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Nose, T.; Babanin, A., and Ewans, K., 2024. Directional characteristics of infragravity waves during storms in the nearshore coastal region. Journal of Coastal Research, 40(2), 353–365. Charlotte (North Carolina), ISSN 0749-0208. Presented is an infragravity wave analysis of field observations that were made using acoustic Doppler wave gauges for nearshore waters with depths typically less than 10 m. The study found a correlation between total infragravity wave energy with the wind-generated waves and the relative depth, which was robust for high waves during storms. Directional distributions of nearshore infragravity waves were derived from Acoustics Doppler gauges (Acoustic Waves and Currents (AWACs)); it was found that bimodal directional peaks emerged during storms. Previous infragravity wave studies suggest dominant energy is in the propagation sector outward from the coast, i.e. reflected waves, but the analysis here showed that the dominant infragravity wave energy was in the propagation sector incident to the coast. A numerical model that models free infragravity wave evolution from the bound infragravity wave liberation was used to reproduce the observed bimodal peaks during several storm events; however, in contrast to the observations, the dominant energy of the modelled infragravity waves is in the propagation sector outward from the coast. The AWAC directional analysis and its comparison with the model indicate that the breakpoint generation mechanism may contribute to the shoreward propagating infragravity wave energy during storm events. Using the correlation obtained from the AWAC data between the total infragravity wave energy and the relative depth parameter, an empirical model was developed to simulate the directionally discretised infragravity wave heights. The feasibility was demonstrated with reasonable skill values for the total and reflected model infragravity wave heights, which may be a computationally inexpensive tool to provide bulk infragravity wave statistics for preliminary engineering designs. This study demonstrated that AWAC data are useful for infragravity wave studies in nearshore coastal waters. [ABSTRACT FROM AUTHOR]

Waves critically modulate the air‐sea fluxes, and upper‐ocean thermodynamics in a Tropical Cyclone (TC) system. This study improves the modeling of TC intensification by incorporating non‐breaking wave‐induced turbulence and sea spray from breaking waves into an atmosphere‐ocean‐wave coupled model. Notably, wind forecast error decreased by around 10% prior to TCs' peak intensity. The positive feedback of sea spray along with compensatory negative feedback from non‐breaking waves, overall enhanced TCs' intensity. These breaking and non‐breaking wave‐coupled processes consistently cool sea surface temperature, resulting in improvement of the modeled SST. Observed improvements in full‐year TC cases ranging from Categories I to IV in this study suggest that an accurate characterization of ocean wave‐coupled processes is crucial for improving TCs' intensity forecasts and advancing our understanding of severe weather events in both, the atmosphere and ocean. Plain Language Summary: Tropical Cyclones (TCs), such as hurricanes and typhoons, are destructive natural disasters that can cause extensive damage. Our study focused on understanding the role of ocean waves and related processes in TCs. Through numerical modeling, we found that ocean waves, specifically breaking and non‐breaking waves, have a substantial influence on TCs' intensity. Breaking waves contribute positively through the production of sea spray droplets, while non‐breaking wave‐induced turbulence has a compensatory negative effect, resulting in an enhancement in TCs' intensity. Incorporating both wave mechanisms into the models improved the accuracy of TCs' intensity and their underlying sea surface temperature. By highlighting the importance of ocean wave‐coupled physics, we aim to enhance our understanding of TCs and improve disaster preparedness to mitigate their impacts on coastal communities. Key Points: Full‐year regional hindcast of Tropical Cyclones (TCs) at the North West AustraliaInclusion of wave‐coupled processes improves TCs modeling, by reducing forecast errors and enhancing rapid intensification simulationsSea spray increases TC development while nonbreaking wave turbulence has the opposite effect with the first process dominating [ABSTRACT FROM AUTHOR]

Wing-in ground effect (WIG) vehicles and planing hulls are exposed to unsteady, high magnitude hydrodynamic forces as their bow enters water. The resulting forces can lead to structural damage and uncomfortable riding conditions. This paper aims to provide deeper understanding on the influence of structural flexibility throughout the water entry process of a hard-chine section. A finite volume method (FVM) based flexible fluid-structure interaction (FFSI) model is used to solve multi-physics. Quantitative comparisons are made between experimental and computational data. Simulations demonstrate that structural responses can attenuate the pressure acting on the body of hard-chine sections impinging water with deadrise angles of 10 deg, 20 deg, and 30 deg. However, they cannot affect that of a section with deadrise angle of 45 deg since its pressure distribution pattern is different. It is shown that the impact speed has an important role in hydroelastic response while the sectional Young's modulus affects impact pressures and resulting equivalent stresses. The former increases under the increase of Young's modulus. The latter may increase when the impact speed is low and decreases when the impact speed is high. It is concluded that the results presented may be useful for preliminary design. [ABSTRACT FROM AUTHOR]

Ocean waves are crucial for driving various oceanic processes. In this study, the spatial and temporal distribution of significant wave height (SWH) in the North Pacific (NP) is analyzed using the 42-year ERA5 reanalysis dataset from European Centre for Medium-Range Weather Forecasts (ECMWF). The presence of an ENSO signal is confirmed in wave fields of the North Pacific. Furthermore, the spatial distributions of swells and wind waves are analyzed using the Empirical Orthogonal Function (EOF) method, revealing that waves can transport large-scale signals from the NP to lower latitudes through swells. In addition, our research reveals a relationship between ENSO and Stokes drift in the NP. Stokes drift contributes positively to the maintenance of stable sea surface temperatures (SSTs) by transporting more (less) water towards the equatorial Pacific during El Niño (La Niña year) years. It is further noted that during strong ENSO events, the strength of the Stokes drift anomaly intensifies accordingly, which implies a strong link between wave-induced transport and ENSO. [ABSTRACT FROM AUTHOR]

Extreme significant wave height estimates, and their probability of exceedance, are fundamental offshore and coastal engineering design parameters. These estimates are characterized by uncertainty due to an incomplete understanding of the atmosphere‐ocean energy and momentum exchanges during intense storms. This particularly affects extreme wave statistics of ocean regions exposed to large and frequent synoptic disturbances such as Extra‐Tropical Cyclones (ETCs). In this work, we assessed the performance of global phase‐averaged spectral wave models in representing the 1 in 100‐year sea state generated by a Southern Ocean ETC in April 2021. We collected in situ and remote sensing observations, from the storm generation region to its decaying phase and the impact on South‐East Australian coastlines. We compared the observations with a suite of reanalysis and hindcast global wave model data sets. While comparing well for wind speed up to 20 m/s, the models presented differences in solving the air‐sea momentum exchange between the atmosphere and the ocean for wind speed velocities between 20 and 35 m/s, which are a distinctive characteristic of ETCs. Despite marked differences in the storm generation region, the models converged to a similar representation of the swell systems impacting the South‐East Australian coastlines, as demonstrated by a comparison with deep‐water buoy observations close to the coastlines. Furthermore, we found that the energy of the ERA5 reanalysis, which assimilates satellite wave height measurements is quickly dispersed and, as such, of little advantage in representing the 9.9 m significant wave heights that impacted the South‐East Australian coastlines on 10 April 2021. Plain Language Summary: Ocean wind‐wave extreme events are a major driver of coastal erosion and a fundamental aspect in the design of offshore and coastal structures. Engineers rely on accurate one‐in‐N‐year significant wave height return period estimates, and in a changing climate, accurate estimates of wind‐wave extremes are also crucial to implement efficient and resilient coastal climate adaptation strategies. Global wave reanalysis data sets are commonly used to estimate wind and wave statistical properties and design parameters. However, despite the impressive accuracy of such data sets in representing average significant wave height conditions, models still underestimate wind‐wave extremes. In this work, we take advantage of a well‐documented one‐in‐100‐year sea state generated by a Southern Hemisphere Extra‐Tropical Cyclone (ETC) to analyze the performance of state‐of‐the‐art global wave models in representing wind‐wave extremes. The aim is to support informed extreme value analysis statistical studies and suggest improvements to wave models to better represent extreme climate in the Northern and Southern Hemisphere ocean regions exposed to ETCs. Key Points: The performance of phase‐averaged global wave models is evaluated for a 100‐year sea state generated by a Southern Hemisphere Extra‐Tropical Cyclone (ETC)Lack of understanding of air‐sea momentum exchange at wind speed between 20 and 35 m/s challenges the modeling of ETC sea statesNovel atmosphere‐ocean coupled models and new ETC sea state in situ measurements are needed to improve air‐sea momentum exchange modeling [ABSTRACT FROM AUTHOR]

In situ observations of wave attenuation by sea ice are required to develop and validate wave–ice interaction parameterizations in coupled wave models. To estimate ice-induced wave attenuation in the field, the wave field is typically assumed to be stationary. In this study we investigate the validity of this assumption by creating a synthetic wave field in sea ice for different attenuation rates. We observe that errors in estimates of the wave attenuation rates are largest when attenuation rates are small or temporal averaging periods are short. Moreover, the adoption of the wave stationarity assumption can lead to negative estimates of the instantaneous wave attenuation rate. These apparent negative values should therefore not be attributed to wave growth or erroneous measurements a priori. Surprisingly, we observe that the validity of the wave stationarity assumption is irrelevant to the accuracy of estimates of wave attenuation rates as long as the temporal averaging period is taken sufficiently long. This may provide opportunities in using satellite-derived products to estimate wave attenuation rates in sea ice at global scales. [ABSTRACT FROM AUTHOR]

In the Northwest Pacific (NWP), where a unique monsoon climate exists and where both typhoons and extratropical storms occur frequently, hazardous waves pose a significant risk to maritime safety. To analyze the 20-year variability of hazardous waves in this region, this study utilized hourly reanalysis data from the ECMWF ERA5 dataset covering the period from 2001–2020, alongside the wave risk assessment method. The ERA5 data exhibits better consistency, in both the temporal and spatial dimensions, than satellite data. Although hazardous wind seas occur more frequently than hazardous swells, swells make hazardous waves travel further. Notably, the extreme wave height (EWH) shows an increasing trend in high- and low-latitude areas of the NWP. The change in meridional wind speeds is the primary reason for the change in the total wind speed in the NWP. Notably, the maximum annual increase rate of 0.013 m/year for EWH exists in the region of the Japanese Archipelago. This study elucidated the distributions of wave height intensity and wave risk levels, noting that the EWHs of the 50-year and 100-year return periods can reach 20.92 m and 23.07 m, respectively. [ABSTRACT FROM AUTHOR]

Climate models do not explicitly account for the smaller scale processes of ocean surface waves. However, many large-scale phenomena are essentially coupled with the waves. In particular, waves enhance mixing in the upper ocean and thereby accelerate the ocean response to atmospheric changes. Here, we introduced a representation of wave-induced turbulent mixing into the one-way coupled ACCESS-OM2-025 ocean model to study its effect on ocean heat content throughout the 21st century under the RCP4.5 scenario. We made two projections on ocean heat uptake for the end of the century: one which accounts for wave-induced mixing (the 'modified' projection) and the other which does not (the 'standard' projection). Both projections showed upper ocean heat content to increase by more than 2.2 × 1022 J. This projected ocean heat uptake was reduced by about 3% in the modified projection. Whilst the inclusion of wave-induced mixing reduces projected ocean heat uptake globally, some areas are expected to warm considerably faster, particularly the North Atlantic sub-tropics, the Tasman Sea, the Sea of Japan, and parts of the South Atlantic. [ABSTRACT FROM AUTHOR]

In spite of massive efforts directed to development of climate models over recent decades, accurate climate simulations and prediction remain a grand challenge. Large sea surface temperature model bias is one of the key indicators of the problem, among others. Qiao and his team suggested the concept of surface wave‐induced turbulence and elaborated the way for such coupling, through turbulent processes at both sides of the air‐ocean interface. These are the wave mixing in the ocean and wave modulation of air‐sea fluxes. This wave‐ocean coupled approach led to essential improvements of performance of ocean circulation and climate models, essentially introducing the next generation of large‐scale air‐sea interaction models. This Commentary reviews three recent JGR publications where the Qiao theory was implemented. The first paper (Huang & Qiao, 2021; https://doi.org/10.1029/2020JC016839) reported that the momentum gain by the ocean could be larger than the wind stress input, due to the ocean waves. The second paper (Chen et al., 2022; https://doi.org/10.1029/2021JC018360) demonstrated that, also due to waves, the drag coefficients in the atmospheric boundary layer have a spatial asymmetry during tropical cyclones. The third paper (Zhao et al., 2022; https://doi.org/10.1029/2022JC019015), based on combination of wave‐coupled effects on both sides of air‐sea interface, demonstrates their impact on simulation of tropical cyclone intensity. All papers are based on unique in situ measurements and their data analysis. The Commentary is further used as an opportunity to outline and review the current state of the small‐large scale coupling topic with respect to ocean, weather and climate modeling. Plain Language Summary: Understanding the nature of climate change and predicting its trends have been one of the highest priorities for scientific communities and of great importance for the public. Climate simulations, however, have been facing challenges which persist for decades, and apparently mean that some of the physical processes in their description are missing. A large set of such processes rest with the coupled nature of small‐ and large‐scale air‐sea interaction phenomena. Since the spatio‐temporal scales of surface waves, around 100 m and 10 s, are too far from those in the climate system, that is, thousands to tens thousands kilometers and years to decades, their coupling have never been incorporated by climate models due to lack of understanding of physics of such interactions and computing capabilities. Recent publications indicate that surface waves can both change the upper ocean through non‐breaking wave‐induced mixing and, on the atmospheric side, air‐sea fluxes through modulating the interface of ocean and atmosphere. As a result, ocean and climate predictions can be essentially improved by considering surface waves in climate models. The Commentary mainly discusses three recent papers dedicated to this topic. Key Points: This Commentary reviews three recent JGR publications dedicated to wave‐coupled approaches to large‐scale air‐sea systemsThis wave‐ocean coupled approach led to essential improvements of performance of ocean circulation and climate modelsThe Commentary is further used as an opportunity to outline and review the current state of the small‐large scale coupling topic [ABSTRACT FROM AUTHOR]

Theoretical models for the prediction of decay rate and dispersion process of gravity waves traveling into an integrated ice cover expanded over a long way are introduced. The term "wet beam" is chosen to refer to these models as they are developed by incorporating water-based damping and added mass forces. Presented wet beam models differ from each other according to the rheological behavior considered for the ice cover. Two-parameter viscoelastic solid models accommodating Kelvin–Voigt (KV) and Maxwell mechanisms along with a one-parameter elastic solid model are used to describe the rheological behavior of the ice layer. Quantitative comparison between the landfast ice field data and model predictions suggests that wet beam models, adopted with both KV and Maxwell mechanisms, predict the decay rate more accurately compared to a dry beam model. Furthermore, the wet beam models, adopted with both KV and Maxwell mechanisms, are found to construct decay rates of disintegrated ice fields, though they are built for a continuous ice field. Finally, it is found that wet beam models can accurately construct decay rate curves of freshwater ice, though they cannot predict the dispersion process of waves accurately. To overcome this limitation, three-parameter solid models, termed standard linear solid (SLS) mechanisms, are suggested to be used to re-formulate the dispersion relationship of wet beam models, which were seen to construct decay rates and dispersion curves of freshwater ice with an acceptable level of accuracy. Overall, the two-parameter wet beam dispersion relationships presented in this research are observed to predict decay rates and dispersion process of waves traveling into actual ice covers, though three-parameter wet beam models were seen to reconstruct the those of freshwater ice formed in a wave flume. The wet beam models presented in this research can be implemented in spectral models on a large geophysical scale. [ABSTRACT FROM AUTHOR]

Accurate quantification of air-sea gas transfer velocity is critical for our understanding of air-sea CO2 gas fluxes, global carbon budget and climate responses. CO2 transfer velocity is predominantly subject to constraints of wave-related dynamic processes at the ocean surface layer but is typically parameterized with wind speed. This study proposes and compares two parameterizations which accommodate dimensionless wave terms. The validations are conducted using both laboratory and field measurements of CO2 transfer and wave statistics. A scaling of bubble-mediated gas transfer is implemented into the formula that is linked to wave breaking probability. The improved parameterizations are capable of collapsing combined laboratory and field data sets which comprise diversified conditions of wind, wave and wave breaking. [ABSTRACT FROM AUTHOR]

When a wave breaks, it produces bubbles whose sizes depend on the breaking severity. This paper attempts to estimate wave breaking dissipation through a passive acoustic method. Initially, regular waves were forced to break in a flume. The breaking energy loss (severity) and the underwater acoustic noise were recorded. Two kinds of thresholds, in terms of sound wave amplitude and the ratio of sound wave height to period, respectively, were used together to identify the sound waves generated by newly formed bubbles. The frequencies of these sound waves are connected with the bubble sizes. Thus, a relationship between the mean bubble radius and the breaking severity was established and found to be linear. This laboratory relationship was then applied to Lake George data to study the breaking dissipation rate across the spectrum. An average acoustic spectral density threshold was proposed to identify breaking events from acoustic records in the field. The sound waves associated with bubble formation were selected by means of the same two kinds of threshold as used in the laboratory. Thus, the mean bubble radius of each breaking event was obtained and translated into the breaking severity. The values of experimental dissipation were compared with previous relevant results obtained through different methods as well as the wave breaking dissipation source terms ST6 (WAVEWATCH-III model) and are in good agreement with both of them. [ABSTRACT FROM AUTHOR]