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1.
A hydrodynamic model of the Bay of Toulon has been developed for use as a post-accident radionuclide dispersion simulation tool. Located in a Mediterranean urban area, the Bay of Toulon is separated into two basins by a 1.4-km long seawall. The Little Bay is semi-enclosed and connected to the Large Bay by a fairway channel. This channel is the site of significant water mass exchange as a result of both wind-driven currents and bathymetry. It is therefore a focal point for marine contamination. As part of the model calibration and validation process, the first step consisted of studying the water mass exchange between the two basins. An Acoustic Doppler Current Profiler was moored in the channel for 1 year. The present study analyses in situ data to determine the current intensity and direction, and also to better understand the vertical current profile, which is highly correlated with meteorological forcing. Comparisons of model-generated and measured data are presented, and various atmospheric forcing datasets are used to enhance computed results. It appears that accurate meteorological forcing data is needed to enhance the accuracy of the hydrodynamic model. This channel is an important location for water mass renewal in the Bay of Toulon, and model results are used to quantify these exchanges. The mean calculated annual water exchange time is approximately 3.4 days. However, this duration is strongly wind dependent and shortens during windy winter months. It ranges from 1.5 days during strong wind periods to 7.5 days during calm weather. Residence time values calculated through tracer dispersion modelling after release at the back of the Little Bay are found to be comparable to the mean exchange time values, especially for windy conditions.  相似文献   

2.
Many crucial tasks in seismology, such as locating seismic events and estimating focal mechanisms, need crustal velocity models. The velocity models of shallow structures are particularly important in the simulation of ground motions. In southern Ontario, Canada, many small shallow earthquakes occur, generating high-frequency Rayleigh (Rg) waves that are sensitive to shallow structures. In this research, the dispersion of Rg waves was used to obtain shear-wave velocities in the top few kilometers of the crust in the Georgian Bay, Sudbury, and Thunder Bay areas of southern Ontario. Several shallow velocity models were obtained based on the dispersion of recorded Rg waves. The Rg waves generated by an m N 3.0 natural earthquake on the northern shore of Georgian Bay were used to obtain velocity models for the area of an earthquake swarm in 2007. The Rg waves generated by a mining induced event in the Sudbury area in 2005 were used to retrieve velocity models between Georgian Bay and the Ottawa River. The Rg waves generated by the largest event in a natural earthquake swarm near Thunder Bay in 2008 were used to obtain a velocity model in that swarm area. The basic feature of all the investigated models is that there is a top low-velocity layer with a thickness of about 0.5 km. The seismic velocities changed mainly within the top 2 km, where small earthquakes often occur.  相似文献   

3.
Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.  相似文献   

4.
A three-dimensional baroclinic model of the Balearic Sea region is used to examine the processes influencing the distribution of near-inertial currents and waves in the region. Motion is induced by a spatially uniform wind impulse. By using a uniform wind, Ekman pumping due to spatial variability in the wind is removed with the associated generation of internal waves. However, internal waves can still be produced where stratification intersects topography. The generation and propagation of these waves, together with the spatial distribution of wind-forced inertial oscillations, are examined in detail. Diagnostic calculations show that in the near-coastal region inertial oscillations are inhibited by the coastal boundary. Away from this boundary the magnitude of the inertial oscillations increases, with currents showing a 180° phase shift in the vertical. The inclusion of an along-shelf flow modifies the inertial currents due to non-linear interaction between vorticity in the flow and the inertial oscillations. Prognostic calculations show that besides inertial oscillations internal waves are generated. In a linear model the addition of an along-shelf flow produces a slight reduction in the energy at the near-inertial frequency due to enhanced viscosity associated with the flow and changes in density field. The inclusion of non-linear effects modifies the currents due to inertial oscillations in a manner similar to that found in the diagnostic model. A change in the effective inertial frequency also influences the propagation of the internal waves. However, this does not appear to be the main reason for the enhanced damping of inertial energy, which is due to the along-shelf advection of water of a different density into a region and increased viscosity and mixing associated with the along-shelf flow.Responsible Editor: Phil Dyke  相似文献   

5.
The baroclinic response of a stratified coastal embayment (Lunenburg Bay of Nova Scotia) to the observed wind forcing is examined using two numerical models. A linear baroclinic model based on the normal mode approach shows skill at reproducing the observed isotherm movements and sub-surface currents during a time of strong stratification in the bay. The linear model also shows that the isotherm movement in Lunenburg Bay is influenced by the wind forcing and propagation of baroclinic Kelvin waves from neighbouring Mahone Bay. The effects of nonlinearity and topography are investigated using a three-dimensional nonlinear coastal circulation model. The nonlinear model results demonstrate that the nonlinear advection terms generate a gyre circulation at the entrance of Lunenburg Bay, and the slope bottom topography at the mouth of the bay strengthens the sub-surface time-mean inflow on the southern side of the bay. A comparison of model-calculated currents in different numerical experiments clearly shows that baroclinicity plays a dominant role in the dynamics of wind-driven circulation in Lunenburg Bay.  相似文献   

6.
Barotropic responses of the East China Sea to typhoon KOMPASU are investigated using a high-resolution, three-dimensional, primitive equation, and finite volume coastal ocean model. Even the fact that the typhoon KOMPASU only brushed across the brink of China mainland without landing, it still imposed great influence across China's east coastal area, where storm surges ranging from 35 to 70 cm were intrigued during this event and a large wake of water setdown due to the outward radial transport driven by the cyclonic wind stress was generated after the KOMPASU traveled across the Yellow Sea. Analysis of the numerical results reveals that the barotropic waves propagating along the coast after the typhoon's landing can be identified as Kelvin wave and the currents associated with the storm are geostrophic currents. A series of model runs are initiated to diagnose the effects of wind stress, atmospheric pressure, and storm track variation on the surge's spatial distribution in the East China Sea. The barotropic waves affected by the atmospheric disturbance due to the typhoon in deep Pacific Ocean travel far more rapidly, arriving at the coastal regions at least 60 h ahead of the typhoon. The wave amplitudes are merely 0.2–0.4 cm and damp gradually due to friction. The model experiments also confirm that the surge levels in nearshore regions are highly dominated by winds, whereas the water level variations in deeper areas are controlled by the atmospheric pressure forcing during typhoon events in the East China Sea.  相似文献   

7.
Abstract

In an ocean with a horizontal bottom where no wind is blowing it is shown that the spin (angular momentum) of the ocean is conserved. Thus, when energy is dissipated, at least one of three things will happen: i) Wave spectra may move towards lower frequencies. ii) The directional distribution may be changed towards long-crested waves. iii) Shear currents may be generated. By neglecting ii) and iii), the frequency shift of a spectrum is calculated due to molecular dissipation. When all energy transforming phenomena as e.g. wave breaking and turbulence generation are taken into account, the conservation of spin seems to be able to explain the frequency shift of wave spectra. In shallow water it is shown that there is energy transfer from the waves to shear currents.  相似文献   

8.
Yangshan near-shore sea area is the multi-island and multi-channel area with strong flow velocity and high suspended sediment concentration. Based on the characteristics of tidal currents, waves, and sediment in the Yangshan area, a two-dimensional numerical model of tidal currents, sediment transport, and sea bed deformation is developed. In the model, the effects of tidal currents and wind waves on sediment transport are considered. According to characteristics of the study area, unstructured grids are applied to fit the boundaries of the near-shore sea area. The results show that the calculated values are in good agreement with the measured data. The field of tidal currents, suspended sediment concentrations, and the deformation of the seabed can be successfully simulated.  相似文献   

9.

A coupled wave and ocean model is applied to the region of Galway Bay in the west of Ireland, using the numerical modelling suite COAWST. The coupled model was validated in a previous study. Here we focus on the impact of the currents and sea level on the sea state during Storm Hector (2018/06/14). The purpose of the research is to improve the wave dynamics knowledge specifically in Galway Bay by highlighting and quantifying the dominant current-induced mechanisms on the sea state observed numerically. We want to know where wave-current interaction is modifying the sea state in the bay, and if the change is significant to justify the use of a coupled model for an operational application. We show that the impacts of the tidal sea surface height on bottom friction and of the current-induced refraction on the spatial distribution of the waves are the dominant mechanisms. Those two effects are well-documented and observed in the literature already. A strong feedback impact of the coupling is also put into evidence. The wave-induced response in terms of currents leads to a noticeable variation in terms of wave height. Less documented in the literature, we discuss the link between current-induced refraction and the reduction of wave generation by wind.

  相似文献   

10.
The mechanisms governing dispersion processes in the northern Yucatan coast are investigated using a barotropic numerical model of coastal circulation, which includes wind-generated and large scale currents (i.e. Yucatan Current). This work provides the foundations for studying the dispersion of harmful algal blooms (HABs) in the area. Modelling experiments include effects of climatic wind (from long term monthly mean NCEP reanalysis), short term wind events (from in situ point measurements), and Yucatan Current (YC) characteristics. Its magnitude was approximated from published reports, and its trajectory from geostrophic current fields derived from altimeter data. These provided a range of real and climatic conditions to study the routes in which phytoplankton blooms may travel. The 2-D model results show that a synthetic and conservative bloom seeded in the Cabo Catoche (CC) region (where it usually grows), moves along the coast to the west up to San Felipe (SF), where it can either move offshore, or carry on travelling westwards. The transport to the west up to SF is greatly influenced by the trajectory, intensity and proximity of the YC jet to the peninsula, which enhances the westward circulation in the Yucatan Shelf. Numerical experiments show that patch dispersion is consistently to the west even under the influence of northerly winds. When the YC flows westward towards the Campeche Bank, momentum transfer caused by the YC jet dominates the dispersion processes over wind stress. On the other hand, when it flows closer to Cuba, the local processes (i.e. wind and bathymetry) become dominant. Coastal orientation and the Coriolis force may be responsible for driving the patch offshore at SF if external forcing decreases.  相似文献   

11.
Ocean Dynamics - A dense network of instruments has been deployed within harbors along the Mediterranean coast, in the Toulon Metropole area, between the Hyères islands and the Sanary Bay in...  相似文献   

12.
Wave measurement and modeling in Chesapeake Bay   总被引：4，自引：0，他引：4  
Three recently measured wind and wave data sets in the northern part of Chesapeake Bay (CB) are presented. Two of the three data sets were collected in late 1995. The third one was collected in July of 1998. The analyzed wind and wave data show that waves were dominated by locally generated, fetch limited young wind seas. Significant wave heights were highly correlated to the local driving wind speeds and the response time of the waves to the winds was about 1 h. We also tested two very different numerical wave models, Simulation of WAves Nearshore (SWAN) and Great Lakes Environmental Research Laboratory (GLERL), to hind-cast the wave conditions against the data sets. Time series model–data comparisons made using SWAN and GLERL showed that both models behaved well in response to a suddenly changing wind. In general, both SWAN and GLERL over-predicted significant wave height; SWAN over-predicted more than GLERL did. SWAN had a larger scatter index and a smaller correlation coefficient for wave height than GLERL had. In addition, both models slightly under-predicted the peak period with a fairly large scatter and low correlation coefficient. SWAN predicted mean wave direction better than GLERL did. Directional wave spectral comparisons between SWAN predictions and the data support these statistical comparisons. The GLERL model was much more computationally efficient for wind wave forecasts in CB. SWAN and GLERL predicted different wave height field distributions for the same winds in deeper water areas of the Bay where data were not available, however. These differences are as yet unresolved.  相似文献   

13.
Blue crab larvae are advected out of Middle Atlantic Bight estuaries immediately after spawning occurs in the estuary entrance. For the next 30 to 50 days the larvae are found offshore and mainly at the surface where they are influenced by wind-driven currents. Using a previously derived circulation model and winds from Norfolk (VA) airport, a backward trace is made from where relatively dense concentrations of megalopae were found in the Chesapeake Bight during 1983 to a point of origin (spawning).During 1983, the megalopae encountered on the shelf had their origin in Chesapeake Bay and took, at minimum, 31 to 36 days to grow to the megalopae stage. Wind forcing dominated the inner shelf region in the summer of 1983 and the resulting dispersion of Chesapeake Bay megalopae occurred briefly in the southern sector early in the season, but toward the northern sector over most of the season. Although no firm conclusions could be drawn regarding the mechanism for return, it did not seem likely that wind advection back to the point of origin would be effective.  相似文献   

14.
The generation of internal lee waves (ILW) in the Strait of Gibraltar takes place in the main sill where the tidal flow interacts with a submarine obstacle. The tidal flow is perturbed by subinertial phenomena of different nature summarized in the subinertial currents that can inhibit the ILW generation. The authors present an attempt to randomize the problem by the introduction of a Gaussian noise in the Taylor–Goldstein equation. The random number sets are generated from the statistical distribution of the previously isolated random part of the subinertial currents from experimental data taken in the area during the Gibraltar Experiment 94–96. The effect of the noise is translated into a continuous spreading of the spectrum around the solution of the noise-free problem. A stability analysis is carried out in order to determine the single neutral modes of oscillations and the phase space is divided onto regions of stability and instability as a function of the inflowing subinertial current. The methodology and results could be useful for the design and timing of oceanographic surveys in straits where the ILWs occur.  相似文献   

15.
This paper presents an assessment of the impact of the ocean circulation on modeled wave fields in the Southern Ocean, where a systematic positive bias of the modeled wave height against altimetry data has been reported. The inclusion of ocean currents in the wave model considerably reduces the positive bias of the simulated wave height for high southern latitudes. The decrease of wave energy in the presence of currents is almost exclusively related to the reduction of the relative wind, caused by an overall co-flowing current field associated with the Antarctic Circumpolar Current. Improvements of the model results are also found for the peak period and the mean period against a long-term moored buoy. At the mooring location, the effect of currents is greater for larger and longer waves, suggesting remotely generated swells are more influenced by the currents than local waves. However, an additional qualitative analysis using high-resolution currents in a finer grid nested to the global coarser grid shows that typical resolution of global hydrodynamic reanalysis is not sufficient to resolve mesoscale eddies, and as a consequence, the simulation of mesoscale wave patterns can be compromised. The results are also discussed in terms of the accuracy of forcing fields.  相似文献   

16.
Variability in the regional setting and morphology of cuspate forelands on the west coast of Western Australia is examined in this paper. In accordance with this aim, principal differences in the geologic and geomorphologic setting of three prominent sites on the west coast were established and their association with historical changes and contemporary oceanographic processes was examined. The cuspate forelands investigated are Jurien Bay, Winderabandi Point and Turquoise Bay. The most significant differences in geologic setting are associated with the structure and location of an extensive offshore reef system. Morphologically, the reef alters from south to north, changing from a discontinuous ridge parallel to the shore along the central west coast, to a nearly continuous fringing reef at Ningaloo. The reefs vary in distance from the shore, being farthest in the south and closest in the north and they impound a series of inshore basins, or lagoons. The deeper southern basins are dominated by locally generated wind waves and wind‐generated currents. The shallower northern basins are most markedly affected by tidal currents and wave pumping across the reef flats. The large cuspate foreland at Jurien on the central west coast has undergone shoreline configuration change in response to changing phases of storminess as well as in response to a change in focus for sediment deposition as a result of offshore reef erosion. At Winderabandi Point on the Ningaloo coast, relict Pleistocene limestone has provided the focus for sedimentation and morphology has been controlled by a balance in refracted wave energy and nearshore currents driven by tidal and wave set‐up variability. At Turquoise Bay, where the lagoonal basin is most shallow and narrow, the morphology of the foreland suggests that it may at some stage have been migratory, but its present asymmetrical shape is maintained by strong northerly longshore drift and strong currents exiting the lagoon through a nearby gap in the reef crest. Fundamental differences between the two coastal regions include the structure of the offshore reef, processes driving flow of water within the lagoons and the role of storminess in evolution of coastal landforms. Although many questions regarding storm surge dynamics and landform change remain unanswered, this research provides a significant contribution to the understanding of the evolution of morphological systems in low‐wave‐energy protected environments. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

17.
Auroral phenomena are controlled by the geomagnetic field.Since the terrestrial field lines connect the auroral oval to the equatorial region at large distances, the collisionless plasma in this remote space environment can act as a power supply for the high-latitude upper atmosphere where auroral emissions take place. The coupling process is intimately linked to currents which flow across the local magnetic field direction both in the equatorial part and at the atmospheric end of the auroral field lines. These two auroral key regions are connected through currents flowing along the terrestrial field lines, thereby completing the auroral current circuit. Such field-aligned currents are carried by Alfvén waves, that is, magnetohydrodynamic shear waves, which are thus a means to exchange momentum and energybetween rather remote parts of the geomagnetically controlledspace environment. Auroral dynamics is further affected by a third key region in the auroral current circuit, namely the auroral acceleration region, where parallel electric fields accelerate particle to keV energies. This review focuses on key region coupling through Alfvén waves. Continuity requirements for currents and electric fields provide a convenient means to describe the interaction of Alfvén waves with different plasma regimes. Basic coupling aspects can be demonstrated with the help of a simplified model. Inhomogeneities and nonlinear feedback can lead to resonance effects and instabilities.  相似文献   

18.
The wave climate of Liverpool Bay—observations and modelling   总被引：1，自引：1，他引：0  
Directional wave measurements have been made in Liverpool Bay by means of wave buoys and acoustic instruments within the footprint of a phased-array high frequency (HF) radar system, which measures currents and waves. Several years of data have now been collected and are supplemented by an 11-year wave model hindcast. Wave parameters have been derived from the various instruments and compared: the directional waverider buoy is taken to provide the ground truth, confirming the good observations obtained from the ADCP; the HF radar wave data have a positive bias, while the model data have a negative bias. The variation of wave climate over various time-scales from seasonal and inter-annual to inter-decadal is examined. Significant wave–current interactions may occur in this area of shallow water and high tidal range and the measurements provide a good test of coupled hydrodynamic-wave models. The waves are mainly fetch-limited: largest events are due to depressions, which track across the UK from SW, generating westerly and WNW winds in the right rear quadrant. Hence, the future extreme wave events will be closely related to future North Atlantic storm tracks. Projections of 50-year return period wave heights differ between different instruments and model datasets. The future wave climate of Liverpool Bay is not expected to change much from the present day; although a slight increase in the severity of the most extreme events is projected, the frequency of extreme wind and wave events in general is slightly reduced. There is evidence for variability on decadal time-scales, with some correlation with the North Atlantic oscillation.  相似文献   

19.
The Northern current is the main circulation feature of the North-Western Mediterranean Sea. While the large-scale to mesoscale variability of the northern current (NC) is well known and widely documented for the Ligurian region, off Nice or along the Gulf of Lions shelf, few is known about the current instabilities and its associated mesoscale dynamics in the intermediate area, off Toulon. Here, we took advantage of an oceanographic cruise of opportunity, the start of a HF radar monitoring programme in the Toulon area and the availability of regular satellite sea surface temperature and chlorophyll a data, to evaluate the realism of a NEMO-based regional high-resolution model and the added value brought by HF radar. The combined analysis of a 1/64° configuration, named GLAZUR64, and of all data sets revealed the occurrence of an anticyclonic coastal trapped eddy, generated inside a NC meander and passing the Toulon area during the field campaign. We show that this anticyclonic eddy is advected downstream along the French Riviera up to the study region and disturbs the Northern current flow. This study aims to show the importance of combining observations and modelling when dealing with mesoscale processes, as well as the importance of high-resolution modelling.  相似文献   

20.
The Basque coastal area, in the southeastern Bay of Biscay, can be characterised as being more influenced by land climate and inputs, than other typically ‘open sea’ areas. The influence of coastal processes, together with the presence of irregular and steep topography, complicate greatly the water circulation patterns. Water movement along the Basque coastal area is not well understood; observations are scarce and long-term current records are lacking. The knowledge available is confined to the surface currents: the surface water circulation is controlled mainly by wind forcing, with tidal and density currents being weak. However, there is a lack of knowledge available on currents within the lower levels of the water column; likewise, on the main time-scales involved in the water circulation. This study quantifies the contribution of the tidal and wind-induced currents, to the overall water circulation; it identifies the main time-scales involved within the tidal and wind-induced flows, investigating difference in such currents, throughout the water column, within Pasaia Bay (Basque coast). Within this context, extensive oceanographic and meteorological data have been obtained, in order to describe the circulation. The present investigation reveals that the circulation, within the surface and the sub-surface waters, is controlled mainly by wind forcing fluctuations, over a wide range of meteorological frequencies: third-diurnal, semidiurnal and diurnal land–sea breezes; synoptic variability; frequencies, near fortnightly periods; and seasonal. At the lower levels of the water column, the main contribution to the water circulation arises from residual currents, followed by wind-induced currents on synoptic time-scales. In contrast, tidal currents contribute minimally to the overall circulation throughout the water column.  相似文献   

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