共查询到20条相似文献，搜索用时 46 毫秒
1.
Influence of topography on tide propagation and amplification in semi-enclosed basins 总被引：3，自引：2，他引：1
An idealized model for tide propagation and amplification in semi-enclosed rectangular basins is presented, accounting for
depth differences by a combination of longitudinal and lateral topographic steps. The basin geometry is formed by several
adjacent compartments of identical width, each having either a uniform depth or two depths separated by a transverse topographic
step. The problem is forced by an incoming Kelvin wave at the open end, while allowing waves to radiate outward. The solution
in each compartment is written as the superposition of (semi)-analytical wave solutions in an infinite channel, individually
satisfying the depth-averaged linear shallow water equations on the f plane, including bottom friction. A collocation technique is employed to satisfy continuity of elevation and flux across
the longitudinal topographic steps between the compartments. The model results show that the tidal wave in shallow parts displays
slower propagation, enhanced dissipation and amplified amplitudes. This reveals a resonance mechanism, occurring when the
length of the shallow end is roughly an odd multiple of the quarter Kelvin wavelength. Alternatively, for sufficiently wide
basins, also Poincaré waves may become resonant. A transverse step implies different wavelengths of the incoming and reflected
Kelvin wave, leading to increased amplitudes in shallow regions and a shift of amphidromic points in the direction of the
deeper part. Including the shallow parts near the basin’s closed end (thus capturing the Kelvin resonance mechanism) is essential
to reproduce semi-diurnal and diurnal tide observations in the Gulf of California, the Adriatic Sea and the Persian Gulf. 相似文献
2.
Sea level changes coherently along the two coasts of Japan on the seasonal timescale. Archiving, validation, and interpretation
of satellite oceanographic altimetry data and ocean general circulation model for the Earth Simulator results indicate that
the variation propagates clockwise from Japan’s east coast through the Tsushima Strait into the Japan/East Sea (JES) and then
northward along the west coast. In this study, we hypothesize and test numerically that the sea-level variability along the
west coast of Japan is remotely forced by the Kuroshio Extension (KE) off the east coast. Topographic Rossby waves and boundary
Kelvin waves facilitate the connection. Our 3D Princeton Ocean Model when forced by observed wind stress reproduces well the
seasonal changes in the vicinity of JES. Two additional experiments were conducted to examine the relative roles of remote
forcing and local forcing. The sea-level variability inside the JES was dramatically reduced when the Tsushima Strait is blocked
in one experiment. The removal of the local forcing, in another experiment, has little effect on the JES variability. Both
experiments support our hypothesis that the open-ocean forcing, possibly through the KE variability, is the leading forcing
mechanism for sea-level change along the west coast of Japan. 相似文献
3.
The cross-sectional stability of double inlet systems is investigated using an exploratory model that combines Escoffier’s stability concept for the evolution of the inlet’s cross-sectional area with a two-dimensional, depth-averaged (2DH) hydrodynamic model for tidal flow. The model geometry consists of four rectangular compartments, each with a uniform depth, associated with the ocean, tidal inlets and basin. The water motion, forced by an incoming Kelvin wave at the ocean’s open boundary and satisfying the linear shallow water equations on the f -plane with linearised bottom friction, is in each compartment written as a superposition of eigenmodes, i.e. Kelvin and Poincaré waves. A collocation method is employed to satisfy boundary and matching conditions. The analysis of resulting equilibrium configurations is done using flow diagrams. Model results show that internally generated spatial variations in the water motion are essential for the existence of stable equilibria with two inlets open. In the hydrodynamic model used in the paper, both radiation damping into the ocean and basin depth effects result in these necessary spatial variations. Coriolis effects trigger an asymmetry in the stable equilibrium cross-sectional areas of the inlets. Furthermore, square basin geometries generally correspond to significantly larger equilibrium values of the inlet cross-sections. These model outcomes result from a competition between a destabilising (caused by inlet bottom friction) and a stabilising mechanism (caused by spatially varying local pressure gradients over the inlets). 相似文献
4.
The cross-sectional stability of double inlet systems is investigated using an exploratory model that combines Escoffier’s stability concept for the evolution of the inlet’s cross-sectional area with a two-dimensional, depth-averaged (2DH) hydrodynamic model for tidal flow. The model geometry consists of four rectangular compartments, each with a uniform depth, associated with the ocean, tidal inlets and basin. The water motion, forced by an incoming Kelvin wave at the ocean’s open boundary and satisfying the linear shallow water equations on the f -plane with linearised bottom friction, is in each compartment written as a superposition of eigenmodes, i.e. Kelvin and Poincaré waves. A collocation method is employed to satisfy boundary and matching conditions. The analysis of resulting equilibrium configurations is done using flow diagrams.
Model results show that internally generated spatial variations in the water motion are essential for the existence of stable equilibria with two inlets open. In the hydrodynamic model used in the paper, both radiation damping into the ocean and basin depth effects result in these necessary spatial variations. Coriolis effects trigger an asymmetry in the stable equilibrium cross-sectional areas of the inlets. Furthermore, square basin geometries generally correspond to significantly larger equilibrium values of the inlet cross-sections. These model outcomes result from a competition between a destabilising (caused by inlet bottom friction) and a stabilising mechanism (caused by spatially varying local pressure gradients over the inlets).
相似文献5.
The 1953 North Sea floods, the Big Flood, was one of the worst natural disasters in Europe in modern times and is probably one of the most studied severe coastal floods. Several factors led to the devastating storm surge along the southern North Sea coast in combination of strong and sustained northerly winds, invert barometric effect, high spring tide, and an accumulation of the large surge in the Strait of Dover. However, the storm waves and their roles during the 1953 North Sea storm surge are not well investigated. Therefore, the effect of wave setup due to breaking waves in the storm surge processes is investigated through numerical experiments. A coupled process-based tide-wave-surge model was used to investigate and simulate the storm surge in the North Sea during January 31–February 1, 1953 and validated by comparing with historical water level records at tide gauges and wave observations at light vessels in the North Sea. Meteorological forcing inputs for the period, January 27–February 3, 1953 are reproduced from ERA-20C reanalysis data with a constant correction factor for winds. From the simulation results, it is found that, in addition to the high water due to wind setup, wave setup due to breaking waves nearshore play a role of approximately 10% of the storm surge peaks with approximately 0.2 m. The resulting modeling system can be used extensively for the preparedness of the storm surge and wave of extreme condition, and usual barotropic forecast. 相似文献
6.
Numerical study of the barotropic responses to a rapidly moving typhoon in the East China Sea 总被引：2，自引：1，他引：1
Yang Ding Huaming Yu Xianwen Bao Liang Kuang Caixia Wang Wenjuan Wang 《Ocean Dynamics》2011,61(9):1237-1259
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.
Dynamical Control of Pacific Oceanic Low-frequency Variability on Western Boundary and Marginal Seas
The adjustment of sea surface height (SSH) around the coasts of the Japan/East Sea (JES) and the South China Sea (SCS) basins subjected to extratropical Pacific Oceanic low frequency variability is studied using a Kelvin-planetary wave model and a high resolution numerical model. It is found that the modulation of SSH around the coast of Japan is mainly determined by slow adjustment of planetary waves, which radiate from the west coast of Honshu and Hokkaido due to the coastal Kelvin wave. In contrast, the SSH modulation around the cost of the South China Sea basin is mainly determined by the coastal Kelvin wave, which transfers the anomalous SSH into the SCS via the Luzon Strait and out via the Mindoro Strait. The planetary waves radiating from the west coast of Palawan establish a nearly uniform SSH anomaly in the southern part of the SCS, bounded by an eastward jet at the latitude of the Mindoro Strait. Along the western boundary, SSH anomaly decreases almost linearly toward the south, in accordance with the changing local deformation radius. In these two marginal seas, the mean subtropical Pacific gyre circulation enhances SSH modulation induced by extratropical Pacific low frequency variability. Overall, the SSH adjustment in the JES and the SCS predicted by the analytical model agrees well with the numerical model simulation. Application of this model to interaction between these marginal seas and the open ocean is discussed. 相似文献
8.
Applying a two-dimensional, non-linear hydrodynamic numerical model in combination with a semiempirical equation for bedload
sediment transport, the influence of geometry on the formation of sandbanks is investigated. In the first experiment, the
formation of sandbanks in an ideal rectangular basin, resembling the Taylor’s problem, was calculated. Sandbanks occur in
a small area at the closed boundary. Similar experiments were carried out for a range of wavelengths of the incident Kelvin
wave. The results reveal that large wavelengths favor the generation of sandbanks. In subsequent calculations, the basin was
modified by introducing new geographical features like bays and peninsulas. The numerical experiments show that geometry is
a fundamental factor to determine the position where groups of sandbanks appear. The results suggest that in regions where
the Kelvin wave is diffracted, the formation of sandbanks occurs. An experiment, in which we applied an ideal geometric configuration
representing that of the Southern Bight of the North Sea, generated sandbank patterns resembling those observed in the region. 相似文献
9.
《Continental Shelf Research》2007,27(10-11):1568-1583
A study is presented where satellite images (SeaWiFS), in situ measurements (tidal cycle and snapshot) and a 2D hydrodynamic numerical model have been combined to calculate the long term SPM (Suspended Particulate Matter) transport through the Dover Strait and in the southern North Sea. The total amount of SPM supplied to the North Sea through the Dover Strait is estimated to be 31.74×106 t. The satellite images provide synoptic views of SPM concentration distribution but do not take away the uncertainty of SPM transport calculation. This is due to the fact that SPM concentration varies as a function of tide, wind, spring-neap tidal cycles and seasons. The short term variations (tidal, spring-neap tidal cycle) have not been found in the satellite images, however seasonal variations are clearly visible. Furthermore the SPM concentration in the satellite images is generally lower than in the in situ measurements. The representativness of SPM concentration maps derived from satellites for calculating long term transports has therefore been investigated by comparing the SPM concentration variability from the in situ measurements with those of the remote sensing data. The most important constraints of satellite images are related to the fact that satellite data is evidence of clear sky conditions, whereas in situ measurements from a vessel can be carried out also during rougher meteorological conditions and that due to the too low time resolution of the satellite images the SPM concentration peaks are often missed. It is underlined that SPM concentration measurements should be carried out during at least one tidal cycle in high turbidity areas to obtain representative values of SPM concentration. 相似文献
10.
An unstructured mesh model of the west coast of Britain, covering the same domain and using topography and open boundary forcing
that are identical to a previous validated uniform grid finite difference model of the region, is used to compare the performance
of a finite volume (FV) and a finite element (FE) model of the area in determining tide–surge interaction in the region. Initial
calculations show that although qualitatively both models give comparable tidal solutions in the region, comparison with observations
shows that the FV model tends to under-estimate tidal amplitudes and hence background tidal friction in the eastern Irish
Sea. Storm surge elevations in the eastern Irish Sea due to westerly, northerly and southerly uniform wind stresses computed
with the FV model tend to be slightly higher than those computed with the FE model, due to differences in background tidal
friction. However, both models showed comparable non-linear tide–surge interaction effects for all wind directions, suggesting
that they can reproduce the extensive tide–surge interaction processes that occur in the eastern Irish Sea. Following on from
this model comparison study, the physical processes contributing to surge generation and tide–surge interaction in the region
are examined. Calculations are performed with uniform wind stresses from a range of directions, and the balance of various
terms in the hydrodynamic equations is examined. A detailed comparison of the spatial variability of time series of non-linear
bottom friction and non-linear momentum advection terms at six adjacent nodes at two locations in water depths of 20 and 6 m
showed some spatial variability from one node to another. This suggests that even in the near coastal region, where water
depths are of the order of 6 m and the mesh is fine (of order 0.5 km), there is significant spatial variability in the non-linear
terms. In addition, distributions of maximum bed stress due to tides and wind forcing in nearshore regions show appreciable
spatial variability. This suggests that intensive measurement campaigns and very high-resolution mesh models are required
to validate and reproduce the non-linear processes that occur in these regions and to predict extreme bed stresses that can
give rise to sediment movement. High-resolution meshes will also be required in pollution transport problems. 相似文献
11.
Three finite element codes, namely TELEMAC, ADCIRC and QUODDY, are used to compute the spatial distributions of the M2, M4 and M6 components of the tide in the sea region off the west coast of Britain. This region is chosen because there is an accurate
topographic dataset in the area and detailed open boundary M2 tidal forcing for driving the model. In addition, accurate solutions (based upon comparisons with extensive observations)
using uniform grid finite difference models forced with these open boundary data exist for comparison purposes. By using boundary
forcing, bottom topography and bottom drag coefficients identical to those used in an earlier finite difference model, there
is no danger of comparing finite element solutions for “untuned unoptimised solutions” with those from a “tuned optimised
solution”. In addition, by placing the open boundary in all finite element calculations at the same location as that used
in a previous finite difference model and using the same M2 tidal boundary forcing and water depths, a like with like comparison of solutions derived with the various finite element
models was possible. In addition, this open boundary was well removed from the shallow water region, namely the eastern Irish
Sea where the higher harmonics were generated. Since these are not included in the open boundary, forcing their generation
was determined by physical processes within the models. Consequently, an inter-comparison of these higher harmonics generated
by the various finite element codes gives some indication of the degree of variability in the solution particularly in coastal
regions from one finite element model to another. Initial calculations using high-resolution near-shore topography in the
eastern Irish Sea and including “wetting and drying” showed that M2 tidal amplitudes and phases in the region computed with TELEMAC were in good agreement with observations. The ADCIRC code
gave amplitudes about 30 cm lower and phases about 8° higher. For the M4 tide, in the eastern Irish Sea amplitudes computed with TELEMAC were about 4 cm higher than ADCIRC on average, with phase
differences of order 5°. For the M6 component, amplitudes and phases showed significant small-scale variability in the eastern Irish Sea, and no clear bias between
the models could be found. Although setting a minimum water depth of 5 m in the near-shore region, hence removing wetting
and drying, reduced the small-scale variability in the models, the differences in M2 and M4 tide between models remained. For M6, a significant reduction in variability occurred in the eastern Irish Sea when a minimum 5-m water depth was specified. In
this case, TELEMAC gave amplitudes that were 1 cm higher and phases 30° lower than ADCIRC on average. For QUODDY in the eastern
Irish Sea, average M2 tidal amplitudes were about 10 cm higher and phase 8° higher than those computed with TELEMAC. For M4, amplitudes were approximately 2 cm higher with phases of order 15° higher in the northern part of the region and 15° lower
in the southern part. For M6 in the north of the region, amplitudes were 2 cm higher and about 2 cm lower in the south. Very rapid M6 tidal-phase changes occurred in the near-shore regions. The lessons learned from this model inter-comparison study are summarised
in the final section of the paper. In addition, the problems of performing a detailed model–model inter-comparison are discussed,
as are the enormous difficulties of conducting a true model skill assessment that would require detailed measurements of tidal
boundary forcing, near-shore topography and precise knowledge of bed types and bed forms. Such data are at present not available. 相似文献
12.
The distribution of zinc, manganese, nickel, copper and cadmium in water and biological material has been measured in the southern North Sea and Straits of Dover, and off the north-east coast of England. These investigations provide baseline values against which future pollution changes can be measured. 相似文献
13.
Merja H. Schlüter Agostino Merico Karen H. Wiltshire Wulf Greve Hans von Storch 《Ocean Dynamics》2008,58(3-4):169-186
We compiled homogeneous long-term time series comprising 39 variables representing the German Bight and for the period 1975–2004. A diverse set of variables was selected to cover multiple trophic levels and different environmental forcing thus to examine long-term changes in this coastal region. Previous studies have hypothesised the presence of regime shifts in observations extending over the entire North Sea. Focusing on a smaller spatial scale, and closer to the coast, we investigated the major modes of variability in the compiled time series using principal component analysis. The results obtained confirm a previously identified regime shift in the North Sea in 1987/1988 and suggest that the German Bight is dominantly characterised by long-term modes of variability. In the German Bight, the shift of 1987/1988 is driven primarily by temperature, Gulf Stream index, frost days and Secchi depth. Changes in some of the ecosystem variables (plankton and fish) appear to be related to changes in these driving variables. In particular, we documented strong positive correlations between the long-term trend showed by the first principal component and herring, Noctiluca scintillans, and, to a lesser extent, Pleurobrachia pileus. Two gadoids, namely cod and saithe, showed negative correlations with the observed long-term mode of variability. Changes in the sum of five small calanoid copepods were, however, less marked. Phosphate and ammonium exhibited a decreasing trend over the last 30 years. Diatoms and Calanus helgolandicus did not show evidence of changes in concert to this trend. Specific analyses of the data divided into three different subsets (biological, climatic and chemical) characterise the climate of the German Bight as highly dynamic also on short timescales (a few years) as compared to much smoother biological and chemical components. The dynamic regime of the German Bight taken together with a low correlation between the major mode of variability and phytoplankton and zooplankton data suggests that the lower trophic levels of this ecosystem are remarkably resilient. 相似文献
14.
Large-scale redistribution of sand by hydrodynamical processes in shelf seas is important for basin and coastal evolution on time scales of a thousand to tens of thousands of years. The influence of tides on the large-scale net sand-transport patterns in the North Sea has received much attention, but the influence of wind-driven flow and wind waves has hardly been investigated. Here, to establish the present-day situation and to develop a method that can also be used for palaeo-situations and forecasts for different sea levels, this influence is assessed for the present southern North Sea using a numerical flow model, a parametric wave model and a wave-averaged sand-transport formulation. Various forcing combinations are used to identify the dominant transport mechanisms: tides only, tides and wind, tides and waves, and combined tides, wind and waves. Wind forcing is applied in two ways to find an efficient, but still representative, method of incorporating this stochastic process: a statistical wind climatology and an observed time series. The results show that (i) the wind climatology yields a good approximation of the sand transport computed using the time series; (ii) wind-driven flow and waves only contribute significantly to the net sand transport by tides when acting together where tidal currents are small; and (iii) various combinations of forcings dominate the net sand transport in different regions of the southern North Sea: (a) tides dominate in the southern, middle and northwestern parts of the Southern Bight and in the region of The Wash; (b) tides, wind-driven flow and waves all are important in the northeastern part of the Southern Bight; and (c) wind-driven flow and waves dominate north of the Friesian Islands, in the German Bight and on the Dogger Bank. Qualitative comparison with observations shows good agreement. 相似文献
15.
16.
Greater Cook Strait (GCS) lies between the North and the South Islands of New Zealand. Its location at the convergence of
the Pacific and Indo-Australian tectonic plates leads to interesting bathymetry with an adjacent shallow shelf and deep ocean
trench as well as numerous crossing faults and complex shoreline geometry. Our purpose in this study is to examine tides and
currents in GCS and, in particular, identify the major forcing mechanisms for the residual currents. Toward this end, we use
an unstructured-grid numerical model to reproduce the tides and currents, verify these results with observations and then
use the model to separate the various forcing mechanisms. The physical forcing includes nonlinear generation from tides and
tidal currents, differences in sea level between the Pacific Ocean and Tasman Sea boundaries, density variations, wind stress
and river discharge into GCS. Each of these mechanisms is important in different areas. 相似文献
17.
A two-dimensional vertically integrated model of the North Sea is used to compute the distribution of M2 and M4 tidal elevations and currents over the region. Comparison of computed and observed elevations and currents in the area shows that the model can accurately reproduce the M2 tide in the North Sea, although there are difficulties with the M4 tide particularly in the northern North Sea.Comparison between model and a large number of observations collected in a shallow water region off the east coast of England, revealed that the model can accurately reproduce the tides even in near coastal regions, where model resolution problems can occur. Comparisons of computed and observed M2 tidal energy fluxes in this region, show that model and observations agree to within the order of 10% (the error associated with the necessary interpolation of the observations in order to compute the energy flux).The problem of computing energy dissipation in the area by subtracting the energy fluxes into and out of the region is shown to be ill-conditioned in that the energy dissipation in the area is comparable to the error in the energy flux. Consequently for the sea region considered here it is not meaningful to compare this energy budget with energy dissipation due to bottom friction.Energy dissipation for the whole of the North Sea is computed using the numerical model and the geographical distribution of dissipation due to bottom friction is given for the M2 tide. 相似文献
18.
Maialen Irazoqui Apecechea Martin Verlaan Firmijn Zijl Camille Le Coz Herman Kernkamp 《Ocean Dynamics》2017,67(6):729-749
The impact of the self-attraction and loading effect (SAL) in a regional 2D barotropic tidal model has been assessed, a term with acknowledged and well-understood importance for global models but omitted for boundary-forced, regional models, for which the implementation of SAL is non-trivial due to its non-local nature. In order to understand the impact of the lack of SAL effects in a regional scale, we have forced a regional model of the Northwest European Continental Shelf and the North Sea (continental shelf model (CSM)) with the SAL potential field derived from a global model (GTSM), in the form of a pressure field. Impacts have been studied in an uncalibrated setup and with only tidal forcing activated, in order to isolate effects. Additionally, the usually adopted simple SAL parameterization, in which the SAL contribution to the total tide is parameterized as a percentage of the barotropic pressure gradient (typically chosen 10%), is also implemented and compared to the results obtained with a full SAL computation. A significant impact on M2 representation is observed in the English Channel, Irish Sea and the west (UK East coast) and south (Belgian and Dutch Coast) of the North Sea, with an impact of up to 20 cm in vector difference terms. The impact of SAL translates into a consistent M2 amplitude and propagation speeds reduction throughout the domain. Results using the beta approximation, with an optimal domain-wide constant value of 1.5%, show a somewhat comparable impact in phase but opposite direction of the impact in amplitude, increasing amplitudes everywhere. In relative terms, both implementations lead to a reduction of the tidal representation error in comparison with the reference run without SAL, with the full SAL approach showing further impacted, improved results. Although the overprediction of tidal amplitudes and propagation speeds in the reference run might have additional sources like the lack of additional dissipative processes and non-considered bottom friction settings, results show an overall significant impact, most remarkable in tidal phases. After showing evidence of the SAL impact in regional models, the question of how to include this physical process in them in an efficient way arises, since SAL is a non-local effect and depends on the instantaneous water levels over the whole ocean, which is non-trivial to implement. 相似文献
19.
The contributions of bottom cold water and planetary β-effect to the formation of the East Korean Warm Current (EKWC), the western boundary current in the East/Japan Sea (EJS), were evaluated using an idealized three-dimensional numerical model. The model results suggest that the bottom cold water and, to a lesser extent, the planetary β-effect both contribute to the formation of the EKWC. The cold water functions as the bottom of the upper layer, to control the EKWC via conservation of potential vorticity. It is known that cold waters, such as the North Korean Cold Water and Korea Strait Bottom Cold Water often observed during summer along the southwestern coast of the EJS, originate from the winter convection in the northern area. Observational studies consistently show that the EKWC strengthens in summer when the cold water extends further south along the western boundary. 相似文献
20.
Wind-driven wave heights in the German Bight 总被引：1，自引：0，他引：1
Wind speed, friction velocity and significant wave height data from the FINO1 platform in the southern German Bight 45 km
off the coast for the years 2004 to 2006 have been evaluated and related to each other. The data show a clear dependence of
the hourly mean wave height to the hourly mean friction velocity and wind speed. Wave heights increase with decreasing stratification
and increasing fetch. Synoptic weather patterns for the highest wave heights in the southern German Bight are determined.
The analysis is made separately for four wind direction sectors. The two strongest storms in the evaluated period, “Britta”
and “Erwin”, are analysed in more detail. Finally, the 50-year extreme significant wave height has been estimated to be about
11 m most probably coming from northerly directions. 相似文献