渤海环流与输运季节变化的数值模拟

渤海的风和温度层结有明显的季节变化 ,因而其环流与输运亦有明显的季节信号。以季节平均的海面气象条件和开边界的潮波系统驱动三维斜压水动力模型———HAMSOM ,模拟了渤海冬、夏季的总环流。渤海环流冬强夏弱 ,表层风漂流常被下层逆风流所补偿。深度平均环流 ,即水柱内的输运 ,流型有显著的季节变化 :冬季在渤海中部沿逆时针方向旋转 ,辽东湾顶有一个顺时针流涡 ,阻碍了湾顶水与外海水的交换 ;夏季则为一个大的贴岸的顺时针流环 ,内嵌许多局地涡旋。这些与渤黄东海海洋水文图集中给出的多年观测的环流基本相同 ,同时也被水文要素分布及耐盐浮游动物的出现所佐证。风的季节变化决定了渤海大部分海区、特别是海峡附近环流的季节变化 ,但辽东湾东岸众多的岬角涡旋却不随季节变化 ,因为它们是由潮波系统与岬角岸型变化的非线性相互作用产生的。     

Near-equatorial eddies off South America

A considerable amount of the Amazon River water that is discharged into the equatorial Atlantic is then advected northward along the shelf by the strong North Brazil Current (NBC). Being relatively fresh, this water remains in the near-surface layer and can serve as an excellent tracer for the complex and variable flow of the offshore mesoscale eddies. Both surface salinity observations and CZCS (Coastal Zone Color Scanner) imagery can be mapped to estimate the circulation patterns of the eddies. Presented here are two sets of XBT (expendable bathythermograph) sections that give the thermal structure of eddies off the Demerara Rise (6–9°N). They were occupied nearly contemporaneously with CZCS imagery obtained during October 1980 and November 1981. Several studies have shown from ship drift data, from CZCS observations, and from Geosat altimetry that, particularly during late summer and fall, the NBC is found to retroflect offshore to the east, supplying the North Equatorial Counter Current (NECC) and is associated with eddies along the coast. Good agreement is shown between the CZCS and a NAVOCEANO AXBT (airborne bathythermograph) survey during this period as well as observations of surface phytoplankton and geopotential anomaly from an earlier 1964 survey. Estimates of volume transport within the eddy structure indicate that at times the offshore retroflection during spring as well as autumn can amount to 10 × 10⁶ m³ s^–1. The pronounced eddy variability off South America is shown by comparing a number of past hydrographic surveys. These suggest that considerable spatial variability can occur as can seasonal changes in volume transport of the NBC and the associated eddy circulation.     

Robust adaptive control of underactuated ships on a linear course with comfort

This paper addresses an important problem in ship control application—the robust stabilization of underactuated ships on a linear course with comfort. Specifically, we develop a multivariable controller to stabilize ocean surface ships without a sway actuator on a linear course and to reduce roll and pitch simultaneously. The controller adapts to unknown parameters of the ship and constant environmental disturbances induced by wave, ocean current and wind. It is also robust to time-varying environmental disturbances, time-varying change in ship parameters and other motions of the ship such as surge and heave. The roll and pitch can be made arbitrarily small while the heading angle and sway are kept to be in reasonably small bounds. The controller development is based on Lyapunov’s direct method and backstepping technique. A Lipschitz continuous projection algorithm is used to update the estimate of the unknown parameters to avoid the parameters’ drift due to time-varying environmental disturbances. Simulations on a full-scale catamaran illustrate the effectiveness of our proposed controller.     

Seasonal and Spatial Variations of Iceberg Drift off Dronning Maud Land, Antarctica, Detected by Satellite Scatterometers

Seasonal and spatial variations of iceberg drift were studied using continuous satellite scatterometer images off Dronning Maud Land, East Antarctica. Generally, iceberg drift speed showed a westward increase to the Greenwich Meridian. Seasonal variations of the drift speed were high in autumn—early winter and low in spring, and their magnitudes also increased westward. Seasonal variations of the drift speed were significantly correlated with variations of sea levels at Syowa and Mawson Stations, and hence qualitatively consistent with geostrophic current variations. Thus, the scatterometer data are demonstrated to be useful in monitoring iceberg trajectory and oceanic current variations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Late Quaternary history of contourite drifts and variations in Labrador Current flow,Flemish Pass,offshore eastern Canada

Contourite drifts of alternating sand and mud, shaped by the Labrador Current, formed during the late Quaternary in Flemish Pass seaward of the Grand Banks of Newfoundland, Canada. The drifts preserve a record of Labrador Current flow variations through the last glacial maximum. A high-resolution seismic profile and a transect of four cores were collected across Beothuk drift on the southeast side of Flemish Pass. Downcore and lateral trends in grain size and sedimentation rate provide evidence that, between 16 and 13 ka, sediment was partitioned across Beothuk drift and the adjacent Flemish Pass floor by a strong current flow but, from 29 to 16 ka, sedimentation was more of a blanketing style, represented by draped reflections interpreted as being due to a weaker current. The data poorly resolve the low sedimentation rates since 13 ka, but the modern Labrador Current in Flemish Pass is the strongest it has been in at least the past 29 ka. Pre-29 ka current flow is interpreted based on reflection architecture in seismic profiles. A prominent drift on the southwestern side of Flemish Pass formed above a mid-Miocene erosion surface, but was buried by a mass-transport deposit after the penultimate glacial maximum and after drift deposition switched to eastern Flemish Pass. These findings illustrate the temporal complexity of drift sedimentation and provide the first detailed proxy for Labrador Current flow since the last glacial maximum.     

南沙群岛海区西南季风变化与表层流结构和演变关系的探讨

根据中国科学院南沙综合科学考察的现场资料和海区的历史资料，讨论了西南季风的文化及其与海区表层地转流的结构和演变间的关系。结果表明，海区西部的表层流结构随西南季风的盛衰而有变化，说明西南季风对南沙群岛海区表层流的调控作用西部大于东部；但由于密度流和地形效应等的作用，表层流的漂流性质不明显。     

Features of eddy kinetic energy and variations of upper circulation in the South China Sea

The features of eddy kinetic energy (EKE) and the variations of upper circulation in theSouth China Sea (SCS) are discussed in this paper using geostrophic currents estimated from Maps of Sea Level Anomalies of the TOPEX/Poseidon altimetry data. A high EKE center is identified in the southeast of Vietnam coast with the highest energy level 1 400 cm2 ·s~(-2) in both summer and autumn. This high EKE center is caused by the instability of the current axis leaving the coast of Vietnam in summer and the transition of seasonal circulation patterns in autumn. There exists another high EKE region in the northeastern SCS, southwest to Taiwan Island in winter. This high EKE region is generated from the eddy activities caused by the Kuroshio intrusion and accumulates more than one third of the annual EKE, which confirms that the eddies are most active in winter. The transition of upper circulation patterns is also evidenced by the directions of the major axises of velocity variance ellipses between 10°and 14.5°N     

CERTAIN PROPERTIES AND CAUSES OF VARIATIONS OF THE SOUTH EQUA-TORIAL COUNTERCURRENT IN THE PACIFIC OCEAN

Marine investigations were carried out in the western Central Equatorial Pacific region from 1976 to 1979 by three Chinese research vessels "Xiangyanghong 05", "Xiangyanghong 09" and "Shijian" belonging to the National Bureau of Oceanography. The data of currents, surface wind, drift of the ship, temperature, salinity, and so on, were obtained during the investigations, which provides more reliable basis for further studies on the South Equatorial Countercurrent in the Pacific Ocean. In this paper certain properties and causes of variations of the South Equatorial Countercurrent in the Pacific Ocean are analysed according to the above-mentioned data.     

Subtidal Flow Patterns in Western Florida Bay

Recent observations using moored current meters, shipboard ADCP transects, salinity mapping and drifters have been used to study the residual circulation including wind drift in western Florida Bay.Rapid, nearly synoptic surveys of salinity over a large area was an effective tracer-mapping technique, when salinity gradients were sufficiently strong, and provided qualitative information on Lagrangian water motion for the entire study area. The salinity maps indicated a general south-eastward advection, which was only subordinate to tidal mixing in a narrow zone adjacent to the Florida Keys.Drifter data collected simultaneously, allowed quantitative estimates to be added to the transport pattern suggested by salinity maps. The selectively deployed drifters yielded estimates of total drift velocities. In addition, moored current meters and shipboard current profiling were used to determine the distribution of flow across the mouth of the bay facing the Gulf of Mexico and the transport through Long Key Channel, a major connection between the bay and the Atlantic Ocean.Analysis showed that from 64 to over 92% of the drifter trajectory variances could be explained by the combination of a local wind drift, expressed in terms of a wind drift factor multiplied by the surface shear velocity, and an ambient current. For a 1 m high drifter deployed at the surface of the water column, the wind drift factor was found to be approximately 0·125m, making the drift speed roughly equal to 0·45% of wind speed. The mean drifter speeds were linearly proportional to mean transport estimates derived from the current meter observations in Long Key Channel, enhancing confidence in both data sets.The total south-eastward directed residual current varied between 100 and 5000 m day⁻¹and was weaker in summer than in winter, when southward winds associated with periodic passage of cold fronts boost the residual flow. The estimated contribution from local wind drift varied between 500 m day⁻¹in summer to 1000 m day⁻¹in winter. The remaining contribution to the observed Lagrangian residual circulation in western Florida Bay is caused by other forcing, including tidal rectification, remote wind forcing and large-scale current systems (the Gulf Stream and Florida Current systems).     

Observed and computed lateral circulation patterns in a partly mixed estuary

Observations of lateral residual circulation patterns are presented for three sections in the upper reaches of the Tamar Estuary. The data include measurements over spring and neap tidal cycles, and are compared with predictions from a depth-averaged, numerical model of the lateral circulation.The model shows features of the lateral structure which also occur in the observed data. The computed mass-transport Stokes drift has a similar lateral structure at spring and neap tides for all sections, and is up-estuary in the deeper, central part of a section, and down-estuary on the intertidal areas near the banks. A distinctive feature of this drift is the reduction in lateral structure when axial density gradients are ignored.The mass-transport residual current has a characteristic lateral structure when the run-off is not too high. The current in the central part of a section is slow (less than a few cm s⁻¹), and may be up- or down-estuary, depending on the magnitude of the run-off. The current over the intertidal areas is faster (∼ 10 cm s⁻¹) and directed down-estuary. This distribution consists of three components: (a) a run-off induced current which has a river-like form, (b) density currents which are up-estuary in the deeper part of a section and down-estuary over the intertidal and shallow areas, and (c) tidally-driven currents which have a similar form to density currents, and whose formation depends strongly on the existence of intertidal areas.Results from this paper are compared with published observations of lateral circulation patterns for several other estuaries.     

Ocean Model Simulation of Southern Indian Ocean Surface Currents

The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N–60°S and 30°E–120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.     

Ocean Model Simulation of Southern Indian Ocean Surface Currents

The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N-60°S and 30°E-120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.     

Development of the POLCOMS–WAM current–wave model

The continuous research and improvement of ocean modelling helps to provide a more sustainable development of coastal and offshore regions. This paper focuses on ocean modelling at the NW Mediterranean using the POLCOMS–WAM model with new developments. The Stokes’ drift effect on currents has been included and the distribution of surface stress between waves and currents has also been considered. The system is evaluated in the NW Mediterranean and an evaluation of different forcing terms is performed. The temperature and salinity distributions control the main patterns of the Mediterranean circulation. Currents are typically small and therefore the modification of waves due to the effect of currents is minimal. However, the wave induced currents, mainly caused by a modified wind drag due to waves, produce changes that become an important source of mass transport. POLCOMS was able to reproduce the main Mediterranean features, its coupling with WAM can be a very useful tool for ocean and wave modelling in the Mediterranean and other shelf seas.     

动力定位船舶二阶低频慢漂力模型试验研究

对一艘动力定位船舶二阶低频慢漂力进行了模型试验,并将试验得到的纵向慢漂力谱、横向慢漂力谱与势流理论方法得到的理论值进行比较,结果表明,该模型试验方法与理论计算较为吻合。可为动力定位系统的设计和应用提供参考。     

海上失事目标搜救应急预报系统

详细介绍了国家海洋环境预报中心发展的海上失事目标搜救应急预报系统.该系统基于四阶精度的拉格朗日漂移路径模型,以预报中心发展的高分辨率风场和流场数值预报的结果作为环境动力强迫条件,预报落水人员或失事船舶(渔船)的漂移轨迹,预报结果可基于Googleearth平台显示.该系统的应用有助于提高海上搜救行动的及时性和有效性,减...     

Variability of Sea Surface Circulation in the Japan Sea

Composite sea surface dynamic heights (CSSDH) are calculated from both sea surface dynamic heights that are derived from altimetric data of ERS-2 and mean sea surface that is calculated by a numerical model. The CSSDH are consistent with sea surface temperature obtained by satellite and observed water temperature. Assuming the geostrophic balance, sea surface current velocities are calculated. It is found that temporal and spatial variations of sea surface circulation are considerably strong. In order to examine the characteristics of temporal and spatial variation of current pattern, EOF analysis is carried out with use of the CSSDH for 3.5 years. The spatial and temporal variations of mode 1 indicate the strength or weakness of sea surface circulation over the entire Japan Sea associated with seasonal variation of volume transport through the Tsushima Strait. The spatial and temporal variations of mode 2 mostly indicate the temporal variation of the second branch of the Tsushima Warm Current and the East Korean Warm Current. It is suggested that this variation is possibly associated with the seasonal variation of volume transport through the west channel of the Tsushima Strait. Variations of mode 3 indicate the interannual variability in the Yamato Basin.     

热力学效应及斯托克斯漂流对混合层影响的研究

本文通过理想化的外部强迫以及海洋站点实测数据驱动普林斯顿海洋模式来研究海洋热力学效应和斯托克斯漂流对上混合层数值模拟的影响。在Mellor-Yamada湍流闭合方案中,经常出现夏季海表面温度偏暖和混合层深度偏浅的模拟误差。实验表明,斯托克斯漂流在冬季和夏季均能增强湍流动能,加深混合层深度。这种效应可以改善夏季的模拟结果,但与观测数据相比,将增大冬季混合层深度的模拟误差。斯托克斯漂流可以通过增强湍动能来加深混合层深度。结果表明,将斯托克斯漂流与冷皮层和暖层对上部混合层的热效应相结合,可以正确地模拟混合层深度。在夏季,海洋冷皮层和暖层通过“阻挡结构”和双温跃层结构模拟出更真实的上混合层变化。在冬季,海洋热力学效应通过增强上层海洋层结平衡了斯托克斯漂流的影响,并且由斯托克斯漂流引起的过度混合被校正。     

西南黄海夏季环流数值模拟研究

本文采用Regional Ocean Modeling System（ROMS）来研究西南黄海夏季环流,模拟的结果与浮标和锚定观测符合的很好。表层的海流流向东北,离岸一侧的流速大于近岸的流速,表层以下为约沿着25米等深线的气旋式流动。我们通过一系列过程导向实验研究海表风应力和底层温度锋面对环流的影响,结果表明,东南风驱动了表层东北向流动,底层温度锋面驱动了表层以下气旋式流动。底层温度锋面形成于近岸垂向混合充分水体和离岸层化水体之间。     

Wave-induced drift of an elliptical surface film

This study investigates experimentally the drift velocity of an elliptical surface film advected by deep-water waves. Thin polyethylene sheets were used to simulate the inextensible surface film. The drift velocities were obtained by recording and analyzing a sequence of images captured using a video camera. The results show that the drift velocity increases with the longitudinal length of the polyethylene sheet until approximately 0.8 times the wavelength. Beyond that, further increment would not result in substantial increase in the drift velocity. The effect due to the normalized transverse width is found to be significant within a particular range. At large wave steepness, the drift velocity appears to be limited by the Stokes drift. A set of best-fit empirical equations based on the sigmoidal function is introduced for oil spill trajectory prediction.     

Current Measurements of the Japan Sea Proper Water and the Intermediate Water by ALACE Floats

The subsurface current of the Japan Sea was observed by two Autonomous Lagrangian Circulation Explorer (ALACE) floats. One float, having a 20-day cycle, was deployed on 29 July 1995 in the eastern Japan Basin and drifted in the northeastern part of the basin until 15 September 2000. The other float, with a 10-day cycle, was deployed on 4 August 1995 in the western Japan Basin and drifted in the western Japan Basin, in the Yamato Basin and around the Yamato Rise until it reached its life limit in mid-May 2000. An anticlockwise circulation in the eastern Japan Basin was observed and it was assumed to be in the upper portion of the Japan Sea Proper Water (UJSPW) or in the intermediate water. The spatial scale of the circulation increased as the depth decreased. A clockwise circulation was observed around the Yamato Rise in the UJSPW. Smaller clockwise and anticlockwise rotations were observed in the western Japan Sea, where a seasonal variation was seen in drift speed with different phase by depth. The correlation coefficient between drift speeds of two floats indicated little coherence among the subsurface circulation between the east and the west of the Japan Basin, or between the north and the south of the subpolar front. This revised version was published online in August 2006 with corrections to the Cover Date.