Decadal sea level trends in the Bay of Biscay from tide gauges, GPS and TOPEX

Sea level time series derived from TOPEX altimeter and from tide gauge measurements in the Bay of Biscay (Eastern North Atlantic Ocean) are used to investigate the regional sea level rise. Altimetry sea level anomalies are computed from TOPEX measurements and resampled into fixed along track bins in order to obtain consistent records and to approach as close as possible to the coast. Tidal corrections are critical in the estimation of sea level trends; therefore an additional analysis has been carried out in order to identify and correct for residual tidal signals. The obtained mean sea level rise in the region is + 3.09 ± 0.21 mm/year over the period 1993–2002. Tide gauges have been corrected for vertical land motions by means of collocated GPS measurements. GPS-corrected tide gauges and nearby altimetry trends are found to be statistically consistent. The relationship with the atmospheric forcing is also investigated revealing that 15% of this sea level rise is attributed to the atmospheric pressure effects.     

Numerical simulations of seasonal and interannual variability of the Black Sea thermohaline circulation

The Black Sea general circulation is simulated by a primitive equation model with active free surface. The forcing is seasonally variable and is based on available climatic data. The model reproduces the main features of the Black Sea circulation, including the river discharge effects on the mean sea level and the Bosphorus outflow. Model results show that the simulated sea surface elevation increases in spring over the whole sea, reaching a maximum in the Danube delta area. In the same region, a minimum is observed in winter. The amplitude of the seasonal oscillations (about 8–12 cm over the whole basin) is of the same order of magnitude as the maximum horizontal variations (about 15–18 cm between the coastal areas and the basin interior). This strong signal formed mostly by river discharges, along with the seasonal variability in the other forcing functions and the local dynamics creates a well-pronounced interannual variability. The performance of the model in simulating the seasonal and interannual variability is critically analyzed, with a special attention on the cold intermediate water formation and the circulation in the upper 150 m. The simulations demonstrate that the source of intermediate waters is on the shelf, and that the water mass in the core of cold intermediate layer changes with time as a response to the periodic forcing at sea surface. This type of variability is characterized by pronounced interannual changes, proving that important differences could exist between water mass structure in different years, even when using identical atmospheric forcings each year.     

Circulation features in the Japan/East Sea related to statistically obtained wind patterns in the warm season

A response of the circulation in the Japan/East Sea (JES) to different kinds of wind forcing is studied, with the emphasis on the warm season, using a primitive equation oceanic model. Wind forcing is based on typical patterns obtained from complex empirical orthogonal functions of 1°-gridded NCEP/NCAR 6 h winds for 1998–2005. These patterns are distinguished by a prevailing wind direction. Northwestern wind and strong cyclonic (C) curl prevail in winter, while a variety of patterns occur in the warm season, differing in the wind direction and curl. Three model runs are performed to examine the circulation in response to a prevailing C wind stress curl or an alternating C and anticyclonic (AC) curl or a strong C curl in the warm season. The simulated features are consistent with the observational evidence, in particular with thermal fronts and frequent eddy locations derived from multi-year infrared satellite imagery. The simulated C circulation intensifies and the subarctic region extends southward with the strengthening of a summer C wind stress curl over the JES. Variability of Subarctic Front (SF) in the western JES (between 130°E and 133°E) is strongly affected by summer wind stress curl. Forcing by an AC curl tends to shift SF northward, while SF shifts to the south under the forcing by a C curl, reaching the southern Ulleung Basin in the case of the strong C curl. In the northwestern JES (off Peter the Great Bay, Russia, and North Korea), the SF northwestern branch (NWSF) is simulated. It is a known feature in autumn and early winter and can also occur in the warm season. The simulation results suggest an AC wind stress curl as the forcing of the formation of the NWSF in the warm season. The Siberia Seamount and sharply bending coastline near Peter the Great Bay facilitate partial separation of the Primorye (Liman) Current from the coast. The wind stress curl can be an additional forcing of the Tsushima Warm Current (TWC) branching off the Korea Strait to the East Korea Warm Current (EKWC) and the offshore branch (OB). In the warm season, the simulated TWC bifurcation occurs farther north, the EKWC is strong, and the OB is weak under the forcing of the AC wind stress curl. The EKWC is weak and the OB is strong under the forcing of the strong C wind stress curl.     

Resolving the impact of short-term variations in physical processes impacting on the spawning environment of eastern Baltic cod: application of a 3-D hydrodynamic model

Variations in oxygen conditions below the permanent halocline influence the ecosystem of the Baltic Sea through a number of mechanisms. In this study, we examine the effects of physical forcing on variations in the volume of deep oxygenated water suitable for reproductive success of central Baltic cod. Recent research has identified the importance of inflows of saline and oxygenated North Sea water into the Baltic Sea for the recruitment of Baltic cod. However, other processes have been suggested to modify this reproduction volume including variations in timing and volume of terrestrial runoff, variability of the solubility of oxygen due to variations in sea surface temperature as well as the influence of variations in wind stress. In order to examine the latter three mechanisms, we have performed simulations utilizing the Kiel Baltic Sea model for a period of a weak to moderate inflow of North Sea water into the Baltic, modifying wind stress, freshwater runoff and thermal inputs. The model is started from three-dimensional fields of temperature, salinity and oxygen obtained from a previous model run and forced by realistic atmospheric conditions. Results of this realistic reference run were compared to runs with modified meteorological forcing conditions and river runoff.From these simulations, it is apparent that processes other than major Baltic inflows have the potential to alter the reproduction volume of Baltic cod. Low near-surface air temperatures in the North Sea, the Skagerrak/Kattegat area and in the western Baltic influence the water mass properties (high oxygen solubility). Eastward oriented transports of these well-oxygenated highly saline water masses may have a significant positive impact on the Baltic cod reproduction volume in the Bornholm Basin.Finally, we analysed how large scale and local atmospheric forcing conditions are related to the identified major processes affecting the reproduction volume.     

比斯开湾风浪形成与航法

比斯开湾是世界著名大风浪区之一。强大的西风环流、冷空气和气旋活动频繁以及独特的地形,形成了季节性狂风恶浪,为来往于直布罗陀海峡—多佛尔海峡航线的船舶带来威胁。只有准确预报该海域的天气状况,采取正确航法,才能安全驶过这一险恶海域。     

A two-dimensional response to a tropical storm on the Gulf of Mexico shelf

Surface current data from drifting buoys and remotely sensed wind data recorded over the continental shelf in the northeastern Gulf of Mexico during the passage of tropical storm Josephine in October 1996 are examined. Drifter data show the existence of a strong surface jet (velocities reaching 1 m s⁻¹) that moves up the west Florida shelf and westward along the Louisiana–Texas shelf, and lasts for nearly 1 week. The coastal jet occurs during an intense synoptic scale wind event where wind speeds reach 15 m s⁻¹. A simple force balance and statistical analysis are performed to assess the role of strong wind forcing. The primary balance shows an Ekman-type current. The role of local acceleration is greatest when winds are directed along bathymetry. A simple two-dimensional strongly forced shelf response model developed from the linear steady-state momentum equations also indicates larger along-shore currents due to both Ekman-type forcing by cross-shore winds and a cross-shore pressure gradient arising from conservation of mass. Model parameters fit empirically are within 15% of theoretical values. The simple model explains 30% and 46% of the variance in the observed along-shore and cross-shore surface currents, respectively.     

台湾海峡外海港口项目的建设要点

随着海峡西岸经济区开发的加快进行,福建沿海港湾资源的布局正重新整合、调整,煤炭、原油、集装箱等能源、物流基础设施建设正全面展开。尽管海峡西岸具有海域条件良好的兴化湾、湄州湾、泉州港、厦门港等港湾,但随着海运船舶的大型化,港口工程向外海发展也成为趋势。由于特殊的水域条件,在台湾海峡外海建设港口项目有着特殊的要求。结合最近几年在海峡外海按照工程总承包模式建设的几个大型原油、散货码头工程,提出工程建设的经验和体会。     

Sound scattering from rough bubbly ocean surface based on modified sea surface acoustic simulator and consideration of various incident angles and sub-surface bubbles’ radii

The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator (SSAS) developed based on optimization of the Helmholtz–Kirchhoff–Fresnel (HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS (MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall–Novarini model and optimized HKF method. The extended Hall–Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests (CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.     

Preoperational ocean forecasting in the southeastern Mediterranean Sea: Implementation and evaluation of the models and selection of the atmospheric forcing

Within the framework of several local and international programs, a quasi-operational ocean-forecasting system for the Southeastern Mediterranean Sea has been established and evaluated through a series of preoperational tests. The Princeton Ocean Model (POM) is used for simulating and predicting the hydrodynamics while the Wave Model (WAM) is used for predicting surface waves. Both models were set up to allow varying resolution and multiple nesting. In addition, POM was set up to be easily relocatable to allow rapid deployment of the model for any region of interest within the Mediterranean Sea. A common requirement for both models is the need for atmospheric forcing. Both models require time varying wind or wind stress. In addition, the hydrodynamic model requires initial conditions as well as time dependent surface heat fluxes, fresh water flux, and lateral boundary conditions at the open boundaries. Several sources of atmospheric forcing have been assessed based on their availability and their impact on the quality of the ocean models' forecasts. The various sources include operational forecast centers, other research centers, as well as running an in-house regional atmospheric model. For surface waves, higher spatial and temporal resolution of the winds plays a central role in improving the forecasts in terms of significant wave height and the timing of various high wave events. For the hydrodynamics, using the predicted wind stress and heat fluxes directly from an atmospheric model can potentially produce short range ocean forecasts that are nearly as good as hindcasts forced with gridded atmospheric analyses. Finally, a high-resolution, nested version of the model has shown to be stable under a variety of forcing conditions and time scales, thus indicating the robustness of the selected nesting strategy. For the southeastern corner of the Mediterranean, at forecast lead times of up to 4 days the high-resolution model shows improved skill over the coarser resolution driving model when compared to satellite derived sea surface temperatures. Most of the error appears to be due to the analysis error inherent in the initial conditions.     

Variability of the Bohai Sea circulation based on model calculations

The circulation and the hydrography of the Bohai Sea are simulated with the Hamburg Shelf Ocean Model (HAMSOM). The model is three-dimensional, prognostic baroclinic and has a resolution of 5 min in latitude and longitude and 10 layers in the vertical. It is initialised and forced with the five main tidal constituents, temperature and salinity distributions taken from the Levitus database, monthly mean river run-off values and European Centre for Medium Range Weather Forecast (ECMWF) re-analysed data of air pressure, wind stress and of those parameters relevant for the calculation of heat fluxes. The simulation period covers 14 years from 1980 to 1993 due to the availability of the time-dependent ECMWF forcing.The results are analysed by means of time series and EOFs focussing on the interpretation of fluctuations with periods above the tidal cycle. Furthermore, tracer simulations are carried out and turnover times are calculated in order to evaluate the importance of these fluctuations on the renewal and transport of water masses in the Bohai Sea.One of the major outcomes of the investigation is the overall dominance of the annual cycle in all hydrographic parameters and the importance of stochastic weather fluctuations on the transport of water masses in the Bohai Sea.     

Winter phytoplankton blooms in the shallow mixed layer of the South China Sea enhanced by upwelling

The South China Sea (SCS) is the largest marginal sea in the world. Previous studies, including recent intensive paleo-oceanographic studies, suggest that the SCS is sensitive to many types of physical forcing on the short-term (e.g., internal waves and tides, mesoscale eddies, typhoons, etc.), annual (e.g., monsoon), inter-annual (e.g., El Niño), and very long-term (e.g., climate change) time scales. To better understand how various types of physical forcing influence biogeochemical cycles in the water column, a time-series study was initiated. Bimonthly hydrographic surveys occupied stations in the subtropical–tropic SCS at 19°N, 118.5°E. Results suggest that the Southeast Asian monsoons, northeasterly from October to April and southwesterly from May to September, have important effects on biogeochemical cycles in the upper water column. Hydrographic data showed that the mixed layer depth was much shallower in winter than in other seasons. During the winter monsoon period, the nitricline became shallower and upwelling sustained an elevated phytoplankton standing stock. Mean chlorophyll concentrations (0.65 mg Chl m^− 3) in winter were 8 times higher than in summer, and the integrated primary productivity over the euphotic zone reached as high as ca. 684 mg C m^− 2 day^− 1 in winter. The upwelling is produced by convergence of currents in the cyclonic gyre near the Luzon Strait, where the Kuroshio intrudes. In summer the current reverses following the wind change. The nitricline is depressed as downwelling occurs off northwest Luzon, resulting in strong nutrient limitation and very low chlorophyll concentrations.     

博斯普鲁斯海峡海上事故原因探析

博斯普鲁斯海峡是世界上最危险和最繁忙的航道之一,在地理政治学上、战略上和经济上具有重要意义。博斯普鲁斯海峡的海上事故取决于很多因素,包括特殊的地理条件、海洋和天气条件下可见性缺乏、人为错误(领航)、技术无效性,以及海峡交通密度等。通过使用往年的数据对海上事故原因进行研究和分析。     

Interactions of wind and density driven currents in North Sea ROFIs—a model study

Three different versions of a baroclinic three-dimensional circulation model of the North Sea are used to obtain information on the wind and density interactions in the North Sea ROFIs (Regions Of Freshwater Influence): the standard version with fully prognostic treatment of salinity and temperature is compared to a barotropic model run on the same grid on the one hand and to an also fully prognostic model run on a four times coarser grid on the other hand. In order to gain knowledge on the wind and density interactions, two opposing wind directions are chosen for investigation, namely a time of strong north wind, 21st–28th April 1982, and a time of strong southwest wind, 22nd–24th May 1982. In the April case the effect of the salinity gradients on the border of the ROFIs of Rhine, Weser, Ems and Elbe, i.e. along the continental shore, is shown to lead to a clear enhancement of the mean surface currents. In May this result is partly disguised by the additional effect of the thermocline in the deeper parts of the North Sea, i.e. in the classical shelf sea regime region. Nevertheless, the same pattern of enhanced mean surface currents along the coast is detected and is of the same order of magnitude as in the April case. It is thus concluded that although the circulation in the North Sea is reversed by the wind, the density induced component of the general circulation is modified only slightly.     

The impacts of strait and canal blockages on the transportation costs of the Chinese fleet in the shipping network

ABSTRACT

Straits and canals have always served as key nodes in shipping networks. The blockage of a strait or canal will lead to ship deviations and increased transportation costs. To measure this impact on the Chinese fleet, our study develops a mathematical model that is based on a programming formulation. Each strait or canal is assumed to be blocked in turn, and the increased transportation costs for the Chinese fleet in different scenarios are calculated and compared using the proposed programming formulation in order to measure the impact of the blocked strait or canal on the Chinese fleet. Larger increases in transportation costs have greater impacts on the fleet. The results show that a blockage of the Strait of Hormuz would have the greatest impact of all straits and canals; it would cause the Chinese fleet to lose a portion of its import and export market, and such a blockage cannot be addressed through ship deviations. Based upon increased transportation costs, the four straits or canals that would have the greatest impact if blocked are the Mandeb Strait, the Suez Canal, the Sunda Strait and the English Channel.     

Inorganic carbon fluxes through the boundaries of the Greenland Sea Basin based on in situ observations and water transport estimates

A carbon budget for the exchange of total dissolved inorganic carbon C_T between the Greenland Sea and the surrounding seas has been constructed for winter and summer situations. An extensive data set of C_T collected over the years 1994–1997 within the European Sub-polar Ocean Programmes (ESOP1 and ESOP2) are used for the budget calculation. Based on these data, mean values of C_T in eight different boxes representing the inflow and outflow of water through the boundaries of the Greenland Sea Basin are estimated. The obtained values are then combined with simulated water transports taken from the ESOP2 version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The fluxes of inorganic carbon are presented for three layers; a surface mixed layer, an intermediate layer and a deep layer, and the imbalance in the fluxes are attributed to air–sea exchange, biological fixation of inorganic carbon, and sedimentation. The main influx of carbon is found in the surface and the deep layers in the Fram Strait, and in the surface waters of direct Atlantic origin, whereas the main outflux is found in the surface layer over the Jan Mayen Fracture Zone and the Knipovich Ridge, transporting carbon into the Atlantic Ocean via the Denmark Strait and towards the Arctic Ocean via the Norwegian Sea, respectively. The flux calculation indicates that there is a net transport of carbon out of the Greenland Sea during wintertime. In the absence of biological activity, this imbalance is attributed to air sea exchange, and requires an oceanic uptake of CO₂ of 0.024±0.006 Gt C yr⁻¹. The flux calculations from the summer period are complicated by biological fixation of inorganic carbon, and show that data on organic carbon is required in order to estimate the air–sea exchange in the area.     

海峡两岸海上直航分析

金融海啸席卷全球,面对严峻的经济形势,海峡两岸能否携手开展金融合作、经济合作,共同应对危机冲击显得尤为重要和迫切。2008年11月4日,海峡两岸关系协会与台湾海峡交流基金会签署了《海峡两岸海运协议》,标志着海峡两岸实现海上直航。针对这一重大举措,文中首先对海上直航的重要性进行了分析,然后结合海峡两岸海上直航现状,深入探讨了直航的前景,最后提出了几点两岸共同应对国际金融危机的对策建议。     

南海北部湾台风浪数值模拟方法研究

对第三代近岸海浪数值模式SWAN控制方程进行简要介绍,并利用由藤田和高桥公式相互嵌套的方法提供了台风风场,用SWAN模式采用大小模型范围嵌套的方式对影响南海北部湾海域的8303号台风浪过程进行了模拟验证,并利用该模式预报了该海域在不同台风作用下的台风浪过程.结果表明,模拟结果与实际海浪观测资料吻合较好,计算预报结果可以为该海域台风浪防灾等提供较为重要的参考.     

东海区近海强风预报模式研究

本文探讨东海区近海强风预报模式。作者首先介绍建立预报模式的思路和步骤,然后作了模式使用说明。为了验证东海区近海等于、大于8级的强风预报模式和判别条件,作者用1986、1987两年日本传真天气图进行试报,准确和基本准确率合为91.1％,文中还展示了随船试验预报结果,准确和基本准确率合为90％。该模式可供航海驾驶人员为航线设计及航行途中订正强风预报时参考。     

Late summer stratification, internal waves, and turbulence in the Yellow Sea

Microstructure profiling measurements at two locations in the Yellow Sea (a deeper central basin and a local shelf break) were analyzed focusing on tidal and internal-wave induced turbulence near the bottom and in the pycnocline. A classical three-layer density structure consisting of weakly stratified surface and bottom boundary layers and a narrow sharp pycnocline is developed by the end of warm season. Turbulence in the surface layer was not influenced by the tidal forcing but by the diurnal cycle of buoyancy flux and wind forcing at the sea surface. The enhanced dissipation and diffusivity generated by the shear stress at the seafloor was found in the water interior at heights 10–15 m above the bottom with a phase shift of ~ 5–6 m/h. No internal waves, turbulence, or mixing were detected in the pycnocline in the central basin, in contrast to the pycnocline near the local shelf break wherein internal waves of various frequencies were observed all the time. The thickness of the surface layer near the local shelf break slightly exceeded that of the bottom layer (20 vs. 18 m). A 5–6 m high vertical displacement of the pycnocline, which emerged during the low tide, was arguably caused by the passage of an internal soliton of elevation. During this episode, the gradient Richardson number decreased below 0.25 due to enhanced vertical shear, leading to local generation of turbulence with dissipation rates exceeding the background level by an order of magnitude.     

中国海岸波浪特征与建港条件研究

分析了中国渤海、黄海、东海和南海海岸的风与波浪特征。提出用代表波高描述海区年均波浪强度。时波高极大值应进行重现研究和归并处理。时港址选择、波要素推算和防浪设计有指导意义。