river discharge is a major factor affecting the salinity stratification in the estuarine system.The water exchange is mainly driven by the tidal forcing at the estuary mouth,except under high river flow conditions when the freshwater extends its influence from the river’s head to its mouth.  相似文献   

10.
A numerical simulation and an experimental study on vortex-induced motion (VIM) of a new type of deep draft multi-columns floating drilling production, storage and offloading (FDPSO) are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform''s sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ Vr ≤ 8.9. The typical ‘8’ shape trajectory does not appear in the platform''s motion trajectories.  相似文献   

11.
In this study we test Talley's hypothesis that Oyashio winter mixed-layer water (26.5–26.6σ θ) increases its density to produce the North Pacific Intermediate Water (NPIW) salinity minimum (26.7– 26.8σθ) in the Mixed Water Region, assuming a combination of cabbeling and double diffusion. The possible density change of Oyashio winter mixed-layer water is discussed using an instantaneous ratio of the change of temperature and salinity along any particular intrusion (R l ). We estimate the range of R l DD required to convert Oyashio winter mixed-layer water to the NPIW salinity minimum due to double diffusion, and then assume double-diffusive intrusions as this conversion mechanism. A double-diffusive intrusion model is used to estimate R l DD in a situation where salt fingering dominates vertical mixing, as well as to determine whether Oyashio winter mixed-layer water can become the NPIW salinity minimum. Possible density changes are estimated from the model R l DD by assuming the amount of density change due to cabbeling. From these results, we conclude that Oyashio winter mixed-layer water contributes to a freshening of the lighter layer of the NPIW salinity minimum (around 26.70σθ) in the MWR.  相似文献   

12.
湍流扩散过程导致的硝酸盐垂向输运对海水表层的浮游植物生长和初级生产力的大小有着重要影响。本文基于2018年夏季黄、东海水文环境、硝酸盐浓度和湍动能耗散率的同步、原位数据，分析了海域温度、盐度和硝酸盐的空间分布特征，结果表明营养盐含量丰富的黄海冷水团、长江冲淡水、东海北部底层混合水与黑潮次表层水是影响研究海域硝酸盐分布的主要水团。利用垂向湍扩散硝酸盐通量公式，计算了三个选定断面上的硝酸盐垂向扩散通量，其高值区与湍流扩散系数的高值区的位置基本一致。针对存在明显硝酸盐跃层的站位，计算得到跨硝酸盐跃层的垂向通量FND的范围在-9.78—36.60mmol/（m2·d）之间，在黄海冷水团区，夏季温跃层限制了该区营养盐向近表层的湍流垂向扩散；东海北部底层混合水区，湍流垂向扩散向上层补充了大量硝酸盐，促进了跃层之上浮游植物的生长；黑潮次表层水影响海区，夏季中层水体混合较弱，跨跃层的垂向通量也普遍偏低。开展硝酸盐垂向扩散通量的计算与分析，对进一步明确营养盐的输运机制有着重要研究意义。  相似文献   

13.
A simple hydraulic model is used to estimate the deep water fluxes of Cretan Deep Water (CDW), through the Cretan Arc Straits and into the Eastern Mediterranean Basins. The input to the model consists of the height of the deep water reservoir above sill depth and its density difference from the overlying water masses. Data from four hydrographic cruises, which took place in 1995, 1991 and 1987, are used to estimate the depth of the reservoir above the sill and the density difference. The results show a significant CDW outflow of 0.75×106 m3 s−1 in early 1995. The outflow of CDW through Kassos Strait, in the east, is 0.53×106 m3 s−1, while 0.22×106 m3 s−1 outflows through the Antikithira Strait in the west. The model results agree with fluxes estimated from current meter observations.The CDW outflow has been neither steady nor uniform during the period 1987–95. In the Kassos Strait, the outflow commenced in 1987 and increased rapidly until 1991; since then, it appears to have stabilised. In the Antikithira Strait, in contrast, the outflow has increased steadily since 1987. Such modifications in the CDW outflow are associated with changes in its hydrographic characteristics. The salinity of CDW increased constantly, by approximately 0.1, between 1987 and 1995 while its temperature warmed, between 1987 and 1991, and then cooled.  相似文献   

14.
潮致余流和潮混合对长江口外东北海域低盐水团的作用   总被引：1，自引：0，他引：1  
长江冲淡水对黄海、东海水文环境有重要影响,它主要以羽状形态向外海扩展,在某些年份的特殊时间段也存在孤立的低盐水团现象。在低盐水团的动力机制研究中,风、径流量、台湾暖流、天文潮和斜压不稳定的作用已得到讨论。天文潮对冲淡水及低盐水团的影响主要包括潮致余流和潮混合,潮致余流作用仍缺乏讨论。本文对1983年8月低盐水团的动力机制进行数值模拟分析,重点讨论了潮致余流和潮混合的影响。结果表明:潮致Lagrange余流促使一部分冲淡水从口门向北输运,在32°N附近呈舌状转向东,有利于在口外东北海域形成低盐水团;小潮转大潮的垂向混合作用加强,浅水区表层盐度升高的速度快于较深水区,也有利于在口外东北海域形成低盐水团。  相似文献   

15.
A 1/8° global version of the Navy Coastal Ocean Model (NCOM) is described with details of its formulation, implementation, and configuration of the vertical coordinate. NCOM is a baroclinic, hydrostatic, Boussinesq, free-surface ocean model that allows its vertical coordinate to consist of σ coordinates for the upper layers and z-levels below a user-specified depth. This flexibility allows implementation of a hybrid σ–z coordinate system that is expected to mitigate some of the weaknesses that can be associated with either pure coordinate option. For the global NCOM application, the σ–z coordinate is used to allow terrain-following σ coordinates in the upper ocean, providing better resolution and topographic fidelity in shelf regions where flow is most sensitive to its representation. Including z coordinates for deeper regions efficiently maintains high near-surface vertical resolution in the open ocean. Investigation into the impact of the selected coordinate system focuses on differences between atmospherically-forced free-running (no assimilation) global solutions using σ–z and pure z coordinates. Comparisons with independent temperature observations indicate that global NCOM using the σ–z coordinate has improved skill relative to its z coordinate implementation. Among other metrics, we show that in comparison with time series of surface temperature from National Oceanic Data Center (NODC) buoys, mostly located in coastal regions, root mean squared differences (RMSD) improved for 63% and correlation improved for 71% of the stations when σ–z coordinates were used instead of pure z. For the exclusively open-ocean Tropical Atmosphere-Ocean (TAO) buoys, differences between the simulations were small, with the σ–z showing smaller RMSD for 45% of the stations and higher correlation for 65% of the stations. Additional comparisons using temperature profile observations further confirm a tendency for improved performance using the hybrid σ–z coordinates.  相似文献   

16.
In a previous paper (Oguma and Nagata, 2002), it was shown that frequency distributions of temperature and salinity in the sea off Sanriku Coast, Japan are skewed, and sometimes observed values exceed m + 5σ (m = mean, σ = standard deviation). This means that, if we apply a 3σ criterion for a range check, many real data would be lost. We have expanded our analysis to the subarctic North Pacific, the subarctic North Atlantic and their surrounding areas, by computing the distributions of skewness and kurtosis. It is found that the region of high positive skewness extends in an east-north-east direction in the Mixed Water Region from off Sanriku, and reaches to about 155°E. A high negative skewness zone is recognized along the southern margin of the Kuroshio Extension. These are thought to be generated by the breaking of the meander of the Kuroshio Extension and subsequent ejection of warm and cold eddies to the north and south, respectively. Other high positive skewness areas are found to the south of Kuril Islands and in the Japan Sea. These are generated due to very sharp vertical gradients of temperature and salinity. The situation in the North Atlantic is very similar to the North Pacific, though the detailed nature is changed due to differences of oceanographic condition. The effect of grid size on the skewed nature of the distribution is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
Six newly developed floats, which were set to drift on the 26.7 σθ isopycnal surface and to profile temperature, salinity and pressure above 1000 dbar once a week, were deployed in the Oyashio and Kuroshio Extension (KE) in order to examine the circulation, formation site and time scale of newly formed North Pacific Intermediate Water (NPIW). The floats were deployed in February or May 2001, and the data from their deployments to December 2002 are analyzed here. Four of the six floats were deployed near the KE axis at around the first meander crest, and they moved eastward to 157°E–176°W at latitudes of 30°N–45°N. The other two floats deployed in the Oyashio water with low-potential vorticity near the south coast of Hokkaido moved southward to reach the KE front and then moved eastward to the same region as the first four floats. The temperature and salinity at 26.7 σθ measured by the profiling floats indicate that the source waters of NPIW, Oyashio and Kuroshio waters are drastically mixed and modified in the mixed water region west of 160°E. The floats were separated into the three paths east of 160°E between the Kuroshio Extension front and the north of Water-Mass front (nearly subarctic front). New NPIW is judged to be formed along these three paths since the vertical profiles of temperature and salinity are quite smooth, having a salinity minimum at about 26.7σθ along each path. Kuroshio-Oyashio isopycnal mixing ratios of the new NPIW are 7:3, 6:4 and 5:5 at 26.7σθ along the southern, middle and northern paths, respectively. Potential vorticity converges to about 14–15 × 10−11 m−1s−1 along these paths. The time scale of new NPIW formation is estimated to be 1–1.5 years from the merger of Oyashio and Kuroshio waters to the formation of the new NPIW. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

18.
The sediment–water partitioning of radiolabelled Cd, Hg and Zn has been investigated along an estuarine salinity gradient using samples from the Mersey Estuary, UK. Partitioning was studied using untreated particles, and particles that had been extracted using either a reducing agent (NH2OH.HCl–HOAc) or an oxidising agent (H2O2) in order to qualitatively evaluate the relative roles of Fe–Mn oxides and particulate organic matter (POM), respectively, on metal uptake. The extent of Cd partitioning between sediment and water, parameterised in terms of the distribution coefficient, KD, exhibited a reduction with increasing salinity, regardless of whether or not particles had been digested. However, the magnitude of KD decreased significantly following either chemical treatment, suggesting that both oxides and organic matter are important sorbents for Cd. The KD for Hg in the presence of untreated particles increased with increasing salinity, and chemical reduction of the particles enhanced the uptake of Hg and reinforced this trend. Particle oxidation led to a significant reduction in the KD for Hg, and uptake by the particles decreased with increasing salinity. These observations suggest that POM is considerably more important than Fe–Mn oxides in the removal of aqueous Hg, and that its presence is a prerequisite for enhanced sorption (or salting out) at elevated salinities. The salinity dependence of KD for Zn displayed characteristics of both Cd (below salinities of about 5) and Hg (at greater salinities). However, the magnitude of KD for Zn uptake was relatively insensitive to either chemical treatment, suggesting that oxides, POM, and residual phases contribute to the overall sorption of Zn by estuarine particles. Regression analyses of the metal partition data suggest that sorption to oxides and POM is nonadditive, and that the salinity dependence of metal partitioning results mainly from salinity-controlled interactions between metal and organic matter. Sequential extraction of metals bound to untreated and chemically treated particles in the partitioning experiments indicated that the exchangeability or lability of all metals increased on removal of either oxides or POM. This implies that sorption sites of relatively high energy are destroyed (or become less accessible), or sorption sites of relatively low energy are created (or become more accessible) on chemical treatment. These observations support a conceptual model for the particle surface whose integrity and binding properties are only maintained by the coexistence of and interaction between oxides and organic matter.  相似文献   

19.
Data from the R/V Mirai cruise (May–June 2000) have been examined to discover how mesoscale processes associated with eddy dynamics direct affect the water masses, the distributions and the vertical fluxes of the dissolved oxygen, nutrients and dissolved inorganic carbon in the western subarctic Pacific. Using maps of the temperature, salinity, dissolved oxygen, nutrients, chlorophyll and sea-air pCO2 difference we show that the boundaries of the anticyclone eddies in the study region were composed of high productivity coastal Oyashio water. The coastal waters were wrapped around the anticyclone eddies (thus creating a high productivity belt) and intruded inside of them. Using SeaWifs data we demonstrate that temporal variations in the position and the strength of anticyclone eddies advected the Kuril island coastal high productivity waters to the pelagic part, resulting in temporal variations of the chlorophyll in the Oyashio region. Computed vertical fluxes of the dissolved oxygen (DO), inorganic carbon (DIC) and silicate show that the anticylonic eddies in the Kuroshio-Oyashio Zone are characterized by enhanced vertical fluxes of the DO and DIC between the upper (σθ = 26.7–27.0) and lower (σθ = 27.1–27.5) intermediate layer, probably due to the intrusions of the Oyashio waters into the eddies. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

20.
East-west vertical sections centered on Kinmei Seamount (35N, 172E) of potential temperature, salinity, and oxygen, based on recent standard hydrographic measurements, and vertical profiles ofin situ temperature and density ( 4) east of the seamount, based on STD data, show contrasting variability in the deep water characteristics east and west of the seamount. These data are consistent with horizontal variations in water mass properties (temperature-salinity and temperature-oxygen curves) east of the seamount between 2,600–3,900 m but not west of the seamount. East of the seamount on surfaces of constant potential temperature (or density) salinity and oxygen are higher at a station 200 km from the seamount than at stations on either side. From these relations and from known deep water properties of the North Pacific, it is suggested that east of the seamount, between 2,600–3,900 m, the observations are consistent with northward flow, which is interpreted to be a western boundary current with an east-west scale of about 300 km.  相似文献   

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