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1.
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
2.
A variable mesh finite element model of the Irish and Celtic Sea regions with/without the inclusion of the Mersey estuary is used to examine the influence of grid resolution and the Mersey upon the higher harmonics of the tide in the region. Comparisons are made with observations and published results from finite difference models of the area. Although including a high resolution representation of the Mersey had little effect upon computed tides in the western Irish Sea it had a significant effect upon tidal currents in the eastern Irish Sea. In addition the higher harmonics of the M2 tide in near-shore regions of the eastern Irish Sea particularly the Solway and Mersey estuary together with Morecambe Bay showed significant small scale variability. The Mersey was used to test the sensitivity to including estuaries because high resolution accurate topography was available. The results presented here suggest that comparable detailed topographic data sets are required in all estuaries and near-shore regions. In addition comparisons clearly show the need for an unstructured grid model of the region that can include all the estuaries. Such an unstructured grid solution was developed here within a finite element approach, although other methods in particular the finite volume, or coordinate transformations/curvilinear grids and nesting could be applied. 相似文献
3.
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
4.
A finite element model of the Irish and Celtic Sea regions with a range of grid resolutions is used to examine the influence of resolution upon the higher harmonics of the tide in the region. Comparisons are also made with published results from finite difference models of the area, and observations. Calculations using fine near-shore elements with non-zero water depths in coastal regions were found to be more accurate and less time consuming than those using a zero coastal water depth. A detailed examination of the spatial variability of the higher harmonics in near-shore regions of the eastern Irish Sea particularly the Solway and Morecambe Bay showed significant small-scale variability. This together with the variation in higher harmonics in the eastern Irish Sea and adjacent estuaries, clearly shows the need for an unstructured grid model of the region that can include the estuaries. To match the high resolution of the model in near-shore regions accurate high-resolution topography is required. 相似文献
5.
A finite element model (namely TELEMAC) with a range of mesh refinements and assumptions of coastal water depths is used to
determine an optimal mesh for computing the M
2 tide in a region of significant geographical extent. The region adopted is the west coast of Britain covering the Irish and
Celtic Seas. The nature of the spatially varying topography and tidal distribution, together with a comprehensive set of measurements
and existing accurate finite difference model makes it ideal for such a study. Calculations show that a water-depth dependent
criterion for determining element size gives an optimal distribution over the majority of the region. However, local refinements
in narrow channels such as the North Channel and Bristol Channel are required. Although the specification of a zero coastal
water depth, leads to a fine near coastal grid, this does not yield the most accurate solution. In addition the computational
cost is high. In practice in a large area model the use of a non-zero coastal water depth yields optimum accuracy at minimal
computational cost. However, calculations show that accuracy is critically dependent upon nearshore water depths. Comparison
with the finite difference model shows that the bias in elevation amplitude in the finite difference solution is removed in
the finite element calculation. 相似文献
6.
An unstructured grid storm surge model of the west coast of Britain, incorporating a high-resolution representation of the
Mersey estuary is used to examine storm surge dynamics in the region. The focus of the study is the major surge that occurred
during the period 11–14 November 1977, which has been investigated previously using uniform grid finite difference models
and a finite element model of the west coast of Britain. However, none of these models included the Mersey estuary. Comparison
of solutions in the eastern Irish Sea with those computed with these earlier models showed that, away from the Liverpool Bay
region, the inclusion of the Mersey estuary had little effect. However, at the entrance to the Mersey, its inclusion did influence
the solution. By including a detailed representation of the Mersey estuary within the model, it was possible to conduct a
detailed study of storm surge propagation in the Mersey, which had never previously been performed. This detailed study showed
for the first time that the surge’s temporal variability within the estuary is influenced by surge elevation at its entrance.
This varies with time as a function of spatial and temporal variations of wind stress over the west coast of Britain. Within
the Mersey, calculations show that the spatial variability is mainly determined by changes in bottom topography, which had
not been included in earlier finite difference models. However, since water depth is influenced by variations in tidal elevation,
this, together with tide surge interaction through bottom friction and momentum advection, influences the surge. The ability
of the finite element model to vary the mesh in near-shore regions to such an extent that it can resolve the Mersey and hence
the impact of the Mersey estuary upon the Liverpool Bay circulation shows that it has distinct advantages over earlier finite
difference models. In the absence of detailed measurements within the Mersey at the time of the surge, it was not possible
to validate predicted surge elevations within the Mersey. However, significant insight into physical processes influencing
the surge propagation down the estuary, its reflection and spatial/temporal variability could be gained. 相似文献
7.
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
8.
An irregular mesh model of the west coast of Britain is used to examine the sensitivity of tidal residuals to mesh resolution in the region. Computed residuals are compared with earlier published results determined with a high resolution (1 km grid) finite difference model of the eastern Irish Sea. Initial calculations show that tidal residuals are largest in nearshore regions particularly in the vicinity of headlands. Local refinement of the mesh in these regions leads to a more detailed picture of the flow field, particularly adjacent to the coast. Although large scale offshore features of the flow can be resolved using the high resolution finite difference model, such an approach leads to a “stair case” representation of the coastal boundary with an adjacent near coastal region of spurious tidal residuals. By using an irregular mesh that follows the coast, this effect is removed. In the Mersey river region the tidal residual is resolved with a mesh resolution of 120 m, although calculations show that its distribution is particularly sensitive to small scale features of the topography. A variable mesh that can accurately represent the lateral variations in river width and details of topography in both the nearshore and estuarine environment appears essential in modelling the coastal spread of freshwater plumes from rivers and pollutants discharged into the near coastal environment. 相似文献
9.
Storm surge computations for the west coast of Britain using a finite element model (TELEMAC) 总被引：1，自引：1，他引：0
An unstructured mesh finite element model of the sea region off the west coast of Britain is used to examine the storm surge event of November 1977. This period is chosen because accurate meteorological data to drive the model and coastal observations for validation purposes are available. In addition, previous published results from a coarse-grid (resolution 7 km) finite difference model of the region and high-resolution (1 km) limited area (namely eastern Irish Sea) model are available for comparison purposes. To enable a “like with like” comparison to be made, the finite element model covers the same domain and has the same meteorological forcing as these earlier finite difference models. In addition, the mesh is based on an identical set of water depths. Calculations show that the finite element model can reproduce both the “external” and “internal” components of the surge in the region. This shows that the “far field” (external) component of the surge can accurately propagate through the irregular mesh, and the model responds accurately, without over- or under-damping, to local wind forcing. Calculations show significant temporal and spatial variability in the surge in close agreement with that found in earlier finite difference calculations. In addition, root mean square errors between computed and observed surge are comparable to those found in previous finite different calculations. The ability to vary the mesh in nearshore regions reveals appreciable small-scale variability that was not found in the previous finite difference solutions. However, the requirement to perform a “like with like” comparison using the same water depths means that the full potential of the unstructured grid model to improve resolution in the nearshore region is inhibited. This is clearly evident in the Mersey estuary region where a higher resolution unstructured mesh model, forced with uniform winds, had shown high topographic variability due to small-scale variations in topography that are not resolved here. Despite the lack of high resolution in the nearshore region, the model showed results that were consistent with the previous storm surge models of the region. Calculations suggest that to improve on these earlier results, a finer nearshore mesh is required based upon accurate nearshore topography. 相似文献
10.
《Continental Shelf Research》2006,26(12-13):1519-1541
Initially a brief overview of the problem of computing the wind-induced circulation on the west coast of Britain is reviewed together with storm surge modelling. To date this work has primarily been performed with finite difference models. However, here new work is presented using a finite element model with a range of mesh refinements in shallow water regions to examine the influence of mesh resolution upon the wind-induced circulation off the west coast of Britain. Steady state current fields are computed for uniform westerly and southerly winds and compared with a uniform grid (of order 7 km) finite difference model solution. Calculations show that in deep water regions away from the coastal influence, the large-scale circulation features in the finite element solution are in good agreement with those found in the finite difference model. This suggests that they can be adequately resolved on a 7 km mesh. In the nearshore region and within estuaries a significantly finer mesh is required, with the variable mesh finite element model showing significant small scale variability in the nearshore area. Refining the mesh in the Mersey and using an accurate topographic data set, shows that although the larger scale features in the estuary can be resolved in the coarser mesh model, accurate topography is required to model their exact location. In addition smaller scale features are found that were not resolved in the coarser mesh models. Due to the effects of “wetting and drying” and the importance of non-linear processes in shallow regions difficulties occurred in de-tiding the full solution in order to determine the wind forced residual. Determining the wind forced solution in shallow water from a calculation in which wind and tidal forcing are included poses problems as to how to “de-tide” the solution in such a highly non-linear region. An approach based upon the harmonic analysis of the total solution, rather than subtracting a “tide only” solution is shown to be most effective and has implications for storm surge prediction.General and specific conclusions on the importance of highly accurate bathymetry, good mesh resolution and de-tiding method upon the accuracy of the wind forced solution in nearshore regions are summarized in the final part of the paper. The implications for storm surge prediction together with suggestions for future research to enhance the accuracy of storm surge prediction, namely “the way forward” are given at the end of the paper. 相似文献
11.
A three-dimensional finite volume unstructured mesh model of the west coast of Britain, with high resolution in the coastal regions, is used to investigate the role of wind wave turbulence and wind and tide forced currents in producing maximum bed stress in the eastern Irish Sea. The spatial distribution of the maximum bed stress, which is important in sediment transport problems, is determined, together with how it is modified by the direction of wind forced currents, tide–surge interaction and a surface source of wind wave turbulence associated with wave breaking. Initial calculations show that to first order the distribution of maximum bed stress is determined by the tide. However, since maximum sediment transport occurs at times of episodic events, such as storm surges, their effects upon maximum bed stresses are examined for the case of strong northerly, southerly and westerly wind forcing. Calculations show that due to tide–surge interaction both the tidal distribution and the surge are modified by non-linear effects. Consequently, the magnitude and spatial distribution of maximum bed stress during major wind events depends upon wind direction. In addition calculations show that a surface source of turbulence due to wind wave breaking in shallow water can influence the maximum bed stress. In turn, this influences the wind forced flow and hence the movement of suspended sediment. Calculations of the spatial variability of maximum bed stress indicate the level of measurements required for model validation. 相似文献
12.
Longhai Zhu Rijun Hu Haijun Zhu Shenghui Jiang Yongchen Xu Nan Wang 《Ocean Dynamics》2018,68(12):1625-1648
Over the past 30 years, reclamation projects and related changes have impacted the hydrodynamics and sediment transport in the Bohai Sea. Three-dimensional tidal current models of the Bohai Sea and the Yellow Sea were constructed using the MIKE 3 model. We used a refined grid to simulate and analyze the effects of changes in coastline, depth, topography, reclamation, the Yellow River estuary, and coastal erosion on tidal systems, tide levels, tidal currents, residual currents, and tidal fluxes. The simulation results show that the relative change in the amplitude of the half-day tide is greater than that of the full-day tide. The changes in the tidal amplitudes of M2, S2, K1, and O1 caused by coastline changes accounted for 27.76–99.07% of the overall change in amplitude from 1987 to 2016, and water depth changes accounted for 0.93–72.24% of the overall change. The dominant factor driving coastline changes is reclamation, accounting for 99.55–99.91% of the amplitude changes in tidal waves, followed by coastal erosion, accounting for 0.05–0.40% of the tidal wave amplitude changes. The contribution of changes in the Yellow River estuary to tidal wave amplitude changes is small, accounting for 0.01–0.12% of the amplitude change factor. The change in the highest tide level (HTL) is mainly related to the amplitude change, and the correlation with the phase change is small. The dominant factor responsible for the change in the HTL is the tide amplitude change in M2, followed by S2, whereas the influence of the K1 and O1 tides on the change in the HTL is small. Reclamation resulted in a decrease in the vertical average maximum flow velocity (VVAM) in the Bohai Sea. Shallower water depths have led to an increase in the VVAM; deeper water depths have led to a decrease in the maximum flow velocity. The absolute value of the maximum flow velocity gradually decreases from the surface to the bottom, but the relative change value is basically constant. The changes in the tidal dynamics of the Bohai Sea are proportional to the degree of change in the coastline. The maximum and minimum changes in the tidal flux appear in Laizhou Bay (P-LZB) and Liaodong Bay (P-LDB), respectively. The changes in the tidal flux are related to the change in the area of the bay. Due to the reduced tidal flux, the water exchange capacity of the Bohai Sea has decreased, impacting the ecological environment of the Bohai Sea. Strictly controlling the scale of reclamation are important measures for reducing the decline in the water exchange capacity of the Bohai Sea and the deterioration of its ecological environment. 相似文献
13.
A three-dimensional model covering the northwest European Shelf and part of the adjacent Atlantic Ocean is used to examine the influence of water depth change upon the distribution of maximum tidal bed stress. The direction of bed stress is an indicator of sediment movement as bed load and various regions of convergence and divergence in good agreement with observations are identified. Calculations are performed with water depths reduced by 35 m, corresponding to 10 000 years before present (B.P.). Initially, the model is forced by only the M2 tide, although subsequently five constituents, namely M2, S2, N2, K1 and O1, are used for tidal forcing. Although the distribution of extreme bed stresses computed with only M2 tidal forcing is comparable to that computed with five tides, the additional tidal constituents modify the magnitude of the bed stress. In particular the diurnal tides show regions of local enhanced current amplitude in the shelf-edge region with corresponding changes in bed stress. When water depths are reduced such that the North Sea and English Channel are separated, then there is a significant change in the tidal distribution in the shallow Southern Bight which influences bed-stress distributions and hence bed-load sediment transport in the area. Besides changes in shallow regions, the distribution of tides at the shelf edge is affected. A discussion of the limitations of the present coarse-grid model in shelf-edge regions and how it can be used to provide boundary conditions for limited-area three-dimensional models that can include stratification is presented. Also the importance of stratification for sediment movement at the shelf edge is briefly discussed.Responsible Editor: Phil Dyke 相似文献
14.
15.
本文实现了可控源电磁(CSEM)场三维自适应矢量有限元正演算法,该算法采用非结构四面体单元进行三维网格剖分,能够真实模拟地形起伏和复杂电性异常体.采用一次场和二次场分离的方式计算电磁场响应,能够有效解决有限元模拟中的源点奇异性,提高场源附近电磁场数值精度,其中一次场利用CSEM一维正演算法解析求得,二次场采用矢量有限元方法求得.并利用基于后验误差估计的自适应网格细化算法指导网格细化,以减少人为设计网格导致的误差.通过一维和三维模型的数值模拟,验证了本文算法的有效性:一维模型有限元解与解析解吻合得很好,电磁场振幅相对误差在1%左右,相位差整体小于1°;三维模型有限元解与有限体积解吻合得也很好.模拟了一个含三维倾斜板状异常体的可控源电磁响应,表明了本文算法模拟复杂地电结构电磁场的能力和有效性. 相似文献
16.
Initially the development of shallow sea three-dimensional barotropic tidal models is briefly reviewed with a view to determining what were the key measurements that allowed progress in this field and rigorous model validation. Subsequently this is extended to a brief review of baroclinic tidal models to try to determine a “way forward” for baroclinic model development. The difficulty of high spatial variability, and wind influence are identified as possibly important issues that must be considered in validating baroclinic tidal models. These are examined using a three-dimensional unstructured grid model of the M2 internal tide on the shelf edge region off the west coast of Scotland. The model is used to investigate the spatial variability of the M2 internal tide, and associated turbulence energy and mixing in the region. Initial calculations are performed with tidal forcing only, with subsequent calculations briefly examining how the tidal distribution is modified by down-welling and up-welling favourable winds. Calculations with tidal forcing only, show that there is significant spatial variability in the internal tide and associated mixing in the region. In addition, these are influenced by wind effects which may have to be taken into account in any model validation exercise. The paper ends by discussing the comprehensive nature of data sets that need to be collected to validate internal tidal models to the same level currently attained with three dimensional barotropic tidal models. 相似文献
17.
The tides and tidal energetics in the Indonesian seas are simulated using a three-dimensional finite volume coastal ocean
model. The high-resolution coastline-fitted model is configured to better resolve the hydrodynamic processes around the numerous
barrier islands. A large model domain is adopted to minimize the uncertainty adjacent to open boundaries. The model results
with elevation assimilation based on a simple nudge scheme faithfully reproduced the general features of the barotropic tides
in the Indonesian Seas. The mean root-mean-square errors between the observed and simulated tidal constants are 2.3, 1.1,
2.4, and 1.5 cm for M2, S2, K1, and O1, respectively. Analysis of the model solutions indicates that the semidiurnal tides in the Indonesian Seas are primarily
dominated by the Indian Ocean, whereas the diurnal tides in this region are mainly influenced by the Pacific Ocean, which
is consistent with previous studies. Examinations of tidal energy transport reveal that the tidal energy for both of the simulated
tidal constituents are transported from the Indian Ocean into the IS mainly through the Lombok Strait and the Timor Sea, whereas
only M2 energy enters the Banda Sea and continues northward. The tidal energy dissipates the most in the passages on both sides of
Timor Island, with the maximum M2 and K1 tidal energy transport reaching about 750 and 650 kW m–1, respectively. The total energy losses of the four dominant constituents in the IS are nearly 338 GW, with the M2 constituent dissipating 240.8 GW. It is also shown that the bottom dissipation rate for the M2 tide is about 1–2 order of magnitudes larger than that of the other three tidal components in the Indonesian seas. 相似文献
18.
The problem of resolving or parameterising small-scale processes in oceanographic models and the extent to which small-scale
effects influence the large scale are briefly discussed and illustrated for a number of cases. For tides and surges in near-shore
regions, the advantages of using a graded mesh to resolve coastal and estuarine small-scale features are demonstrated in terms
of a west coast of Britain unstructured mesh model. The effect of mesh resolution upon the accuracy of the overall solution
is illustrated in terms of a finite element model of the Irish Sea and Mersey estuary. For baroclinic motion at high Froude
number, the effect of resolving small-scale topography within a non-hydrostatic model is illustrated in terms of tidally induced
mixing at a single sill, or two closely spaced sills. The question of how to parameterise small-scale non-linear interaction
processes that lead to significant mixing, in a form suitable for coarser grid hydrostatic models, is briefly considered.
In addition, the importance of topographically induced mixing that occurs in the oceanic lateral boundary layer, namely, the
shelf edge upon the large-scale ocean circulation is discussed together with the implications for coarse grid oceanic climate
models. The use of unstructured grids in these models to enhance resolution in shelf-edge regions in a similar manner to that
used in storm surge models to enhance near coastal resolution is suggested as a suitable “way forward” in large-scale ocean
circulation modelling. 相似文献
19.
Study on linear and nonlinear bottom friction parameterizations for regional tidal models using data assimilation 总被引：2，自引：0，他引：2
Data assimilation technique (adjoint method) is applied to study the similarities and the differences between the Ekman (linear) and the Quadratic (nonlinear) bottom friction parameterizations for a two-dimensional tidal model. Two methods are used to treat the bottom friction coefficient (BFC). The first method assumes that the BFC is a constant in the entire computation domain, while the second applies the spatially varying BFCs. The adjoint expressions for the linear and the nonlinear parameterizations and the optimization formulae for the two BFC methods are derived based on the typical Largrangian multiplier method. By assimilating the model-generated ‘observations’, identical twin experiments are performed to test and validate the inversion ability of the presented methodology. Four experiments, which employ the linear parameterization, the nonlinear parameterizations, the constant BFC and the spatially varying BFC, are carried out to simulate the M2 tide in the Bohai Sea and the Yellow Sea by assimilating the TOPEX/Poseidon altimetry and tidal gauge data. After the assimilation, the misfit between model-produced and observed data is significantly decreased in the four experiments. The simulation results indicate that the nonlinear Quadratic parameterization is more accurate than the linear Ekman parameterization if the traditional constant BFC is used. However, when the spatially varying BFCs are used, the differences between the Ekman and the Quadratic approaches diminished, the reason of which is analyzed from the viewpoint of dissipation rate caused by bottom friction. Generally speaking, linear bottom friction parameterizations are often used in global tidal models. This study indicates that they are also applicable in regional ocean tidal models with the combination of spatially varying parameters and the adjoint method. 相似文献
20.
A three-dimensional prognostic hydrodynamic model in cross sectional form is used to examine the influence of bottom friction,
mixing and topography upon the spin-down and steady-state circulation in a cold water bottom-dome. Parameters characteristic
of the Irish Sea or Yellow Sea cold water domes are used. In all calculations, motion is induced by specifying an initial
temperature distribution characteristic of the dome, and an associated along frontal flow. The spin-down of the dome is found
to be influenced by the coefficient of bottom friction, with a typical time scale of order 10 days, and in general to be independent
of the chosen initial vertical profile of along frontal flow. However, in the case in which the along frontal flow is such
that the near bed velocity is zero, then bottom stress is also zero, and there is no appreciable spin-down. Calculations showed
that the formulation of viscosity and diffusivity had a greater effect upon the steady-state circulation than topography,
suggesting that background mixing of tidal origin is important. The lack of topographic influence was due mainly to the formulation
of the initial conditions which were taken to be independent of topography. The steady-state circulation was characterized
by a cyclonic flow in the surface region, with an anti-cyclonic current near the bed, where frictional effects produced a
bottom Ekman layer and an across frontal flow. This gave rise to vertical circulation cells in the frontal region of the dome
with prevailing downwelling motion inside the dome. A detailed analysis of the dynamic balance of the various terms in the
hydrodynamic equations yielded insight into the processes controlling the steady-state circulation in cold water domes.
Responsible Editor: Phil Dyke 相似文献