Calculation of energy of the barotropic-baroclinic interaction in the strait of Bab el Mandeb

Equations for the kinetic, potential, and total energy in the curvilinear boundary-fitted coordinates are considered in the strait area and adjacent regions of the Red Sea and Gulf of Aden. The budgets of different forms of energy are presented, making it possible to assess the correctness of the formulation of the three-dimensional boundary-value problem, the accuracy of the calculation of the barotropic-baroclinic interaction in an energy norm, and the relationship between the components of energy balance. The energy fluxes in the boundary sections of the strait are estimated for the interaction of thermohaline currents with main tidal harmonics and with the total tide, as well as for the amplitude of fluctuations in boundary energy fluxes in a synodic month. The results illustrating the behavior of some dynamical characteristics and components of energy balance at vertical and horizontal sections of the strait are given.     

Internal tide in the Kara Gates Strait

We observed strong internal tidal waves in the Kara Gates Strait. Internal tides are superimposed over a system of mean currents from the Barents to the Kara Sea. Field studies of internal tides in the Kara Gates were performed in 1997, 2007, and 2015. In 2015, we analyzed data from towed CTD measurements, numerical model calculations, and satellite images in the region. An internal tidal wave with a period of 12.4 h is generated due to the interaction between the currents of the barotropic tide and the bottom relief on the slopes of a ridge that crosses the strait from Novaya Zemlya to the continent. The depths of the ridge crest are 30–40 m. A constant current of relatively warm water flows from the Barents to the Kara Sea. An internal wave propagates in both directions from the ridge. In the Barents Sea, internal waves are intensified by the current from the Barents to the Kara Sea. Internal bores followed by a packet of short-period internal waves are found in both directions from the strait. Satellite images show that short-period internal waves are generated after the internal bore. A hydraulic jump was found on the eastern side of the strait. Numerical modeling agrees with the experimental results.     

马六甲海峡的潮汐特征分析

马六甲海峡是亚洲东南部的重要海峡通道,沟通太平洋和印度洋,具有重要的经济和战略地位.本文利用马六甲海峡及其毗邻海域验潮站的实测水位资料,分析了马六甲海峡及马来半岛东岸的潮汐特征.研究表明,半日分潮平均振幅最大的区域位于马六甲海峡内部,而全日分潮平均振幅最大的区域为马来半岛的东海岸.马六甲海峡内部以正规半日潮为主,马来半岛东侧则为混合潮港,北部为不正规全日潮,南部则为不规则半日潮.半日分潮M2,S2和全日分潮K1在马六甲海峡内的传播为自西北向东南,而全日分潮O1则为自东南向西北方向.马来半岛东岸的半日潮传播方向以中部的Cendering站为分界线,南、北两部海区分别向南、向北相背传播,而全日潮传播方向相同,统一为自北向南.     

Numerical study of M2 internal tide generation and propagation in the Luzon Strait

Based on the z-coordinate ocean model HAMSOM,we introduced the internal-tide viscosity term and applied the model to numerically investigate the M2 internal tide generation and propagation in the Luzon Strait (LS).The results show that (1) in the upper 250 m depth,at the thermocline,the maximum amplitude of the generated internal tides in the LS can reach 40 m;(2) the major internal tides are generated to the northwest of Itbayat Island,the southwest of Batan Island and the northwest of the Babuyan Islands;(3) during the propagation the baroclinic energy scattering and reflection is obvious,which exists under the effect of the specific topography in the South China Sea (SCS);(4) the westward-propagating internal tides are divided into two branches entering the SCS.While passing through 118 E,the major branch is divided into two branches again.The strongest internal tides in the LS are generated to the northwest of Itbayat Island and propagate northeastward to the Pacific.However,to the east of 122 E,most of the internal tides propagate southeastward to the Pacific as a beam.     

A study of SAR remote sensing of internal solitary waves in the north of the South China Sea:I.Simulation of internal tide transformation

For settlement of the well-known problem of contemporary radar imaging models,i.e.,the pmblem of a general underestimation of radar signatures of hydrodynamic features over oceanic internal waves and underwater bottom topography in tidal watels at at high radar frequency bands(X-band and C-band),the impact of the ocean surface mixed layer turbulence and the significance of strat-ified oceanic model on SAR remote sensing of internal solitary waves are proposed.In the north of the South China Sea by utilizing seme observed data of background field the nonlinearity coefficient,the dispersion coefficient,the horizontal variability coefficient and the phase speed in the generalized K-dV equation are determined approximately.Through simulations of internal tide transfor-mation the temporal evolution and spatial distribution of the vertical displacement and horizontal velocity of intereal wave field are obtained.The simulation results indicate that the maximum amplitudes of internal solitary waves occur at depth 35 m,but the maximum current speeds take place at depth 20 m in this area of the sea(about 20°30'N,114°E)in August.It was noticed that considering the effects of flood current and ebb current respectively is appropriate to investigate influence of the background shear flow on coefficients of the K-dV equation.The obtained results provide the possibility for the simulation of SAR signatures of inter-nal solitary waves under considering the impact of ocean surface mixed layer turbulence in the companion paper.     

Development of the red tide in the Ka tela Bay (Adriatic Sea)

Ka tela Bay is a semi-enclosed coastal bay in the Middle Adriatic which behaves as a dilution basin, as the result of a freshwater inflow. The area near a river mouth is heavily polluted by a number of sewage outfalls. Red tide (RT) events have been observed there regularly every summer in the last decade. During summer 1988, the concentrations of the RT organisms and bacterioplankton, and some chemical and hydrographic parameters, were monitored. The purpose of this paper is to determine, on the basis of the RT monitoring results, whether there is an interaction between concentrations of RT organisms and state variables, i.e. pH, dissolved oxygen, temperature and salinity. Additionally, the relationship between the concentration of the RT organisms and bacterioplankton is examined. Attention is also focused on the dependence of the concentration of the RT organisms on the wind field variations. The empirical orthogonal function (EOF) analysis method is applied. The results of the study suggest that quiescent periods are characterized by the highest concentration of RT organisms. On the other hand, vertical mixing induced by strong wind events is associated with a decrease of concentration of RT organisms. Variations in the oxygen concentration in the surface layer are associated with the phytoplankton density.     

Pole tide in the Baltic Sea

The pole tide, which is driven by the Chandler Wobble, has a period of about 14 months and typical amplitudes in the World Ocean of ～0.5 cm. However, in the Baltic Sea the pole tide is anomalously high. To examine this effect we used long-term hourly sea level records from 23 tide gauges and monthly records from 64 stations. The lengths of the series were up to 123 years for hourly records and 211 years for monthly records. High-resolution spectra revealed a cluster of neighboring peaks with periods from 410 to 440 days. The results of spectral analysis were applied to estimate the integral amplitudes of pole tides from all available tide gauges along the coast of the Baltic Sea. The height of the pole tide was found to gradually increase from the entrance (Danish Straits, 1.5–2 cm) to the northeast end of the sea. The largest amplitudes—up to 4.5–7 cm—were observed in the heads of the Gulf of Finland and the Gulf of Bothnia. Significant temporal fluctuations in amplitudes and periods of the pole tide were observed during the 19th and 20th centuries.     

Simulation of surface and internal semidiurnal tides in the Kara Sea

The problem of the dynamics of surface and internal waves M ₂ in the Kara Sea is solved within the QUODDY-4 3D finite-element hydrostatic model. It is shown that the conventional concept of surface-tide wave generation due to the interaction of two tidal waves (one arrives from the Barents Sea and the other is generated in the Arctic Ocean (AO) and propagates southward along the west coasts of Severnaya Zemlya) is only partially valid: the east branch of the tidal wave generated in the AO actually exists, but there is also a west branch that propagates along the St. Anna trough and another tidal wave that penetrates in the Kara Sea from the Laptev Sea through the Vilkitsky Strait. Simulated spatial distributions of the tidal velocities, amplitudes of internal tidal waves at the pycnocline depth, and some components of the budgets of barotropic and baroclinic tidal energy are discussed.     

Internal tide and nonlinear internal wave behavior at the continental slope in the northern south China Sea

A field program to measure acoustic propagation characteristics and physical oceanography was undertaken in April and May 2001 in the northern South China Sea. Fluctuating ocean properties were measured with 21 moorings in water of 350- to 71-m depth near the continental slope. The sea floor at the site is gradually sloped at depths less than 90 m, but the deeper area is steppy, having gradual slopes over large areas that are near critical for diurnal internal waves and steep steps between those areas that account for much of the depth change. Large-amplitude nonlinear internal gravity waves incident on the site from the east were observed to change amplitude, horizontal length scale, and energy when shoaling. Beginning as relatively narrow solitary waves of depression, these waves continued onto the shelf much broadened in horizontal scale, where they were trailed by numerous waves of elevation (alternatively described as oscillations) that first appeared in the continental slope region. Internal gravity waves of both diurnal and semidiurnal tidal frequencies (internal tides) were also observed to propagate into shallow water from deeper water, with the diurnal waves dominating. The internal tides were at times sufficiently nonlinear to break down into bores and groups of high-frequency nonlinear internal waves.     

Lithology and mineralogy of surface sediments in the vicinity of the Kafireas Strait (Aegean Sea)

The surface sediments of the Kafireas Strait and Petalion Gulf, the area between the islands of Evvoia, Andros, Gyaros and Kea in the Aegean Sea, were examined for grain size, mineralogical composition and geotechnical properties. Contents of sand, silt, clay and carbonates as well as porosity, absolute and relative water contents, grain density and bulk mineralogy were determined in samples collected at 35 localities during two oceanographic cruises in April 1986 and July 1991. In addition, current measurements were carried out at three localities in the periods May-June 1988 and July 1991. Muddy sand and sand (52-96% sand) cover the continental shelf, whereas sandy mud (3-49% sand) predominates in deeper areas. Absolute water content varied between 22 and 42%, whereas the values for relative water content were 28-73%. Porosity showed a moderate range of values (36-62%), whereas grain density varied between 2.52 and 2.77 g/cm³. Carbonate content showed a wide range of values (30-72%). Mica and kaolinite are the dominant minerals (average contents 32 and 16.6%, respectively), and quartz, plagioclase, calcite and aragonite showed lower contents of 12.9, 9.8, 13.5 and 9.6%, respectively. Higher mica, kaolinite, chlorite and plagioclase contents closer to Evvoia Island may be related to local mica-amphibolitic-chloritic schists and cipollin outcrops, whereas higher percentages of mica, calcite and aragonite probably relate to the mica schists and marbles of Andros Island. Strong currents were recorded near the seabed in the vicinity of the Kafireas Strait (24 and 38 cm/s maximum velocity on the continental shelf off Evvoia and Andros islands, respectively). The regional geomorphology and bathymetry, the texture and mineralogical composition of terrigenous material, and the particular meteorological and hydrodynamic conditions in the area are the main factors which control the texture, mineralogy and distribution of seabed sediments in the vicinity of the Kafireas Strait.     

南海东沙岛西南大陆坡内潮特征

2008年4月-10月,在南海东沙岛西南大陆坡底部布放了1套全剖面锚系,同时沿大陆坡底部布放了3套近底锚系,应用谱分析和调和分析方法分析温度和海流连续观测资料,进而研究该海域的内潮特征.结果表明,东沙岛西南大陆坡存在强内潮现象,大陆坡底部温度变化受到内潮波的影响,上层海洋存在强日潮周期的内潮波振动;正压潮和斜压潮均以O...     

Barotropic tide in the northeast South China Sea

A moored array deployed across the shelf break in the northeast South China Sea during April-May 2001 collected sufficient current and pressure data to allow estimation of the barotropic tidal currents and energy fluxes at five sites ranging in depth from 350 to 71 m. The tidal currents in this area were mixed, with the diurnal O1 and K1 currents dominant over the upper slope and the semidiurnal M2 current dominant over the shelf. The semidiurnal S2 current also increased onshelf (northward), but was always weaker than O1 and K1. The tidal currents were elliptical at all sites, with clockwise turning with time. The O1 and K1 transports decreased monotonically northward by a factor of 2 onto the shelf, with energy fluxes directed roughly westward over the slope and eastward over the shelf. The M2 and S2 current ellipses turned clockwise and increased in amplitude northward onto the shelf. The M2 and S2 transport ellipses also exhibited clockwise veering but little change in amplitude, suggesting roughly nondivergent flow in the direction of major axis orientation. The M2 energy flux was generally aligned with the transport major axis with little phase lag between high water and maximum transport. These barotropic energy fluxes are compared with the locally generated diurnal internal tide and high-frequency internal solitary-type waves generated by the M2 flow through the Luzon Strait.     

Short-period internal waves in the frontal zones of non-tidal seas (the Black Sea and the Aegean Sea)

This paper reports empirical data on short-period internal waves in the Black Sea and Aegean frontal zones, collected through the use of distributed temperature sensor arrays. Peculiar features of the behaviour and propagation of the internal waves in these zones are shown. It is shown that the wavefield is anisotropic and reduction of the wave lengths diminishes during the climb up a sloping pycnocline. The energy level of the spectra of internal wave oscillations in the frontal zones of non-tidal seas was found to be lower than that relating to oceanic frontal zones.Translated by Vladimir A. Puchkin.     

Circulation in the Gulf of Aqaba (Red Sea) during winter—spring

This study is devoted to oceanographic features of the semi-enclosed Gulf of Aqaba, Red Sea. The data were recorded in winter—spring 1999 on the R/V Meteor cruise leg 44/2. Temperature and salinity profiles were measured at six positions (I—VI). The shipboard NarrowBand Acoustic Doppler Current Profiler (NB ADCP) 150 kHz continuously recorded current profiles down to 350 m en route. The research revealed that the current near the Strait of Tiran front (position VI) represents a semidiurnal signal of an internal tide wave (∼12 h period; 0.2 ms⁻¹ amplitude) that might be generated by the barotropic tide at the sill of the Strait. A sequence of cyclonic and anticyclonic eddy pairs is found along the axis of the Gulf of Aqaba during winter-spring seasons. These sub-mesoscale signals are dominant above the main thermocline and might be caused by wind forcing and the narrowness of the Gulf; it might remain in other seasons with different dimensions in relation to the depth of thermocline. The total diameter of each pair was twice the baroclinic Rossby radius (R ≈ 10 km). A single anti-cyclonic eddy was observed in the upper 300 m in the northern tip of the Gulf with a diameter of about 5–8 km.     

基于FVCOM 的渤海潮波数值模拟

基于有限体积法海洋数值模型(FVCOM),对渤海当前水深岸线状况下的潮汐潮流进行了数值计算。模式采用不规则三角形网格,较好地提高了黄河口处网格分辨率,模拟了渤海海域K1,O1,M2和S2四个主要分潮。利用渤海沿岸19个验潮站的资料对模拟结果进行了验证,K1分潮振幅绝均差2.39 cm,迟角绝均差4.36°,O1分潮振幅绝均差1.40 cm,迟角绝均差4.29°,M2分潮振幅绝均差为3.55 cm,迟角绝均差为5.69°,S2分潮振幅绝均差1.72 cm,迟角绝均差8.86°,结果显示各分潮模拟结果合理,较真实地反映了渤海海域四个分潮传播情况。     

渤海冰漂移对海面风场、潮流场的响应

在对海冰漂移动力学分析基础上,利用MODIS资料,采用MCC方法获取渤海大范围冰覆盖的海域冰速场,并利用NCEP风速资料和潮流资料进行回归分析,得到渤海冰漂移速度与风速和流速的关系.利用MODIS和NOAA/AVHRR资料获取的渤海冰速资料的综合分析显示:渤海海冰运动,除受盛行风控制外,还受到复杂的海岸地形、流和冰内应力的共同作用,所得到的大范围海冰运动规律和多年历史观测资料分析结果基本一致,并清楚地显示了冰边缘带海冰运动的特征,弥补了局地、单站海冰观测的局限性.     

Numerical simulations of the internal tide in a submarine canyon

Three-dimensional numerical simulations of the generation and propagation of the semidiurnal internal tide in a submarine canyon with dimensions similar to those of the Monterey Canyon are carried out using a primitive equation model. Forcing with just sea level at the offshore boundary in an initially horizontally homogeneous ocean with realistic vertical stratification, internal tides are generated at the canyon foot and rim, and along portions of the canyon floor. The results compare favorably with observations, both indicating enhancement of energy along the canyon floor propagating at an angle consistent with linear internal wave theory. Due to the earth's rotation, internal tide energy is distributed asymmetrically in the cross-canyon direction, favoring the southern side. The effect of canyon floor slope is explored, with the finding that small changes in the slope result in large changes in the amount and distribution of the internal tide energy. Canyons whose floors are subcritical with respect to the semidiurnal frequency along their entire length have very little baroclinic energy, whereas canyons that are near-critical along much of their length, such as the Monterey Canyon, develop strong internal tides that propagate shoreward. Canyons that are near-critical at their mouths but supercritical further inshore generate the most internal tidal energy overall, although little of it makes it onto the continental shelf shoreward of the canyon head. The effects of internal tides within the canyons can be seen outside the canyons as well. Water is transported from depth onto the adjacent continental shelf along the canyon rims. This tidal pumping can be responsible for alongshore internal tide propagation and tidal-period surface currents with relatively small horizontal scales of variability.     

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     

Study of dissolved oxygen content in the Eastern Bosporus Strait (Peter the Great Bay,Sea of Japan)

Seasonal changes in the dissolved oxygen (DO) content in water were analyzed based on long-term observations (2006–2013) in the Eastern Bosporus Strait (Peter the Great Bay, Sea of Japan). It was found that the monthly average DO concentrations at the bottom of the strait were significantly lower in summer than the average annual long-term data. The minimum DO contents were recorded during four months, from July to October. It was shown that the DO content in water depended on changes in current directions in the strait: lower DO contents resulted from hypoxic water inflow, mostly from Amur Bay.