Circulation

Low-frequency current and temperature variability on the southeast US continental shelf during summer conditions of weak wind forcing and vertical stratification was found to be similar in many aspects to previous findings for winter, when stronger wind forcing and vertical homogeneity prevails. Subtidal variability in the outer shelf is dominated by the weekly occurrence of Gulf Stream frontal eddies and meanders. These baroclinic events strongly affect the balance of momentum in the outer shelf, but not at mid-shelf. A negative alongshore sea level slope of order −10⁻⁷ is required to balance mean along-shelf momentum at the shelf edge, similar to oceanic estimates, and can contribute to the observed northward mean flow over the shelf.Low-frequency flow at mid-shelf and coastal sea level fluctuations appear to occur as a forced wave response to local alongshore wind stress events that are coherent over the shelf domain. Momentum balances indicate a trapped wave response similar to the arrested topographic wave found in the mid-Atlantic Bight (CSANADY, 1978). Density driven currents from river discharge do not appear to be significant at mid-shelf. Cold, subsurface intrusions of deeper, nutrient rich Gulf Stream waters can occasionally penetrate to mid- and inner-shelf regions north of Cape Canaveral, causing strong phytoplankton and zooplankton responses. These events were observed following the simultaneous occurrence of upwellings from northward winds and Gulf Stream frontal eddies at the shelf break during periods when the Stream was in an onshore position. Subsurface Gulf Stream intrusions to mid-shelf occur only during the summer, when the shelf is vertically stratified and cross-shelf density gradients do not present a barrier as in winter.     

我国水产品流通模式及其流通效率

为优化水产品流通模式和提高水产品流通效率,文章系统梳理相关文献,从水产品流通模式、我国水产品流通的主要模式及其流通效率3个方面综述相关研究成果。研究结果表明:水产品流通模式连接水产品的生产和消费,由流通主体、流通渠道和流通节点有机构成,伴随商流、物流、资金流和信息流;我国水产品流通主要包括批发商主导、合作社主导、加工企业主导、超市主导和渔民直销的流通模式,其中批发商主导的流通模式最为常见;根据流通效率的投入和产出评价指标,基于核心流通主体的流通效率,超市主导和渔民直销的流通模式的流通效率较高;目前研究成果已较丰富,未来应进一步完善研究对象、内容和方法等。     

Circulation in Tasman Bay

Direct current measurements at four locations in Tasman Bay and numerical model results are used to analyse the mean flow in Tasman Bay. The mean circulation conforms to that previously found from drift card experiments: a clockwise circulation in Golden Bay, and an anti‐clockwise flow in Tasman Bay, with a return south‐westerly flow on the coast near Nelson. Typical mean speeds are 0.02–0.05 m.s^‐1. The circular flow appears asymmetrical in both bays, with a stronger outflow along Farewell Spit in Golden Bay and near D'Urville Island in Tasman Bay.

An analytical tidal solution is used to exhibit the influence of Cook Strait in producing smaller tidal amplitudes in eastern Tasman Bay. Tidal speeds of 0.15–0.30 nus^‐1 are typical, with tidal ellipses having degenerated into north‐east, south‐west lines.     

Modeling the Global Thermohaline Circulation

This paper reviews recent progress and problems in modeling the thermohaline circulation of the world ocean by use of z-coordinate ocean general circulation models. Discussions focus on four issues: sea surface forcing, mixing in the deep ocean interior, eddy-induced tracer transport, and bottom boundary layer processes. Although some widely used techniques and parameterizations deal with these issues, some aspects are still overlooked and more sophistication is certainly required. This revised version was published online in August 2006 with corrections to the Cover Date.     

东中国海拉格朗日环流数值模拟Ⅰ--自适应环流模型

海洋环流是海洋科学研究的1个焦点.本文首次建立了东中国海环流自适应数值模型.由于所设计的自适应网格既与边界适应,又在水深变化急剧的东海陆坡处得以加密,从而使坐标变换下的三维斜压模式克服了跨越陆坡计算这一难题,并以期获得更为精确的数值研究成果.该模型基于Lagrange时均观点,而非Euler观点.它可计算海域三维斜压流场,从而得到其风生-热盐-潮致Lagrange环流.模拟结果与实测及现有的数值研究结果比较,合理可信.其中黄海暖流的起源问题,计算结果与传统观点相悖,而与近期实测结果一致.本文为系列报道之首篇.     

Circulation in the Bras d'Or Lakes

The Bras d'Or Lakes are a system of interconnecting basins open through two narrow channels to the Sydney Bight at the mouth of the Gulf of St Lawrence. Hydrographic surveys between 1972 and 1974 showed that surface waters can warm by more than 10 °C from May to July and that horizontal salinity differences of up to 10 psu can exist between Sydney Bight (30 psu) and the innermost regions of the Lakes. Using the data from May and June 1974 to derive horizontal and vertical exchanges, a simple budget model has been set up consisting of two or three layers in each of nine separate regions. The model has a bottom inflow from Sydney Bight, deep inflow through the narrow channels to other basins and a surface outflow. The exchanges agree reasonably well with estimates derived from available current meter data. The model's predicted temperatures and salinities for July 1974 had rms errors of about 1·5 °C and 0·82 psu, respectively. The dissolved oxygen concentrations in four of the more isolated basins are similar to those calculated from the model, giving support to the derived circulation.     

大洋环流的诊断计算

采用二维的全球高分辨率（1／4°×1／4°）的自由表面诊断模型结合动力计算估算全球大洋环流,模拟结果与其他模拟结果非常相似。流函数的分布表明,全球大洋中的主要流系均得到体现,包括大洋环流的西向强化的现象（黑潮、湾流等）。黑潮主轴的流量约54Sv（1Sv=10^6m^3／s）,非常接近实测值：各层水平流场分布情况显示,各大洋的一些基本流系都能得到很好的再现。如黑潮和南极绕极流可深达底层。湾流不能到达深层,大约在1000～2000m之间海流即已转向。     

Circulation and hydrology of Manukau Harbour

Abstract

Current meter and current drogue measurements made over tidal periods show that the circulation in Manukau Harbour is mainly tidal, with strongest flows within the inner harbour in the four main channels. In the entrance channel, peak tidal speeds reach 2.25 m.s^?1 at the surface, and 0.6 m.s^?1 near the bottom. Salinity and temperature observations show that the water is nearly homogeneous with depth in summer. A residence time of 22 d is calculated, assuming the small horizontal salinity contrast is maintained by freshwater inflow and evaporation.     

大洋环流的诊断计算

采用二维的全球高分辨率(1/4°×1/4°)的自由表面诊断模型结合动力计算估算全球大洋环流,模拟结果与其他模拟结果非常相似。流函数的分布表明,全球大洋中的主要流系均得到体现,包括大洋环流的西向强化的现象(黑潮、湾流等)。黑潮主轴的流量约54Sv(1Sv=106m3/s),非常接近实测值;各层水平流场分布情况显示,各大洋的一些基本流系都能得到很好的再现。如黑潮和南极绕极流可深达底层。湾流不能到达深层,大约在1000～2000m之间海流即已转向。     

Oil dispersal modelling: reanalysis of the Rena oil spill using open-source modelling tools

ABSTRACT

Oil spill forecast modelling is typically used immediately after a spill to predict oil dispersal and promote mobilisation of more effective response operations. The aim of this work was to map oil dispersal after the grounding of the MV Rena on Astrolabe Reef and to verify the results against observations. Model predictions were broadly consistent with observed distribution of oil contamination. However, some hot spots of oil accumulation, likely due to surf-zone and rip current circulation, were not well represented. Additionally, the model was run with 81 differing wind conditions to show that the events occurring during the grounding represented the typical likely behaviour of an oil spill on Astrolabe Reef. Oil dispersal was highly dependent on prevailing wind patterns; more accurate prediction would require better observations of local wind patterns. However, comparison of predictions with observations indicated that the GNOME model was an effective low-cost approach.     

Developments in ocean climate modelling

This paper presents some research developments in primitive equation ocean models which could impact the ocean component of realistic global coupled climate models aimed at large-scale, low frequency climate simulations and predictions. It is written primarily to an audience of modellers concerned with the ocean component of climate models, although not necessarily experts in the design and implementation of ocean model algorithms.     

波浪变形的数学模型

本文给出一个在复杂水深地形条件下计算包括折射和绕射效应的线性波浪变形数学模型。该模型用差分方法进行求解,并应用于兴化湾江阴岛码头及航道的波浪要素计算,所得结果与其他方法的结果进行比较。通过实际应用说明它是计算开阔海域波浪变形的有力工具。     

海滩侵蚀的数值分析模型

介绍了有关海滩侵蚀造成海岸演变问题的数学分析模型。根据海岸线演化和海滩断面的沉积物迁移理论建立一种顺岸方向和垂直岸线方向海岸形状变化的耦合模型。将海滩沉积物被海浪迁移的机理看作由于海水在海滩介质孔隙内渗流侵蚀和海浪对海滩介质冲刷所致的海滩介质的孔隙损伤变化。这种结合数值和解析分析的综合方法可用于模拟海岸演变问题中海岸线 (沿岸方向 )和海滩断面 (垂直海岸线方向 )的变迁情况     

Mathematical modelling of volcanic tsunamis

The height of widespread tsunami runup about the Bay of Plenty from various volcanic scenarios involving eruptions at White Island is shown to be insignificant in all cases considered, except for Krakatoa‐type explosions. The problem of localised inundation remains unanswered. Some definitions describing volcanic tsunami risk, introduced recently by J. Latter (Bulletin volcanologique 1982), are briefly mentioned. All numerical calculations assumed cylindrical symmetry and used a flux‐corrected Lax‐Wendroff algorithm to solve the modified shallow water equations of Peregrine.     

Wave theory modelling: a convenient approach to CW and pulsepropagation modelling in low-frequency acoustics

The most commonly used continuous-wave (CW) propagation models are presented and their areas of applicability indicated. Furthermore, it is shown how these numerical codes can be extended to provide pulse results by Fourier synthesis of CW solutions. The ability of the acoustic models to describe sound propagation accurately in complicated ocean environments is demonstrated through a sequence model/date comparisons involving both CW and pulse-propagation results. It is also shown that the full complexity of real ocean environments must be considered in the numerical models to accurately predict the propagation conditions for a broad range of source frequencies. In conclusion, it is noted that the biggest difficulty today in sonar performance prediction modelling is not associated with the modelling tools themselves, but rather with the lack of environmental information to be used as input to the models     

Circulation and mixing in the Faroese Channels

The hydrographic properties of the dense waters overflowing the Greenland–Scotland Ridge through the Faroese Channels are greatly modified during the transit. In this study, we consider conditions both upstream and downstream of the sill, using a combination of hydrographic measurements (CTD, nutrients) and direct velocity measurements (expendable current profilers, lowered acoustic Doppler current profiler) from several repeated lines across the channel system. The purpose is to identify and quantify regions of enhanced mixing and frictional drag. The method of quantification used in both cases (Thorpe scaling) is independent of budget calculations and thus lends itself useful for non-steady-state flows. The method appears to be successful in this case as (1) the numbers obtained are non-random, (2) they support the qualitative interpretation of mixing made from water mass analysis, and (3) they are supported by companion log-layer estimates of bottom boundary layer friction. Large buoyancy fluxes were deduced within the dense water masses all along the channel system, also upstream of the sill where the velocities are low. The largest implied mixing (∼3×10⁻⁷ W/kg) was observed roughly 100 km downstream of the sill, where the plume starts to descend. Frictional stress within the water column was also elevated throughout the channel system; the log-layer formulae yielding a drag coefficient for the entire data set of about 4×10⁻³. The average stress at the sill was roughly 2 Pa.     

Spectral modelling of wave energy converters

A spectral model suitable for the representation of wave energy converters is developed. A spectral model is an extension of a frequency-domain model that allows inclusion of non-linear forces and thereby provides improved estimates of wave energy converter performance, without the high computational cost of a time-domain model. The suitability and accuracy of a spectral model representation is demonstrated for a flap-type wave energy converter, by modelling the effect of vortex shedding and large amplitudes of motion. The development of a spectral model of wave energy converters also means that they can be represented in spectral wave models and included explicitly in software tools such as SWAN or Mike21 SW. This means that tools familiar to the industry could be used to determine the environmental impact and energy yield of wave farms efficiently.     

Boussinesq modelling of transient rip currents

The flow on a plane beach with a random, directionally spread wave field was simulated with a Boussinesq model. The random wave spectra were directionally symmetric with their central direction perpendicular to the beach, so no constant longshore current was generated. Variable wave-averaged currents were generated because of the spatially variable wave field, and sometimes formed offshore directed rip currents that appear in variable longshore locations. The rip currents are associated with a vortex pair which is generated within the surfzone and subsequently propagates offshore. Analysis of the vorticity balance show that the main vorticity input occurs within the inner surfzone. Three different beach slopes and four different wave spectra are simulated. The frequency, duration, and intensity of the transient rips depend on both the beach slope and the incident wave spectra. The results have important engineering implications for the transport of material in the nearshore zone, in particular on longshore uniform beaches.