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1.
The characteristics of air pollution in Tarragona (Spain) were investigated. Tarragona has an important petrochemical industry in a coastal region with a complex terrain. The numerical study was made in sea breeze conditions with a three-dimensional mesoscale model. Temporal and spatial variations of the wind fields have been used in the Eulerian equation for a non-reactive pollutant. The results of this study reveal the complexity of the dispersion patterns due to the combined effects of the sea breeze circulation and the orography. This work presents a comparison between the model output and the observed wind data by sodar and surface wind measurements. The evaluation shows that the model is capable of providing very realistic wind fields within this domain.  相似文献   

2.
A particle-tracking model to simulate the dispersion of contaminants in the Strait of Gibraltar has been developed. The model solves the hydrodynamic equations off-line and tidal analysis is carried out to determine tidal constants for the two main constituents. Tidal constants and residuals are stored in files that are read by the dispersion model. A lagrangian approach is used to solve dispersion; diffusion and decay are simulated by a Monte Carlo method. A method for assessing the areas of the Strait with higher probability of being affected by contamination occurring after an accident in the shipping routes is given. Generally speaking, the fate of a pollutant discharge strongly depends on wind conditions. Winds from the east tend to retain contamination into the Strait. As a consequence, transverse mixing occurs and both Spain and Morocco coasts are affected by contamination. Under calm conditions and west winds, contaminants are flushed out of the Strait faster and transverse mixing does not occur. Thus, only part of Morocco coast has a higher probability of being affected by contamination.  相似文献   

3.
The two-dimensional barotropic, hydrodynamic and transport model MOHID is applied to the Patos Lagoon system using a nested modelling approach to reproduce both the lagoon and estuary hydrodynamics. A new Lagrangian oil spill model is presented and used to simulate a hypothetical oil spill in the estuary. Hydrodynamic fields are validated and used to force the oil model. Results show that the hydrodynamics of this system is mainly controlled by the wind and freshwater discharge. The dispersion, concentration and thickness evolution of the oil in the first day after the spill is determined by the equilibrium between these two factors. The freshwater discharge is the major factor controlling the oil dispersion for discharges greater than 5000 m3 while the wind assumes control for lower discharge amounts. The results presented are a first step toward a coastal management tool for the Patos Lagoon.  相似文献   

4.
A random walk model to describe the dispersion of pollutants in shallow water is developed. By deriving the Fokker-Planck equation, the model is shown to be consistent with the two-dimensional advection-diffusion equation with space-varying dispersion coefficient and water depth. To improve the behaviour of the model shortly after the deployment of the pollutant, a random flight model is developed too. It is shown that over long simulation periods, this model is again consistent with the advection-diffusion equation. The various numerical aspects of the implementation of the stochastic models are discussed and finally a realistic application to predict the dispersion of a pollutant in the Eastern Scheldt estuary is described.  相似文献   

5.
Three rapid-response Lagrangian particle-tracking dispersion models have been developed for southern Spain coastal waters. The three domains cover the Gulf of Cádiz (Atlantic Ocean), the Alborán Sea (Mediterranean), and the Strait of Gibraltar with higher spatial resolution. The models are based on different hydrodynamic submodels, which are run in advance. Tides are calculated using a 2D barotropic model in the three cases. Models used to obtain the residual circulation depend on the physical oceanography of each region. Thus, two-layer models are applied to Gibraltar Strait and Alborán Sea and a 3D baroclinic model is used in the Gulf of Cádiz. Results from these models have been compared with observations to validate them and are then used by the particle-tracking models to calculate dispersion. Chemical, radioactive and oil spills may be simulated, incorporating specific processes for each kind of pollutant. Several application examples are provided.  相似文献   

6.
A steady-state three-dimensional analytical model for the dispersion of a pollutant from a continuously emitting point source in a finite inversion layer has been proposed. The advection along the mean wind and the diffusion in all three directions have been accounted. A closed-form analytical solution of the proposed problem has been obtained using the method of integral transform and the same happens out to be non-Gaussian. Various limiting cases including the crosswind integrated concentration and the standard Gaussian-plume formula have been deduced from the solution obtained.The present model has been evaluated using Hanford diffusion experiment (DORAN et al., 1984) in stable conditions and IIT diffusion experiment (SINGH et al., 1991) in unstable conditions. The dispersion parameters have been computed using the various sigma schemes in accordance with the available observations. The proposed model has performed reasonably well with the data from both the diffusion experiments considered here.  相似文献   

7.
MYJ和YSU方案对WRF边界层气象要素模拟的影响   总被引：20，自引：5，他引：15       下载免费PDF全文
研究新一代中尺度气象模式WRF中两种大气边界层方案(MYJ,YSU)对沈阳冬季大气边界层结构模拟的影响,重点分析温度层结、低层风场、边界层高度等对污染物扩散有重要影响的气象要素.和观测数据的比对表明WRF基本能够模拟出温度风速的日变化特征,但模拟风速偏大.YSU方案由于模拟的边界层顶卷挟和边界层内混合作用较强,夜间接地逆温强度低于MYJ方案,逆温维持时间比MYJ方案短4小时,同时模拟边界层高度也高于MYJ方案,有利于污染物垂直扩散.边界层高度的3种计算方法中,湍流动能方法计算的边界层高度最高,Richardson数方法次之,位温方法得到的高度最低.Richardson数方法对临界值的选取较敏感.  相似文献   

8.
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9.
A chain of three nested models, based on the MARS 3D code, is used to simulate the North-western Mediterranean Sea circulation with a finest grid of 1.2 km resolution and 30 vertical sigma levels. This modelling system allows to resolve the coastal dynamics taking into account the influence of the general basin circulation. The aim of this study is to assess the ability of the nested MARS-3D models to reproduce most of the circulation features observed in the North-western Mediterranean Basin and in the Gulf of Lions. Comparisons of modelled sea surface temperature and salinity with MEDAR/MEDATLAS climatology and NOAA/AVHRR satellite measurements show that the model accurately reproduces the large and coastal scale variability. Over the Northern Basin, the seasonal changes of the cyclonic gyre extension are correctly simulated, even though in summer, the modelled temperature of the surface layer remains in basin-average 1°C cooler than the satellite measured temperature. As soon as the stratification erodes, modelled and observed temperatures become closer. Over the Gulf of Lions, realistic coastal responses are obtained under different wind conditions. Upwellings are correctly located and their intensity and spatial extension were here improved by the use of Aladin wind fields (10 km spatial resolution) and the introduction of a drag coefficient fitted according to the stability of the planetary boundary layer. The dispersion of fresh Rhone water discharge and the mesoscale circulation simulated by MARS-3D also agree with satellite measurements.  相似文献   

10.
Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides, flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for 2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring on the adjacent inner continental shelf, especially during storm and coastal upwelling events.  相似文献   

11.
A three-dimensional baroclinic nonlinear numerical model is employed to investigate the summer upwelling in the northern continental shelf of the South China Sea (NCSCS) and the mechanisms of the local winds inducing the coastal upwelling, associated with the QuikSCAT wind data. First, the persistent signals of the summer upwelling are illustrated by the climatological the Advanced Very High-Resolution Radiometer (AVHRR) Sea Surface Temperature (SST) image over 1985–2006 and field observations in 2006 summer. Then, after the successful simulation of the summer upwelling in the NCSCS, four numerical experiments are conducted to explore the different effects of local winds, including the wind stress and wind stress curl, on the coastal upwelling in two typical strong summer upwelling regions of the NCSCS. The modeled results indicate that the summer upwelling is a seasonal common phenomenon during June–September in the NCSCS with the spatial extent of a basin-scale. Typical continental shelf upwelling characteristics are clearly shown in the coastal surface and subsurface water, such as low temperature, high salinity and high potential density in the east of the Hainan Island, the east of the Leizhou Peninsula and the southeast of the Zhanjiang Bay (noted as the Qiongdong-QD), and the inshore areas from the Shantou Coast to the Nanri Islands of the Fujian Coast (noted as the Yuedong-YD). The analysis of the QuikSCAT wind data and modeled upwelling index suggests that the local winds play significant roles in causing the coastal upwelling, but the alongshore wind stress and wind stress curl have different contributions to the upwelling in the Qiongdong (QDU) and the coastal upwelling in the Yuedong (YDU), respectively. Furthermore, model results from the numerical experiments show that in the YD the stable alongshore wind stress is a very important dynamic factor to induce the coastal upwelling but the wind stress curl has little contribution and even unfavorable to the YDU. However, in the QD the coastal upwelling is strongly linked to the local wind stress curl. It is also found that not only the offshore Ekman transport driven by the alongshore wind stress, the wind stress curl-induced Ekman pumping also plays a crucial effect on the QDU. Generally, the wind stress curl even has more contributions to the QDU than the alongshore wind stress.  相似文献   

12.
A limited domain, coastal ocean forecast system consisting of an unstructured grid model, a meteorological model, a regional ocean model, and a global tidal database is designed to be globally relocatable. For such a system to be viable, the predictability of coastal currents must be well understood with error sources clearly identified. To this end, the coastal forecast system is applied at the mouth of Chesapeake Bay in response to a Navy exercise. Two-day forecasts are produced for a 10-day period from 4 to 14 June 2010 and compared to real-time observations. Interplay between the temporal frequency of the regional model boundary forcing and the application of external tides to the coastal model impacts the tidal characteristics of the coastal current, even contributing a small phase error. Frequencies of at least 3 h are needed to resolve the tidal signal within the regional model; otherwise, externally applied tides from a database are needed to capture the tidal variability. Spatial resolution of the regional model (3 vs 1 km) does not impact skill of the current prediction. Tidal response of the system indicates excellent representation of the dominant M 2 tide for water level and currents. Diurnal tides, especially K 1, are amplified unrealistically with the application of coarse 27-km winds. Higher-resolution winds reduce current forecast error with the exception of wind originating from the SSW, SSE, and E. These winds run shore parallel and are subject to strong interaction with the shoreline that is poorly represented even by the 3-km wind fields. The vertical distribution of currents is also well predicted by the coastal model. Spatial and temporal resolution of the wind forcing including areas close to the shoreline is the most critical component for accurate current forecasts. Additionally, it is demonstrated that wind resolution plays a large role in establishing realistic thermal and density structures in upwelling prone regions.  相似文献   

13.
A two-dimensional numerical model is applied to a coastal ocean wherein alongshore elevation and density gradients, normally calculated by a three-dimensional model, are instead supplied by climatologically averaged data for the California Current System between 25 and 40°N. Surface wind stress is also obtained from climatological data. Both surface and bottom boundary layers are resolved in the model calculations; a second moment turbulence closure submodel supplies vertical diffusivities. Near steady state solutions are possible when surface buoyancy flux is imposed at the surface.Model results are as follows: Southward wind stress produces a broad equatorward current with an embedded coastal jet in accordance with previous studies. Positive wind stress curl reduces the jet current and produces a poleward undercurrent which then surfaces as the curl is increased. The jet currents are reduced and poleward flow increases as bottom steepness increases; to a lesser extent, inclusion of the beta effect has a similar effect. The existence of near bottom, poleward or equatorward flow is explained rather simply in terms of the bottom stress resulting from the alongshore balance of surface wind stress and vertically integrated pressure gradient, the latter involving the alongshore surface elevation and density gradient. A further finding is that the upwelling circulation associated with wind stress is confined to the top 200 to 300 m of the ocean along the California coast.  相似文献   

14.
A hybrid near-field/far-field thermal discharge model for coastal areas   总被引：1，自引：0，他引：1  
A hybrid technique has been used to simulate the dispersion of heat from surface discharges in coastal areas. Characteristics of the near field thermal dispersion are described by the CORMIX3 model. A two-dimensional harmonic finite element hydrodynamic model (TEA) and a Eulerian–Lagrangian transport model (ELA) are applied for the far-field computation. A Gaussian puff algorithm in ELA, which represents the near field plume as a series of patches, is used to link the two regimes. The computed results are compared to available field measurements. Very reasonable agreement is observed.  相似文献   

15.
A model for the numerical simulation of tephra fall deposits   总被引：4，自引：2，他引：4  
A simple semianalytical model to simulate ash dispersion and deposition produced by sustained Plinian and sub-Plinian eruption columns based on the 2D advection–dispersion equation was applied. The eruption column acts as a vertical line source with a given mass distribution and neglects the complex dynamics within the eruption column. Thus, the use of the model is limited to areas far from the vent where the dynamics of the eruption column play a minor role. Vertical wind and diffusion components are considered negligible with respect to the horizontal ones. The dispersion and deposition of particles in the model is only governed by gravitational settling, horizontal eddy diffusion, and wind advection. The model accounts for different types and size classes of a user-defined number of particle classes and changing settling velocity with altitude. In as much as wind profiles are considered constant on the entire domain, the model validity is limited to medium-range distances (about 30–200 km away from the source).The model was used to reconstruct the tephra fall deposit from the documented Plinian eruption of Mt. Vesuvius, Italy, in 79 A.D. In this case, the model was able to broadly reproduce the characteristic medium-range tephra deposit. The results support the validity of the model, which has the advantage of being simple and fast to compute. It has the potential to serve as a simple tool for predicting the distribution of ash fall of hypothetical or real eruptions of a given magnitude and a given wind profile. Using a statistical set of frequent wind profiles, it also was used to construct air fall hazard maps of the most likely affected areas around active volcanoes where a large eruption is expected to occur.  相似文献   

16.
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   

17.
Particle models are often used to simulate the spreading of a pollutant in coastal waters in case of a calamity at sea. Here many different particle tracks starting at the point of release are generated to determine the particle concentration at some critical locations. This Monte Carlo method, however, consumes a large CPU time. Recently, Milstein, et al. [Milstein, GN, Schoenmakers JGM, Spokoiny, V. Transition density estimation for stochastic differential equations via forward–reverse representations. Bernoulli 2004:10(2);281–312] introduced the concept of reverse-time diffusion and derived a reverse particle model from the original forward simulation model. While the original forward model provides results on where the pollutant will go to, the reverse system gives information about where the pollutant came from. The Monte Carlo estimator for the particle concentration can also be based on realizations of this reverse system. In this paper we apply this concept to estimate particle concentrations in coastal waters. The results of the experiments show that the CPU time compared with the classical Monte Carlo method is reduced at least order of magnitude.  相似文献   

18.
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   

19.
Local and remote wind-coherent responses of sea surface heights (SSHs) off the US West Coast (USWC) are described with statistical and analytical models. The wind transfer functions are statistically derived from surface wind stress at National Data Buoy Center (NDBC) buoys, located within 50 km from the shoreline, and detided SSHs (SSH anomalies; SSHAs) at shoreline tide gauges for 15 years (1995 to 2009) using linear regression in the frequency domain. A two-dimensional analytical model constrained by the coastal boundary provides a dynamical framework to interpret the data-derived statistical model. Although both transfer functions agree well at low frequency [σ ≤ 0.4 cycles per day (cpd)], they appear to be inconsistent at high frequency (σ ≥ 0.8 cpd; e.g., diurnal and its harmonic frequencies) because of incoherent signals between wind stress and SSHAs as well as their low signal-to-noise ratios. A multivariate regression analysis using wind stress at multiple wind buoys is implemented with a modified expectation maximization. The cross-validated skill increases and becomes saturated as the number of regression basis functions increases, demonstrating the influence of local and remote winds. The skill computed from all available winds off the USWC has a maximum as 0.1 in southern California, 0.2 to 0.3 in central California, and 0.3 to 0.5 in northern California, Oregon, and Washington. The residual SSHAs, incoherent components with all available coastal wind stress off the USWC, still contain poleward propagating signals, considered as components forced by remote winds outside of the domain.  相似文献   

20.
The western Baltic Sea infront of the German coast is a highly variable dynamical system, dominated by a complex and small-scale morphometry, the water exchange between the Baltic and North Seas, and driven by local wind. Neither data collection, nor satellite images or model simulations alone were able to explain the observed spatial patterns and transport processes. Therefore, all these methods were combined to explain the dynamical features and to systematise them according to the typical local wind pattern and time series. The aim was to develop an instrument for regional authorities which supports the interpretation of coastal water monitoring data and forms a basis for an improved monitoring strategy. Satellite data of sea surface temperature and ocean colour from the sensors NOAA-AVHRR and SeaWiFS were applied for synoptic investigations in the entire region and Landsat-7-ETM+ for regional studies. Model simulations were performed for the western Baltic using a 3D model MOM-3 and for the Szczecin Lagoon using 2D model FEMFLOW. For the first time, regional particularities in the coastal dynamical features and processes are derived for the main wind directions and for transitions between dominant wind situations west and east as derived from wind statistics. The simulated transport of particles released from different coastal and open sea sources indicate the affected areas during changing forcing conditions. The results support the interpretation of acquired coastal monitoring data as well as the assessment and optimisation of the monitoring programme.  相似文献   

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