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1.
Quantifying the long-term variability in wave conditions incident on a coastline is critical for predicting its resilience to future changes in the wave climate. In this study, a 40-year wave hindcast of the southern Indian Ocean has been created to assess the inter-annual variability and longer-term changes in the wave climate around Western Australia (WA) between 1970 and 2009. The model was validated against measurements from five wave buoys located along the WA coast. Changes in the mean annual significant wave height, 90th percentile wave height, peak period and mean wave direction were assessed, and the tracks of all wave events generating wave heights above 7 m were digitised and analysed for significant changes. Results show strong annual and inter-annual variability in the mean significant wave height, the 90th percentile wave height and the number of large events (wave height > 7 m) that impact the WA coastline. A significant positive trend in annual mean wave height was found in the southwest region of WA over the 40-year simulation. This appears to be due to an increase in intensity of the storm belt in the Southern Ocean which is associated with an increasing positive polarity in the Southern Annular Mode. However, no significant trends were found in the 90th percentile wave height or the number of large wave events impacting Western Australia. Although the number of large wave events in the southern Indian Ocean have increased, their potential to impact the coastal regions of Western Australia are reduced due to storm tracks being located further south, therefore balancing the number of large wave events reaching the WA coast.  相似文献   

2.
Concurrent observations of waves at the base of a southern California coastal cliff and seismic cliff motion were used to explore wave–cliff interaction and test proxies for wave forcing on coastal cliffs. Time series of waves and sand levels at the cliff base were extracted from pressure sensor observations programmatically and used to compute various wave impact metrics (e.g. significant cliff base wave height). Wave–cliff interaction was controlled by tide, incident waves, and beach sand levels, and varied from low tides with no wave–cliff impacts, to high tides with continuous wave–cliff interaction. Observed cliff base wave heights differed from standard Normal and Rayleigh distributions. Cliff base wave spectra levels were elevated at sea swell and infragravity frequencies. Coastal cliff top response to wave impacts was characterized using microseismic shaking in a frequency band (20–45 Hz) sensitive to wave breaking and cliff impacts. Response in the 20–45 Hz band was well correlated with wave–cliff impact metrics including cliff base significant wave height and hourly maximum water depth at the cliff base (r2 = 0.75). With site‐specific calibration relating wave impacts and shaking, and acceptable anthropogenic (traffic) noise levels, cliff top seismic observations are a viable proxy for cliff base wave conditions. The methods presented here are applicable to other coastal settings and can provide coastal managers with real time coastal conditions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
Abstract

The weakly nonlinear evolution of a free baroclinic wave in the presence of slightly supercritical, vertically sheared zonal flow and a forced stationary wave field that consists of a single zonal scale and an arbitrary number of meridional harmonics is examined within the context of the conventional two-layer model. The presence of the (planetary-scale) stationary wave introduces zonal variations in the supercriticality and is shown to alter the growth rate and asymptotic equilibrium of the (synoptic-scale) baroclinic wave via two distinct mechanisms: The first is due to the direct interaction of the stationary wave with the shorter synoptic wave (wave-wave mechanism), and the second is due to the interaction of the synoptic wave with that portion of the mean field that is corrected by the zonally rectified stationary wave fluxes (wave-mean mechanism). These mechanisms can oppose or augment each other depending on the amplitude and spatial structure of the stationary wave field. If the stationary wave field is confined primarily to the upper (lower) layer and consists of only the gravest cross-stream mode, conditions are favorable (unfavorable) for nonzero equilibrium of the free wave.

In addition to the time dependent heat flux generated by baroclinic growth of the free wave, its interaction with a stationary wave field consisting of two or more meridional harmonics generates time dependent heat fluxes that vary with period of the free wave. However, if the stationary wave field contains several meridional harmonics of sufficiently large amplitude, the free baroclinic wave is destroyed.  相似文献   

4.
The main objective of this study is the characterization of the wave climate in the Southern Brazilian Shelf (SBS) based on a thorough review of existing field data and on numerical modeling experiments. A quantitative knowledge about the wave climate of this area is important to understand the mechanisms driving episodic mud bank attachments to the sandy shore, and the interaction of these banks with the flow and waves. The statistical analysis of existent data on the wave climate throughout the SBS indicates that the predominant wave directions are 100° and 160° (E–SE), with wave heights varying between 1 and 1.50 m. The wave period varies between 6 and 14 s, with predominance of mean wave period of 8 s (sea conditions) and 12 s (swell conditions). The spectral wave model SWAN version 40.41 [Booij, N., Haagsma, I.J.G., Holthuijsen, L.H., Kieftenburg, A.T.M.M., Ris, R.C., van der Westhuysen, A.J., Zijlema, M., 2004. SWAN Cycle III Version 40.41 Users Manual, Delft University of Technology, Delft, The Netherlands, p. 118, http://fluidmechanics.tudelft.nl/swan/index.htm] is used to simulate the wave climate for the region. Special attention is given to Cassino Beach, describing the wave climate observed during the Cassino Experiment, carried out in 2005. The verification of the standard SWAN model was carried out based on the comparison between numerical modeling results and available data of significant wave height, peak period, mean wave direction and energy density for the period relative to February of 1998. Results showed satisfactory model predictions of significant wave height and reasonably accurate predictions of peak spectral wave period and direction. The model performance is also considered satisfactory in the representation of the wave climate of the region when the wave spectrum has only one spectral peak, but presents limitations for bimodal wave spectrum. When two spectral peaks are observed, the SWAN model agrees with the spectral level observed in the low frequency, but underestimates the spectral level in the high-frequency band. When considering the presence of mud deposits in the area, model results predict that although the presence of mud attenuates most of the wave energy on the low frequency peak, it has a smaller effect in attenuating the wave energy on the high frequency peak.  相似文献   

5.
A numerical study of irregular waves in the Norwegian continental shelf wind farm (HAVSUL-II) was conducted using 3rd generation spectral wave models. The study was composed of two parts: the study of the effect of a single windmill monopile in the local incoming wave field using an empirical JONSWAP spectrum, and a wave hindcast study in the wind farm area using realistic incoming wave spectra obtained from large scale simulations for the 1991-1992 winter period. In the single windmill monopile study the SWAN wave model was used, while the hindcast study was conducted by successively nesting from a coarse grid using the WAM model up to a high-resolution (56 m) grid covering 26.2 km2 of the HAVSUL-II windmill farm using the SWAN model. The effect of a single monopile on incident waves with realistic spectra was also studied. In the single windmill study the monopile was represented as a closed circular obstacle and in the hindcast study it was represented as a dry grid point. The results showed that the single windmill monopile creates a shadow zone in the down wave region with lower significant wave height (Hs) values and a slight increase of Hs in the up wave region. The effects of the windmill monopile on the wave field were found to be dependent on the directional distribution of the incoming wave spectrum and also on the wave diffraction and reflection. The hindcast study showed that the group of windmill monopiles may contribute to the reduction of the wave energy inside the offshore wind farm and that once the waves enter into the offshore wind farm they experience modifications due to the presence of the windmill monopiles, which cause a blocking of the wave energy propagation resulting in an altered distribution of the Hs field.  相似文献   

6.
Based on wave equation a fundamental formula for plane wave propagaton is derived, the theoretical method of inverting wave volocity structure of earth interior through the observational wave field is discussed in this paper. The observational wave field can be decomposed into the surface plane wave field by using τ −p transform. The maximum amplitude curve in the plane wave field can show stably the change tendency of wave velocity with depth in the Earth. This property can be used to restrict the solution space. By using the wave field continuation method more useful information from the observational wave field can be extracted and the inverion solution not only can be obtained simply and quickly, but also is stable and less influenced by the subjective factor. The wave field continuation is a fine inversion method. Theoretical analysis and numerical modelling are carried out in the study of wave field continuation. By applying homomorphic decovolution the signal — to — noese ratio is improved. Finaly a sonar refraction profile in the northern part of the South China Sea is interpreted and computed. It is found as a result that there is a velocity interface from 1.76 km/s to 2.21 km/s at the depth of 1.4 km. The velocity gradients in the upper and lower layers are 0.54 km · s−1/km and 0.63 km · s−1/km respectively. A discussion of the characteristics of shallow sea structure in the view of tectonic movements is geven. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13. 41–52, 1991.  相似文献   

7.
This paper addresses the quantification of gravity wave drag due to small hills in the stable boundary layer. A single column atmospheric model is used to forecast wind and temperature profiles in the boundary layer. Next, these profiles are used to calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and “wave drag events” is presented for the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify the wind speed sufficiently to substantially change the surface sensible heat flux.  相似文献   

8.
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9.
Summary An irregular wave group (here called pseudospherical), the existence of which is connected with the velocity boundary at which the velocity decreases discontinuously, is investigated. A schlieren modelling device was chosen for a model investigation of this wave since it permits the investigation of wave fields inside the measured models. The model consisted of two layers of transparent gels, the source lay in the layer of higher velocity. The measurements have shown that an irregular wave in the layer of lower velocity exists only in a certain region along the boundary; its wave front has a spherical form and its intensity decreases rapidly with increasing distance of the source from the boundary. The wave always comes only after the regular refracted wave which conforms with the ray theory. These properties correspond to the properties of a wave first described byOtt [1]3) andBrekhovskikh [2]. In the conclusion of the present paper the possibilities of recording pseudospherical waves in seismology are outlined.  相似文献   

10.
《国际泥沙研究》2023,38(5):629-642
Sand waves of approximately 2 m in height were observed to migrate nearly 40 m with counterclockwise rotation between two bathymetric surveys performed three months apart near the southeastern corner of Martha's Vineyard, Massachusetts. The region is characterized by strong tidal currents, intermittent energetic surface wave events, and shallow water with local depth ranging from 2 to 7 m. This study uses the process-based model, Delft3D, with a three-dimensional approach to examine the sand wave dynamics by incorporating surface waves, winds, currents, and bathymetric observations. The model successfully simulates sand wave migration in comparisons to observations. Model sensitivity analyses show that the sand wave migration reduces by 65% with the absence of the surface waves. The modeled sand wave migration speed is correlated with the tidal current Shields parameter, and sharp increases in migration speed occur when the wave-driven Shields parameter increases in response to energetic surface wave events. The combined effect of tides, surface waves, and bathymetry is the origin of the rotational aspect of the sand wave, using the Shields parameter as an indicator of tidal currents and surface wave influence on sand wave dynamics.  相似文献   

11.
粘弹性VTI介质地震波模拟特征分析   总被引：2，自引：0，他引：2       下载免费PDF全文
本文首先利用有限差分法分别对弹性和粘弹性VTI介质进行地震波传播数值模拟,并针对波场快照和波场记录特征,分析不同品质因子组合对波场能量衰减和频率吸收作用的影响.结果表明：对应于膨胀滞弹性形变的品质因子变化主要影响qP波的能量衰减;对应于剪切滞弹性形变的品质因子变化主要影响qSV波的能量衰减;对于qSH波,两个品质因子分别对应于垂直和水平方向的能量衰减;品质因子较小时,qSV波和qSH波的频率向低频方向移动,qP波频率变化不明显.  相似文献   

12.
Currently, numerical simulations of seismic channel waves for the advance detection of geological structures in coal mine roadways focus mainly on modeling twodimensional wave fields and therefore cannot accurately simulate three-dimensional (3-D) full-wave fields or seismic records in a full-space observation system. In this study, we use the first-order velocity–stress staggered-grid finite difference algorithm to simulate 3-D full-wave fields with P-wave sources in front of coal mine roadways. We determine the three components of velocity Vx, Vy, and Vz for the same node in 3-D staggered-grid finite difference models by calculating the average value of Vy, and Vz of the nodes around the same node. We ascertain the wave patterns and their propagation characteristics in both symmetrical and asymmetric coal mine roadway models. Our simulation results indicate that the Rayleigh channel wave is stronger than the Love channel wave in front of the roadway face. The reflected Rayleigh waves from the roadway face are concentrated in the coal seam, release less energy to the roof and floor, and propagate for a longer distance. There are surface waves and refraction head waves around the roadway. In the seismic records, the Rayleigh wave energy is stronger than that of the Love channel wave along coal walls of the roadway, and the interference of the head waves and surface waves with the Rayleigh channel wave is weaker than with the Love channel wave. It is thus difficult to identify the Love channel wave in the seismic records. Increasing the depth of the receivers in the coal walls can effectively weaken the interference of surface waves with the Rayleigh channel wave, but cannot weaken the interference of surface waves with the Love channel wave. Our research results also suggest that the Love channel wave, which is often used to detect geological structures in coal mine stopes, is not suitable for detecting geological structures in front of coal mine roadways. Instead, the Rayleigh channel wave can be used for the advance detection of geological structures in coal mine roadways.  相似文献   

13.
The mechanism of acceleration of the mean zonal flow by a planetary wave is explained intuitively by considering the wave drag which a corrugated bottom feels when it excites the wave. The explanation is justified by solving the problem of vertical propagation of a planetary wave packet and the second order mean motion induced around it. The discussion is slightly extended to the case of small damping, to illustrate in a compact form the fact that the mean zonal acceleration is determined by a forcing due to wave transience plus that due to wave dissipation.The mean flow induced by a steady, dissipating planetary wave is discussed, and it is shown that it depends largely on the dissipation scale-height of the wave whether the northern region is heated or cooled. For example, if the wave velocity-amplitude increases upward in spite of dissipation, the induced easterly flow increases with height and the temperature of the northern region increases relative to that in the southern region. A similar point has been made byDunkerton (1979) in connection with westerly flows induced by Kelvin waves.The Lagrangian-mean motion induced by a planetary wave is briefly discussed in connection with the mechanism of acceleration of the mean zonal flow, in the case of a slowly varying wave packet. Further, in order el elucidate the effects of wave dissipation and time dependence of wave amplitude, the results obtained for a steady, dissipating wave and for a growing baroclinic wave are mentioned.  相似文献   

14.
We investigated the properties of guided wave propagating in grouted rock bolts and the formation of the interface wave through theoretical analysis along with experimental and numerical simulations. Experimental and numerical simulations reveal that the wave propagating in anchorage structure is related to boundary conditions within the range of excitation wave frequencies. Waves with different frequencies have different propagation velocities and attenuation characteristics. The optimal excitation wave occurs in grouted rock bolts with minimized attenuation and maximized propagation distance, and the end reflection of grouted rock bolts can be observed clearly. Longitudinal wave propagating in rock bolts is very sensitive to anchorage strength. With the increase of anchorage strength, longitudinal wave gradually attenuates and eventually disappears. Subsequently, interface wave appears and the velocity of wave propagating in the grouted part becomes that of the interface wave. Based on these studies, ultrasonic guided wave was used to study the end reflection of embedded rock bolts with different anchorage strengths and bonding lengths. The relationships among anchorage strength, bonding length and attenuation coefficient K, as well as the means to inspect the bonding quality of the embedded rock bolts were also evaluated.  相似文献   

15.
Shear‐wave statics in marine seismic exploration data are routinely too large to be estimated using conventional techniques. Near‐surface unconsolidated sediments are often characterized by low values of Vs and steep velocity gradients. Minor variations in sediment properties at these depths correspond to variations in the shear‐wave velocity and will produce significant static shifts. It is suggested that a significant proportion of the shear‐wave statics solution can be estimated by performing a separate high‐resolution survey to target near‐surface unconsolidated sediments. Love‐wave, shear‐wave refraction and geotechnical measurements were individually used to form high‐resolution near‐surface shear‐wave velocity models to estimate the shear‐wave statics for a designated survey line. Comparisons with predicted statics revealed that shear‐wave statics could not be estimated using a velocity model predicted by substituting geotechnical measurements into empirical relationships. Empirical relationships represent a vast simplification of the factors that control Vs and are therefore not sufficiently sensitive to estimate shear‐wave statics. Refraction measurements are potentially sensitive to short‐wavelength variations in sediment properties when combined with accurate navigational data. Statics estimated from Love‐wave data are less sensitive, and sometimes smoothed in appearance, since interpreted velocity values represent an average both laterally and vertically over the receiver array and the frequency–depth sensitivity range, respectively. For the survey site, statics estimated from near‐surface irregularities using shear‐wave refraction measurements represent almost half the total statics solution. More often, this proportion will be greater when bedrock relief is less.  相似文献   

16.
Few studies of wave processes on shore platforms have addressed the hydrodynamic thresholds that control wave transformation and energy dissipation, especially under storm conditions. We present results of a field experiment conducted during a storm on a sub‐horizontal shore platform on the east coast of Auckland, New Zealand. Small (<0.5 m) locally generated waves typically occur at the field site, whereas during the experiment the offshore wave height reached 2.3 m. Our results illustrate the important control that platform morphology has on wave characteristics. At the seaward edge of the platform a scarp abruptly descends beneath low tide level. Wave height immediately seaward of the platform was controlled by the incident conditions, but near the cliff toe wave height on the platform was independent of incident conditions. Results show that a depth threshold at the seaward platform edge > 2.5 times the gravity wave height (0.05–0.33 Hz) is necessary for waves to propagate onto the platform without breaking. On the platform surface the wave height is a direct function of water depth, with limiting maximum wave height to water depth ratios of 0.55 and 0.78 at the centre of the platform and cliff toe, respectively. A relative ‘platform edge submergence’ (water depth/water height ratio) threshold of 1.1 is identified, below which infragravity (<0.05 Hz) wave energy dominates the platform energy spectra, and above which gravity waves are dominant. Infragravity wave height transformation across the platform is governed by the relative platform edge submergence. Finally, the paper describes the first observations of wave setup on a shore platform. During the peak of the storm, wave setup on the platform at low tide (0.21 m) is consistent with measurements from planar sandy beaches, but at higher tidal stages the ratio between incident wave height and maximum setup was lower than expected. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Wave-induced sediment resuspension in nearshore regions has been observed occurring in an event-like manner and associated with the passage of wave groups. This paper describes field measurements of turbulent velocities obtained simultaneously with suspended sediment concentration and water surface elevation from Floreat Beach, Perth, Western Australia. The data were used to study the relationship between turbulent kinetic energy (TKE) on suspension events caused by wave groups and the intermittent nature of bottom turbulence production and sediment suspension. The field measurements showed the high TKE events occurred under wave crests, and sometimes under wave toughs, when the wave heights were increasing during the passage of a wave group; the TKE decreased after the maximum wave in the wave group had passed over the measurement location. High suspended sediment concentrations (ssc) and the intermittent high TKE events were not related rather the higher ssc events were associated with a secondary peak in the surface elevation, close to the maxima in the offshore velocity, and “burst” events in the Reynolds stress.  相似文献   

18.
Zonal mean data and amplitudes and phases of planetary zonal waves were derived from daily hemispheric maps for tropospheric and stratospheric levels, for the four winters 1975–76 to 1978–79. Important year-to-year fluctuation in zonal means and wave activity are described, most notable of which are the changes from 1975–76 to 1976–77. Comparison of the relative strengths of the stratospheric and tropospheric jet streams shows a strong negative correlation (–0.8) between monthly mean zonal stratospheric winds (at 10 mb, 65°N) and zonal tropospheric winds (at 200 mb, 32.5°N, in the jet core) and a positive correlation (+0.7) between the stratospheric 10 mb winds and the tropospheric 200 mb winds at 65°N. Parameters correlated were the departures from the climatological mean zonal winds. The structure of correlation between wave amplitudes in the same wave number (1, 2) at different altitudes and between wave numbers 1 and 2 is investigated. We find a high correlation (+0.93) between wave 1 in the stratosphere (10 mb height) and wave 2 (height) in the troposphere at 65°N; but only a weak correlation (+0.2) between wave 1 amplitudes in the stratosphere and troposphere. These results suggest the possible importance of wave-wave interactions in processes linking the stratosphere and troposphere. The wave correlations presented here are based on comparisons of monthly means of daily amplitudes; the correlation structure in individual wave developments may differ, in view of the likelihood of altitudinal lags in wave amplification.  相似文献   

19.
The impact of a non-rigid seafloor on the wave climate at Cassino Beach, Brazil, May–June 2005 is studied using field measurements and a numerical wave model. The measurements consist of wave data at four locations; rheology and mud thickness from grab samples; and an estimate of the horizontal distribution of mud based on echo-soundings. The dissipation of waves by a non-rigid bottom is represented in the wave model by treating the mud layer as a viscous fluid. Applied for 431 time periods, the model without this type of dissipation has a strong tendency to overpredict nearshore wave energy, except during a period of large storm waves. Two model variations which include this dissipation have a modest tendency to underpredict the nearshore wave energy. An inversion methodology is developed and applied to infer an alternate mud distribution which, when used with the wave model, yields the observed waveheights.  相似文献   

20.
Climate models are increasingly being used to force dynamical wind wave models in order to assess the potential climate change-driven variations in wave climate. In this study, an ensemble of wave model simulations have been used to assess the ability of climate model winds to reproduce the present-day (1981–2000) mean wave climate and its seasonal variability for the southeast coast of Australia. Surface wind forcing was obtained from three dynamically downscaled Coupled Model Intercomparison Project (CMIP-3) global climate model (GCM) simulations (CSIRO Mk3.5, GFDLcm2.0 and GFDLcm2.1). The downscaling was performed using CSIRO’s cubic conformal atmospheric model (CCAM) over the Australian region at approximately 60-km resolution. The wind climates derived from the CCAM downscaled GCMs were assessed against observations (QuikSCAT and NCEP Re-analysis 2 (NRA-2) reanalyses) over the 1981–2000 period and were found to exhibit both bias in mean wind conditions (climate bias) as well as bias in the variance of wind conditions (variability bias). Comparison of the modelled wave climate with over 20 years of wave data from six wave buoys in the study area indicates that direct forcing of the wave models with uncorrected CCAM winds result in suboptimal wave hindcast. CCAM winds were subsequently adjusted for climate and variability bias using a bivariate quantile adjustment which corrects both directional wind components to align in distribution to the NRA-2 winds. Forcing of the wave models with bias-adjusted winds leads to a significant improvement of the hindcast mean annual wave climate and its seasonal variability. However, bias adjustment of the CCAM winds does not improve the ability of the model to reproduce the storm wave climate. This is likely due to a combination of storm systems tracking too quickly through the wave generation zone and the performance of the NRA-2 winds used as a benchmark in this study.  相似文献   

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