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Past work has shown that interannual California coastal sea level variability is mostly of equatorial origin, and decades of satellite sea surface height (SSH) and in situ dynamic height observations indicate that this interannual signal propagates westward from the California coast as nondispersive Rossby waves (RWs). These observations agree with standard linear vertical mode theory except that even when mean flow and bottom topography are considered, the fastest baroclinic vertical mode RW in each case is always much slower (1.6–2.3 cm s−1) than the observed 4.2 cm s−1. This order-1 disagreement is only resolved if the standard bottom boundary condition that the vertical velocity w′ = 0 is replaced by perturbation pressure p′ = 0. Zero p′ is an appropriate bottom boundary condition because south of San Francisco the northeastern Pacific Ocean boundary acts approximately like an impermeable vertical wall to the interannual equatorial wave signal, and therefore equatorial quasigeostrophic p′ is horizontally constant along the boundary. Thus, if equatorial p′ = 0 at the bottom, then this condition also applies off California. The large-scale equatorial ocean boundary signal is due to wind-forced eastward group velocity equatorial Kelvin waves, which at interannual and lower frequencies propagate at such a shallow angle to the horizontal that none of the baroclinic equatorial Kelvin wave signal reaches the ocean floor before striking the eastern Pacific boundary. Off California this signal can thus be approximated by a first baroclinic mode with p′ = 0 at the bottom, and hence the long RW speed there agrees with that observed (both approximately 4.2 cm s−1). Significance Statement: The California Current System is one of the most biologically rich and best-documented coastal regions in the world. In this region coastal sea level propagates westward from the coast at about 110 km month−1, slow enough to enable us to make large-scale ocean climate forecasts of the California Current ecosystem using coastal sea level. Although the westward speed seems slow, theoretically it is about double what we would expect. Offered here is an explanation of why this speed is "too fast" by linking the California wave signal to the equator, El Niño, and the shallow equatorial ocean response to the wind. [ABSTRACT FROM AUTHOR]

This study presents the observation and evaluation of a meteotsunami in the Indian Ocean triggered by the Hunga‐Tonga volcanic eruption. The event was detected through tide gauges and bottom‐pressure recordings across the Indian Ocean, with an amplitude of 10–15 cm, lasting for a few days. A numerical model was used to understand the ocean's response to meteotsunami and evaluate the dynamics behind it. The model results show that the sea‐level oscillations result from the ocean waves generated by a propagating Lamb wave. In addition to interaction with bathymetry, refracted and reflected waves also determine the sea‐level variability. Our analysis shows that bathymetric slope plays a vital role in near‐shore processes. The spectral and spatial characteristics of the meteotsunami were reminiscent of seismic tsunamis. Our research on this rare event elucidates the unresolved issues and eventually leads to designing a blueprint for future observation and modeling of meteotsunamis and seismic tsunamis. Plain Language Summary: This study evaluates the observation of a rare meteotsunami event that occurred in the Indian Ocean. An atmospheric pressure wave generated by the eruption of the Hunga‐Tonga volcano in the Pacific Ocean caused the meteotsunami. The signatures of this event were captured by tide gauges installed along the coast and pressure recorders moored at the ocean floor. We demonstrate using a numerical model that fast‐moving atmospheric pressure waves, Lamb waves, caused the sea‐level oscillations. Interactions with bathymetry further influenced sea‐level variability in the basin, reflected waves, and refracted waves. The vulnerable areas showed a striking resemblance to the area impacted by the tsunami that hit the Indian Ocean in 2004. This research eventually helps to identify and incorporate observational and modeling issues associated with seismic tsunamis and meteotsunami. Key Points: We present the first comprehensive evaluation of meteotsunami in the Indian Ocean using observation and modelingA forced wave to free wave transformation happens on the continental slope, and the bathymetry slope is crucial to near‐shore processesThe meteotsunami exhibits a spectral and spatial similarity to seismic tsunamis that previously occurred in the Indian Ocean [ABSTRACT FROM AUTHOR]

We present an asymptotic approach to solving the water wave scattering by undulating bottom topography in the presence of uniform currents where a flexible membrane covers the upper surface. The interest in this problem lies in the development of asymptotic solutions using the Fourier transform under the action of uniform currents. The method allows the physical processes involved in the sea-bed topography and membrane-covered surface and wave interactions to be studied. In particular, we identify the existence of Bragg resonance between gravity waves and the bottom ripples, which are associated with the reflection of incident wave energy. We consider the impacts of uniform current, and we highlight the central role of the asymptotic expansion method in the evolution of the response of current. For depth Froude number in the range of 0.4–0.7, the effects of bottom topography on Bragg resonance dominate. The current shifts the frequency of the most reflected wave components, and wave action conservation results in amplified reflected wave energies for the following currents. The theory developed in the frequency domain is illustrated in the time domain using discrete Fourier transform with the Joint North Sea Wave Observation Project (JONSWAP) spectrum [Hasselmann et al., J. Phys. Oceanogr. 10, 1264 (1980)] to analyze wave propagation through the whole system. [ABSTRACT FROM AUTHOR]

This study presents an approach to better characterize the P‐wave and S‐wave velocity structure of the seafloor sediment layer using ocean bottom seismometers. The presence of low‐velocity seafloor sediment layers influences the observed seismic record at the seafloor over a broad frequency range, such that detailed knowledge of this sediment structure is essential to predict its effect on teleseismic records. We use the radial component of teleseismic P waves and autocorrelation functions of the radial, vertical, and pressure components of teleseismic P and S waves to obtain sediment layer models using the Markov chain Monte Carlo approach with parallel tempering. Synthetic tests show that the body waves constrain the P‐ and S‐wave impedances and travel times and the P‐ to S‐wave velocity ratio of the sediment layers. The proposed method resolves thin layers at a high resolution, including the uppermost thin (∼50 m to a few hundred meters) low S‐wave velocity layer. Real data applications at sites across the Pacific Ocean that are coincident with previous in situ studies demonstrate the effectiveness of this method in characterizing the seafloor sediment unit. The sediment models characterized by this new approach will allow us to more accurately predict and correct the effects of sediment layers in generating P‐ and S‐wave reverberations. Plain Language Summary: Ocean bottom seismometers are powerful tools for investigating the detailed structure of the oceanic mantle. However, most ocean bottom seismometers are placed above the low‐velocity water‐saturated sediment layer, such that their seismic records are inevitably affected by this seafloor sediment layer. Detailed constraints on the structure of the seafloor sediment layer allow us to accurately predict its effects on the observed seismic records. The seafloor sediment layer may consist of multiple discontinuities and vary regionally. This study proposes a new approach for characterizing the seismic properties of the seafloor sediment layer using teleseismic body waves recorded at ocean bottom seismometers. Synthetic tests show that the method can resolve thin sublayers within the sediment layer, such as a very thin low shear‐wave velocity layer and sharp seismic velocity jumps. Real data applications show that the sediment models obtained using this approach are in good agreement with those obtained from direct measurements and previous body‐wave analyses. Our proposed method will enable more detailed prediction and correction of the influence of the sediment layer on ocean bottom seismometer records, thereby providing more accurate constraints on deeper Earth structures. Key Points: The seismic properties of the seafloor sediment layer are characterized using ocean bottom seismometer teleseismic body‐wave recordsThe P‐ and S‐wave impedances and travel times and the VP/VS values of each sublayer within the sediment layer are resolvedIn situ seafloor sediment structure constraints will enable accurate correction and prediction of shallow structure effects [ABSTRACT FROM AUTHOR]

The analysis of ocean wave-induced dynamic response of a porous seabed is particularly important for coastal and geotechnical engineers when designing and constructing maritime structures. In this study, an analytical solution is presented to analyze the dynamic response and liquefaction potential of a poro-elastic seabed induced by partial standing waves with arbitrary reflectivity. The porous seabed is modeled using Biot's theory describing the propagation of elastic waves, and coupled deformation and water flow of porous media, whereas the ocean waves are described using linear ocean wave theory. Based on the mixed boundary-value conditions, explicit expressions of displacements, effective stresses and excess pore water pressure of seabed are derived with consideration of the effects of inertial forces, compressibility of solid and fluid, and arbitrary reflectivity of standing waves. The results of degenerated analytical solutions are compared with the existing ones to verify the correctness of the proposed method. The effects of several pertinent parameters of ocean wave-seabed system, including reflection coefficient, phase lag and period of standing waves, depth of water, permeability, degree of saturation, and shear modulus of seabed deposits, etc., on the dynamic response of seabed and liquefaction potential, are examined and discussed. It is found that the reflection of standing wave has a significant effect on the dynamic response and liquefaction potential of porous elastic seabed. Compared with that of no wave reflection, the liquefaction depth of seabed induced by fully-reflected standing waves increases 82.49% under certain conditions of wave-seabed system. In addition, phase lag, wave period, water depth and mechanical and physical properties of seabed soil such as saturation, permeability and shear modulus have different effects on the dynamic response and liquefaction potential of porous elastic seabed. The investigation of the dynamic response and liquefaction of the porous elastic seabed under partial standing ocean waves will help to better predict the influence of standing waves on breakwaters and seabed soil, and can provide some guidance for the design of offshore structures. [ABSTRACT FROM AUTHOR]

With the increasing demand of transport construction in coastal areas, seabed instability around tunnels subjected to ocean waves and protection of the tunnels are becoming increasingly important. Current analytical solutions on the seepage field around subsea shield tunnels induced by waves are generally based on the impermeable lining, without considering the permeability. Furthermore, previous studies seldom take account of the influence of nonlinear wave loads under the sloping seabed terrain. For better tunnel stability, this paper presents a new set of analytical solutions for predicting Stokes wave-induced seepage pressure responses around a shield tunnel in a sloping seabed considering the influence of the permeable tunnel lining. The accuracy of the presented solutions is then verified by comparison with the numerical solution and experimental data, showing reasonable alignments. Moreover, parametric analyses are also performed to assess the influence of wave characteristics, seabed properties, and tunnel lining permeability on seepage pressure responses, in which the distribution of the excess pore pressure response outside the lining and excess pore pressure around the tunnel circumference is described in detail. In general, the analytical solutions provide an effective insight into the wave-induced seepage pressure response around a shield tunnel, which can serve as a credible theoretical basis in the preliminary design of tunnels. [ABSTRACT FROM AUTHOR]

We show large "shields" can significantly reduce horizontal component noise levels for ocean bottom seismometers by shielding the seismic sensors from shaking due to ocean currents. However, at short period (<1 s) some noise from vibration or rocking of the shield under current can partly couple through the ground causing peaks in the noise spectra. Deformation of the seafloor under ocean wave loading ("compliance") raises noise levels at long period (>5 s) for both vertical and horizontal components at shallow water sites. Pressure gauge data is now routinely used to predict and remove this source of noise on vertical component data. We have developed horizontal pressure gradient (HPG) gauges to measure and remove this source of noise from horizontal component data. The combination of HPG data and shielding enables low noise long period seismic observations at otherwise very noisy shallow seafloor sites. Plain Language Summary: There is a compelling need to install seismometers on the shallow seafloor to measure underlying Earth structure and to better understand tsunami and seismic hazard, particularly hazard associated with subduction zone earthquakes. Measurements on the shallow seafloor are invariably very noisy due to strong seafloor currents and the deformation of the seafloor under ocean wave loading. We show large metal covers can substantially shield the sensors from the effects of current, thus removing much of this noise. Ocean wave loading noise can be measured and predicted and removed by measuring the ocean wave loading using collocated sensors that measure seafloor pressure and horizontal gradients of pressure at the seafloor making the detection of small amplitude seismic signals more possible. Key Points: Heavy shields can eliminate current induced tilt noise at long period on seafloor seismometers but may raise noise levels at short periodOcean waves raise long period noise levels on the horizontal component seismic data as the seafloor deforms under wave loadingData from horizontal pressure gradient sensors can be used to remove up to 25 dB of wave loading noise from the seismic data [ABSTRACT FROM AUTHOR]

The time-domain motion of a finite depth ocean subject to an arbitrary (in both time and space) imposed displacement of the bottom is studied under the assumption of linear theory. This solution provides results for this limiting case which may be helpful for benchmarking. The focus is on the numerical simulation of the near-field waves with application to the simulation of tsunami waves. The fluid domain is assumed two-dimensional, and the effect of compressibility is included. The time-domain solution is built from the frequency domain solution taking a Fourier series expansion of the bottom motion. This expansion allows complex displacements to be simulated. The solution in the frequency domain is expressed as a sum over modes. The time-domain solution is calculated by numerical evaluation of the Fourier transform in time, allowing arbitrary time-dependent motion. This code is extremely efficient and highly accurate, and there is no time–stepping so that errors do not accumulate in time. The eigenfunction expansion method to obtain the velocity potential for a flat ocean bottom case is independently derived. A shallow water limit for all the above cases is provided, giving a method to check the correctness of the numerical solution. Separate treatment for all the situations under the compressible assumption is also performed. The horizontal and vertical particle velocities are graphically presented for the time-harmonic oscillation. Time-dependent surface wave propagation is computed to show the initiation of tsunami waves in the deep ocean and their subsequent propagation. The calculations presented here allow for the simulation of tsunami wave generation and to investigate various effects, including the role of acoustic gravity waves. It is shown that the compressibility is not always significant, but that when the water is either sufficiently deep or the rise sufficiently rapid, acoustic gravity waves are produced. It is shown that, in this case, the ocean surface undergoes a rapid oscillation and that this may be a method to detect tsunamis. [ABSTRACT FROM AUTHOR]

It has long been recognized that specific ambient seismic noise is generated within the ocean. Therefore, ocean bottom seismometers have advantages to reveal the noise characteristics directly in the deep sea. We use the seismic recordings around Tristan da Cunha collected by 20 OBSs and two island stations to investigate the ambient noise sources in the middle of the South Atlantic. We analyzed the power spectral density, ambient noise cross‐correlations, and correlations with wave heights model. While primary microseisms (∼10–20 s) in this region are deficient, the secondary microseisms are strong and dominate the ambient noise at periods of ∼1–10 s, with the peak broadening to shorter periods (1–3 s). The secondary microseisms are strongly correlated with the local wave heights, especially at shorter periods (∼1–3 s), suggesting that the microseisms are affected mostly by local wave interactions. We observed clear Empirical Green's functions at periods of ∼3–10 s, indicating the existence of distant sources of secondary microseisms. Results of asymmetry analysis of cross‐correlations suggest the prominent direction of the distant source should be located to the Southwest and show barely seasonal variations. The correlations with wave heights indicate a possible source region in the southeast Pacific Ocean. Therefore, besides the dominating local wave‐wave interactions, the secondary microseisms around Tristan region are affected simultaneously by persistent distant sources from the deep basin in the Southeast Pacific Ocean, which might be related to the intense wave‐wave interactions caused by the blocking effect of the Drake Passage on ocean currents and waves. Plain Language Summary: Ambient seismic noises are the ubiquitous and low‐amplitude background signals recorded by the seismic stations worldwide. Microseisms are the strongest parts of ambient noise, which are generated within the oceans by wave interactions. Previous studies of ambient noise or microseisms had been carried out in many regions, but no study had focused yet on the South Atlantic Ocean due to the lack of seismological data. In this study, we computed the probabilistic power spectral densities to analyze the spectral characteristics of oceanic ambient noise around Tristan region in the middle of the South Atlantic Ocean. We observe that the microseisms have strong correlations with the local wave heights, indicating that local wave interactions are dominant sources here. The analysis of ambient noise cross‐correlations shows there are distant sources for this region obscured by dominant local sources. Based on asymmetry analysis of the ambient noise cross‐correlations, we estimate the direction of the major distant sources. Combined with the correlation analysis with global wave heights model, we identify the predominant distant sources, which are located in the Southeast Pacific Ocean and related to the blocking effect of the Drake Passage on ocean currents and wave systems. Key Points: We analyzed the spectral characteristics of oceanic ambient noise around Tristan da Cunha island in the South Atlantic OceanThe secondary microseisms in the middle South Atlantic are affected by both nearby and distant sources, but local sources are much strongerWe identified the predominant distant source region of secondary microseisms in this region, which is in the southeastern Pacific Ocean [ABSTRACT FROM AUTHOR]

The 2022 eruption of the Hunga Tonga-Hunga Ha'apai volcano excited an atmospheric Lamb wave, which induced a fast-traveling tsunami. This tsunami was driven by the pressure-forced wave traveling at the speed of the Lamb wave and, thus, was much faster than conventional tsunamis. This was the first case in which ocean bottom monitoring systems widely observed an air pressure-induced tsunami. We found that the pressure-forced waves split and generated ocean gravity waves after passing the Japan Trench based on the S-net data. Our simulations show that changes in water depth can amplify or decrease the pressure-forced wave. Simultaneously, an ocean gravity wave is generated due to the conservation of water volume. Because the ocean gravity wave was slower than the pressure-forced wave near Japan, it was separated from, and traveled behind, the pressure-forced wave. We explained the wave separation phenomenon and reproduced the waveforms of different splitting stages observed by the stations near the Japan Trench. [ABSTRACT FROM AUTHOR]

In this paper, a new extended (3 + 1)‐dimensional generalized Kadomtsev–Petviashvili (KP)–Boussinesq equation, with two additional terms utt$$ {u}_{tt} $$ and uxz$$ {u}_{xz} $$, is proposed and investigated. This new equation models both left and right going waves like the Boussinesq equation and describes the transmission of tsunami waves at the bottom of the ocean and nonlinear ion‐acoustic waves in the magnetized dusty plasm. We have constructed one set of breathers and first order periodic waves from the two‐soliton solution. Moreover, the four‐soliton solution consists of two sets of breathers, second order periodic waves, and a hybrid of breathers and periodic line waves. Then, we introduce two kinds of "long wave" limits to obtain the rational and semi‐rational solutions for N=2,3,4$$ N=2,3,4 $$. Under specific parametric constraints, the obtained rational and semi‐rational solutions are nonsingular. The rational solution can be classified as first order line rogue wave, single breather, second order line rogue wave, double breather, a hybrid of breather and line rogue wave, a hybrid of breather, and single soliton. The semi‐rational solution can be classified as the first and second order kink‐shaped rogue wave, a hybrid of breather and one (two) soliton(s), a hybrid of a set of breathers, and a single soliton (breather). In addition, we give Theorem 2.1 for the higher order rational solutions. [ABSTRACT FROM AUTHOR]

An efficient mathematical model is presented for predicting the transfer of ocean waves to ice shelf flexure along two‐dimensional transects. The model incorporates varying ice shelf thickness and seabed bathymetry profiles, and is able to predict responses of large ice shelves over a broad frequency spectrum. The model is used to generate displacement and strain transfer functions for the Ross Ice Shelf (RIS) using geometries from the Bedmap2 data set. The transfer functions are validated against recent observations and used to study the influence of geometrical variations on strain transfer close to the shelf front. Predictions of RIS strain in response to example irregular incident swell and infragravity waves are generated over a wide region, and show similar maximum strains but contrasting spatial strain patterns. The model and results provide a basis for studying destabilizing impacts of ocean waves on the RIS. Plain Language Summary: The outer margins of Antarctic ice shelves bend and flex rhythmically in response to ocean waves, which imposes potentially damaging stresses and strains on the shelves. We model the flexural response of the world's largest ice shelf, the Ross Ice Shelf (RIS), to ocean waves. We incorporate reflection of incident waves from the open ocean by the shelf front, and realistic ice shelf and seabed geometries. We validate the model using recent groundbreaking observations, and show that the RIS experiences large strains in response to a broad range of ocean waves, from swell generated by storms over the ocean to infragravity waves generated at distant coastlines. The predictions will underpin improved understanding of RIS stability, and, thus, contribute toward more accurate projections of global sea level rise. Key Points: Model predictions of Ross Ice Shelf flexure in response to ocean waves, incorporating real shelf thickness and seabed profilesModel validated against observations, and swell and infragravity waves found to generate maximum flexural strains of similar magnitudePredictions will empower studies of ocean wave influence on crevasse expansion, rift propagation, and iceberg calving [ABSTRACT FROM AUTHOR]

Evaluating the seismic site effect by the ambient noise based horizontal-to-vertical spectral ratio (HVSR) method is strongly affected by the spatial and temporal variations of the ambient noise sources. Therefore, it is necessary to locate the source regions of ambient noise and investigate the relationships between the source energy and HVSR values at the predominant frequency (HVSRf0) of the site. The generation mechanisms of the single- and double-frequency microseisms (SFMs, 0.05–0.085 Hz and DFMs, 0.1–0.5 Hz) in ambient noise are better understood than the noise in other frequency bands and they are dominantly composed of fundamental Rayleigh (Rg) waves. With this advantage, the recordings of SFMs and DFMs at 30 stations in the east coast region of the United States are used to demonstrate a study on locating their source regions with reasonable certainty and constructing the functional relationship between the HVSRf0 and the source energy of SFMs and DFMs. The recordings are processed in four sub-frequency bands (Fs) of SF and DF bands and a polarization analysis is carried out to select the ellipsoids approximating the particle motions of Rg waves. Then the probability density functions of the back azimuths of the ellipsoids' semi-major axes are computed for each F and station, and are projected on the ocean to determine their possible source regions. These regions are further constrained by (1) the correlation coefficients between the SFMs and the WAVEWATCH III (WWIII) hindcasts of ocean wave spectra in the SF band, or between the DFMs and the modeled DF energy on ocean surface in the selected time windows in the DF band, (2) the energy contribution defined by (i) the average WWIII ocean wave energy and the ocean bottom topographical gradient in the SF band, or (ii) the average modeled DF energy on ocean surface and a frequency and water depth dependent coefficient measuring the conversion efficiency of DF energy from water to solid earth in the DF band, and (3) the percentile retained energy of Rg waves in both the SF and DF bands. Results of source regions reveal that (1) the SFMs recorded in eastern US result from the interactions of low frequency (0.05–0.085 Hz) ocean waves with the continental slope and shelf of western North Atlantic Ocean; (2) the source regions for long- (0.1–0.2 Hz) period DFMs are located in the deep ocean close to the continental slope; and (3) the short- (0.2–0.5 Hz) period DFMs are generated in the continental shelf. Finally, the correlation analyses between the simulated source energy and the HVSRf0values at the stations whose f0s fall in DF band are carried out revealing significant source effect on thick sediments at low frequencies. [ABSTRACT FROM AUTHOR]

This study presents robust algorithms for tsunami early warning using synthetic tsunami wave data at ocean bottom sensor (OBS) arrays with sequential multiple linear regression. The study focuses on the Tohoku region of Japan, where an S-net OBS system (150 pressure sensors) has been deployed. To calibrate the tsunami early warning system using realistic tsunami wave profiles at the S-net stations, 4000 stochastic tsunami simulations are employed. Forecasting models are built using multiple linear regression together with sequential feature selection based on Akaike Information Criterion and knee-point method to identify sensors that improve the accuracy most significantly. The study considers tsunami wave amplitude at a nearshore location and regional tsunami loss for buildings to develop hazard-based and risk-based tsunami warning algorithms. The models identify an optimal configuration of OBS stations and waiting time for issuing tsunami warnings. The model performance is compared against a base model, which only uses the earthquake magnitude and epicenter location. The result indicates that estimating the tsunami amplitude and loss via S-net improves accuracy. For the hazard-based forecasting, adding six sensors from the S-net improves the accuracy of the estimation most significantly with an optimal waiting time of 3 min. For the risk-based forecasting, a longer waiting time between 5 and 10 min is suitable. [ABSTRACT FROM AUTHOR]

Distributed Acoustic Sensing (DAS) is a new method for recording oceanographic processes using seafloor fiber-optic cables, such as telecommunication cables. DAS returns spatially distributed measurements of cable strain, which can be related to hydrodynamic pressure, turning a submarine cable into a dense sampling array. A reinforced fiber-optic cable was installed in the cross-shore from the dune toe to ∼15-m-water depth at the USACE Field Research Facility in Duck, NC to quantitatively compare DAS strain to co-located pressure sensors. We develop a methodology for transferring DAS strain to dynamic pressure and evaluate the performance of DAS to measure shallow- and intermediate-water waves in the incident band (0.04–0.4 Hz). A frequency-dependent empirical transfer function from DAS strain to dynamic pressure at the seabed is derived from the ratio of strain and pressure power spectra. DAS-derived significant wave heights and peak periods were consistent with pressure sensors (typical rmse = 0.2 m and 1 s) over a wide range of dynamic conditions (0.24–4 m wave heights and 3–18 s periods). DAS data were input into the cBathy algorithm to calculate cross-shore bathymetric profiles and were used to calculate cross-shore wave reflection. Preliminary applications of DAS to record wave splitting and shoreline position were explored. With this field data, we demonstrate new applications of DAS for measuring nearshore processes and encourage further exploration. The promising potential of DAS lies in the near-bed data volume provided, real-time capability, and ability to sample in any weather or light. • Distributed Acoustic Sensing can measure nearshore ocean waves. • An empirical transfer function is proposed to convert cable strain to pressure. • DAS-derived pressure provides a wide resolution for ocean analyses. • DAS is promising for nearshore monitoring on existing or custom fiber-optic cables. [ABSTRACT FROM AUTHOR]

Ocean-bottom pressure gauges of wide and dense ocean-bottom observation networks around Japan, S-net and DONET, observed ocean waves caused by the Tonga eruption that started at approximately 13:00 JST (UTC + 0900) on January 15, 2022. We scrutinized the waveform records of the arriving ocean waves to evaluate their nature and found two significant disturbances between 20:00 and 21:00 and after 22:00. The first disturbance with a positive-polarity pulse dominated by long-period components (1000–3000 s) arrived at S-net and DONET stations between 20:00 and 21:00 from the southeast, corresponding to the direction of the short great circle between Tonga and Japan. This arrival was much earlier than expected for a direct tsunami from the volcano and can be explained by assuming that the waves propagated along the short great circle path at a velocity of approximately 300 m/s. After 22:00, significant phases dominated by relatively shorter period components (< 1000 s) arrived from the southeast direction in both observation networks. In DONET, another phase arrived from the south–southeast direction at approximately 23:30 with shorter period components (approximately 500 s). Most of the near-trench S-net stations recorded the peak amplitude during the first disturbance, whereas the near-coast S-net stations and DONET stations observed their peak after 22:00. The amplitudes of ocean-bottom pressure changes in both networks increased as the water depth decreases. This amplification behavior differed between the first and second disturbances, which is attributed to the differences in the natures of the arriving ocean and air waves. This study also found several arrivals of air-wave disturbances to be correlated with the ocean-wave phases, which implies that multiple disturbances of ocean-bottom pressures were generated by the interactions of several disturbances of air waves following the 2022 Tonga eruption with ocean waves. [ABSTRACT FROM AUTHOR]

We investigate a hydrodynamic equation system which—with some approximation—is capable of describing the tsunami propagation in the open ocean with the time-dependent self-similar Ansatz. We found analytic solutions of how the wave height and velocity behave in time and space for constant and linear seabed functions. First, we study waves on open water, where the seabed can be considered relatively constant, sufficiently far from the shore. We found original shape functions for the ocean waves. In the second part of the study, we also consider a seabed which is oblique. Most of the solutions can be expressed with special functions. Finally, we apply the most common traveling wave Ansatz and present relative simple, although instructive solutions as well. [ABSTRACT FROM AUTHOR]

We analyze theoretically ultra-low frequency electromagnetic noise caused by deformations of seabed and porous coastal rocks subjected to incident long oceanic waves. A variable pressure on the seabed due to propagation of long gravity waves (LGWs) gives rise to variations in pore pressure gradient followed by groundwater filtration in pores and channels of porous rocks. These processes result in the generation of telluric electric currents in water-saturated porous rock of the seashore due to electrokinetic effect. In the model a displacement of the sea surface in LGWs is described in the "shallow water" approximation. A set of basic equations describing rock strain and electrokinetic effect is solved in quasi-static approximation. The telluric electric field in the porous rocks of coastal zone are found as a function of depth and distance to the coastline at different frequencies of LGWs. The theoretical analysis has shown that telluric electric noise produced by the LGW can exceed the level of natural electric noise during geomagnetically quiet period in a coastal strip about several tens of meters. [ABSTRACT FROM AUTHOR]

The patterns of internal waves are common occurrences in remote sensing images of the ocean. Internal waves are usually induced by undulating terrain on the sea floor or moving sources in the stratified ocean, especially in an offshore sea or straits in which there exists a relatively significant density stratification of the seawater. In this paper, a new method for simulating the synthetic aperture radar (SAR) images of the internal wave wake excited by underwater vehicles is presented. The flow field of the wake is solved directly using the Reynolds averaged Navier–Stokes solver, and the ambient waves on the sea surface are considered as random wind waves. To consider a continuously stratified ocean, a special multiphase flow model is implemented, which can be used to obtain arbitrary stratified structures numerically. To estimate the scattering distribution of the wakes on the sea surface, an improved facet scattering model is proposed, in which the hydrodynamic modulation of the ambient waves by the wake is considered. Based on the results calculated by the scattering model, the velocity-bunching integral is implemented to simulate the intensity of SAR images of a disturbed sea surface having embedded internal wave wakes. [ABSTRACT FROM AUTHOR]

The importance of resources contained in the sea and on the sea floor is increasing with each passing day. Hence, exploration of the sea and sea floor has become a very important requirement. Underwater imaging is a science that has gained importance over the past two decades. Underwater images indicate the state of sea floor and transmitting such images through the harsh and turbulent oceanic medium can cause deterioration of the information contained in the image due to diminished color reproduction, low contrast and blur. In this paper, we have performed the simulation studies to understand perturbations induced during the transmission of sea floor images using high-speed optical signaling through the underwater channels. The transmitted irradiance often suffers from underwater turbulence and beam attenuation. The bit error rate (BER) of the system proposed to transmit information through channels has been determined through analytic means and validated through Monte-Carlo simulation. Comparison between the transmitted and received images in the presence of turbulence and attenuation have been presented. The BER performance of the proposed system is evaluated in the presence of beam attenuation and underwater turbulence. The turbulence induced errors are minimized using the transmit/receive diversity and multiple input multiple output (MIMO) techniques. In addition to the diversity techniques, median and adaptive median filters used to minimize the distortion in the received image. The BER results show that the 4 × 5 MIMO system gains 19.50 dB of transmit power at BER of 10 - 5 , when compared with the single input single output system. Similarly, an improvement of at-least 18 dB peak signal to noise ratio obtain using the adaptive median filter based system over the un-filter based system. [ABSTRACT FROM AUTHOR]

Ocean surface waves and currents can interact to produce strong seabed shear stress and sediments mobilization affecting infrastructure safety, benthic habitat distribution and decision for sustainable development of the oceans. Modelled waves, tidal current and circulation current data for a 3-year period were used in a combined-flow sediment transport model to simulate the seabed shear stresses and the mobilization of observed sediments on the Canadian Atlantic Shelf. The modelling results are presented and analyzed to update the framework of seabed disturbance and sediment mobility on the Atlantic Shelf. The Atlantic Shelf is affected by strong waves and tidal currents. Maximum mean significant wave height over the modelled period can reach 3.5 m and mean tidal currents reach up to 1.2 m s−1. Our modeling results indicate that the mean wave and tidal current shear velocities both reach the maximum values of ∼4 cm s−1. Observed sediments on the Atlantic Shelf can be mobilized by tidal currents at least once during the modelled 3-year period over 30 % of the shelf area while storms can mobilize sediments over 35 % of the shelf area suggesting a slightly stronger sediment mobilization by storms. Furthermore, waves and currents interact to cause enhanced combined wave-current shear velocities >5 cm s−1 that is capable of mobilizing sediments over 63 % of the shelf area, double that due to tides or waves alone. The spatial variation of the relative importance of waves, tidal current and circulation current in mobilizing sediments was used to classify the Atlantic Shelf into six disturbance types. Wave-dominant and tide-dominant disturbance types are equally important and both occupy ∼25 % of the shelf area. Mixed disturbance is insignificant and accounts for only 3 % of the shelf area. Universal Seabed Disturbance Index (SDI) and Sediment Mobility Index (SMI) were applied to better quantify the exposure of the seabed to oceanographic processes and sediment mobilization, incorporating both the magnitude and frequency of these processes. The values of SDI and SMI on the Canadian Atlantic Shelf are found to be comparable to those on the Australian shelves and the Irish Sea shelf. These indices, together with the seabed disturbance type classification scheme, potentially can be used as standard parameters to quantify seabed disturbance and sediment mobility on other shelves of the world. • Wave, current and combined-flow sediment transport models applied on Canadian Atlantic Shelf. • Characterized magnitude and frequency of shear stresses and sediment mobilization due to various processes. • Mean combined wave-current shear velocity reaches >5 cm·s−1 and mobilizes sediments over 63 % of the shelf area. • Six disturbance types were classified and their spatial distribution mapped. • Shear stress and sediment mobility maps can be used in siting offshore infrastructure and informing marine spatial planning. [ABSTRACT FROM AUTHOR]

Seismic waves from earthquakes recorded on the seafloor are composed of complex multiple arrivals. Here, distributed acoustic sensing (DAS) observations along a cable located offshore the Sanriku Coast, Japan, show that the local earthquake wavefield is particularly rich in Scholte waves. We introduce a processing pipeline to extract these surface waves from DAS records. We then invert hundreds of dispersion curves along a section of the cable to form a shallow high‐resolution shear‐wave velocity model. Moreover, we focus on the possible generation mechanisms of Scholte waves through a series of 2D and 3D full‐wavefield numerical simulations. We show that water phase reverberations greatly contribute to the generation of Scholte waves on the ocean floor. This study demonstrates the potential of DAS to observe and better understand a poorly known marine wave phenomenon and image the offshore shallow seismic structure with an unprecedented spatial resolution. Plain Language Summary: Distributed acoustic sensing (DAS) is a measurement technique that has recently demonstrated its utility for marine geophysics. DAS offers the possibility to observe the seismic wave at a scale and an extent previously unattainable with traditional passive seismic surveys. Here, we use a linear DAS array located offshore the Sanriku Coast, Japan. We propose a processing pipeline to extract surface waves from local earthquake DAS records and obtain hundreds of measurements along the cable. These measurements are used to infer a high‐resolution model of the near‐shore subsurface. Supported by a series of numerical simulations, we suggest that acoustic reverberations in the water column greatly contribute to the generation of surface waves on the ocean floor. This study further demonstrates that DAS can be used to understand marine wave phenomena better and image offshore seismic structures. Key Points: Passive high‐resolution Vs imaging of shallow sedimentary layers with ocean‐bottom distributed acoustic sensing and low‐magnitude earthquakesGridded slant‐stack method to extract Scholte waves from local earthquake wavefieldsFull‐wavefield simulations suggest that water phase reverberations generate Scholte waves at the ocean floor [ABSTRACT FROM AUTHOR]

Observations of ocean surface waves at three sites along the northern coast of Alaska show a strong correlation with seasonal sea ice patterns. In the winter, ice cover is complete, and waves are absent. In the spring and early summer, sea ice retreats regionally, but landfast ice persists near the coast. The landfast ice completely attenuates waves formed farther offshore in the open water, causing up to a two‐month delay in the onset of waves near shore. In autumn, landfast ice begins to reform, though the wave attenuation is only partial due to lower ice thickness compared to spring. The annual cycle in the observations is reproduced by the ERA5 reanalysis product, but the product does not resolve landfast ice. The resulting ERA5 bias in coastal wave exposure can be corrected by applying a higher‐resolution ice mask, and this has a significant effect on the long‐term trends inferred from ERA5. Plain Language Summary: Ocean waves facilitate coastal erosion in the Arctic (and worldwide). Wave energy reaching Arctic coasts is controlled by seasonal sea ice, which includes landfast ice attached to the coastlines or sea floor, and mobile pack ice further seaward. Wave energy in the Arctic is increasing due to the loss of pack ice, and these effects are generally well‐represented in regional climate models. Landfast ice continues to form at the coast each year; when it lasts longer than pack ice, it provides protection against wave erosion. However, landfast ice is difficult to include in models which can lead them to overestimate the wave energy reaching the coasts. Using observations of waves from three coastal sites in Alaska, we demonstrate the importance of including landfast ice into regional models, and propose an effective method of combining public datasets to account for its effects on waves. These results can help the research community predict how much wave energy will be available for coastal erosion processes in the coming decades. Key Points: Year‐long observations show a seasonal cycle of wave exposure at three sites along the Arctic coast of northern AlaskaThe persistence of landfast ice in the late spring/early summer dramatically reduces the wave energy reaching the coastCoastal protection by landfast ice is not represented in global climate models, but it can be parameterized [ABSTRACT FROM AUTHOR]

Eulerian and Lagrangian measurements of orbital velocities in waves approaching a beach are analyzed with the goal of understanding the relative influence of wave‐by‐wave variations in mean‐water level, wave height and incipient wave breaking on mass transport properties of waves in the surf zone. It is shown quantitatively that elevated local mean‐water level correlates positively with increased Lagrangian mass transport at the free surface. Eulerian ADV measurements in the fluid column suggest that the depth‐integrated wave‐by‐wave mass transport also correlates positively with the local mean‐water level, and is only weakly linked to wave height and wave‐breaking events. Plain Language Summary: A sea state is defined broadly by an average wave period and an average perceived (significant) wave height, but wave heights and periods of individual waves may differ significantly from these average values. The differences between individual waves are exacerbated as the waves approach the shore and interact with the bottom topography in shallow water. In particular, the mean‐water level may vary from wave to wave. In the present study, particle tracers are used in connection with stereo imaging to study particle trajectories in waves approaching a beach. Particle positions and trajectories are found using data analysis of individual camera frames. In addition, fluid velocities are measured directly using acoustic Doppler velocimetry. It is found that the most significant factor in the overall horizontal fluid velocity and net transport of particles by an individual wave toward the beach is not the wave height or period, but the local mean‐water level, that is how the average wave elevation in a single wave is situated with respect to the sea bed. Key Points: Measurements of Lagrangian and Eulerian velocities are combined with pressure sensor data to explore wave properties in the surf zoneWave‐by‐wave oscillations of mean‐water level exert a strong influence on mass transport in the fluid columnThe motion of Lagrangian tracers is well matched by dispersive long‐wave theory [ABSTRACT FROM AUTHOR]

The authors improve the numerical method of calculating multi-wave models to increase the speed and monotonize (reduce the oscillations of numerical calculations) the numerical solution of problems of multi-wave dynamics for lengthy systems such as space tethers tens of kilometers long; pipelines in air and in liquid; underwater towed systems; airlifts 5 to 10 km long for the extraction of minerals from the bottom of the oceans, etc. The method is based on the decomposition of the numerical algorithm by wave types and wave velocities. It is shown that due to quantization in calculating longitudinal and transverse waves, it is possible to achieve a further increase in the computation speed compared to the wave factorization algorithm and compared to solving the full system of equations, without reducing the range of sustainable calculation. The final increase in the productivity of the program code is at least 50 to 200% when performing calculations, depending on the required accuracy and options for the decomposition of multi-wave models. This modification of the wave factorization method is relevant in solving the problems of controlling a distributed system, operative analysis of transient motion modes, etc., where the pace of calculations is critically important. A comparative evaluation of the accuracy of the full algorithm, the of wave factorization method, and of the decomposition by wave types and wave velocities has been carried out. Comparative analysis of the calculated data showed the monotonicity of the numerical solution profile on the basis of factorized algorithms, their lower sensitivity to errors in the initial data. A finite-difference scheme factorized by perturbation directions and wave types with variable dispersion-diffusion properties is constructed. [ABSTRACT FROM AUTHOR]

A solution method is developed for a linear model of ice shelf flexural vibrations in response to ocean waves, in which the ice shelf thickness and seabed beneath the ice shelf vary over distance, and the ice shelf/sub–ice-shelf cavity are connected to the open ocean. The method combines a decomposition of the ice shelf displacement profile at a prescribed frequency of motion into mode shapes of free vibrations, a finite-element method for the cavity water motion and a non-local operator to connect to the open ocean. An investigation is conducted into the effects of ice shelf thickening, seabed shoaling and the grounding-line conditions on time-harmonic ice shelf vibrations, induced by regular incident waves in the swell regime. Furthermore, results are given for ice shelf vibrations in response to irregular incident waves by superposing time-harmonic responses, and ocean-to-ice-shelf transfer functions are derived. The findings add to evidence that ice shelves experience appreciable flexural vibrations in response to swell, and that ice shelf thickening and seabed shoaling can have a considerable influence on predictions of how ice shelves respond to ocean waves. [ABSTRACT FROM AUTHOR]

With the role of surface winds in the generation of ocean waves, secondary microseisms induced by ocean wave‐wave interactions represent a unique interconnection between the solid Earth, the ocean and global atmospheric circulation patterns. In this study, temporal changes in the ocean generated seismic wavefield in Northeast Atlantic are monitored offshore West of Ireland using ocean bottom seismometers located on top of a thick sedimentary basin. Comparisons with numerical seismic simulations and ocean wave model hindcast data suggest those variations are correlated with changing patterns in ocean wave‐wave interactions closely linked to secondary microseism generation areas. Here we show how those changes, accentuated by the specific structure of the Irish offshore margin, reveal the signature of the North Atlantic Oscillation (NAO) in the Earth's background seismic wavefield. In the North Atlantic, secondary microseism sources likely fluctuate with the changing storm track in response to variations in the NAO. Plain Language Summary: Ocean waves continuously generate seismic waves at the seafloor that are observed all over the world. In this study, we show how such vibrations recorded at the seafloor offshore West of Ireland are sensitive to long term weather and climate fluctuations in the Northeast Atlantic. Combining ocean wave and seismic simulation models with observations, we show that the North Atlantic Oscillation (NAO) climate index is hidden in the seismic records. Key Points: Fluctuating secondary microseism sources in the Northeast Atlantic highlight the variability of the NAO climate index through timeAmbient seismic noise recorded at key locations on the seafloor exhibits detailed sensitivity to global atmospheric circulation patternsTemporal changes in the modal excitation of secondary microseism Rayleigh waves reveal changing patterns in local ocean wave‐wave interactions [ABSTRACT FROM AUTHOR]

The sediment transport in the seabed boundary layer due to wave-induced streaming has been investigated for nonzero angle between the current and the waves. The mean sediment transport is a result of interaction between streaming due to wave skewness, the Longuet-Higgins streaming, and the wave-current interaction. For colinear waves, the mean sediment transport is directed along the wave propagation direction, with the largest transport taking place beneath the waves propagating in the direction of the current. Mean sediment transport decreases with increasing angle between the current and the waves. For a particular angle, the mean sediment transport beneath second-order Stokes waves is largest and decreases in the following order: linear propagating waves followed by horizontally uniform Stokes forcing and smallest for horizontally uniform linear forcing. The direction of the mean sediment transport is rotated toward the current away from the direction in which the wave propagates. The magnitude of rotation is smallest for second-order Stokes waves and increases in the following order; linear propagating waves followed by horizontally uniform Stokes forcing, and largest for horizontally uniform linear forcing. [ABSTRACT FROM AUTHOR]

The seabed resident event-driven profiling system (SREP) was deployed in the northeastern Arabian Sea for winter convention studies. SREP is an autonomous profiling system consisting of two parts: a stationary seabed unit and a positively buoyant tethered profiling unit (profiler). It offers a novel and optimized approach to profiling in coastal waters from close to seabed (14.63 m above seabed) to the sea surface. The seabed unit houses an underwater winch system, underwater acoustic modem, pressure sensor, low-power electronics, batteries and divinylcell hydraulic crush point foam for subsea applications. The profiler houses a suite of oceanographic sensors: conductivity-temperature-depth, DO, chlorophyll, PAR, underwater acoustic modem, low-power electronics, batteries and divinylcell hydraulic crush point foam for subsea applications. The underwater winch system on the seabed unit spools out and spools in the profiler throughout the water column. Data acquisition on the profiler is done during ascending. The profiler ascends gradually in the water column at an average velocity of 20 cm/s. The seabed unit and the profiling unit communicate using a pair of underwater acoustic modems operating at 18-34 kHz. SREP was developed to obtain time-series water column measurements of coastal waters during the summer monsoon season (June-September) when the sea wave and wind conditions are extreme, thus making it difficult to deploy profiling packages from the ship. A description of SREP and observations made during the field deployment are presented in this article. [ABSTRACT FROM AUTHOR]

The authors have investigated the possibility of using the background seismoacoustic noise generated Scholte-type surface waves on the ocean floor in order to study the structure of the geophysical medium using passive seismoacoustic tomography. The paper presents the results of reconstructing the deep structure of the Hawaiian Islands region by processing experimental data obtained by a network of broadband ocean bottom seismographs. The solution to the inverse problem consists of two stages. First, the dispersion relations of the phase and group velocities of surface waves are estimated by analyzing the cross-correlation function of the background noise between different pairs of bottom geophones. At the second stage, the problem of inverting the estimated dispersion curves into a vertically layered elastic model of the lithosphere is solved. Comparison of the inversion results with the known velocity models of the Hawaiian Islands region demonstrates the reliability of the estimates obtained with this approach. The results also indicate the possibility of reducing the time of data acquisition in a field experiment compared to methods that use earthquake signals, which involve sounding the studied area from different directions. [ABSTRACT FROM AUTHOR]

We analyze data retrieved from an ocean floor pressure sensor continuously operated for 48 days in the Mentawai Strait during the Spring of 2016, as part of Project Hazard SEES. Initial processing through systematic spectrogram analysis has identified ten distant earthquakes recorded through the variation of pressure accompanying the passage of seismic waves on the bottom of the ocean. The analysis of the corresponding wavetrains allows the recovery of the standard magnitude M s of seven of the events (two more being intermediate depth, and the tenth antipodal) with a residual not exceeding 0.3 logarithmic units. We also show that the classical energy-to-moment ratio computation can be successfully adapted by defining a response function of the pressure sensor to teleseismic P waves. In addition, six local earthquakes, occurring at distances of 58–670 km from the sensor, but with moment magnitudes less than 5.7, were also recorded. We show that an estimate of the seismic energy radiated by these events can be obtained from a simple integration of the square of the pressure signal. Thus our results indicate that meaningful quantitative estimates of the source characteristics of both teleseismic and regional events can be obtained through robust methods based on single-station pressure recordings on the ocean floor. [ABSTRACT FROM AUTHOR]

Freak wave is an extreme sea state with unexpected and huge wave height, which becomes a potential risk for lay barge and offshore pipeline during deepwater installation. In order to investigate the dynamic responses of deepwater S-lay pipeline induced by freak waves, this study developed a comprehensive numerical model with the particular consideration of the freak wave effect. An enhanced superposition method of combined transient wave trains and random wave trains was presented, and a series of freak wave trains were generated. The induced pipelay vessel motions were simulated by the use of displacement response amplitude operators (RAOs). The pipe-stinger roller interactions in the overbend and the cyclic contacts between the pipeline and seabed soil in the touchdown zone (TDZ) were fully taken into consideration. The developed S-lay model was subsequently utilized to calculate the dynamic responses of the pipelay vessel and offshore pipeline under random waves and freak waves for a comparison. The results illustrated the remarkable influence of freak waves on the systematic behaviors of deepwater S-laying pipeline, which offer a significant theoretical basis for the pipe structure design and pipelay operation safety. [ABSTRACT FROM AUTHOR]

The presence of a sill alters the traditional flat seabed conditions, imposing significant effects on hydrodynamic characteristics of the wave-body interaction problem. Eigenfunction matching method (EMM), which is a typical analytical method, is employed to precisely evaluate these effects on two-dimensional radiation of linear water waves by a rectangular buoy. The agreement with the published data and numerical results by the boundary element method (BEM) indicates the correctness of the present EMM. Four aspects involving varying height of the sill, varying width of the sill, varying water depth of the right semi-infinite subdomain, and varying relative positions between the buoy and the sill are considered. Analytical results show that among all the hydrodynamic coefficients, the added mass coefficient of heave is affected most by the varying sill. [ABSTRACT FROM AUTHOR]

A variational approach for solving the boundary value problem of computing ray trajectories and fronts of ocean waves is presented. The solution method is based on Fermat's principle (of stationary time). A distinctive feature of the proposed approach is that the Fermat functional is optimized directly without solving the Euler–Lagrange equation; moreover, the locations of the wave source and receiver are fixed. Multipath propagation in the boundary value problem is addressed by finding various types of stationary points of the Fermat functional. The technique is numerically tested by applying the method of bicharacteristics with the use of analytical seabed models. The advantages of the variational approach and the prospects of its further development as applied to ocean wave computation are described. The relations between various types of stationary points of the travel time functional, caustics, and foci are discussed. [ABSTRACT FROM AUTHOR]

Global plastic litter pollution has been increasing alongside demand since plastic products gained commercial popularity in the 1930's. Current plastic pollutant research has generally assumed that once plastics enter the ocean they are there to stay, retained permanently within the ocean currents, biota or sediment until eventual deposition on the sea floor or become washed up onto the beach. In contrast to this, we suggest it appears that some plastic particles could be leaving the sea and entering the atmosphere along with sea salt, bacteria, virus' and algae. This occurs via the process of bubble burst ejection and wave action, for example from strong wind or sea state turbulence. In this manuscript we review evidence from the existing literature which is relevant to this theory and follow this with a pilot study which analyses microplastics (MP) in sea spray. Here we show first evidence of MP particles, analysed by μRaman, in marine boundary layer air samples on the French Atlantic coast during both onshore (average of 2.9MP/m3) and offshore (average of 9.6MP/m3) winds. Notably, during sampling, the convergence of sea breeze meant our samples were dominated by sea spray, increasing our capacity to sample MPs if they were released from the sea. Our results indicate a potential for MPs to be released from the marine environment into the atmosphere by sea-spray giving a globally extrapolated figure of 136000 ton/yr blowing on shore. [ABSTRACT FROM AUTHOR]

Violante-Carvalho, N.; D'Avila, V.; Heringer Villena, H.H., and Mendonça Filippo, A.M., 2020. The Flying Anchor: An original technique for beach profile measurements in the surf zone. Journal of Coastal Research, 36(3), 654–660. Coconut Creek (Florida), ISSN 0749-0208. An original method is proposed to measure beach profiles in the surf zone. Surveying this dynamic and energetic region is usually a challenge when waves are large, which is exactly when the nearshore processes are more intense. The lack of bathymetry and wave data is indisputably a limiting factor hindering the understanding of the physics involved. Countless techniques have been proposed in the last decades to increase the temporal and spatial density of such measurements, with different degrees of success. Seeking to bring new approaches to address these issues, the proposed operation consists of launching a specially designed anchor from the beach face over the surf zone, carrying a graduated cable. When the cable is drawn taut, a pressure sensor is hand towed along the sea floor measuring the profile, as well as yielding the wave energy spectrum. The technique is efficient and fast and employs a small team at a very low cost. Some of the main limitations of the known in situ techniques, such as sea state dependency, high cost per profile, and longshore drift, are mitigated. [ABSTRACT FROM AUTHOR]

Double sandbar systems often characterize the surf zone of wave-dominated beaches and display a variety of poorly explained spatial configurations. Here, we explore the morphodynamic stability of double-barred beaches using a model based on linear stability analysis. Surf zone hydrodynamics are described by coupling depth and wave-averaged conservation of mass and momentum with the wave energy and phase equations, including roller dynamics. A simplified sediment transport formulation relates flow to seabed changes. Under normal wave incidence, an alongshore uniform coast with a cross-shore profile characterized by the presence of two sandbars can be unstable, thereby resulting in the development of crescentic and/or rip channel patterns. Our study demonstrates that sandbar coupling can be either in phase (highs and lows of both sandbars are at the same alongshore position) or out of phase (highs and lows of one sandbar correspond to lows and highs of the other sandbar). In line with observations, results of simulations show a large variability in the possible emerging bottom patterns. Our analysis indicates that modes of which the amplitude of the inner sandbar perturbation is larger than that of the outer sandbar are dominant for large height–depth differences between the two sandbar crests and small offshore wave heights. Patterns related to the outer sandbar dominate for small values of the difference in sandbar depth. For intermediate differences between the two sandbar depths, patterns on both longshore bars appear to be fully coupled (similar growth rates and strongly correlated pattern shapes). For relatively large waves and large depth over the outer sandbar, patterns can also develop close to the shoreline and/or inner surf zone together with patterns in the inner or outer sandbar. [ABSTRACT FROM AUTHOR]

Atkin, E.A.; Mead, S.T., and Phillips, D., 2019. Investigations of offshore wave preconditioning. In: Bryan, K.R. and Atkin, E.A. (eds.), Surf Break Management in Aotearoa New Zealand. Journal of Coastal Research, Special Issue No. 87, pp. 78–90. Coconut Creek (Florida), ISSN 0749-0208. The way in which a wave breaks is largely a function of the path wave orthogonals and the bathymetry that wave orbitals encounter as the wave propagates shoreward. This effect is commonly referred to in surf science literature as preconditioning and occurs at a range of scales. This work considers seabed features that do not cause wave breaking but influence the way in which they break. An assessment first quantifies the dimensions of a number of known wave preconditioning features, and then involves iterative numerical model simulations of heuristic seabed features. The impact of an offshore feature is descried in terms of the wave propagation in the lee of the feature and breaking patterns, or surf zone plan-shape, near the shoreline. It is proposed that offshore features be considered as either disruptive or focus preconditioners. The former results in complex and chaotic interference patterns resulting in multiple peaks at the shoreline, with the latter creating a more singular or defined peak with less widespread disruption. A key component for surfing wave quality to be influenced by offshore preconditioning is the establishment of longshore wave height gradients, which are often associated with the bifurcation, or "snapping" of wave crests. The degree to which a feature sets up longshore wave height gradients and bifurcates wave crests is shown to be influenced by the size of the preconditioning feature relative to the incident wave conditions. [ABSTRACT FROM AUTHOR]

Atkin, E.A.; Mead, S.T., and Phillips, D., 2019. Investigations of offshore wave preconditioning. In: Bryan, K.R. and Atkin, E.A. (eds.), Surf Break Management in Aotearoa New Zealand. Journal of Coastal Research, Special Issue No. 87, pp. 78–90. Coconut Creek (Florida), ISSN 0749-0208. The way in which a wave breaks is largely a function of the path wave orthogonals and the bathymetry that wave orbitals encounter as the wave propagates shoreward. This effect is commonly referred to in surf science literature as preconditioning and occurs at a range of scales. This work considers seabed features that do not cause wave breaking but influence the way in which they break. An assessment first quantifies the dimensions of a number of known wave preconditioning features, and then involves iterative numerical model simulations of heuristic seabed features. The impact of an offshore feature is descried in terms of the wave propagation in the lee of the feature and breaking patterns, or surf zone plan-shape, near the shoreline. It is proposed that offshore features be considered as either disruptive or focus preconditioners. The former results in complex and chaotic interference patterns resulting in multiple peaks at the shoreline, with the latter creating a more singular or defined peak with less widespread disruption. A key component for surfing wave quality to be influenced by offshore preconditioning is the establishment of longshore wave height gradients, which are often associated with the bifurcation, or "snapping" of wave crests. The degree to which a feature sets up longshore wave height gradients and bifurcates wave crests is shown to be influenced by the size of the preconditioning feature relative to the incident wave conditions. [ABSTRACT FROM AUTHOR]

In this paper, a 2D poro-elastoplastic model for wave-induced dynamic response in an anisotropic seabed is derived analytically. The seabed is treated as a porous medium and characterized by Biot's consolidation equations. The soil plasticity and wave non-linearity are included in the model and both the pore fluid and the soil skeleton are assumed to be compressible. The nonlinear ocean waves are respectively considered as progressive and standing waves. The previous experimental data is used to validate the proposed model. Numerical results demonstrate that the influence of nonlinear wave components should not be ignored without committing substantial error. A significant difference between progressive and standing waves is also observed for the development of residual pore pressure, as well as the distribution of liquefied zone. A detailed parametric investigation reveals that the nonlinear wave-induced seabed response is also affected significantly by cross-anisotropic soil parameters. [ABSTRACT FROM AUTHOR]

This study focuses on the buckling of pipelines in shallow waters subjected to surface gravity waves. The wave-induced uplift forces on pipelines buried in sandy seabeds are investigated using Biot's consolidation model. Empathetic imperfection model proposed by Taylor and Tran (1994, "Experimental and Theoretical Studies in Subsea Pipeline Buckling," Mar. Struct., 9(2), pp. 211-257.) is used for the study. Thereafter, buckling analyses are performed on the pipeline with the combined temperature and the wave-induced loads. The differences in the critical buckling temperatures for the pipe with consideration of wave loads are analyzed within a range of sea states. The influence of wave loads is found significant for low burial depth ratios. [ABSTRACT FROM AUTHOR]

The responses of a monopile offshore wind turbine subjected to irregular wave loads are investigated numerically and experimentally, considering a range of sea states. An extensive experimental campaign was carried out on a fully flexible model, representative of a 5 MW offshore wind turbine, at 1:40 scale. An assessment of the experimental results for the response amplitude operator for regular waves and the 90th percentile seabed bending moment in long-crested irregular waves is carried out using two models (analytical and numerical) for uncertainty propagation, suggesting that bias errors in the model properties and in the wave elevation contribute the most to the total uncertainty. The experimental results are also compared to a numerical model using beam elements and Morison-type wave loads with second order wave kinematics. The numerical model does not capture all of the responses within the level of uncertainty of the experiments, and possible reasons for the discrepancies are discussed. [ABSTRACT FROM AUTHOR]

Seismic reflections at the interface of heterogeneous porous media are significantly affected by the multi-scale fluid-flow losses. In this work, we study the seismic reflection dispersion from the ocean bottom separating seawater and heterogeneous porous seabed, described by the effective Biot theory where the mesoscopic loss is present. The analytical reflection coefficient is obtained based on the displacement potentials and suitable boundary conditions. Two reflection scenarios, including the water/water-bearing medium contact and water/gas-saturated medium interface, are considered. The shear-wave attenuation is also considered by using a Cole-Cole complex shear modulus. Numerical results showing the variation in reflection magnitude versus frequency and incidence angle are presented, revealing that the P-wave mesoscopic attenuation, complex shear modulus, boundary conditions and permeability can significantly affect the frequency and angle dependence of the reflection coefficients. Reflections at the water/gas-saturated medium interface exhibit quite different behaviors from those at the water/water-bearing medium contact. The open-pore interface gives frequency-dependent reflections, whereas in sealed-pore case, the reflection magnitudes remain unchanged for all frequencies, due to the fact that the interface degrades into a water/elastic solid one. The study can be relevant for reservoir prediction and fluid identification based on the reflected marine data. • Seismic reflection dispersion at the ocean bottom in the presence of mesoscopic loss is analyzed. • Impact of saturated fluid in porous seabed is investigated. • Effects of mesoscopic loss, complex shear modulus and interface conditions are discussed. [ABSTRACT FROM AUTHOR]

A model is proposed to determine the sediment transport rate generated by the combined action of sea waves and tidal currents, the latter being modelled as a sequence of steady currents because of the large values of the Keulegan-Carpenter number of the tidal flows, which allow to neglect inertial effects in their modelling. The hydrodynamic module solves Reynolds-averaged momentum equations by introducing a two-equation turbulence model, which considers also the flow in the region closest to the sea bottom and enforces the no-slip condition and the vanishing of the turbulent kinetic energy at the bottom without the need to assume the existence of a logarithmic velocity profile and to fix the normal derivative of the turbulent kinetic energy close to the sea bed. Hence, the evaluation of the velocity profile in the near-bed region turns out to be accurate. The sediment transport module determines the sediment concentration and sediment transport for a mixture of non-cohesive and cohesive sediments. To validate the model, its predictions are compared with laboratory measurements and field data collected over rippled beds at two different tidal estuaries. Then, results are obtained for values of the parameters chosen to mimic a site close to Punta Umbría (Huelva, Spain) and considering different hydrodynamic conditions and different sediment mixtures. The influence of the waves on the suspended sediment concentration is lower for the cohesive fraction than for the non-cohesive fraction. For all the sediment mixtures, it turns out that the cohesive fraction is well mixed over the whole water depth, meanwhile the concentration of the non-cohesive fraction has significant values only near the bottom, thus showing that an accurate description of turbulence dynamics in the buffer layer and viscous sublayer (if it exists) is important to quantify the sediment transport rate. • Sediment transport module that reproduces the concentration of cohesive fraction is presented. • Tidal current is modelled as a sequence of steady-currents due to the large values of the Keulegan-Carpenter number. • Menter's turbulence model to predict the turbulence structure both in the wave bottom boundary layer and in the core region. • Turbulence dynamics description in the buffer layer and viscous sublayer is important to quantify the sediment transport. • Applicable to any type of sediment mixture. [ABSTRACT FROM AUTHOR]

Using a recently developed asymptotic theory of internal solitary wave propagation over a sloping bottom in a rotating ocean, some new qualitative and quantitative features of this process are analyzed for internal waves in a two-layer ocean. The interplay between different singularities--terminal damping due to radiation and disappearing quadratic nonlinearity, and reaching an "internal beach" (e.g., zero lower-layer depth)--is discussed. Examples of the adiabatic evolution of a single solitary wave over a uniformly sloping bottom under realistic conditions are considered in more detail and compared with numerical solutions of the variable- coefficient, rotation-modified Korteweg-de Vries (rKdV) equation. [ABSTRACT FROM AUTHOR]

A hydro-elastic frame has been considered to investigate the proliferation of waves over small base deformation on an infinitely extended flexible seabed. The flexible base surface is assumed as a thin elastic plate of very small thickness and it depends on the Euler–Bernoulli beam equation. For any particular frequency, there are two different modes of time-harmonic propagating wave exists rather than one mode of propagating wave along the positive horizontal direction. The waves with smaller wavenumber spread along the free-surface of the sea (say, free-surface mode) and the waves with higher wavenumber spread along the flexible base surface (say, flexural mode). A simplified perturbation approach is utilised to bring down the entire equations which govern the original boundary value problem (bvp) to a less complex bvp for the first-order velocity potential function. The first-order potential function along with the first-order reflection and transmission coefficients for both modes are calculated by a procedure based upon Fourier transform approach. A shape of sinusoidal swells flexible base surface is taken as an example to approve the scientific results. It is observed that when the train of normal incident propagating wave spreads over base distortion because of either the free-surface unsettling influence or the flexural wave movement in the sea, the reflected and transmitted energy are always feasible to be exchanged from one particular wave mode to another wave mode. Furthermore, we notice that the realistic changes in the flexural rigidity behaviour on the flexible base surface of the sea have a significant effect on the problem of water wave proliferation over small base deformation. Moreover, the energy conservation equation is derived with the help of the Green's integral theorem. The results for the values of reflection and transmission coefficients obtained for both the free-surface unsettling influence as well as flexural wave movement in the fluid are found to satisfy the energy conservation equation almost accurately. [ABSTRACT FROM AUTHOR]

Abstract The seabed is sloped in shallow coastal regions, where strong nonlinear shoaling waves can generate sheet-flow sediment transport. Both wave nonlinearity and bottom slope can lead to a wave-averaged (net) sediment transport rate, but the bottom slope effect is often overlooked in existing sediment transport models. A full-scale experimental study of sheet-flow sediment transport under the oscillatory flows with nonlinear features (skewness or asymmetry) was conducted in an inclinable oscillatory water tunnel, so the bottom-slope-induced net transport rate in the context of nonlinear waves was experimentally investigated. The tests cover a variety of nonlinear wave shape, bottom slope (0 to 2. 5 ∘ ) and two sediment diameters (0.24 and 0.51 mm). Since the downslope direction is the "offshore" direction in our tests, it is found that bottom slope reduces the net "onshore" transport rate due to wave nonlinearity. The slope contribution to the net transport rate is evaluated by taking the difference between the measured net transport rate from a sloping-bed experiment and the measured net transport rate from the corresponding horizontal-bed experiment. The results suggest that slope-induced net transport rate is insensitive to wave nonlinearity, and its variation with bottom slope can be considered linear in the context of predicting net transport rate. Comparisons between this study and a preceding sinusoidal-flow study of Yuan et al. (2017b) suggest that nonlinear waves can be approximated as sinusoidal flows for estimating the slope contribution to the net transport rate. Subsequently, an empirical model for predicting net sheet-flow transport rate due to bottom slope is established based on dimensional analysis. This model can be simply added to existing sheet-flow sediment transport models to improve their applicability in coastal regions. Highlights • Presented experiments on the sheet-flow sediment transport under skewed and asymmetric oscillatory flows above a sloping bed. • Test results show that the slope-induced net transport rate is insensitive to nonlinear wave shape. • Proposed an empirical model for slope's contribution in net sheet-flow sediment transport rate. [ABSTRACT FROM AUTHOR]