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1.
The effect of wind waves on water level and currents during two storms in the North Sea is investigated using a high-resolution Nucleus for European Modelling of the Ocean (NEMO) model forced with fluxes and fields from a high-resolution wave model. The additional terms accounting for wave-current interaction that are considered in this study are the Stokes-Coriolis force, the sea-state-dependent energy and momentum fluxes. The individual and collective role of these processes is quantified and the results are compared with a control run without wave effects as well as against current and water-level measurements from coastal stations. We find a better agreement with observations when the circulation model is forced by sea-state-dependent fluxes, especially in extreme events. The two extreme events, the storm Christian (25–27 October 2013), and about a month later, the storm Xaver (5–7 December 2013), induce different wave and surge conditions over the North Sea. Including the wave effects in the circulation model for the storm Xaver raises the modelled surge by more than 40 cm compared with the control run in the German Bight area. For the storm Christian, a difference of 20–30 cm in the surge level between the wave-forced and the stand-alone ocean model is found over the whole southern part of the North Sea. Moreover, the modelled vertical velocity profile fits the observations very well when the wave forcing is accounted for. The contribution of wave-induced forcing has been quantified indicating that this represents an important mechanism for improving water-level and current predictions.  相似文献   

2.
Typhoon-induced waves and surges are important when predicting potential hazards near coastal regions. In this paper, we applied a coupled modeling system for ocean–wave interaction to examine prediction capabilities for typhoon-induced waves and surges around the Korean Peninsula. To identify how ocean–wave coupling impacts wave and surge simulations during typhoon conditions, a set of comparative experiments was performed during Typhoon Bolaven (2012): (1) a fully coupled ocean–wave model, (2) a one-way coupled ocean–wave model without surface current feedback and ocean-to-wave water levels, and (3) a stand-alone ocean model without considering wave-based sea surface roughness (SSR). When coupled with the ocean model, the surface current reduced significantly the wave height on the right-hand side of the advancing typhoon track and improved prediction accuracy along the southern coast of Korea. Compared with the observed surge levels, the simulated surge height yielded improved results for peak height magnitude and timing compared with the uncoupled model. For wave-to-surge feedback, we found that wave-induced SSR plays an important role by modulating wind stress in the surface layer. The modulated wind stress directly affected the surge height, which improved surge peak prediction during the typhoon.  相似文献   

3.
Field measurements of wave ripples and megaripples were made with a Sand Ripple Profiler in the surf and shoaling zones of a sandy macrotidal dissipative beach at Perranporth, UK in depths 1–6 m and significant wave heights up to 2.2 m. A frequency domain partitioning approach allowed quantification of height (η), length (λ) and migration rate of ripples and megaripples. Wave ripples with heights up to 2 cm and wavelengths ～20 cm developed in low orbital velocity conditions (u m?<?0.65 m/s) with mobility number ψ?<?25. Wave ripple heights decreased with increasing orbital velocity and were flattened when mean currents were >0.1 m/s. Wave ripples were superimposed on top of megaripples (η?=?10 cm, λ?=?1 m) and contributed up to 35 % of the total bed roughness. Large megaripples with heights up to 30 cm and lengths 1–1.8 m developed when the orbital velocity was 0.5–0.8 m/s, corresponding to mobility numbers 25–50. Megaripple heights and wavelengths increased with orbital velocity but reduced when mean current strengths were >0.15 m/s. Wave ripple and megaripple migrations were generally onshore directed in the shoaling and surf zones. Onshore ripple migration rates increased with onshore-directed (+ve) incident wave skewness. The onshore migration rate reduced as offshore-directed mean flows (undertow) increased in strength and reached zero when the offshore-directed mean flow was >0.15 m/s. The migration pattern was therefore linked to cross-shore position relative to the surf zone, controlled by competition between onshore-directed velocity skewness and offshore-directed mean flow.  相似文献   

4.
Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.  相似文献   

5.
Wave climate plays an important role in the air-sea interaction over marginal seas. Extreme wave height provides fundamental information for various ocean engineering practices, such as hazard mitigation, coastal structure design, and risk assessment. In this paper, we implement a third generation wave model and conduct a high-resolution wave hindcast over the East China Sea to reconstruct a 15-year wave field from 1988 to 2002 for derivation of monthly mean wave parameters and analysis of extreme wave conditions. The numerical results of the wave field are validated through comparison with satellite altimetry measurements, low-resolution reanalysis, and the ocean wave buoy record. The monthly averaged wave height and wave period show seasonal variation and refined spatial patterns of surface waves in the East China Sea. The climatological significant wave height and mean wave period decrease from the open ocean in the southeast toward the continental area in the northwest, with the pattern generally following the bathymetry. Extreme analysis on the significant wave height at the buoy station indicates the hindcast data underestimate the extreme values relative to the observations. The spatial pattern of extreme wave height shows single peak emerges at the southwest of Ryukyu Island although a wind forcing with multi-core structure at the extreme is applied.  相似文献   

6.
We report on an experimental study conducted to investigate the influence of small-scale wind waves on the airflow structure in the immediate vicinity of the air–water interface. PIV technique was used to measure the two-dimensional velocity fields at wind speeds of 3.7 and 4.4 m?s?1 and at a fetch of 2.1 m. The flow structure was analyzed as a function of wave phase. In the near-surface region, significant variations were observed in the flow structure over the waveform. The phase-averaged profiles of velocity, vorticity, and Reynolds stress showed different behavior on the windward and leeward sides of the wave in the near-surface region. The influence of wave-induced velocity was restricted within a distance of three significant wave heights from the surface, which also showed opposite trends on the windward and leeward sides of the crest. The results also show that the turbulent Reynolds stress mainly supports downward momentum transfer whereas the wave-induced Reynolds stress is responsible for the upward momentum transfer from wave to wind. In the immediate vicinity of the air–water interface, the momentum is transferred from waves to wind along the windward side, whereas, the momentum transfer is from wind to waves along the leeward side.  相似文献   

7.
The impact of the gustiness on surface waves under storm conditions is investigated with focus on the appearance of wave groups with extreme high amplitude and wavelength in the North Sea. During many storms characterized by extremely high individual waves measured near the German coast, especially in cold air outbreaks, the moving atmospheric open cells are observed by optical and radar satellites. According to measurements, the footprint of the cell produces a local increase in the wind field at sea surface, moving as a consistent system with a propagation speed near to swell wave-traveling speed. The optical and microwave satellite data are used to connect mesoscale atmospheric turbulences and the extreme waves measured. The parameters of open cells observed are used for numerical spectral wave modeling. The North Sea with horizontal resolution of 2.5?km and with focus on the German Bight was simulated. The wind field “storm in storm,” including moving organized mesoscale eddies with increased wind speed, was generated. To take into account the rapid moving gust structure, the input wind field was updated each 5?min. The test cases idealized with one, two, and four open individual cells and, respectively, with groups of open cells, with and without preexisting sea state, as well the real storm conditions, are simulated. The model results confirm that an individual-moving open cell can cause the local significant wave height increase in order of meters within the cell area and especially in a narrow area of 1–2?km at the footprint center of a cell (the cell's diameter is 40–90?km). In a case of a traveling individual open cell with 15?m·s?1 over a sea surface with a preexisting wind sea of and swell, a local significant wave height increase of 3.5?m is produced. A group of cells for a real storm condition produces a local increase of significant wave height of more than 6?m during a short time window of 10–20?min (cell passing). The sea surface simulation from modeled wave spectra points out the appearance of wave groups including extreme individual waves with a period of about 25?s and a wavelength of more than 350?m under the cell's footprint. This corresponds well with measurement of a rogue wave group with length of about 400?m and a period of near 25?s. This has been registered at FiNO-1 research platform in the North Sea during Britta storm on November 1, 2006 at 04:00 UTC. The results can explain the appearance of rogue waves in the German Bight and can be used for ship safety and coastal protection. Presently, the considered mesoscale gustiness cannot be incorporated in present operational wave forecasting systems, since it needs an update of the wind field at spatial and temporal scales, which is still not available for such applications. However, the scenario simulations for cell structures with appropriate travel speed, observed by optical and radar satellites, can be done and applied for warning messages.  相似文献   

8.
The transition zone separating estuarine environments from the coastal ocean is characterized not only by distinctive morphological and sedimentary trends but by unique hydrodynamic forces as well. Lower Chesapeake Bay, a large coastal estuary within the Mid-Atlantic Bight of the U.S. East Coast, experiences complex wave and current-induced forces produced during winter storms. Wave and current measurements made near Thimble Shoal Light over five winter seasons show that most storms simultaneously produce both ocean and bay-generated wave trains that appear as distinct bimodal peaks in directional spectra. Analysis of selected storm wave records reveal that lower-frequency ocean waves, although nominally lower in amplitude than higher-frequency bay waves, are roughly equivalent to bay waves in terms of energy expended on beds of fine- to medium-grained sand at either end of the Thimble Shoal Channel. Grain-friction energy dissipation estimates calculated for waves and currents suggest that waves provide more net energy capable of transporting bottom sediment than currents, although strong barotropic flows briefly encountered during a major storm on 13–14 March 1993, exceeded wave energy expended at the bed by almost an order of magnitude. From analyses of wave orbital velocity spectra, it is shown that dual wave trains characterized by differences in peak frequency and direction may assist each other through interactions that increase their combined contribution to frictional energy dissipation and inferred sediment transport at the bed.  相似文献   

9.
The development of ocean waves under explosive cyclones (ECs) is investigated in the Northwestern Pacific Ocean using a hindcast wave simulation around Japan during the period 1994 through 2014. A composite analysis of the ocean wave fields under ECs is used to investigate how the spatial patterns of the spectral wave parameters develop over time. Using dual criteria of a drop in sea level pressure below 980 hPa at the center of a cyclone and a decrease of at least 12 hPa over a 12-h period, ECs are identified in atmospheric reanalysis data. Two areas under an EC were identified with narrow directional spectra: the cold side of a warm front and the right-hand side of an EC (relative to the propagating direction). Because ECs are associated with atmospheric fronts, ocean waves develop very differently under ECs than they do under tropical cyclones. Moreover, ECs evolve very rapidly such that the development of the ocean wave field lags behind the peak wind speed by hours. In a case study of an EC that occurred in January 2013, the wave spectrum indicates that a warm front played a critical role in generating distinct ocean wave systems in the warm and cold zones along the warm front. Both the warm and cold zones have narrow directional and frequency spectra. In contrast, the ocean wave field in the third quadrant (rear left area relative to the propagation direction) of the EC is composed of swell and wind sea systems propagating in different directions.  相似文献   

10.
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11.
A numerical simulation of very severe cyclonic storm ‘Phailin’, which originated in southeastern Bay of Bengal (BoB) and propagated northwestward during 10–15 October 2013, was carried out using a coupled atmosphere-ocean model. A Model Coupling Toolkit (MCT) was used to make exchanges of fluxes consistent between the atmospheric model ‘Weather Research and Forecasting’ (WRF) and ocean circulation model ‘Regional Ocean Modelling System’ (ROMS) components of the ‘Coupled Ocean-Atmosphere-Wave-Sediment Transport’ (COAWST) modelling system. The track and intensity of tropical cyclone (TC) Phailin simulated by the WRF component of the coupled model agrees well with the best-track estimates reported by the India Meteorological Department (IMD). Ocean model component (ROMS) was configured over the BoB domain; it utilized the wind stress and net surface heat fluxes from the WRF model to investigate upper oceanic response to the passage of TC Phailin. The coupled model shows pronounced sea surface cooling (2–2.5 °C) and an increase in sea surface salinity (SSS) (2–3 psu) after 06 GMT on 12 October 2013 over the northwestern BoB. Signature of this surface cooling was also observed in satellite data and buoy measurements. The oceanic mixed layer heat budget analysis reveals relative roles of different oceanic processes in controlling the mixed layer temperature over the region of observed cooling. The heat budget highlighted major contributions from horizontal advection and vertical entrainment processes in governing the mixed layer cooling (up to ?0.1 °C h?1) and, thereby, reduction in sea surface temperature (SST) in the northwestern BoB during 11–12 October 2013. During the post-cyclone period, the net heat flux at surface regained its diurnal variations with a noontime peak that provided a warming tendency up to 0.05 °C h?1 in the mixed layer. Clear signatures of TC-induced upwelling are seen in vertical velocity (about 2.5 × 10?3 m s?1), rise in isotherms and isohalines along 85–88° E longitudes in the northwestern BoB. The study demonstrates that a coupled atmosphere-ocean model (WRF + ROMS) serves as a useful tool to investigate oceanic response to the passage of cyclones.  相似文献   

12.
Summary Data are presented concerning Reynolds Stresses in wind waves obtained from time series records of horizontal and vertical velocity components of motion beneath the ocean free surface. The stresses, of the order of 25 dyne cm–2, are generally positive indicating horizontal momentum transfer downward through the dynamic wind wave regime. The magnitude of the observed stress increases with wind speed and sea state. The co-spectra show strong negative peaks which appear at the ambient wave frequencies and indicate that the correlations or eddy stresses of the gross wave motions are responsible for the momentum flux. This is a corroboration of results reported previously by the writer in this journal.  相似文献   

13.
The Turkish plate is covered by hundreds of accelerometer and broadband seismic stations with less than 50 km inter-station distance providing high-quality earthquake recordings within the last decade. We utilize part of these stations to extract the fundamental mode Rayleigh and Love surface wave phase and group velocity data in the period range 5–20 s to determine the crust structure beneath the Aegean region in southwest Turkey. The observed surface wave signals are interpreted using both single-station and two-station techniques. A tomographic inversion technique is employed to obtain the two-dimensional group velocity maps from the single-station group velocities. One-dimensional velocity–depth profiles under each two-dimensional mesh point, which are jointly interpreted to acquire the three-dimensional image of the shear-wave velocities underneath the study area, are attained by utilizing the least-squares inversion technique, which is repeated for both Rayleigh and Love surface waves. The isotropic crust structure cannot jointly invert the observed Rayleigh and Love surface waves where the radial anisotropic crust better describes the observed surface wave data. The intrusive magmatic activity related to the northward subducting African plate under the Turkish plate results the crust structure deformations, which we think, causing the observed radial anisotropy throughout complex pattern of dykes and sills. The magma flow resulting in the mineral alignment within dykes and sills contributes to the observed anisotropy. Due to the existence of dykes, the radial anisotropy in the upper crust is generally negative, i.e., vertically polarized S-waves (Vsv) are faster than horizontally polarized S-waves (Vsh). Due to the existence of sills, the radial anisotropy in the middle-to-lower crust is generally positive, i.e., horizontally polarized S-waves (Vsh) are faster than vertically polarized S-waves (Vsv). Similar radial anisotropic results to those of the single-station analyses are obtained by the two-station analyses utilizing the cross-correlograms. The widespread volcanic and plutonic rocks in the region are consistent with the current seismic interpretations of the crustal deformations.  相似文献   

14.
The scale factors to permit a laboratory analogue model study of the problem of magnetic fields induced by ocean waves in the earth's field are derived. An analogue model employing surface fluid waves in mercury to simulate ocean waves is described. In the analogue model, magnetic field measurements were made 1 cm above a 2 cm deep model mercury ocean for a wave period of 0.21 s. This model simulates measurements 38 m above the surface of a shallow ocean 78 m deep for a wave period of 13 s. The validity of the analogue modelling technique is established by the good agreement obtained in comparing the analogue model measurements of the induced magnetic fields with fields using Podney's expression for an ocean of finite depth.  相似文献   

15.
Strong ground motions recorded on the sedimentary deposits of the Po River alluvial plain during the Emilia (Northern Italy) Mw 5.7 earthquake of May 29, 2012 are used to assess the vertical profile of shear-wave velocity above the limestone basement. Data were collected by a linear array installed for site effect studies after the Mw 5.9 mainshock of May 20, 2012. The array stations, equipped with both strong and weak motion sensors, are aligned in the South–North direction, at distances ranging from 1 to 26 km from the epicenter. The vertical components of ground motion show very distinctive, large-amplitude, low-frequency dispersive wave trains. Wavelet analysis yields group-velocity dispersion curve in the 0.2–0.7 Hz frequency band. The availability of a long ambient noise record allows estimates of the site resonance frequency along with its stability among stations. The joint inversion of dispersion of surface waves and ellipticity curves derived from ambient noise H/V allows extending investigations down to the sediment-limestone interface, at a depth of about 5,000 m. Our results add new information about the velocity structure at a scale that is intermediate between the local scale already investigated by other authors with small-aperture arrays using ambient noise and the regional scale inferred from modeling of seismogram waveforms recorded at hundreds of kilometers from the source.  相似文献   

16.
The January 18, 2010, shallow earthquake in the Corinth Gulf, Greece (M w  5.3) generated unusually strong long-period waves (periods 4–8 s) between the P and S wave arrival. These periods, being significantly longer than the source duration, indicated a structural effect. The waves were observed in epicentral distances 40–250 km and were significant on radial and vertical component. None of existing velocity models of the studied region provided explanation of the waves. By inverting complete waveforms, we obtained an 1-D crustal model explaining the observation. The most significant feature of the best-fitting model (as well as the whole suite of models almost equally well fitting the waveforms) is a strong velocity step at depth about 4 km. In the obtained velocity model, the fast long-period wave was modeled by modal summation and identified as a superposition of several leaking modes. In this sense, the wave is qualitatively similar to P long or Pnl waves, which however are usually reported in larger epicentral distances. The main innovation of this paper is emphasis to smaller epicentral distances. We studied properties of the wave using synthetic seismograms. The wave has a normal dispersion. Azimuthal and distance dependence of the wave partially explains its presence at 46 stations of 70 examined. Depth dependence shows that the studied earthquake was very efficient in the excitation of these waves just due to its shallow centroid depth (4.5 km).  相似文献   

17.
Many boulders are located around the coastal cliffs with height of below 5 m made of coral limestone at Kuro‐shima, Okinawa, Japan. The origin of the boulders appears to be coral limestone cliffs which show developed notches. We undertook stability analysis, involving the wave pressure due to tsunamis, of wave‐induced collapse of the cliffs. We find that extreme waves are capable of inducing cliff collapse, as observed in circumstances where gravity is insufficient. Copyright © 2010 John Wiley and Sons, Ltd.  相似文献   

18.
This paper addresses the spatial and temporal patterns of drivers for sediment dynamics in coastal areas. The basic assumption is that local processes are dominating. The focus is put on the bed shear stress in the southern part of North Sea giving the basic control for deposition–sedimentation and resuspension–erosion. The wave-induced bed shear stress is formulated using a model based on the concept that the turbulent kinetic energy associated with surface waves is a function of orbital velocity, the latter depending on the wave height and period, as well as on the water depth. Parameters of surface waves are taken from simulations with the wave spectrum model WAM (wave model). Bed shear stress associated with currents is simulated with a 3D primitive equation model, Hamburg Shelf Ocean Model. Significant wave height, bed shear stress due to waves and currents, is subjected to empirical orthogonal functions (EOF) analysis. It has been found that the EOF-1 of significant wave height represents the decrease of significant wave height over the shallows and, due to fetch limitation, along the coastlines. Higher order modes are seesaw-like and, in combination, display a basin-scale rotational pattern centred approximately in the middle of the basin. Similar types of variability is also observed in the second and third EOF of bed shear stress. Surface concentrations of suspended matter derived from MERIS satellite data are analysed and compared against statistical characteristics of bed shear stress. The results show convincingly that the horizontal distribution of sediment can, to a larger extent, be explained by the local shear stress. However, availability of resuspendable sediments on the bottom is quite important in some areas like the Dogger Bank.  相似文献   

19.
A moderate shallow earthquake occurred on 5 December 2014 (M W = 4.9) in the north of Lake Hovsgol (northern Mongolia). The infrasonic signal with duration 140 s was recorded for this earthquake by the “Tory” infrasound array (Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Science, Russia). Source parameters of the earthquake (seismic moment, geometrical sizes, displacement amplitudes in the focus) were determined using spectral analysis of direct body P and S waves. The spectral analysis of seismograms and amplitude variations of the surface waves allows to determine the effect of the propagation of the rupture in the earthquake focus, the azimuth of the rupture propagation direction and the velocity of displacement in the earthquake focus. The results of modelling of the surface displacements caused by the Hovsgol earthquake and high effective velocity of propagation of infrasound signal (~ 625 m/s) indicate that its occurrence is not caused by the downward movement of the Earth’s surface in the epicentral region but by the effect of the secondary source. The position of the secondary source of infrasound signal is defined on the northern slopes of the Khamar-Daban ridge according to the data on the azimuth and time of arrival of acoustic wave at the Tory station. The interaction of surface waves with the regional topography is proposed as the most probable mechanism of formation of the infrasound signal.  相似文献   

20.
Surface wave data were initially collected from events of magnitude Ms ≥ 5.0 and shallow or moderate focal depth occurred between 1980 and 2002: 713 of them generated Rayleigh waves and 660 Love waves, which were recorded by 13 broadband digital stations in Eurasia and India. Up to 1,525 source-station Rayleigh waveforms and 1,464 Love wave trains have been processed by frequency-time analysis to obtain group velocities. After inverting the path-averaged group times by means of a damped least-squares approach, we have retrieved location-dependent group velocities on a 2° × 2°-sized grid and constructed Rayleigh- and Love-wave group velocity maps at periods 10.4–105.0 s. Resolution and covariance matrices and the rms group velocity misfit have been computed in order to check the quality of the results. Afterwards, depth-dependent SV- and SH-wave velocity models of the crust and upper mantle are obtained by inversion of local Rayleigh- and Love-wave group velocities using a differential damped least-squares method. The results provide: (a) Rayleigh- and Love-wave group velocities at various periods; (b) SV- and SH-wave differential velocity maps at different depths; (c) sharp images of the subducted lithosphere by velocity cross sections along prefixed profiles; (d) regionalized dispersion curves and velocity-depth models related to the main geological formations. The lithospheric root presents a depth that can be substantiated at ~140 km (Qiangtang Block) and exceptionally at ~180 km in some places (Lhasa Block), and which exhibits laterally varying fast velocity very close to that of some shields that even reaches ~4.8 km/s under the northern Lhasa Block and the Qiangtang Block. Slow-velocity anomalies of 7–10% or more beneath southern Tibet and the eastern edge of the Plateau support the idea of a mechanically weak middle-to-lower crust and the existence of crustal flow in Tibet.  相似文献   

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