正压浅海湍流运动的雷诺应力封闭模型

根据湍流封闭理论,建立一种适用于正压浅海湍流运动的雷诺应力封闭模型(RSM),以代替目前三维浅海动力学模型中普遍采用的湍粘性系数的传统假设。通过直接建立并模化f—平面上正压海洋的雷诺应力传输方程,分别得到的微分形式和代数形式的RSM方程组。并讨论了进行数值计算所需要的边界条件。利用该模型可以进一步研究浅海潮流、风暴潮流及风海流等浅海流动的三维结构和湍流特性。     

Active seepage in two contrasting pockmark fields in the Patras and Corinth gulfs, Greece

Two pockmark fields, located along the coastal zone of the Patras and Corinth gulfs, Greece were surveyed in detail. The pockmark fields, which are 30 km apart, are formed in shallow waters at depths of 20–40 m and are about 0.5–1 km from the shoreline. The oceanographic data suggest that two different mechanisms were responsible for their formation. The pockmark field in the Patras Gulf appears to have been formed as a result of methane seepage from the seabed, whereas the field in the Corinth Gulf appears to have resulted from groundwater seepage.     

Modelling of wind currents in the Donuzlav lake

A barotropic variant of a multilevel numerical model based on primitive equations of sea dynamics is applied to calculate wind-induced circulation in the Donuzlav lake. Water exchange with the open sea is considered. The paper examines several situations involving wind forcing. It shows that a two-layer system of currents occurs in the lake. The effect of the bottom topography is essential, being traceable up to the surface. Translated by Vladimir A. Puchkin.     

Sources and hydrothermal alteration of organic matter in Quaternary sediments: A synthesis of studies from the Central Gulf of California

Deep sea drilling in the Central Gulf of California, a young and active spreading centre, shows that the high heat flow typical of these regions causes extensive alteration of sediment organic matter, especially near sills and above magma chambers where hydrothermal activity is concentrated. Even on the nearby passive margin, where there are no sills, heat flow is moderately high and hydrocarbon generation has begun in immature sequences. Migrating light hydrocarbons are detected especially where hydrothermal activity is concentrated. Thermogenic methane is more widespread, though not in the passive margin bordering the spreading centre. Despite the incidence of hydrocarbon generation and migration, the amounts of hydrocarbons involved are relatively small and apparently do not lead to commercially significant accumulations of petroleum.The organic matter in these sediments is mostly marine because the Gulf of California generally has low runoff from land and highly productive surface waters. Turbidites rich in terrigenous organic material are locally abundant in the mainly pelagic section in the Guaymas Basin. The highest concentrations of organic matter are found in laminated diatomites deposited on the Guaymas passive margin within the oxygen minimum zone.     

A Lagrangian mean theory on coastal sea circulation with inter-tidal transports Ⅱ. Numerical Experiments

The results of the new concept of coastal sea circulation are demonstrated by numerical simulations for the first time. The numerical experiments in three types of rectangular model seas illustrate the dependence of circulation on tidal phases due to the convectively nonlinear effect which is estimated by a newly defined drift dispersion index. Then, the present theory is applied in the Bohai Sea of China. At the Bohai Straits and the Huanghe River mouth area the circulation direction even reverses owing to different initial tidal phases which shows that the theory copes with nonlinearity well. The calculated M2 tideinduced residual circulation shows that a clockwise gyre exists in the center of an anticlockwise gyre in the central Bohai Sea due to the topographic features. In the Bohai Gulf the tide induced circulation shows a 3D structure with outflow at the surface and the inflow at the bottom which can partly explains the spread of the Huanghe River fresh water out of the Bohai Gulf and the inflow of the sediment from the Huanghe River.     

Analysis of characteristics and mechanism of current system on the west coast of Guangdong of China in summer

On the basis of data of drifting bottles＇ tracks and the current measured in anchored stations, as well as temperature and salinity observed in cruise investigations and coastal stations, ADCP current data and AVHRR surface sea temperature （SST） data on the western coast of Guangdong, synthetic results of analysis showed that the coastal currents in the west of the mouth of the Zhujiang River were mainly westward in summer, which constituted the north branch of cyclonic gyre in the east of the Qiongzhou Straits. Part of its water flowed westward into the Beibu Gulf through the Qiongzhou Straits. The coastal current pattern was not identical with the traditional current system which flowed westward in the Qiongzhou Straits in winter and eastward in summer. The summertime＇s coastal current was always westward, maybe temporarily turning northeast only when the southwest wind was strong. The important characteristics of coastal current on the western coast of Guangdong, in the Qiongzhou Straits and in the north of the Beibu Gulf were analyzed and their mechanisms also were explained.     

Patterns of summer vertical and horizontal currents in coastal waters of the northern Gulf of Aqaba, Red Sea

This study was focused on analysis of the horizontal and vertical current components with correspondence to tide variation, heat flux, seiches and relative backscatter intensity in coastal waters of the northern Gulf of Aqaba during the summers of 2001–2004. Spectrum analysis has shown eight distinguishable peaks of the tide measurements. In addition to semidiurnal and diurnal barotropic tides, signal periods of 8.13, 5.89–6.32 and 4.06 h were related to shallow water compound and overtides of the principal solar and lunar constituent and to seiches (second and third mode) generated in the Red Sea, whereas seiches of the first mode might enhance the semidiurnal tide signal. The shortest periods of 1.02–1.05, 0.50 and 0.36 h were related to seiches (first, second and third mode, respectively) generated in the Gulf of Aqaba. The spectrum analysis and cross-correlation tests of the horizontal and vertical current components and relative backscatter intensity suggested that the vertical motion at the diurnal period was either due to migration of zooplankton or to water convection. Both of which were of the same order as vertical motion induced by horizontal motions of water particles projected parallel on the bottom gradient line. On the other hand, semidiurnal and diurnal periods detected in the vertical currents were caused by the strong signal in the cross-shore current component, first mode seiches generated from the Red Sea and tide. This could be considered as an indicator of the dominant force influencing the currents, such as winds, thermocline depth, seiches and tidal forcing. A permanent convection during summer is likely to occur in the shallow coastal waters due to relatively high inclined bottom, high evaporation and blowing of dry air, as well as the observed dominance of the downward vertical currents in coastal waters.     

A Lagrangian mean theory on coastal sea circulation with inter-tidal transports Ⅱ. Numerical Experiments

The results of the new concept of coastal sea circulation are demonstrated by numerical simulations for the first time. The numerical experiments in three types of rectangular model seas illustrate the dependence of circulation on tidal phases due to the convectively nonlinear effect which is estimated by a newly defined drift dispersion in-dex. Then, the present theory is applied in the Bohai Sea of China. At the Bohai Straits and the Huanghe River mouth area the circulation direction even reverses owing to different initial tidal phases which shows that the the-ory copes with nonlinearity well. The calculated M2 tide-induced residual circulation shows that a clockwise gyre exists in the center of an anticlockwise gyre in the central Bohai Sea due to the topographic features. In the Bo-hai Gulf the tide induced circulation shows a 3D structure with outflow at the surface and the inflow at the bottom which can partly explains the spread of the Huanghe River fresh water out of the Bohai Gulf and the inflow of the sediment from the Huanghe River.     

Coanda effect in coastal flows

In the present paper some numerical simulations and experiments were carried out to study jet-wall interaction in shallow waters. Namely, modifications of the hydrodynamic field concerning the interaction of river run-off with a shallow coastal water body, due to the presence of marine structures, were investigated. Stratification effects due to salinity and temperature were neglected, and the interest was focused on barotropic features (Coanda effect). The numerical analysis was carried out by means of shallow water equations, numerically solved by finite difference, and the present method was validated by means of a typical simple-shaped test case. The experiments were carried out in a shallow water tank, flow visualizations were performed, and the velocity field was obtained by PIV. The main features of jet-wall interaction flow were investigated in simple-shaped geometries, and applications were shown for two practical cases: Pescara channel harbour (Adriatic Sea, Italy) and the proposed design of Latina harbour (Tyrrhenian Sea, Italy).     

Combined numerical model of currents, waves, and sediment transport in Lake Donuzlav

We present a numerical model of the dynamics of Lake Donuzlav, which enables one to perform simultaneous numerical analyses of the currents, sea level, waves, and sediment transport. The model is based on the hydrodynamic block and the spectral wave model. For typical storm situations, we study the specific features of the integral circulation of waters and the three-dimensional structure of currents, investigate the wind-induced wave fields, and evaluate the flows of sediments and deformations of the bottom. The presence of intense eddy structures is revealed in the field of currents caused by the bottom topography. A significant intensification of waves in the south part of the lake is established in the case of penetration of storm waves through the strait. It is shown that the account of waves leads to qualitative changes in the structure of circulation in the lake and to the formation of well-pronounced areas of wave-induced elevations and lowerings of the sea level. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 43–65, March–April, 2006.     

Solitary wave generation dynamics at Luzon Strait

A high resolution modeling study is undertaken, with a 2.5-dimensional nonhydrostatic model, of the generation of internal waves induced by tidal motion over the ridges in Luzon Strait. The model is forced by the barotropic tidal components K1, M2, and O1. These tidal components, along with the initial density field, were extracted from data and models. As the barotropic tide moves over the Luzon Strait sills, there is a conversion of barotropic tidal energy into baroclinic tidal energy. Depressions are generated that propagate towards the Asian Seas International Acoustics Experiment (ASIAEX) test site on the Chinese continental shelf. Nonlinear effects steepen the depressions, frequency and amplitude dispersion set in, and disintegration into large amplitude solitary waves occurs. The effects of varying the initial density field, tidal component magnitudes, as well as adding a steady background current to represent the occasional excursions of the Kuroshio Current into the strait, are considered.Depressions are generated at each of the two sills in Luzon Strait which radiate away, steepening and evolving into internal solitary wave trains. Baroclinic fluxes of available potential energy, kinetic energy and linear are calculated for various parameter combinations. The solitary wave trains produced in the simulations generally consist of large amplitude wave trains alternating with small amplitude wave trains. During strong tidal flow, Kelvin–Helmholtz type instabilities can develop over the taller double-humped sill. The solitary waves propagating towards the ASIAEX test site have been observed to reach amplitudes of 120–250 m, depending on the tidal strength. ASIAEX observations indicate amplitudes up to 150 m and the Windy Island Experiment (WISE) measurements contain magnitudes over 200 m. The model results yield solitary wave amplitudes of 70–300 m and half widths of 0.60–3.25 km, depending on parameter values. These are in the range of observations. Measurements by Klymak et al. (2006), in the South China Sea, exhibit amplitudes of 170 m, half widths of 3 km and phase speeds of 2.9 m s^?1. Model predictions indicate that the solitary waves making up the wave packet each experience different background currents with strong near surface shear.The energy in the leading soliton of the large amplitude wave trains ranges between 1.8 and 9.0 GJ m^?1. The smaller value, produced using barotropic tidal currents based on the Oregon State University data base, is the same as the energy estimated to be in a solitary wave observed by Klymak et al. (2006). Estimates of the conversion of barotropic tidal energy into radiating internal wave energy yield conversion rates ranging between 3.6% and 8.3%.     

Short-term fluctuations of the Tsushima Current in waters northwest of Yamaguchi Prefecture

We discussed the short-term fluctuations of the Tsushima Current, using ADCP (acoustic Doppler current profiler) data taken by the quadrireciprocal method (Katoh, 1988) for removing tidal currents from observed currents. Transects were set in waters northwest of Yamaguchi Prefecture to capture the first and second branches of the Tsushima Current. Along the transects, ADCP and STD (salinitytemperature-depth recorder) measurements were repeated in May to July 1989. The velocity of the first branch fluctuated considerably in a short period, while the direction and position of its axis were steadly. The stability of its axis position probably results from the topographic effect. The baroclinic transport, which is based on calculations of geostrophic current with assuming zero velocity near the bottom, of the first branch was almost equal to the barotropic one. The range of fluctuation in the barotropic transport was much larger than that in the baroclinic transport. The barotropic fluctuation was correlated with the difference in atmospheric pressure between the east and west sides of the Tsushima Strait. As for the second branch, not only the velocity but also the position of its axis changed noticeably in a short period. There was such a case where the axis was hardly recognized. The changeability of the axis position for the second branch seems to result from that of the cold water front. The baroclinic transport of the second branch was much larger than the barotropic one, but the ranges of their fluctuations were very similar with each other.     

A numerical experiment on the variations of western boundary currents: Part I. Formation of western boundary currents

A numerical experiment is made using a barotropic model for the western boundary currents. The time-dependent, non-linear vorticity equation is integrated with and without the variable of bottom topography. The inertial and frictional boundary flow is resolved with a fine grid size of 10 km. Connection of the western boundary currents with the general circulation is facilitated by giving the fixed Sverdrup transport at the eastern boundary of the model (400 km offshore).For the flat bottom topography, steady flow forRe=35 shows dynamical balance essentially of a frictional model. The transient response leading to the formation of the western boundary currents in the model seems to support theLighthill's theory (1969). ForRe=350, unsteady features revealed byBryan (1963) is re-established. A phenomenon of barotropic instability is also observed with sufficient resolution. For the model with a continental slope the steady flow is also obtained forRe=35. The boundary currents flow over the continental slope, deviating offshore as they flow northward.     

On the total geostrophic circulation of the South Pacific Ocean: Flow patterns,tracers and transports

I have used the patterns of tracers (temperature, salinity, oxygen, silica, helium-3) and of density to estimate the geostrophic circulation (baroclinic plus barotropic) of the South Pacific Ocean at all depths. That is, the direction of horizontal flow is determined at all depths in a manner that appears to be consonant with the tracer patterns and that satisfies continuity of mass.Within the upper kilometer the velocity shear is much stronger than at greater depths, and the baroclinic flow field alone is closely consonant with the tracer patterns except near the western boundaries. The barotropic components added to the baroclinic to provide a flow field that matches the tracer patterns in the deeper waters and to achieve continuity are quite small except in the western boundary currents, and only there do they provide a combined flow pattern significantly different from the baroclinic alone.The resulting field of flow has equatorward deep western boundary undercurrents in each of the three basins and a poleward flow along the eastern boundary. A part of the Circumpolar Current follows the southern side of the East Pacific Rise around the Southeast Pacific Basin and then through the Drake Passage. The broad-ocean anticyclonic gyre of the upper waters is broken at depth by the Tonga-Kermadec Ridge and the East Pacific Rise into separate gyres in the Tasman Sea and the central basin, where it extends nearly to the bottom in the north.In the central basin the northward abyssal flow is not confined to the western boundary but extends all across the basin, diverted only slightly in the north by the small deep remnant of the anticyclonic gyre.     

Physical oceanographic conditions in the deepwater Gulf of Mexico in summer 2000–2002

The circulation and distribution of water properties in the water column of the Gulf of Mexico influence the flux of carbon to the benthic environment. The eddy field of the upper 1000 m creates environmental conditions that are favorable for biological productivity in an otherwise oligotrophic subtropical ocean. This eddy field results in the transport of nutrients and organic matter into the photic zone through cross-margin flow of shelf waters, upwelling in cyclones, and uplift from the interaction of anticyclones with bathymetry. These conditions then allow the productivity that becomes a possible source of carbon to the benthos.Data from four cruises during summers of 2000–2002 are used to describe the currents and water property distributions in the deepwater Gulf of Mexico, which consists of water depths greater than 400 m. Comparisons are made to historical data sets to provide an understanding of the persistence of the characteristics of the Gulf and the processes that occur there.The currents in the Gulf are surface intensified, have minimum in 800–1000 m depths, and also exhibit bottom intensification, especially near sloping topography. Historical time series records show current speeds near-bottom reach 50–100 cm s⁻¹. At basin scales, these currents tend to flow cyclonically (counter-clockwise) along the bathymetry. These near-bottom, episodic, high-speed currents provide a mechanism for the transport of organic material, in both large and small particle sizes, from one benthic area to another.The distributions of temperature, salinity, nutrients, and dissolved oxygen during the study appear to be unchanged from historical findings. The source waters for the deep Gulf are the water masses brought into the Gulf by the Loop Current system. The properties in the upper 100–200 m are the most variable of the water column, consistent with their proximity to wind mixing, river discharge mixing, and atmospheric influences. Below 1500 m, there are no major horizontal variations in these water properties.     

A survey of baroclinic tides in the Beibu Gulf in the South China Sea

The principal characteristics of the tides are investigated by a shipborne acoustic Doppler current Profiler at a fixed station located in the Beibu Gulf from 4 to 14 April 2003. Data analysis indicates that the diurnal tidal currents dominate local current variations at the observing site. Except the barotropic M_2 constituent, four principal tides comprise both back-and-forth barotropic and baroclinic tidal currents. The baroclinic tidal ellipse parameters vary with depth, showing complicate features, rather than monotonous features being figured. For baroclinic tidal constituents, vertical modes are different to each other. Similarly, the semi-major axes of the tidal constituents vary with depth. In the lower layer, a nonlinear regression approach is used to calculate and obtain the SEMA profiles of diurnal tidal constituents. Results show that in the thin bottom boundary layer, all of the parameters vary drastically with depth, totally distinguished from the vertical profiles above.     

A comparison of two formulations of barotropic–baroclinic splitting for layered models of ocean circulation

In numerical models of ocean circulation, it is widespread practice to split the fast and slow motions into barotropic and baroclinic subsystems, respectively. In the case of the baroclinic equations, the dependent variables can either be (1) slowly-varying baroclinic quantities, obtained from splitting the original flow variables into barotropic and baroclinic components, or (2) the original unsplit variables, which can vary on both the fast and slow time scales. In the second case, the variables in each layer are adjusted after each (long) baroclinic time step to ensure compatibility with the results produced from the barotropic equations. The second approach can be applied to the layer thickness equation to ensure exact conservation of mass within each layer. In the case of the momentum equations, the second approach amounts to replacing unresolved fast portions of Coriolis and pressure forcing with time averages of well-resolved forcing from the barotropic system. In this study, both approaches for the momentum equations are evaluated, in several test problems, by comparing to analytical solutions or to solutions computed with an unsplit code that uses short time steps. The two methods give very similar results in some simple problems for which analytical solutions are known. However, in some eddying double-gyre simulations, the formulation with unsplit variables requires a significant reduction in the baroclinic time step in order to avoid numerical difficulties that include grid noise and inaccurate representation of the flow field. In contrast, the formulation with split variables does not display such difficulties, and in those same examples it can be used with zero explicit horizontal viscosity. All of these computations employ a two-level time-stepping method that was previously developed by the author.     

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 model investigation of the residual circulation in Hauraki Gulf,New Zealand

The homogeneous residual circulation in Hauraki Gulf arising from the tides, steady winds, and oceanic inflows is considered by use of a depth‐averaged 2‐dimensional numerical model. Vertical current structure of the wind‐driven circulation is derived by using the computed wind‐induced sea surface slopes, the wind stress, and a prescribed vertical eddy viscosity. Tidal residual circulation is weak, less than 0.01 ms^‐1 over most of the Gulf. The response of the Gulf to wind‐forcing indicates a preference for north‐west/south‐east directed winds, the flow through the Gulf being more than 3 times as strong as for winds from other directions. Surface currents are mainly in the wind direction, but subsurface currents reveal closed circulation cells in near‐coastal areas. Simple oceanic inflows give rise to water movements which penetrate to the inner part of the Gulf.