Large Wave Research Articles

A Maximisation Technique for Solitary Waves: The Case of the Nonlocally Dispersive Whitham Equation

Recently, two different proofs for large and intermediate-size solitary waves of the nonlocally dispersive Whitham equation have been presented, using either global bifurcation theory or the limit of waves of large period. We give here a different approach by maximising directly the dispersive part of the energy functional, while keeping the remaining nonlinear terms fixed with an Orlicz-space constraint. This method is, to the best of our knowledge new in the setting of water waves. The constructed solutions are bell-shaped in the sense that they are even, one-sided monotone, and attain their maximum at the origin. The method initially considers weaker solutions than in earlier works, and is not limited to small waves: a family of solutions is obtained, along which the dispersive energy is continuous and increasing. In general, our construction admits more than one solution for each energy level, and waves with the same energy level may have different heights. Although a transformation in the construction hinders us from concluding the family with an extreme wave, we give a quantitative proof that the set reaches ‘large’ or ‘intermediate-sized’ waves.

An improved and extended parameterization of the CO2 15 µm cooling in the middle and upper atmosphere (CO2_cool_fort-1.0)

Abstract. The radiative infrared cooling of CO2 in the middle atmosphere, where it emits under non-local thermodynamic equilibrium (non-LTE) conditions, is a crucial contribution to the energy balance of this region and hence to establishing its thermal structure. The non-LTE computation is too CPU time-consuming to be fully incorporated into climate models, and hence it is parameterized. The most used parameterization of the CO2 15 µm cooling for Earth's middle and upper atmosphere was developed by Fomichev et al. (1998). The valid range of this parameterization with respect to CO2 volume mixing ratios (VMRs) is, however, exceeded by the CO2 of several scenarios considered in the Coupled Climate Model Intercomparison Projects, in particular the abrupt-4×CO2 experiment. Therefore, an extension, as well as an update, of that parameterization is both needed and timely. In this work, we present an update of that parameterization that now covers CO2 volume mixing ratios in the lower atmosphere from ∼0.5 to over 10 times the CO2 pre-industrial value of 284 ppmv (i.e. 150 to 3000 ppmv). Furthermore, it is improved by using a more contemporary CO2 line list and the collisional rates that affect the CO2 cooling rates. Overall, its accuracy is improved when tested for the reference temperature profiles as well as for measured temperature fields covering all expected conditions (latitude and season) of the middle atmosphere. The errors obtained for the reference temperature profiles are below 0.5 K d−1 for the present-day and lower CO2 VMRs. Those errors increase to ∼1–2K d−1 at altitudes between 110 and 120 km for CO2 concentrations of 2 to 3 times the pre-industrial values. For very high CO2 concentrations (4 to 10 times the pre-industrial abundances), those errors are below ∼1 K d−1 for most regions and conditions, except at 107–135 km, where the parameterization overestimates them by ∼1.2 %. These errors are comparable to the deviation of the non-LTE cooling rates with respect to LTE at about 70 km and below, but they are negligible (several times smaller) above that altitude. When applied to a large dataset of global (pole to pole and four seasons) temperature profiles measured by MIPAS (Michelson Interferometer for Passive Atmospheric Spectroscopy) (middle- and upper-atmosphere mode), the errors of the parameterization for the mean cooling rate (bias) are generally below 0.5 K d−1, except between 5×10-3 and 3×10-4 hPa (∼85–98 km), where they can reach biases of 1–2 K d−1. For single-temperature profiles, the cooling rate error (estimated by the root mean square – rms – of a statistically significant sample) is about 1–2 K d−1 below 5×10-3 hPa (∼85 km) and above 2×10-4 hPa (∼102 km). In the intermediate region, however, it is between 2 and 7 K d−1. For elevated stratopause events, the parameterization underestimates the mean cooling rates by 3–7 K d−1 (∼10 %) at altitudes of 85–95 km and the individual cooling rates show a significant rms (5–15 K d−1). Further, we have also tested the parameterization for the temperature obtained by a high-resolution version of the Whole Atmosphere Community Climate Model (WACCM-X), which shows a large temperature variability and wave structure in the middle atmosphere. In this case, the mean (bias) error of the parameterization is very small, smaller than 0.5 K d−1 for most atmospheric layers, reaching only maximum values of 2 K d−1 near 5×10-4 hPa (∼ 96 km). The rms has values of 1–2 K d−1 (∼20 %) below ∼2×10-2 hPa (∼80 km) and values smaller than 4 K d−1 (∼2 %) above 10−4 hPa (∼105 km). In the intermediate region between ∼5×10-3 and ∼2×10-4 hPa (85–102 km), the rms is in the range of 5–12 K d−1. While these values are significant in percentage at ∼5×10-3–5×10-4 hPa, they are very small above ∼5×10-4 hPa (96 km). The routine is very fast, taking (1.5–7.5) ×10-5 s, depending on the extension of the atmospheric profile, the processor and the Fortran compiler.

Decomposition of the mechanical stress tensor: from the compressible Navier–Stokes equation to a turbulent potential flow model

We frame the mechanical stress tensor decomposition in a general procedure which involves the Helmholtz–Hodge decomposition. We highlight the impact of the mechanical stress tensor decomposition on the Navier–Stokes equation, with emphasis on the dissipation function. For fluids with low compressibility, we draw some insights on the Reynolds Averaged Navier–Stokes equations, and on the Reynolds stress tensor decomposition. We derive a turbulent potential flow model, and investigate the transition from viscous potential flow to turbulent potential flow. Under low Mach number approximation, we apply the turbulent potential flow model to one-dimensional propagation of large amplitude pressure waves in liquid-filled pipe.

Modeling of low Mach number unsteady turbulent pipe flows

AbstractUnder adiabatic conditions, and neglecting temperature variations due to entropy production, we present a set of Reynolds Averaged Navier–Stokes (RANS) equations for fluids of low compressibility, i.e., fluids in the liquid state. In the low Mach number limit, we specialize the RANS equations to the one-dimensional unsteady pipe flow, and we deduce the dimensionless number that plays a predominant role in the flow behavior. We reduce the system of equations to a linear damped wave equation, and use its analytical solution to investigate the propagation of large amplitude pressure waves in liquid-filled pipes (water hammer phenomenon). We test the model reliability by comparing the analytical solution of the proposed model against experimental data available in the literature.

The morphology and formation of a binary sand ridge in the Beibu Gulf, northwestern South China Sea

The overall morphological characteristics and shallow architecture of a tidal sand ridge were examined for the first time in the Beibu Gulf, northwestern South China Sea. The linear sand ridge is characterized by a unique binary feature in terms of its shape, constituents, architecture, and behavior. In the northern part, the crestline has rotated anticlockwise to the principal tidal currents, the sediment is coarse, and large active sand waves occur on the surface. In the southern part, the crestline is parallel to the principal tidal currents, the sediment is fine, and no large bedforms have developed on the crest. The sand ridge has shrunk in the northern part and elongated at its southern end in recent decades, leading to a southward or southeasterly movement. The upper strata of the northern part mainly comprise inclined bedding, whereas parallel bedding prevails in the southern part. The bedding implies historically dominant transport directions in different sand ridge parts and suggests that flow modification occurred during ridge evolution. The inclined bedding in the lower strata of the northern part dips to the south or southeast, indicating the existence of unidirectionally moving sand waves. This is unusual for a growing sand ridge where convergent sand transport should have already occurred. The present sand ridge is interpreted as a source from the joining of a sand wave assemblage and an adjoining nascent sand ridge, which has experienced stages of connection, accretion, and migration. The transformation of a sand wave assemblage to the northern part is attributed to the hydraulic change from a unidirectional residual flow regime over sand waves to a bidirectional residual flow regime. This flow regime change was not related to sea level changes but benefited from a new sand body that was produced by sand waves merging into the original nascent ridge.

Properties of X-ray diffraction and Raman scattering in PbSe, PbS and PbS0,5Se0,5 thin films

Structural properties of PbSe, PbS and PbS0.5Se0.5 thin films and mechanisms of combinational scattering of light from phonons were studied by X-ray diffraction and Raman spectroscopy methods. The results of X-ray diffraction show that the crystallite sizes found in the thin layers of the studied substances are in the order of nanometers and vary in the interval d~10.7 ÷ 30.8 nm. It was determined that the scattering bands of the PbSe0.5S0.5 sample with large nanoparticle sizes shift to the region of large wave numbers compared to the scattering bands observed in the region of low wave numbers.

Considerations for designing a new wave generator system in an existing flume

Van Halteren Technologies Boxtel B.V. (formerly known as Bosch Rexroth B.V.) has designed, manufactured, installed, and commissioned the new electrical driven wave generator system in the existing Large Wave Flume (GWK) at FZK in Hannover. The aim of the replacement was designing a new wave generator system, with optimized performance in the given space in the existing flume, and replace the hydraulics for an electrically driven system. The width and depth of the flume are five and seven meters respectively. The water depth is variable up to five meters. In order to get the most out of the finite length of the flume the space for the wave maker is limited. Given the limited space for the wave maker we had to apply a dry back wave generator system which has the advantage of a rather compact design compared to a wet back wave generator. This also introduced challenges such as a seal system around the moving wave segment at the side walls and floor as well as a compensator for compensating the static force of the variable water depth. The hydrodynamic forces are provided by the electrically driven system. The wave generator has been provided with an Active Reflection Compensation system (ARC) for compensating the reflected waves traveling to the wave segment. This ARC must be capable to handle variable water depths, even when the water depth is changed in order to simulate high and low water conditions.

Experimental And Numerical Inter-Comparison On Green And Gray Mitigation Alternatives In Flooding Reduction In Coastal Region

Coastal communities in low-lying regions are increasingly vulnerable to severe flooding triggered by high surges and large waves. The sea level rise resulting from climate change induces shorelines to encroach onto coastal land, further exacerbating the flooding damage in coastal areas. Thus, it is necessary to implement coastal structures to mitigate the influence of extreme flooding events on coastal communities. Seawalls, submerged breakwaters, and mangrove forests have been widely constructed worldwide to attenuate wave overflows and their impact on near-coast regions. However, studies on the comprehensive inter-comparison of the protective performance of each measure against flooding events to provide guidelines in coastal design and planning have yet to be limited. Therefore, experimental and numerical models were conducted to investigate the efficiency of natural (mangrove forests) and man-made (seawall and submerged breakwater) coastal structures in reducing the forces, pressures, and hydrodynamics generated by overflows in constructed environments.

Wave Impacts On Cliffs: From The Field To The Laboratory

Rock coasts occupy over 50% of the global shoreline and many sandy beaches are underlain by coastal platforms and rocky cliffs. The problem of wave-driven cliff erosion is of great societal importance, with many coastal communities located on top of cliffs that are at risk from erosion. Continuing global mean sea level rise and changes in storminess are generally expected to exacerbate the erosion of coastlines (Hurst et al., 2016), as larger waves can reach the cliff toe without breaking offshore. However, the science underpinning wave-induced cliff erosion is still at a relatively early stage. Even the relative contributions of waves to cliff erosion, which include hydraulic forces, impulse pressures and abrasion, are not well resolved. Most insights into wave impacts on cliffs come from field observations of coastal ground motion during storm events (e.g. Young et al., 2011, Huppert et al., 2020). These field investigations demonstrate the dependence of large wave impacts on both water levels and wave conditions, and in some cases the correlation of periods of large ground motion with increased erosion (Earlie et al., 2015). Unsurprisingly, although large impacts generally occur at high tide during storms characterised by large significant wave heights, the largest impacts occur when tidal levels and storm surge combine to provide water levels that are conducive to the incident waves breaking on the cliffs (Thompson et al., 2019; 2022). Larger wave heights or shallower water levels tend to lead to breaking further offshore, with a broken wave interacting with the cliff, while smaller wave heights or deeper water levels may preclude strong wave breaking on the cliffs. There have been relatively few experimental studies into wave-driven cliff erosion; these were generally undertaken under very idealised wave conditions (e.g. Sunamura, 1977) and using materials that were either too soft to approximate natural rocks (e.g. Sunamura, 1977; 1982) or too hard to be eroded (Hansom et al., 2008). Although these experiments have informed the development of rocky coast evolution models, their results have not been replicated or verified, and rigorous scaling laws to link laboratory erosion rates to field time scales are currently lacking. However, considering cliffs as steep or vertical (natural) coastal structures, a large body of experimental work has been undertaken to investigate impact pressures and their implications for the failure of engineered structures (e.g. Peregrine, 2003, Bullock et al., 2007). These investigations are complicated by the inherent variability of the wave impact pressures, even within controlled experiments undertaken with highly repeatable incident wave conditions (Raby et al., 2022). Although field and laboratory data are valuable, it is still very challenging to quantify wave contributions to cliff erosion due to the relatively short durations and variable conditions of most field records. On the other hand, most controlled laboratory investigations have typically focused on loads on non-erodible engineered structures such as seawalls. The current project seeks to advance understanding of the fundamental mechanisms and timescales of wave-driven erosion on rocky cliffs, which will be vital in improving assessments of cliff erosion hazard in high-energy wave environments as sea levels rise.

Practical Guide to Large Amplitude Fourier-Transformed Alternating Current Voltammetry-What, How, and Why.

Fourier-transformed alternating current voltammetry (FTacV) is a technique utilizing a combination of a periodic (frequently sinusoidal) oscillation superimposed onto a staircase or linear potential ramp. The advanced utilization of a large amplitude sine wave induces substantial nonlinear current responses. Subsequent filter processing (via Fourier-transformation, band selection, followed by inverse Fourier-transformation) generates a series of harmonics in which rapid electron transfer processes may be separated from non-Faradaic and competing electron transfer processes with slower kinetics. Thus, FTacV enables the isolation of current associated with redox processes under experimental conditions that would not generate meaningful data using direct current voltammetry (dcV). In this study, the enhanced experimental sensitivity and selectivity of FTacV versus dcV are illustrated in measurements that (i) separate the Faradaic current from background current contributions, (ii) use a low (5 μM) concentration of analyte (exemplified with ferrocene), and (iii) enable discrimination of the reversible [Ru(NH3)6]3+/2+ electron-transfer process from the irreversible reduction of oxygen under a standard atmosphere, negating the requirement for inert gas conditions. The simple, homebuilt check-cell described ensures that modern instruments can be checked for their ability to perform valid FTacV experiments. Detailed analysis methods and open-source data sets that accompany this work are intended to facilitate other researchers in the integration of FTacV into their everyday electrochemical methodological toolkit.

LOW-CRESTED AND EMERGENT BREAKWATERS WITH ECO-FRIENDLY ARMOUR UNITS

Artificial coastal defense systems (such as concrete armour units) frequently host less diverse aquatic populations than natural environments and feature higher concentrations of invasive species (Dafforn et al., 2009). Therefore, coastal structures need to be designed or refitted to achieve sustainable goals through the application of ecological engineering solutions applied to coastal defence structures and for the ecosystem, marine habitat, and biodiversity improvement. Ecological engineering, which integrates ecosystems with engineering principles to construct coastal structures that benefit both humans and the ecosystem, is growing as a means of reducing the adverse ecological impacts of coastal infrastructure (Mitsch & Jorgensen, 2003). Thus, creating new eco-friendly breakwater design guidelines is critical and will benefit from the multidisciplinary involvement of marine biologists and ecologists. The purpose of this experimental modelling study was to provide data on the hydraulic performance and stability of low-crested and emergent rubble mound breakwaters (RMBW) constructed using ecologically friendly armour units under various wave conditions. The University of Ottawa, the National Research Council of Canada (NRC), and ECOncrete collaborated to develop and conduct the physical testing program. Several breakwater models were tested to evaluate their performance, as the idea of an eco-friendly breakwater is still a new area of research. Thus, this experimental program is essential to promote environmentally-friendly armour units in the design of new coastal structures (such as Baker et al., 2018), as well as ecological retrofitting of existing coastal structures. The physical tests were conducted between June 2023 and August 2023 in the Large Wave Flume of NRC’s Ocean, Coastal, and River Engineering Research Center in Ottawa, Canada. ECOncrete's Coastalock armour units were tested in various configurations at a 1/15 scale using two-dimensional low-crested and emergent RMBW models. The hydraulic performance and failure mechanisms of these environmentally-friendly breakwater models were tested under severe wave conditions.

Tsunami Ping-Pong: Generating The Whole Tsunami Event

Considerable progress has been made over the past two decades in modelling representative tsunami waves in the laboratory. Developments such as the pneumatic tsunami simulator, TS, (Chandler et al, 2021), large wave paddles (Schimmels et al, 2016) and pump driven systems (Goseberg et al, 2013) have allowed full incident tsunami time series to be reproduced at large enough scales to provide reliable physical modelling data. These developments have enabled new insights into the time-varying influence of tsunami waves on run-up (McGovern et al, 2018), buildings (Foster et al, 2017), coastal structures (McGovern et al, 2022) and in particular the scour of sediments around these structures (McGovern et al, 2019). These advances are changing the way engineers and others design and plan for tsunami. However we are still only modelling ‘half the story’. In all existing published studies, the experiments simulated the effect of a single incident wave. We have so far ignored two significant elements of real tsunami events. Firstly, the rundown or return flow and secondly, the effect of multiple waves within a wave train. Both these aspects are difficult to model physically, particularly as the return flow and subsequent waves require a representative topography downstream of a test section. In most facilities there is not enough flume left to create this overland topography. In addition, changing this bathymetry to represent different scenarios such as a coastal plain or a small foreshore and an inland cliff, requires significant modelling effort and cost. To solve these challenges we propose the use of two TSs facing each other with the test section in between. This concept is shown in Figure 1. This extended abstract presents data from initial trials of the dual TS system conducted at HR Wallingford in 2023 during a three-day test window as part of the MAKEWAVES collaboration. The importance of simulating the return flow from a tsunami is demonstrated through its influence on scour around a rectangular building.

Physical Modelling Of The Wave Field Around An Array Of Centrally Controlled Wave Energy Converters

Stepped revetments have shown to be effective in limiting wave overtopping and wave run-up compared to sloped revetments. However, literature on wave impact pressures and comprehensive design guidelines for these structures is scarce. Laboratory experiments support establishing design recommendations. So far, studies for wave impacts at stepped revetments were mainly performed at small scales. Results from these tests are likely to be subjected to scale effects and therefore inaccurately replicate the wave-structure interaction at full scale. This study quantifies scale effects of wave impact characteristics for design cases based on a comparison to small-scale tests (Kerpen et al., 2018). Full-scale flume experiments were studied with a slope of 1:3 and uniform step heights of 0.17 m and 0.50 m in the Large Wave Flume (GWK) in Hannover, Germany. Horizontal and vertical wave impacts were measured at 15 locations in the plunging region of the revetment for a range of wave steepnesses (). The results show that previous small-scale tests underestimate design wave impact pressures by a factor of up to 7.7. Impact loadings occur considerably faster than at small scale with relative peak rising times decreasing by a factor of up to 5.6. Prediction formulae are derived for the vertical distribution of horizontal impact pressures (Figure 1b) as well as for temporal characteristics of these pressures at stepped revetments.

Performance Assessment Of Two Active Absorption Systems In A Large Wave Flume

The quality of most coastal or ocean laboratory experiment depends on the accuracy, uniformity and stability of the generated waves. Generation of waves in the laboratory seems simple, but it should consider the spatio-temporal variability of the wave profile. As they propagate, waves interact with the boundaries, i.e. changes in water depth, lateral walls, test specimens, instrument supporting structures, passive absorbers, etc., as well as with varying hydrodynamic conditions (wave-induced currents, wave-wave interactions, or nonlinear energy transfer, among others). Reflected, scattered and radiated waves may propagate back to the wave generator and reflect back. Re-reflections from the wave generator may be a non-realistic representation of the intended wave field, to the extent that the total energy content in the testing facility may increase significantly and uncontrollably. Theoretically, for weakly nonlinear unidirectional waves propagating over a relatively small number of wavelengths, and as long as the still water depth and facility width does not change, the wave properties should remain constant in space and time, which can be identified as the uniformity and stability of the waves. Under these conditions, nonuniform or unsteady wave properties can be associated to an inadequate selection of the wave theory (Airy, Stokes n-order, Cnoidal, Stream Function, etc., e.g. Fenton 1999), the approximation of the wave generation technique (first or second order, nonlinear - see e.g. Mohtat et al., 2020), formation of wave instabilities (e.g. Benjamin-Feir, 1967), wave reflection, scattering or radiation, and the performance of the active wave absorption system. It can be said that the performance of the active wave absorption control system is one of the responsible factors that can affect directly the quality of the generated waves. Many laboratories have implemented different passive and active wave absorption systems, but the performance on the uniformity and stability of the generated waves, as well as the performance of the active wave absorption system used, have not been assessed in a systematic way, and related published data and information is quite scarce, with few interesting exceptions, e.g. (Lykke-Andersen, 2016; Spinneken 2010; Schäffer and Skourup 1996). However, a direct comparison among the different available active wave absorption control systems is still missing. This paper presents a thorough experimental study on the performance assessment of two different active wave absorption control systems (MTS and Awasys7) as a means to establish the quality of the experiment in terms of the uniformity (space) and stability (time) of generated wave parameters (descriptors) in the laboratory.

Optimizing Infragravity Wave Attenuation to Improve Coral Reef Restoration Design for Coastal Defense

Coral reefs are effective natural flood barriers that protect adjacent coastal communities. As the need to adapt to rising sea levels, storms, and environmental changes increases, reef restoration may be one of the best tools available to mitigate coastal flooding along tropical coastlines, now and in the future. Reefs act as a barrier to incoming short-wave energy but can amplify low-frequency infragravity waves that, in turn, drive coastal flooding along low-lying tropical coastlines. Here, we investigate whether the spacing of reef restoration elements can be optimized to maximize infragravity wave energy dissipation while minimizing the number of elements—a key factor in the cost of a restoration project. With this goal, we model the hydrodynamics of infragravity wave dissipation over a coral restoration or artificial reef, represented by a canopy of idealized hemispherical roughness elements, using a three-dimensional Navier–Stokes equations solver (OpenFOAM). The results demonstrate that denser canopies of restoration elements produce greater wave dissipation under larger waves with longer periods. Wave dissipation is also frequency-dependent: dense canopies remove wave energy at the predominant wave frequency, whereas sparse canopies remove energy at higher frequencies, and hence are less efficient. We also identify an inflection point in the canopy density–energy dissipation curve that balances optimal energy losses with a minimum number of canopy elements. Through this work, we show that there are an ideal number of restoration elements per across-shore meter of coral reef flat that can be installed to dissipate infragravity wave energy for given incident heights and periods. These results have implications for designing coral reef restoration projects on reef flats that are effective both from a coastal defense and costing standpoint.

Role of spontaneous thermal emissions in inflationary laser Raman instability

The role of thermal fluctuations on the stimulated Raman backscattering instability is investigated by means of Vlasov and particle-in-cell (PIC) simulations in a regime of strong linear Landau damping of the Langmuir wave. The instability is initially convective and amplifies thermal noise, leading to a low-amplitude back-scattered laser sideband. Linear Landau damping of the Langmuir sideband modifies and flattens the electron velocity distribution function at the resonant velocity, leading to a gradual decrease in the Landau damping rate and an increase in the convective amplification. The Langmuir wave traps electrons resulting in a rapid nonlinear absolute instability and large amplitude flashes of backscattered light off large amplitude Langmuir waves with trapped electrons, leading to the production of hot electrons. Conditions for simulating realistic thermal noise with Vlasov and PIC simulations are discussed and defined.

Possible Mechanisms for Tsunami‐Like Surge Deposits Due To the Chicxulub Impact at the K‐Pg Boundary at the Tanis Site, North Dakota

AbstractAt Tanis, a unique bi‐directional sediment package occurs precisely at the Cretaceous‐Paleogene (K‐Pg) boundary, recording the first hours of the Paleogene in uncommonly fine temporal detail. The impact ejecta‐bearing sediment package was rapidly emplaced by two massive, ∼10‐m‐high, potentially impact‐triggered surges, that inundated a steep, deeply incised paleo river valley from the direction of the contemporaneous Western Interior Seaway (WIS). Intermingling of fresh‐ and salt‐water fossils at Tanis, coeval brackish water indicators in the nearby region, and historical tsunami observations, suggest that the WIS paleoshoreline was nearby Tanis at K‐Pg time. The interpreted timing for deposition (including ejecta infall) of ∼1–2‐hr immediately post‐impact precludes a direct tsunami from the Chicxulub impact site, which would have required much more than 10 hr to reach Tanis. Seismic waves from the Mw ∼ 11 Chicxulub earthquake, arriving just minutes post‐impact, might have triggered the surge, for example, via seismic excitation of large water waves in the WIS, as proposed by DePalma et al. (2019, https://doi.org/10.1073/pnas.1817407116). Here, we explore this mechanism via a simple mathematical model of seismic excitation and propagation of a water wave into a shallow river and upstream. Matching the observations implies a relatively long source process time of many minutes, such as generated by Chicxulub crater rebound processes, in order to explain sufficient upriver amplitudes and advective transport. Atmospheric waves due to the expanding Chicxulub ejecta curtain might have provided a smaller, secondary contribution during triggering. Thus, the mechanism(s) for the surges at Tanis are now better‐constrained, yet remain incompletely resolved.

Statistical Observations of Proton‐Band Electromagnetic Ion Cyclotron Waves in the Outer Magnetosphere: Full Wavevector Determination

AbstractElectromagnetic Ion Cyclotron (EMIC) waves mediate energy transfer from the solar wind to the magnetosphere, relativistic electron precipitation, or thermalization of the ring current population, to name a few. How these processes take place depends on the wave properties, such as the wavevector and polarization. However, inferring the wavevector from in‐situ measurements is problematic since one needs to disentangle spatial and time variations. Using 8 years of Magnetospheric Multiscale (MMS) mission observations in the dayside magnetosphere, we present an algorithm to detect proton‐band EMIC waves in the Earth's dayside magnetosphere, and find that they are present roughly 15% of the time. Their normalized frequency presents a dawn‐dusk asymmetry, with waves in the dawn flank magnetosphere having larger frequency than in the dusk, subsolar, and dawn near subsolar region. It is shown that the observations are unstable to the ion cyclotron instability. We obtain the wave polarization and wavevector by comparing Single Value Decomposition and Ampere methods. We observe that for most waves the perpendicular wavenumber (k⊥) is larger than the inverse of the proton gyroradius (ρi), that is, k⊥ρi > 1, while the parallel wavenumber is smaller than the inverse of the ion gyroradius, that is, k‖ρi < 1. Left‐hand polarized waves are associated with small wave normal angles (θBk < 30°), while linearly polarized waves are associated with large wave normal angles (θBk > 30°). This work constitutes, to our knowledge, the first attempt to statistically infer the full wavevector of proton‐band EMIC waves observed in the outer magnetosphere.

Overtopping Flow Velocity Characterisation Of Focused Waves On Promenades Using The Bubble Image Velocimetry Technique

This study characterises the flow velocity of individual extreme waves that overtop promenades using the bubble image velocimetry (BIV) technique (Ryu et al., 2005). Experimental tests were carried out in the small-scale wave flume CIEMito, at the Marine Engineering Laboratory (LIM) of the Universitat Politècnica de Catalunya – BarcelonaTech (UPC), and the obtained images were post-processed to calculate the flow velocities. The ultimate objective of the experimental campaign is to develop more precise models for forecasting wave overtopping of structures with an emergent toe, commonly found on sandy beaches and frequently utilized as promenades or waterfronts in most urbanized coastal environments. The NewWave theory (Tromans et al., 1991) was used to simulate the extreme individual wave overtopping in a real random sea state. The NewWave theory establishes a correlation between the expected form of a large wave in a linear sea state and the bulk characteristics of the sea state. Using focused wave groups instead of long-duration irregular wave time series offers several benefits. It improves the ability to repeat experiments and enhances measurement capabilities by providing greater temporal resolution in models used to investigate significant wave interactions (Hofland et al., 2014). Additionally, due to the compactness of focused wave groups, wave absorption becomes unnecessary. The research identifies two distinct case studies with varying wave forcing, tidal regimes and coastal layouts. This work presents a case study of a typical Mediterranean Sea configuration, which is a micro-tidal environment with steep and relatively short foreshores and pocket beaches. The study aims to characterize the overtopping flow velocity on the selected structure, and the feasibility of non-intrusive measurements such as a BIV technique has been investigated. The work includes preliminary results.

Physical Modelling Tests With Flexible Woody Vegetation Mimics

Riparian forests in front of dikes can dampen incoming waves and thereby contribute to flood safety. In real-scale flume experiments with live pollard willow trees (forming a 40-m-long forest), it was observed that during storm conditions, a maximum reduction of 20 % in incoming wave height could be achieved (van Wesenbeeck, et al., 2022). Notably, this amount of wave damping occurred at a water depth of 3 meters, aligning with the section of the trees with the maximum frontal-surface area. For a larger water depth, measured wave damping however declined. This is potentially partly caused by the natural tapering form of the trees. Typically, trees are characterized by smaller branch diameters and more flexible branches higher up in the canopy (McMahon & Kronauer, 1976); and flexible vegetation mimics are known to dampen less than rigid mimics due to motion (Van Veelen, T, Reeve, & Karunarathna, 2020). Hence, both the frontal-surface area and branch rigidity decrease along the height of the willow trees, potentially leading to less wave damping by the forest when subject to large waves at higher water levels.