Surface Wave Height Research Articles

Particle Size Distribution Slope Changes along the Yellow River Delta Observed from Sentinel 3A/B OLCI Images

Quantitative estimates of particle size in estuaries and shelf areas are important to understand ocean ecology and biogeochemistry. Particle size can be characterized qualitatively from satellite observations of ocean color. As a typical marginal sea, the Yellow River Delta (YRD) with the Bohai Sea experiences a complex hydrodynamic environment. Here, we attempt to quantify the particle size distribution (PSD) slope (ξ) based on its relationship with the particle backscattering exponent from Sentinel-3A/B OLCI. The PSD slope, ξ displays temporal and spatial variability in the YRD with the Bohai Sea. Its value varies between 3 and 4, and typically exceeds 5 in offshore areas. The lowest value of ξ occurs in the winter, indicating the presence of fine inorganic particles in the water, while high values are attained in the spring, when phytoplankton blooms increase the particle size. ξ decreases near the river mouth because of the large sediment-laden discharge debouching into the sea. We detected a slight increase in ξ when turbid waters were present in the period 2016–2022. Environmental factors, such as sea surface temperature, sea surface wave height, and wind, may control particle size and ξ in the long term. Inorganic suspended particle matter is derived along the YRD using the magnitude of ξ. The mean inorganic suspended particle matter area in winter approaches 23,900 km2 when ξ < 4.6. This study thoroughly characterizes variations in ξ in the YRD with the Bohai Sea and clarifies the contributions of driving factors from human activities and climate change.

Statistical distributions of free surface elevation and wave height for out-of-equilibrium sea-states provoked by strong depth variations

As unidirectional irregular wave trains propagate over a steep shoal, the sea-state becomes out-of-equilibrium and is continuously affected by the non-equilibrium dynamics (NED) over dozens of characteristic wavelengths. Using the set of accurate numerical simulations of Zhang et al. (2022), the NED effects on the probability distributions of free surface elevation and wave height, the statistical moments and maximum wave statistics are investigated, in both near-field and far-field regions after the water depth transition. The primary contribution of this work is to assess the applicability and limitations of several popular statistical distribution models in describing non-equilibrium statistics. In addition, a new distribution of the free surface elevation in a lognormal shape is proposed, which predicts the non-equilibrium free surface statistics with satisfactory performance and characterizes well the skewness–kurtosis relationship in the short scale. It is shown that the statistics in the far-field region are significantly influenced by the near-field wave-wave interaction, and beyond the capability of all statistical models considered here. Despite this complexity, the sea-state in the far-field region exhibits lower freak wave probability than a Gaussian sea-state. Implications of these findings for engineering practices are discussed.

Quality Control for Ocean Current Measurement Using High-Frequency Direction-Finding Radar

High-frequency radars (HFRs) are important for remote sensing of the marine environment due to their ability to provide real-time, wide-coverage, and high-resolution measurements of the ocean surface current, wave height, and wind speed. However, due to the intricate multidimensional processing demands (e.g., time, Doppler, and space) for internal data and effective suppression of external noise, conducting quality control (QC) on radar-measured data is of great importance. In this paper, we first present a comprehensive quality evaluation model for both radial current and synthesized vector current obtained by direction-finding (DF) HFRs. In the proposed model, the quality factor (QF) is calculated for each current cell to evaluate its reliability. The QF for the radial current depends on the signal-to-noise ratio (SNR) and DF factor of the first-order Bragg peak region in the range–Doppler (RD) spectrum, and the QF for the synthesized vector current can be calculated using an error propagation model based on geometric dilution of precision (GDOP). A QC method is then proposed for processing HFR-derived surface current data via the following steps: (1) signal preprocessing is performed to minimize the effect of unwanted external signals such as radio frequency interference and ionospheric clutter; (2) radial currents with low QFs and outliers are removed; (3) the vector currents with low QFs are also removed before spatial smoothing and interpolation. The proposed QC method is validated using a one-month-long dataset collected by the Ocean State Monitoring and Analyzing Radar, model S (OSMAR-S). The improvement in the current quality is proven to be significant. Using the buoy data as ground truth, after applying QC, the correlation coefficients (CCs) of the radial current, synthesized current speed, and synthesized current direction are increased by 4.33~102.91%, 1.04~90.74%, and 1.20~62.67%, respectively, and the root mean square errors (RMSEs) are decreased by 2.51~49.65%, 7.86~27.22%, and 1.68~28.99%, respectively. The proposed QC method has now been incorporated into the operational software (RemoteSiteConsole v1.0.0.65) of OSMAR-S.

Wave heights from sea surface and bottom measurements: Variations with different water depths

Wave instruments equipped with pressure sensors have long been recognized as an effective means of obtaining statistical characteristics of wave distributions in complex sea conditions. However, the commonly used theory based on pressure response functions may not accurately capture surface height signals due to the nonlinearity of wave propagation at different water depths. To address this issue, field measurements were conducted at five stations with water depths ranging from 2.4 m to 54.8 m. The validity threshold of the linear wave theory was investigated using surface buoy and bottom pressure measurements. Statistical analyses showed that the classical linear theory performed well in shallow water, but its credibility decreased with increasing depth. In addition, the measured data showed agreement with the Weibull distribution for wave pressure and the Rayleigh distribution for surface wave height. For applications in ocean and coastal engineering, we propose two empirical formulas for estimating wave heights based on seabed or sea surface measurements at intermediate water depths. These formulas take into account the ratio of wave height to water depth, which reflects the nonlinear effects in shallow water, thereby improving the accuracy of surface wave height estimation (with an accuracy of ±10%) compared to the traditional linear theory method.

FUTURE PREDICTION OF WIND VELOCITY AND SIGNIFICANT WAVE HEIGHT IN THE COMPLETELY ICE-FREE ARCTIC OCEAN UNDER RCP8.5 SCENARIO

The summer sea ice extent in the Arctic Ocean has decreased by several million square kilometers over the past decades highly likely due to anthropogenic global warming (Walsh, 2014). In the Arctic Ocean, the decrease in sea ice increases the open water area (and period), which potentially leads to the development of more energetic wave conditions (Wang et al., 2015). In the summertime Arctic Ocean, the maximum wind speed and the maximum significant wave height have been on a long-term upward trend as the sea ice extent has decreased (Waseda et al., 2018). In addition, changes in wind speed will contribute significantly to changes in the wave height in the future Arctic Ocean (Khon et al., 2014). Thus, it is becoming more important to study the sea surface wave heights in the Arctic area under possible future scenarios. The aim of this study is (1) to develop a method to assess wind and wave conditions over the Arctic Ocean and (2) to predict them under global warming considering the RCP 8.5 scenario.

Numerical and experimental study on sloshing damping effects of the porous baffle

Laboratory experiments were conducted to study porous baffle effects on reducing liquid sloshing in a rectangular tank on a six-degrees-of-freedom motion simulation platform. The porous baffle that was a material layer made from spherical particles fully filled into a cage made of perforated stainless-steel plate was proposed. The free surface wave height and the impact pressure on the wall were recorded in laboratory experiments of liquid sloshing in a horizontally excited rectangular tank. These experiments were used to validate the porous media model in OpenFOAM. The OpenFOAM was then employed to simulate sloshing in a rectangular tank with a porous baffle to reveal the sloshing damping mechanism of the porous baffle by changing the external excitation frequency. The results show that the porous baffle is more effective in suppressing impact pressure at a high excitation frequency.

Joint Retrieval of Sea Surface Rainfall Intensity, Wind Speed, and Wave Height Based on Spaceborne GNSS-R: A Case Study of the Oceans near China

In this paper, a method for joint sea surface rainfall intensity (RI), wind speed, and wave height retrieval based on spaceborne global navigation satellite system reflectometry (GNSS-R) data is proposed, which especially considers the effects between these two parameters. A method of rainfall detection (RD) according to different wind speed ranges is also proposed by mitigating the impact of swell and wind speed. The results, with data collected over the oceans near Southeast Asia, show that the RD method has a detection accuracy of up to 81.74%. The RI retrieval accuracy can reach about 2 mm/h by simultaneously correcting the effects of wind speed and swell. The accuracy of wind speed retrieval is improved by about 5% after removing rainfall interference through RD in advance. After considering the influence of wind speed and eliminating rainfall interference, the retrieval accuracy of significant wave height (SWH) is improved by about 18%. Finally, the deep convolutional neural network (DCNN) model is built to estimate the SWH of the swell. The results show that the retrieval accuracy of the swell height is better than 0.20 m after excluding rainfall interference. The proposed joint retrieval method provides an important reference for the future acquisition of multiple high-precision marine geophysical parameters by spaceborne GNSS-R technology.

Surface wave height distributions and rogue wave probabilities on two-layer fluids

Rogue waves are individual ocean surface waves much larger than the prevailing wave field. In high sea states they can be a danger to marine operations. Rogue waves are well studied for unstratified water. However, on a two-layer fluid the surface wave spectra are modified due to triad interactions with interfacial waves. Such triad interactions are not possible in homogeneous water. We find the modified surface spectrum reduces rogue waves. These findings are relevant for the changing polar oceans where prolonged ice melt is expected to facilitate open water with higher sea states while also creating a surface layer of freshwater overlaying salt water, as in our idealized model calculations.

Investigation of Electromagnetic Scattering Mechanisms from Dynamic Oil Spill–Covered Sea Surface

The electromagnetic (EM) scattering mechanism of dynamic oil spill–covered sea surface area is studied in this manuscript. Utilizing the theory of oil film diffusion combined with oil spill volume, a three–dimensional (3D) geometric model of dynamic oil spill–covered sea surface area is established. The changes of the geometric structure and statistical characteristics of the sea surface area under the influence of the oil film are also analyzed. The thinner the oil spill thickness, the more sensitive it is to the sea surface slope and wave height. The facet-based hybrid model and the multilayer dielectric scattering method are combined to measure the EM scattering on the sea surface when covered by dynamic oil spills. In addition, the hydrodynamic and tilt effect are discussed. The EM scattering mechanism of the dynamic oil spill–covered sea surface area is revealed, and the tilt modulation is greater than the hydrodynamic effect in the dynamic process of an oil spill. It provides an important reference for the remote sensing monitoring of oil.

A self-similar description of the wave fields generated by tropical cyclones

Today, advanced operational wave models, e.g. WAM, SWAN or WAVEWATCH-III, provide very accurate solutions. Nevertheless, under extreme weather conditions, surface wave predictions can remain challenging. Indeed, for relatively small-scale tropical cyclones (TCs), rapidly evolving in time and space, and possibly not always well sampled with observing systems, extreme winds may not be properly described, and generated wave systems correctly predicted. In that context, Kudryavtsev et al. (2021b) recently proposed a simplified framework to rapidly assess evolving wave fields under typical TC conditions. Using self-similar functions, termed Tropical Cyclone-Wave Geophysical Model Function (TCW GMF), the proposed methodology and initial results demonstrate robustness and efficiency : 2D functions, assimilating a small number of parameters (maximum wind speed, cyclone radius and translation velocity), provide first-guess estimates of surface wave heights, wave lengths and directions within the intense TC core region. Following this strategy, an improved TCW GMF version is proposed to also cover the TC far zone, providing both wind wave information and outrunning swell conditions. This new version more particularly accounts for the wave field sensitivity to the shape of the wind profile. The procedure follows three main steps: (1) estimation of the characteristics of pure wind waves using self-similar matrices; (2) determination of the contour limiting the transition between wind waves to swell regime using empirically-derived universal functions; (3) derivation of analytical functions to describe the swell parameters using initial parameters estimated at this transition contour. Wind waves and swell systems are further superposed to describe the wave parameters for mixed-sea conditions. In this study, IBTrACS are used to initialize the TC’s wind profiles, coordinates and translation velocities. The proposed methodology is then tested using a large altimeter database. More than 700 altimeter measurements crossing different TCs during 2020–2022 years are used, demonstrating overall convincing agreements between first-guess estimates and satellite data.

Cause of Double-Peak Spectrum in Hyuga-Nada by the HF Radar

High-frequency (HF) radar is a land-based instrument that can observe the radial distribution of oceanographic information, such as surface currents, wave heights, and wind directions. The first-order echo peak of the Doppler spectrum is often splits in this observation, and the levels of the split peaks are of approximately the same magnitude. We call this the double-peak spectrum. Because such a spectral shape may affect the derivation of oceanographic information, we examined the factors that cause double-peak spectra. The Kuroshio Current flows near the observation area of this study’s radar, which may have caused the double-peak spectrum. By mapping the spatial distribution of the double-peak spectra, we found areas in which the double-peak spectra occur relatively often at each radar station. The area of high vorticity ahead of the northeastward Kuroshio Current coincided with the area in which the double-peak spectra occurred, indicating the complexity of the currents occurring there; furthermore, more than two current velocity patterns can be mapped. These results show that the distance and directional continuity of the double-peak spectra can be used to calculate the flow-changing region with better spatial resolution.

Investigation of the Spiral Wave Generation and Propagation on a Numerical Circular Wave Tank Model

A two-phase incompressible flow model in three-dimensional cylindrical coordinates is applied for oblique wave generation in a numerical circular wave tank. The governing equations are discretized by a finite volume method, and a mass source function is added to reproduce oblique waves through a spiral wave generator positioned at the center of the tank. The volume of fluid method is implemented to track the free surfaces between the air and fluid, and the zonal embedded grid system is adopted to obtain a grid-independent solution in the cylindrical coordinates. A permeable, circumferentially sloping topography (1:7), similar to a natural beach profile, is set up for investigating wave propagation and other characteristics. The simulation and physical experimental results are compared, which show a good agreement in randomly selected water surface elevation profiles and wave heights under the same wave and sloping conditions. The spiral waves are reproduced and propagated in a phenomenon similar to that observed in the physical experiment. The results also show that the wave-breaking positions differ in different wave conditions and suggest a relationship with cross-shore and longshore velocity distribution in terms of incident wave heights and wave-breaking positions in different wave periods on the same sloping topography. Furthermore, this model can be used to investigate the mechanism of longshore current generation and the influences of beach slope on the generated wave propagation in a sloping topography.

Application of Electromagnetic Braking to Minimize a Surface Wave in a Continuous Caster.

The turbulent flow in the mold region drastically influences the quality of steel produced during continuous casting. The flow itself can lead to surface defects or slag entrainment based on the formation. A high surface wave can lead to fluctuations and the instability compromises the quality of the steel produced, as well as entrain the slag. To regulate the flow, electromagnetic forces can be applied in the mold, dampening the local turbulent flow. As the electrically conductive molten steel interacts with the induced magnetic field, it reduces the velocity of the steel jet released from the ports of the submerged entry nozzle. Utilizing Star-CCM+, a simulation-based study is conducted modeling the impact of Electromagnetic braking (EMBr) on the flow formation and surface standing wave. Specifically, a parametric study is conducted investigating the impact of submergence entry nozzle (SEN) depth and mold width with applied EMBr. Per the simulation-based study conducted increasing the EMBr strength from 2975 G to 4350 G reduced the average surface wave height by 12.5% and volume of flux rate of decrease by 4.25%. Additionally, increasing the SEN depth from 110 mm to 350 mm increased the average wave height by 19% and volume of flux rate of decrease by 2.6%. Lastly, increasing the mold width from 1.067 m to 1.50 m increased average wave height by 8.71% and volume of flux rate of decrease by 0.9%.

Global ocean wave fields show consistent regional trends between 1980 and 2014 in a multi-product ensemble

Historical trends in the direction and magnitude of ocean surface wave height, period, or direction are debated due to diverse data, time-periods, or methodologies. Using a consistent community-driven ensemble of global wave products, we quantify and establish regions with robust trends in global multivariate wave fields between 1980 and 2014. We find that about 30–40% of the global ocean experienced robust seasonal trends in mean and extreme wave height, period, and direction. Most of the Southern Hemisphere exhibited strong upward-trending wave heights (1–2 cm per year) and periods during winter and summer. Ocean basins with robust positive trends are far larger than those with negative trends. Historical trends calculated over shorter periods generally agree with satellite records but vary from product to product, with some showing a consistently negative bias. Variability in trends across products and time-periods highlights the importance of considering multiple sources when seeking robust change analyses.

Automating the Acoustic Detection and Characterization of Sea Ice and Surface Waves

Monitoring the status of Arctic marine ecosystems is aided by multi-sensor oceanographic moorings that autonomously collect data year-round. In the northeast Chukchi Sea, an ASL Environmental Sciences Acoustic Zooplankton Fish Profiler (AZFP) collected data from the upper 30 m of the water column every 10–20 s from 2014 to 2020. We here describe the processing of the AZFP’s 455 kHz acoustic backscatter return signal for the purpose of developing methods to assist in characterizing local sea ice conditions. By applying a self-organizing map (SOM) machine learning algorithm to 15-min ensembles of these data, we are able to accurately differentiate between the presence of open water and sea ice, and thereby characterize statistical properties surface wave height envelopes and ice draft. The ability to algorithmically identify small-scale features within the information-dense acoustic dataset enables efficient and rich characterizations of environmental conditions, such as frequency of sparse ice floes in otherwise open water and brief open-water leads amidst the ice pack. Corrections for instrument tilt, speed of sound, and water level allow us to resolve the sea surface reflection interface to within approximately 0.06 ± 0.09 m. By automating the acoustic data processing and alleviating labor- and time-intensive analyses, we extract additional information from the AZFP backscatter data, which is otherwise used for assessing fish and zooplankton densities and behaviors. Beyond applications to new datasets, the approach opens possibilities for the efficient extraction of new information from existing upward-looking sonar records that have been collected in recent decades.

Field measurements of boat wake attenuation in salt marshes of coastal Alabama

Four pressure gauges were deployed along natural marsh transects in Mobile, Alabama, to assess the ability of marsh vegetation to reduce the height and energy of oncoming boat wakes. The present study explores the influence of vegetation species, marsh density, wave height, wave frequency, and seabed terrain on the degree of attenuation. The pressure data were translated into instantaneous free surface position and wave height measurements, and the influence of shoaling and wave breaking was accounted for. It was found that attenuation is nonlinear, with an increased concentration of wave height and energy loss occurring in the first few meters, and that the seabed plays a significant role in wave transformation. The highest 1% of wave heights was most effectively reduced due to the combined influence of terrain and vegetation while the mean wave heights were the least reduced wave height statistic. Determination of accurate decay coefficients was complicated by the high degree of variability observed within the study. The results showed a correlation between wave frequency and energy dissipation, with the most substantial loss occurring at the peak frequency. Collectively, the findings highlight the variability between marsh sites and reinforce the recommendation that there be further exploration of wave energy attenuation by marsh grasses.

Unsteady Fluid Flows in the Slab Mold Using Anticlogging Nozzles

The characterization of the fluid flow of liquid steel in a slab mold, using two nozzle designs under unclogged and clogged conditions, is performed using physical and mathematical simulations. Nozzle A, with an expanding and contracting geometry, yields larger sub-meniscus experimental velocities than nozzle B, with internal flow deflectors. The numerical predictions indicate quick time-changing velocity profiles in the submeniscus region between the mold’s narrow face and the nozzles. The flow deflectors in nozzle B have two effects; the high dissipation rate of kinetic energy in the upper-half length induces lower velocities in the ports than nozzle A. The neutralization of the biased flow caused by the sliding gate allows a balanced fluid through the ports. According to the results, nozzle A yields velocity profiles in the sub-meniscus region with larger standard deviations than nozzle B, leading to an unstable bath surface. The clogged nozzles produced biased-asymmetrical flow patterns in the mold, finding approximated matchings between numerical predictions and experimental measurements. The internal protrusions of the deposits lead to covariance losses of the bath surface wave heights. The use of internal deflectors helped to decrease the amount of clog material in nozzle B.

Experimental study of the dam-break waves in triangular channels with a sloped wet bed

There has been little study on the impact of bottom slope on dam break wave propagating along a triangular wet channel. In this study, laboratory experiments are conducted in a large-scale triangular laboratory flume, covering a range of bed slope and rations of upstream over downstream water depth. Water surface and stage hydrograph wave height are collected using the non-intrusive measurement methods, which are used to obtain wave characteristics. Results show that for dry bed, the wavefront celerity increases with the increase of the slope; while for a wet bed, the wavefront celerity decreases as the slope increases and the decrease rate is significantly reduced. Moreover, the wavefront celerity decreases with the increase of water depth ratio. The maximum wave height at each measurement location decreases with the increase of water depth ratio. According to the arrival of the maximum wave height, the dam-break wave can be classified into two modes, namely Type A in which wave height gradually rises to the maximum when flow reaches and Type B in which the maximum wave height appears at the beginning of the dam failure. This study is useful for in-depth understanding of the dam-break wave evolution in sloping triangular wet rivers.

Seamless Projections of Global Storm Surge and Ocean Waves Under a Warming Climate

AbstractFor coastal adaptation purposes, it is important to estimate the climate related changes in extreme sea levels due to storm surges and ocean waves, in addition to mean sea level rise. This study provides the first consistent and continuous estimation of projected changes in global storm surges and ocean waves from the past to the warmer future, based on an extremely high resolution global climate model. The spatial pattern in the trend of annual maximum sea surface heights and wave heights is predominantly driven by changes in tropical cyclone (TC) frequency. In the western North Pacific, future TC frequencies are projected to decrease, and the annual maximum sea surface heights and wave heights show decreasing trends (−20 cm/century and −200 cm/century). Although highly intense tropical cyclones are enhanced in the warmer climate, highly extreme storm surges and wave heights do not necessarily increase due to the large natural variability.

Coastal observation of sea surface tide and wave height using opportunity signal from Beidou GEO satellites: analysis and evaluation

Coastal observation of sea surface tide and wave height using opportunity signal from Beidou GEO satellites: analysis and evaluation