The response of the Sao Paulo Continental Shelf, Brazil, to synoptic winds

The response of the Sao Paulo Continental Shelf (SPCS) to synoptic wind forcing has been analyzed. Two different methods are used for this purpose, one based on hydrographic data, bottom topography, and geographical characteristics, and a second on analyzing currentmeter data directly and using empirical orthogonal functions. Both methods show similar results for an essentially barotropic shelf. The SPCS response in the subinertial frequency band appears to be trapped on the continental shelf. Numerical experiments have also been carried out showing results that qualitatively agree with the observations, including the velocity component parallel to the coastline. Supported by CAPES.     

Estimation of 3-D current fields near the Rhine outflow from HF radar surface current data

HF radar systems are designed to measure spatially variable sea surface currents. A methodology was developed to complement these data with information about the current variability over the water column in a stratified shallow sea. Current profiles were estimated using a diagnostic model driven by surface current measurements from an HF radar system and by sea surface slopes derived from tide gauge data. The structure of the model has a physical basis but its parameters were derived from an analysis of in-situ current profile measurements. Application of the model to HF radar data from the SCAWVEX Rhine outflow experiment showed fair agreement with in-situ current data. As applications, estimation and tidal analysis of current fields are demonstrated.     

Derivation and application of new equations for radiation stress and volume flux

In this paper, new expressions of radiation stress and volume flux for long waves have been analytically derived by inclusion of higher-order surface elevations up to the sixth-order. To quantify these expressions, surface elevations along a beach are first simulated using the fully nonlinear Boussinesq-type model COULWAVE. Then, based on the large amount of numerical data, new equations for radiation stress and volume flux are statistically formulated. The research unveils the essential roles of the Ursell parameter, Irribarren number and wave steepness described by the local wave height, wave length and bottom slope. The study shows the importance of nonlinear wave properties in wave-induced currents and mean water levels (set-up/down). The higher-order formulations produce lower values for radiation stress and volume flux than calculated from the lower-order and linear waves. Case studies suggest that the new formulations produce an accurate estimation for mean water level. However, improvement on the computed current profiles is marginal for some cases. This implies that the accurate prediction of the current profile would require more than just the proposed improvement of the radiation stress and volume flux.     

Estimation of the transports through the Strait of Gibraltar

An acoustic doppler current profiler (ADCP) is used to measure the currents and estimate the transports over the Camarinal Sill at the Strait of Gibraltar. The deepest measurements of the ADCP compare well with an underlying conventional current meter. The exchange interface between the Atlantic and the Mediterranean water is defined as the depth of the maximum vertical shear. The mean depth of the shear interface is 147 m. The time series of the depth of the interface and the currents are used to estimate the transports across the Strait. The resulting values are 0.78 Sv for the Atlantic inflow and −0.67 Sv for the Mediterranean outflow. The time series of the shear interface include fortnightly oscillations of 19 m. The time series of the transports are compared with the pressure and sea level difference records across the Strait. Linear multiple regression is used to estimate the (statistical) contribution of each parameter on the variation of transports. The cross strait sea level difference is well correlated with the Atlantic inflow and accounts for 57% of the variability of the transport records which improves to 78% when the fortnightly and monthly cycles are included in the linear regression. The Mediterranean outflow is best correlated with the along strait sea level difference which accounts for only 10% of the variability of the transport record. Again the addition of the M_sf and the MM cycles improves the percentage of the variance accounted for to 37%. The local, along strait wind component is significantly correlated with, both the Atlantic inflow and the across strait sea level difference.     

Field measurements of coastal waves and currents in Portugal and Greece

The MAST II WAVEMOD Project aimed at improving stochastic modelling of ocean waves and currents in coastal waters. In order to supplement existing data, two measurement campaigns were carried out, one on the Atlantic coast of Portugal, and, secondly, on the northern coast of Crete in the Mediterranean. The Portuguese measurements covered 7 months during winter 1993–1994, while off Crete, measurements started early in February 1994 and continued for 10 months. In both sites, two directional Waveriders and one non-directional Waverider were deployed along a transect out from the coast in water depths between 10 and 100 m. In addition, the Mediterranean site also incorporated measurements of mean current velocities. Available satellite data were analysed to supplement the buoy data. In this paper, both measurement campaigns are described together with a presentation of some of the data collected.     

Discordant patterns of genetic connectivity between two sympatric species,Mullus barbatus (Linnaeus, 1758) and Mullus surmuletus (Linnaeus, 1758), in south-western Mediterranean Sea

Population connectivity scales are important tools to achieve a mechanistic understanding of the factors regulating the abundance and distribution of marine populations and therefore support conservation actions to manage fisheries and stocks. We used 10 microsatellites markers on mullets' samples across the Spanish coast to determine the spatial scale of gene flow as well as the origin of post-larvae caught inside two MPAs. Population structure varied from complete homogeneity for Mullus barbatus, to high spatial variability in Mullus surmuletus samples. Differential habitat utilization by species, geomorphological features and oceanographic patterns are discussed as potential causes of patterns observed. Although we were unable to verify the origin of most post-larvae caught inside MPAs we suggest that they may act as genetic reservoirs due to high heterozigosity levels found in adult specimens inside (M. surmuletus) and nearby (both) them. Our results indicate that early life history traits (i.e. larvae) may not be the only determinant on species dispersal capability, suggesting that other mechanisms such as fine scale adult or juvenile movement may have been underestimated as promoting population connectivity.     

利用Argo浮标定位信息估算分析赤道太平洋中层流场状况

本文利用Argo浮标的定位信息,经过较为严格的质量控制与误差估算,得到2003～2005年赤道太平洋区域中层流场信息,并对其进行较为详细的诊断与分析,得到以下几个结论:(1)棉兰老涡、赤道逆流和南赤道流在中层流场中多数时间清晰可辨,北赤道流较弱,有时不易分辨。(2)棉兰老涡、赤道逆流和南赤道流都存在明显的季节变化。一般在2、3月间最弱,8、9月间最强。(3)棉兰老涡、赤道逆流和南赤道流存在较明显的年际变化。(4)赤道逆流通常表现为两支,分别位于东赤道太平洋和西赤道太平洋,东太平洋支主轴位置大约在7～8°N附近,西太平洋支主轴位置大约在3°N附近。     

2000年东海黑潮和琉球群岛以东海流的变异Ⅱ.冲绳岛东南海域海流及其附近中尺度涡的变异

基于日本“长风丸”调查船在2000年5个航次水文资料及同时期QuikSCAT风场资料,采用改进逆方法计算了冲绳岛东南海域海流的流速与流量等,获得了以下主要结果.(1)在琉球群岛以东海区1~2,4,7,10与11月分别为东北风,东北风,东南风,偏东风,东北风.风速在4与7月较小,1~2,10与11月较大.表层风海流只有7月时偏北向,其余月偏西方向.(2)琉球海流是琉球群岛以东一支东北向的西边界流.琉球海流结构:最大流速在5个航次中1~2,4,7,10与11月分别为40 cm/s以上,15,20,20与55 cm/s.琉球海流的核心一般位于次表层.琉球海流在5个航次中垂向方向可达1 200 m以深,在琉球海流以深存在弱的、西南向海流.(3)琉球海流的流量在1~2与11月时最大,分别为20×106与14.5×10 m3/s,而在4月时流量最小,只有3.1×106m3/s.这表明琉球海流的流量在2000年季节变化很大.(4)在5个调查航次中,琉球海流以东调查海域都存在尺度不同的、各种冷的气旋式和暖的反气旋式涡.1~2月时,计算区域中部与东部,分别存在反气旋暖涡W1,W2和气旋式冷涡C1,C2;在4月时存在一对较强的、水平尺度都较大的、暖的反气旋涡和冷的气旋式涡,在它们中间出现南向流,它们可能组成一个偶极子等.这些表明,在5个航次中,琉球群岛以东调查海域存在各种强度不等的中尺度涡,其变化都很大.(5)琉球海流的流量受其附近各种涡的影响很大,特别是涡的强度增大时,可能减少琉球海流的流量.(6)在5个调查航次中,琉球群岛以东调查海域都存在南向流,其中11月时最大,其流量大于15×106m3/s,其次在1~2月,其流量大于10×106m3/s,在4月最小,流量约为3×106m3/s.上述南向流的季节变化趋向与琉球海流的季节变化趋向基本一致.     

Transmission of obliquely incident waves at low-crested breakwaters: Theoretical interpretations of experimental observations

The paper presents a series of analytical and numerical investigations of oblique wave transmission at low-crested breakwaters. For a smooth breakwater, two important features of wave height and direction are analyzed to establish the generic nature of the wave transmission process at oblique incidence. The proposed framework of research is validated against laboratory data from the EU-sponsored project, DELOS. The numerical simulations exhibit a significant decrease of the transmission coefficient with increasingly oblique incidence at a smooth breakwater. The roles of wave-breaking, nonlinearity, wave-induced currents and set-up in determining the characteristics of oblique wave transmission are demonstrated in the paper. It is found that both the amplitude-dependent phase velocity and the decrease of mean wave period contribute to the change of mean wave direction on the transmission side. An attempt has also been made to qualitatively explain the different behaviour of oblique wave transmission at a rubble-mound breakwater.     

Separation of incident and reflected waves in wave–current flumes

A technique is developed to separate the incident and reflected waves propagating on a known current in a laboratory wave–current flume by analyzing wave records measured at two or more locations using a least squares method. It can be applied to both regular and irregular waves. To examine its performance, numerical tests are made for waves propagating on quiescent or flowing water. In some cases, to represent the signal noise and measurement error, white noise is superimposed on the numerically generated wave signal. For all the cases, good agreement is observed between target and estimation.