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The twin Sentinel‐1 (S1) satellites have been extensively acquiring synthetic aperture radar (SAR) data in the Arctic, providing the unique opportunity to obtain ocean dynamic parameters with both high spatial resolution and wide swath coverage in the Arctic Ocean. In this study, we proposed a method for retrieving the ocean significant wave height (SWH) from S1 SAR data in horizontal‐horizontal (HH) polarization based on a backpropagation neural network (BPNN). A total of 4,273 scenes from S1 extra‐wide swath mode data acquired in the Arctic were collocated with data from four radar altimeters (RA), yielding 126,128 collocated data pairs. These data were separated into training and testing data sets to develop the BPNN model for retrieving SWH. Comparing the S1 retrieved SWH using the testing data set with the RA SWH yielded a bias of 0.17 m, a root‐mean‐square error of 0.71 m and a scatter index (SI) of 23.05% for SWH less than 10 m. The S1 retrieved SWH was further compared with the CFOSAT/SWIM data acquired in the Arctic between August 2019 and May 2020, which suggests that the SWIM has different performances on wave measurements at different beams. Plain Language Summary: The rapid decline of sea ice in the Arctic creates wider marginal ice zone (a transit from open water to sea ice, MIZ) than ever. Some studies have suggested that interaction between ocean dynamics (e.g., sea surface wind and wave) and sea ice is one possible feedback to retreat of sea ice in the Arctic. Therefore, ocean wave data in the Arctic Ocean are highly desirable. Synthetic aperture radar (SAR), as an active remote sensing technique, can operate independent on sunlight and weather conditions and image the earth with high spatial resolution. However, due to the complicated imaging process of ocean waves by spaceborne SAR, retrieval of sea state parameters by SAR data has been investigated for decades. Here, we developed an algorithm based on a back propagation neural network to retrieve significant wave height from spaceborne SAR data. This provides a chance of obtaining wave height information in both large coverages and high spatial resolution from satellite observation, and therefore, can contribute to scientific study, offshore operation and shipping in the Arctic. Key Points: An algorithm is developed to retrieve significant wave height (SWH) in the Arctic ocean from spaceborne synthetic aperture radar (SAR) using a back propagation neural networkComparisons of the SAR‐retrieved SWH with radar altimeter data suggest good agreement independent of the sea stateSWIM data at nadir and the 10° beam in the Arctic ocean are validated in detail by the SAR‐retrieved SWH [ABSTRACT FROM AUTHOR]

Accurate and significant wave height prediction with a couple of hours of warning time should offer major safety improvements for coastal and ocean engineering applications. However, significant wave height phenomenon is nonlinear and nonstationary, which makes any prediction simulation a non-straightforward task. The aim of the research presented in this paper is to improve predicted significant wave height via a hybrid algorithm. Firstly, empirical mode decomposition (EMD) is used to preprocess the nonlinear data, which are decomposed into several simple signals. Then, least square support vector machine (LSSVM) with nonlinear learning ability is used to predict the significant wave height, and particle swarm optimization (PSO) is implemented to automatically perform the parameter selection in LSSVM modeling. The EMD-PSO-LSSVM model is used to predict the significant wave height for 1, 3 and 6 hours leading times of two stations in the offshore and deep-sea areas of the North Atlantic Ocean. The results show that the EMD-PSO-LSSVM model can remove the lag in the prediction timing of the single prediction models. Furthermore, the prediction accuracy of the EMD-LSSVM model that has not been optimized in the deep-sea area has been greatly improved, an improvement of the prediction accuracy of Coefficient of determination (푅??) from 0.991, 0.982 and 0.959 to 0.993, 0.987 and 0.965, respectively, has been observed. The proposed new hybrid model shows good accuracy and provides an effective way to predict the significant wave height for the deep-sea area. [ABSTRACT FROM AUTHOR]

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The article discusses the use of global satellite data to measure oceanic wind speed and wave height to measure global trends related to climate change. Topics include extreme wind and wave trends in the Southern Ocean, the use of data from altimeter sampling, and the use of radiometer data in measuring trends.

The slip distribution of the 1960 Chile earthquake was estimated using geodetic data, local tsunami data, and newly usable transoceanic tsunami data. The large slips triggered a significant tsunami which was recorded by the tide gauges around the Pacific Ocean. We performed a two‐step inversion to estimate the slip distribution. In the first step, we jointly inverted the tsunami waveforms and local geodetic data to recover the ground and seafloor vertical displacement. The transoceanic tsunami data could not be used for waveform inversions until the wave phase and arrival time discrepancies were recently reconciled by improving the long‐wave theory with the phase correction method. The random arrival time discrepancy due to inaccurate local bathymetry and/or instrumental problems was considered by the optimal time alignment. In the second step, we estimated the slip distribution on the plate interface by inverting the vertical displacement obtained in the first step. Checkerboard tests showed that our method and data can resolve displacement at a spatial resolution of at least ~100 km but cannot estimate the rupture velocity. The result for actual data shows a rupture extended about 800 km with a width of about 150 km and three asperities. The large slips are concentrated in the offshore shallow plate interface. Our results indicate that the central and south patches contribute to the large coastal elevation changes at southern source area and high tsunami waves at far field. The estimated moment ranges 1.3–1.9 × 1023 Nm (Mw 9.3–9.4) for rake angles of 90–140°. Key Points: The slip distribution of the 1960 Chile earthquake is estimated from transoceanic tsunami data, local tsunami data, and geodetic dataThe seismic moment is 1.4 x 1023 Nm (Mw 9.4) for rake angle of 110°, and the slip consists of three shallow asperitiesLarge central and south asperities are required to reconstruct the southern high coastal uplift and large tsunami waves at far field [ABSTRACT FROM AUTHOR]

In recent years, deep learning technology has been gradually used for time series data prediction in various fields. In this paper, the restricted Boltzmann machine (RBM) in the classical deep belief network (DBN) is substituted with the conditional restricted Boltzmann machine (CRBM) containing temporal information, and the CRBM-DBN model is constructed. Key model parameters, which are determined by the particle swarm optimization (PSO) algorithm, are used to predict the significant wave height. Observed data in 2016, which are from nearshore and offshore buoys (i.e., 42020 and 42001) belonging to the National Data Buoy Center (NDBC), are taken to train the model, and the corresponding data in 2017 are used for testing with lead times of 1--24 h. In addition, we trained the data of 42040 in 2003 and tested the data in 2004 in order to investigate the prediction ability of the CRBM-DBN model for the extreme event. The prediction ability of the model is evaluated by the Nash--Sutcliffe coefficient of efficiency (CE) and root-mean-square error (RMSE). Experiments demonstrate that for the short-term (#9 h) prediction, the RMSE and CE for the significant wave height prediction are,10 cm and .0.98, respectively. Moreover, the relative error of the short-term prediction for the maximum wave height is less than 26%. The excellent short-term and extreme events forecasting ability of the CRBM-DBN model is vital to ocean engineering applications, especially for designs of ocean structures and vessels. [ABSTRACT FROM AUTHOR]

Ocean currents can strongly impact the propagation of swell systems. Satellite altimetry routinely provides measurements of ocean surface significant wave heights (Hs). A self‐consistent space‐scale decomposition is applied to Hs measurements obtained from different altimeters. This method helps reveal overlooked statistical properties at scales less than 100 km, where mesoscale and submesoscale upper ocean circulation drives a significant part of the variability in the coupled ocean‐atmosphere system. In particular, systematic signatures related to wave‐current interactions are clear at global and regional scales. In the Agulhas current system, the proposed space‐scale decomposition further reveals organized and persistent patterns. To leading order, the redistribution of swell energy follows the cumulative impact of the large‐scale current vorticity field on wave train kinematics. This relationship causes significant swell ray deflection and localized trapping phenomena, which are adequately captured by altimeter measurements. Plain Language Summary: Long and energetic surface waves radiating from distant storms may eventually cover a full ocean basin with a lifetime that can extend over a few weeks. Chances are that these swell fields will propagate over regions characterized by strong ambiant upper ocean currents. Resulting interactions can then trigger sea state variability, including the formation of severe crossing sea conditions. To better document these anticipated effects at global and regional scales, a new methodology is applied to best exploit multisatellite altimeter measurements. As obtained, the resulting augmented data sets provide an unprecedented evidence of the co‐variability of surface waves and currents over all ocean basins. More regionally, the analysis shows that persistent and localized sea state anomalies in the Agulhas current region are well explained by swell refraction and focusing effects in the variable current stream. The proposed methodology opens new perspectives for studies and applications combining numerical modeling and satellite observations. Key Points: Long‐term altimeter sea state measurements exhibit persistent variations linked to surface current gradientsA self‐consistent space‐scale decomposition unveils rich statistical properties at small oceanic scalesSwell refraction and advection processes explain global and regional wave climate variability [ABSTRACT FROM AUTHOR]

Abstract A new experimental device designed and built at Technische Universität Berlin for measuring forces and moments on a ship in waves is described and results of a comprehensive test campaign with the model of cruise ship are discussed. Forces, moments and motions on/of the model have been obtained during tests at forward speed in head waves and at zero speed in oblique incoming waves. Single motions have been restrained during these tests in order to analyse their influence on the mean forces and on other motions. The device allows for extracting non hydrodynamic inertial force contributions from the measured signals. The mean values of these inertial forces are not always zero, but often very significant, and must therefore be subtracted for a reliable comparison with mean wave forces and moments predicted by numerical simulations. Highlights • New experimental device for measuring forces and moments on a ship model in waves. • Results of a comprehensive test campaign with the model of cruise ship are discussed. • Accurate extraction of non hydrodynamic inertial effects from the measured forces. • Mean values of inertial forces must be subtracted for comparison with numerical results. [ABSTRACT FROM AUTHOR]

This paper is the third of a series covering investigations of the wave induced force and motion behavior of ice masses near a fixed structure. The objective of this phase of the study was to determine whether the effects observed in regular waves (Sayeed et al. (2017b, 2018)) still held in irregular seas. In the present case, wave characteristics measured in front of the fixed structure showed that the significant wave heights follow a standing wave pattern generated by the superposition of the incident and reflected peak frequency wave. Thus it may be inferred that the significant surge and heave forces and motions will be increased or decreased at the node and antinode locations in front of the structure as previously observed for regular waves. Force spectra generated from regular wave force data (Sayeed et al. 2017b) and wave measurements from the present study showed that beyond the nodal location at D λ p = 0.25 , the significant surge force goes down and significant heave force goes up as the body gets close to the structure. Direct measurements of irregular wave forces on a fixed berg model at different proximity to the fixed structure demonstrate the change in significant wave forces based on the ratio of separation distance to peak wavelength. When the berg body is positioned closer to the fixed structure, the normalized significant forces in the horizontal direction decrease, and the normalized significant forces in the vertical direction increase. Significant differences were found between the directly measured force spectra and those produced by linear superposition of regular wave force transfer functions. This is attributed to non-linear effects arising from the iceberg profile and low freeboard. Free floating motion experiments showed smaller differences in the surge and heave velocity spectra due to the presence of the structure. This is because there is insufficient motion data at any specific location to capture the motion responses for all the frequencies in the spectrum. The proximity effect on wave loads and wave induced motions in the vertical direction is found to be more pronounced than the same in the horizontal direction. Numerical simulations using RANS based commercial CFD code Flow3D © are compared to the experimental results. Selected test cases from both force and motion experiments are simulated in irregular waves generated from selected experimental wave spectra. Numerical results for irregular waves demonstrate the ability to simulate random waves and resulting forces and motions with trends comparable to the experimental results. [ABSTRACT FROM AUTHOR]

Although the significant wave period is one of the key parameters in the design of coastal structures, it is not calculated by the spectral wave model because it is obtained by the zero-crossing analysis. The present paper examines several formulas that relate the significant wave period to wave spectral parameters such as peak period, mean period, and peakedness parameter. The formulas are derived based on the wave measurements in two locations in the Japan/East Sea (JES). The derived formulas are then compared with the measured significant wave periods in other locations in JES. It is shown that the formula using the mean wave period, T m − 1,0 , is the most accurate. This formula is further used in a spectral wave model, the significant wave periods from which are compared with the measurement. Additionally, the relationship between the significant wave height and period is obtained based on the wave hindcasting, from which the most probable significant wave period can be determined for a specific significant wave height. A comparison with the measurement shows that the relationship is relatively inaccurate in the locations where southerly swell waves are significant, which are not accurately taken into account in the numerical model. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to demonstrate the capability of compact polarized (CP) synthetic aperture radar (SAR) to retrieve ocean wave field parameters. Souyris’ and Nord’s algorithms are used to carry out the reconstruction of CP SAR pseudo quad-polarized data for the ocean surface under both the circular transmit linear receive (CTLR) and π/4 mode. The results show that, for the CP reconstruction, Nord’s algorithm has a better convergence ability than Souyris’. In addition, the investigation of the reconstruction accuracy shows that the CTLR mode is superior to the π/4 mode, in terms of ocean surface reconstruction. It is, therefore, concluded that the reconstructed parameters of CP CTLR mode data by Nord’s algorithm adapt to retrieve ocean wave information. The ocean wave slope spectrum and other main wave parameters are also calculated from reconstructed CP data and compared with measurements from in situ National Data Buoy Center (NDBC) matched-up buoys. Comparison of CP SAR-based wave field information with buoy outputs also shows good agreement in the case of dominate wave height, wave direction, and wave period, with biases of 0.36 m, 17.96°, and 0.88 s, respectively. [ABSTRACT FROM AUTHOR]

Observations on the 2004 tsunami showed that coastal forest vegetation could reduce the impacts of a tsunami or a storm surge in two ways: (i) the well-known wave attenuation and (ii) the protection of coastal areas from storm damage by stabilizing coastal sediments. In this paper, the wave damping performance of mangrove forest of different forest widths is systematically tested in Twin Wave Flumes (without and with the forest model in 1- and 2- m-wide wave flumes, respectively) for both regular and irregular waves. Results reveal that the dissipation coefficient increases with increasing forest width and is strongly related to the transmission coefficient as the contribution of the forest itself to wave reflection is negligibly small. The results also show that an increasing incident wave height causes the transmission coefficient to decrease due to stronger wave breaking. The wave energy dissipation through mangrove forest is also investigated theoretically and demonstrates a good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

ABSTRACT Mun, J.; Kim, S.-W., and Melby, J. A. 2018. A surrogate model for wave prediction based on an artificial neural network using high-fidelity synthetic hurricane modelling. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 876–880. Coconut Creek (Florida), ISSN 0749-0208. A surrogate model for significant wave height and period prediction is developed based on an artificial neural network with synthetic simulations of hurricanes. The neural networks between five input parameters and the wave height or wave period are trained by the Levenberg-Marquardt backpropagation algorithm. A back propagation is a form of supervising training algorithm and the weighting factors and the bias are updated by the back propagation training within a limited epoch. The data consists high intensity 446 storms on west region in Texas. The 14 save points in this area are analysed by the surrogate model. The performance of the static surrogate model for the significant waves is expressed as the correlation coefficient and the mean square error at the 14 save points. The minimum correlation coefficient and the mean square error are respectively 0.981 and 0.011. The predicted wave height and period are good agreement with the target values. [ABSTRACT FROM AUTHOR]

ABSTRACT Lee, J.H. and Kim, T.R., 2018. Study of High Waves caused by Slanting-fetch Effects along the Coast. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 831–835. Coconut Creek (Florida), ISSN 0749-0208. Design wave height estimation for the ports and coastal structures are mainly based on the waves from offshore wind which have long fetches enough to develop high waves. The waves generated by short fetched land wind are usually neglected because they are thought to be small and short period waves. However, in case of land wind oblique to the long coast line with short fetch, unexpected long period high waves are developed along the coast by slanting-fetch effects. These high waves can damage human lives as well as coastal structures, but are difficult to predict using offshore wave measurement system. Therefore, it is important to understand the characteristics of waves by slantingfetch and prepare countermeasures against them. This paper analyzes observed wind and wave data in the East Sea, on Feb. 6–8th and Dec. 12–14th in 2013, when waves were developed by slanting-fetch effects near the coast. During these periods, strong northwest wind of over 15 m/sec lasted more than 24 hours, but southwestward waves with significant wave height of over 1.5 m and peak period of over 10 sec were observed at Hupo Harbor in spite of land wind with short fetch. Unstructured WAVEWATCH III model is executed to simulate the waves generated by slanting-fetch effects and RDAPS/UM wind data with 12 km resolution provided by NCMS/KMA are used as forcing input data. The numerical wave model results at Hupo Harbor show relatively good agreement with in-situ measurement data explaining high waves with long period by slanting-fetch effects, and both observed and simulated wave directional spectrum at Hupo Harbor show strong energy in long period and southwestward direction. [ABSTRACT FROM AUTHOR]

The paper presents a simple analytical method that can be used to estimate wave runup (RU) and wave rundown (RD) on shorelines and coastal structures for sea states based on long-term wind statistics. Eight different recently published wave RU formulae and one RD formula are applied together with wind statistics from the northern North Sea, the North Atlantic and the North-West Shelf of Australia. Examples of results representing realistic field conditions are provided, demonstrating how global wind statistics can be used to make first-order estimates of wave RU and wave RD. [ABSTRACT FROM AUTHOR]

Recently, along with the development of data-driven models, artificial neural networks (ANN) have been used in ocean wave forecasting models. Hybridization of ANN with wavelet analysis or fuzzy logic approach has also been used. The wavelet and neural network hybrid models (WNN models) show better performance than ANN models. However, their accuracy decreases with increasing lead time because they do not consider the relation between wave and meteorological variables. Moreover, the WNN model has been developed to forecast the wave height at a single location where the past wave height data are available. To resolve these problems, in this paper, a hybrid model is developed by combining the empirical orthogonal function analysis and wavelet analysis with the neural network (abbreviated as EOFWNN model). The past wave height data at multiple locations and the past and future meteorological data in the surrounding area including the wave stations are used as input data. The model then forecasts the wave heights at the locations for various lead times. The developed model is employed to forecast the wave heights at eight wave observation stations in the coastal waters around the East/Japan Sea. The EOFWNN model is shown to perform better compared with the WNN model for all lead times regardless of the decomposition level of wavelet analysis. The EOFWNN model is proven to be a promising tool for forecasting wave heights at multiple locations where the past wave height data and the past and future meteorological data in the surrounding area are available. [ABSTRACT FROM AUTHOR]

Methods for measuring waves and winds from a Wave Glider autonomous surface vehicle (ASV) are described and evaluated. The wave method utilizes the frequency spectra of orbital velocities measured by GPS, and the wind stress method utilizes the frequency spectra of turbulent wind fluctuations measured by an ultrasonic anemometer. Both methods evaluate contaminations from vehicle motion. The methods were evaluated with 68 days of data over a full range of open ocean conditions, in which wave heights varied from 1 to 8m and wind speeds varied from 1 to 17ms-1. Reference data were collected using additional sensors on board the vehicle. For the waves method, several additional datasets are included that use independently moored Datawell Waverider buoys as reference data. Bulk wave parameters are determined within 5% error with biases of less than 5%.Wind stress is determined within 4% error with 1% bias. Wave directional spectra also compare well, although the Wave Glider results have more spread at low frequencies. [ABSTRACT FROM AUTHOR]

The properties of directional distributions in ocean wave spectra are studied, with an emphasis on sea states with bimodal directional distributions in the high-frequency tails of single-peaked wave systems. A peaksplitting tendency has been a challenge in the interpretation of results from some data-adaptive estimation methods. After a survey of the theory, mathematical and numerical explanations are presented regarding domains of uni- and bimodality for symmetric Burg and Shannon maximumentropy methods. The study finds that both the Burg and Shannon maximum entropy methods have a tendency to split peaks, and that the domains of uni- and bimodality for these two methods depend on the Fourier coefficients input into the algorithms. Comparisons of data-adaptive methods based on data collected near the Ekofisk oil field in the North Sea and from nonlinear wave simulations are presented. The maximum likelihood (ML) method, the iterative maximum likelihood (IML) method, and the Burg and Shannon maximum entropy methods are applied.Alarge fraction of the directional wave spectra from Ekofisk shows bimodal features for distributions above the spectral peak for all of the abovementioned methods. In particular, strong similarity in bimodal features between the iterative maximum likelihood and the Burg maximum entropy methods are found. In general, the bimodality is consistent with previous observations, and it seems to be associated with wave and spectral development owing to nonlinear wave-wave interactions rather than being associated with the peaksplitting tendency in the estimates from any of the algorithms. The bimodal directional distributions were sometimes persistent and sometimes formed or decayed within the order of hours. [ABSTRACT FROM AUTHOR]

Based on the hindcast data from third-generation wave model WAVEWATCH III, this study presents a notable interannual variability of significant wave height in the northern South China Sea. As indicated by the empirical orthogonal function analysis result of the significant wave height during 1976-2005, the first mode of this analysis captures a monopole structure with maximum amplitude in the southwestern Luzon Strait. Power spectrum analysis of the first empirical orthogonal function time series indicates that the significant wave height peaks at 2.67 and 8 year periods in the northern South China Sea. The first-time series had good correlation with El Niño events, with a correlation coefficient of -0.58. By comparing frequency and total duration of the intense tropical cyclones with the significant wave height in the northern South China Sea, it is revealed that the two were associated during 1978-1998 and that the recent increase of the significant wave height is due to the increase in total duration of intense tropical cyclones during 1999-2005. The sea level pressures also support the interannual variability of significant wave height in the northern South China Sea. [ABSTRACT FROM AUTHOR]

Ocean wind and wave parameters can be measured by in-situ sensors such as anemometers and buoys. Since the 1980s, X-band marine radar has evolved as one of the remote sensing instruments for such purposes since its sea surface images contain considerable wind and wave information. The maturity and accuracy of X-band marine radar wind and wave measurements have already enabled relevant commercial products to be used in real-world applications. The goal of this paper is to provide a comprehensive review of the state of the art algorithms for ocean wind and wave information extraction from X-band marine radar data. Wind measurements are mainly based on the dependence of radar image intensities on wind direction and speed. Wave parameters can be obtained from radar-derived wave spectra or radar image textures for non-coherent radar and from surface radial velocity for coherent radar. In this review, the principles of the methodologies are described, the performances are compared, and the pros and cons are discussed. Specifically, recent developments for wind and wave measurements are highlighted. These include the mitigation of rain effects on wind measurements and wave height estimation without external calibrations. Finally, remaining challenges and future trends are discussed. [ABSTRACT FROM AUTHOR]

Second-order scattering based wave height measurement with high-frequency (HF) radar has always been subjected to problems such as distance limitation and external interference especially under low or moderate sea state. The performance is further exacerbated for a compact system with small antennas. First-order Bragg scattering has been investigated to relate wave height to the stronger Bragg backscatter, but calibrating the echo power along distance and direction is challenging. In this paper, a new method is presented to deal with the calibration and improve the Bragg scattering based wave height estimation from dual-frequency radar data. The relative difference of propagation attenuation and directional spreading between two operating frequencies has been found to be identifiable along range and almost independent of direction, and it is employed to effectively reduce the fitting requirements of in situ wave buoys. A 20-day experiment was performed over the Taiwan Strait of China to validate this method. Comparison of wave height measured by radar and buoys at distance of 15 km and 70 km shows that the root-mean-square errors are 0.34 m and 0.56 m, respectively, with correlation coefficient of 0.82 and 0.84. [ABSTRACT FROM AUTHOR]

Understanding of breaking and broken waves is key for the prediction of nearshore sediment transport and coastal hazards, however the difficulty of obtaining measurements of highly unsteady nearshore waves has limited the availability of field data. This paper reports on a novel field experiment designed to capture the time-varying free-surface throughout the surf and swash zones was conducted on a dissipative sandy beach using an array of 2D LiDAR scanners. Three scanners were deployed from the pier at Saltburn-by-the-Sea, UK for a 6 day period to monitor the surface elevation of nearshore waves from the break point to the runup limit at temporal and spatial resolutions (order of centimetres) rarely achieved in field conditions. The experimental setup and the procedure to obtain a continuous time series of surface elevation and wave geometry is described. A new method to accurately determine the break point location is presented and compared to existing methodologies. [ABSTRACT FROM AUTHOR]

Nonlinear wave-wave interactions among ocean surface waves are dominated by quadruplet wave-wave interactions. Computing the nonlinear 4-wave interactions with the Boltzmann integral requires finding the loci of interactions for the quadruplets or solving the delta functions. This is an important part of the computation, but so far it is done by an iteration method that consumes computational time and may not converge after doing several iterations. In this paper, an explicit methodology to find the loci of the quadruplet interactions is presented. This research target is to develop a better method to compute the loci. To illustrate the method, there are 4 cases that will be discussed in this paper. Results show that the new method gives better results than the previous methods that have been applied. Moreover, without iterations the presented method requires less computational loops and some variables, for example the distance between loci, denoted ds, can be determined without any looping. Therefore, the new method leads to better and faster computations than the previous iteration method. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for the detection and prediction of Segments containing very high Significant Wave Height (SSWH) values in oceans. This kind of prediction is needed in order to account for potential changes in a long-term future operational environment of marine and coastal structures. The methodology firstly characterizes the wave height time series by approximating it using a sequence of labeled segments, and then a binary classifier is trained to predict the occurrence of SSWH periods based on past height values. A genetic algorithm (GA) combined with a likelihood-based local search is proposed for the first stage (detection), and the second stage (prediction) is tackled by an Artificial Neural Network (ANN) trained with a Multiobjective Evolutionary Algorithm (MOEA). Given the unbalanced nature of the dataset (SSWH are rarer than non SSWH), the MOEA is specifically designed to obtain a balance between global accuracy and individual sensitivities for both classes. The results obtained show that the GA is able to group SSWH in a specific cluster of segments and that the MOEA obtains ANN models able to perform an acceptable prediction of these SSWH. [ABSTRACT FROM AUTHOR]

To provide the more accurate simulation of stationary planetary waves and atmospheric tides using the middle and upper atmosphere model (MUAM), the three-dimensional (longitude-latitude-height) semi-empirical climate model of water vapor distribution in the troposphere was developed which takes into account seasonal variations. The modules of radiation heating and cooling in the MUAM model were modified taking into account the dependence of water vapor concentration on longitude. The simulations performed using the modified version of MUAM revealed that the consideration of water vapor concentration variability along the circle of latitude leads to the substantial dependence of solar heating on longitude that affects the amplitudes of stationary planetary waves in the stratosphere. [ABSTRACT FROM AUTHOR]

Incident wave energy flux is responsible for sediment transport and coastal erosion in wave-dominated regions such as the southwestern Australian (SWA) coastal zone. To evaluate future wave climates under increased greenhouse gas concentration scenarios, past studies have forced global wave simulations with wind data sourced from global climate model (GCM) simulations. However, due to the generally coarse spatial resolution of global climate and wave simulations, the effects of changing offshore wave conditions and sea level rise on the nearshore wave climate are still relatively unknown. To address this gap of knowledge, we investigated the projected SWA offshore, shelf, and nearshore wave climate under two potential future greenhouse gas concentration trajectories (representative concentration pathways RCP4.5 and RCP8.5). This was achieved by downscaling an ensemble of global wave simulations, forced with winds from GCMs participating in the Coupled Model Inter-comparison Project (CMIP5), into two regional domains, using the Simulating WAves Nearshore (SWAN) wave model. The wave climate is modeled for a historical 20-year time slice (1986–2005) and a projected future 20-year time-slice (2081–2100) for both scenarios. Furthermore, we compare these scenarios to the effects of considering sea-level rise (SLR) alone (stationary wave climate), and to the effects of combined SLR and projected wind-wave change. Results indicated that the SWA shelf and nearshore wave climate is more sensitive to changes in offshore mean wave direction than offshore wave heights. Nearshore, wave energy flux was projected to increase by ∼10% in exposed areas and decrease by ∼10% in sheltered areas under both climate scenarios due to a change in wave directions, compared to an overall increase of 2–4% in offshore wave heights. With SLR, the annual mean wave energy flux was projected to increase by up to 20% in shallow water (< 30 m) as a result of decreased wave dissipation. In winter months, the longshore wave energy flux, which is responsible for littoral drift, is expected to increase by up to 39% (62%) under the RCP4.5 (RCP8.5) greenhouse gas concentration pathway with SLR. The study highlights the importance of using high-resolution wave simulations to evaluate future regional wave climates, since the coastal wave climate is more responsive to changes in wave direction and sea level than offshore wave heights. [ABSTRACT FROM AUTHOR]

In this paper, the retrieving significant wave height from X-band marine radar images based on shadow statistics is investigated, since the retrieving accuracy can not be seriously affected by environmental factors and the method has the advantage of without any external reference to calibrate. However, the accuracy of the significant wave height estimated from the radar image acquired at the near-shore area is not ideal. To solve this problem, the effect of water depth is considered in the theoretical derivation of estimated wave height based on the sea surface slope. And then, an improved retrieving algorithm which is suitable for both in deep water area and shallow water area is developed. In addition, the radar data are sparsely processed in advance in order to achieve high quality edge image for the requirement of shadow statistic algorithm, since the high resolution radar images will lead to angle-blurred for the image edge detection and time-consuming in the estimation of sea surface slope. The data acquired from Pingtan Test Base in Fujian Province were used to verify the effectiveness of the proposed algorithm. The experimental results demonstrate that the improved method which takes into account the water depth is more efficient and effective and has better performance for retrieving significant wave height in the shallow water area, compared to the in situ buoy data as the ground truth and that of the existing shadow statistic method. [ABSTRACT FROM AUTHOR]

The formulation for wave prediction using multipoint measured data is derived for the short crested waves. The formulation can be applied not only for the stationary process but also the non-stationary process. Based on this formulation, a convolution integral formula which represents the relation of free surface elevation between multipoint measurement and target point prediction is obtained. Examples based on numerical experiments of long crested waves show that prediction error is small when the prediction time is short and the measurement point is sufficiently far from target. Although it is found that the accuracy of the prediction based on the proposed method has a limit for short crested waves, the agreement is fairly good. [ABSTRACT FROM AUTHOR]

Sea-salt aerosol concentrations in the coastal zone are assessed with the numerical aerosol-transport model MACMod that applies separate aerosol source functions for open ocean and the surf zone near the sea-land transition. Numerical simulations of the aerosol concentration as a function of offshore distance from the surf zone compare favourably with experimental data obtained during a surf-zone aerosol experiment in Duck, North Carolina in autumn 2007. Based on numerical simulations, the effect of variations in aerosol production (source strength) and transport conditions (wind speed, air-sea temperature difference), we show that the surf-zone aerosols are replaced by aerosols generated over the open ocean as the airmass advects out to sea. The contribution from the surf-generated aerosol is significant during high wind speeds and high wave events, and is significant up to 30 km away from the production zone. At low wind speeds, the oceanic component dominates, except within 1-5 km of the surf zone. Similar results are obtained for onshore flow, where no further sea-salt aerosol production occurs as the airmass advects out over land. The oceanic aerosols that are well-mixed throughout the boundary layer are then more efficiently transported inland than are the surf-generated aerosols, which are confined to the first few tens of metres above the surface, and are therefore also more susceptible to the type of surface (trees or grass) that determines the deposition velocity. [ABSTRACT FROM AUTHOR]

Ocean waves have multidirectional components. Most wave measurements are taken at a single point, and so fail to capture information about the relative directions of the wave components directly. Conventional means of directional estimation require a minimum of three concurrent time series of measurements at different spatial locations in order to derive information on local directional wave spreading. Here, the relationship between wave nonlinearity and directionality is utilized to estimate local spreading without the need for multiple concurrent measurements, following Adcock & Taylor (Adcock & Taylor 2009 Proc. R. Soc. A 465, 3361–3381. (doi:10.1098/rspa.2009.0031)), with the assumption that directional spreading is frequency independent. The method is applied to measurements recorded at the North Alwyn platform in the northern North Sea, and the results compared against estimates of wave spreading by conventional measurement methods and hindcast data. Records containing freak waves were excluded. It is found that the method provides accurate estimates of wave spreading over a range of conditions experienced at North Alwyn, despite the noisy chaotic signals that characterize such ocean wave data. The results provide further confirmation that Adcock and Taylor's method is applicable to metocean data and has considerable future promise as a technique to recover estimates of wave spreading from single point wave measurement devices. [ABSTRACT FROM AUTHOR]

Wave variability and connections with climate indices along the U.S. West Coast were analyzed in this study. Monthly significant wave height data from five buoy stations that have an observation period ranging 18-37 years along with large-scale climate indices were used in the analysis. The dominant modes of significant wave height variability were determined using continuous wavelet transforms. There is a significant power at the annual scale during the whole measurement period of all stations. Cross-wavelet power spectra was used to explore the possible effects of El Niño Southern Oscillation (ENSO) events on the wave climate variation. Correlation between the significant wave heights and large-scale climate indices at different temporal scales showed that there is a relationship between significant wave heights and indices. This finding indicates that positive ENSO events lead to larger wave heights in the region. [ABSTRACT FROM AUTHOR]

This paper concerns the description of surface water waves, specifically nonlinear changes in the directionality. Supporting calculations are provided to establish the best method of directional wave generation, the preferred method of directional analysis and the inputs on which such a method should be based. These calculations show that a random directional method, in which the phasing, amplitude and direction of propagation of individual wave components are chosen randomly, has benefits in achieving the required ergodicity. In terms of analysis procedures, the extended maximum entropy principle, with inputs based upon vector quantities, produces the best description of directionality. With laboratory data describing the water surface elevation and the two horizontal velocity components at a single point, several steep sea states are considered. The results confirm that, as the steepness of a sea state increases, the overall directionality of the sea state reduces. More importantly, it is also shown that the largest waves become less spread or more unidirectional than the sea state as a whole. This provides an important link to earlier descriptions of deterministic wave groups produced by frequency focusing, helps to explain recent field observations and has important practical implications for the design of marine structures and vessels. [ABSTRACT FROM AUTHOR]

Kim, K.O.; Yuk, J.-H.; Jung, K.T., and Choi, B.H., 2017. Swell propagation caused by typhoon passage to the Yellow and East China Seas. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 144-148. Coconut Creek (Florida), ISSN 0749-0208. Typhoons generate big swells frequently propagating over the East China Sea, the wide continental shelf sea with depth shallower than 200 m. The characteristic features of swell propagation into the Yellow and East China Seas caused by typhoon Herb in 1996 has been investigated applying a ray-tracing technique and a spectral wave model (SWAN) with an unstructured-mesh grid system. This study discusses the generation and propagation of the swells into the Yellow and East China Seas using the integration of ray trajectories and model-based simulated wave. Calculated and observed wave heights and periods at Gadeokdo, Korea are found to be in reasonable agreement with each other. [ABSTRACT FROM AUTHOR]

Severe sea states in the North Sea present a challenge to wave forecasting systems and a threat to offshore installations such as oil and gas platforms and offshore wind farms. Here, we study the ability of a third-generation spectral wave model to reproduce winter sea states in the North Sea. Measured and modeled time series of integral wave parameters and directional wave spectra are compared for a 12-day period in the winter of 2013-2014 when successive severe storms moved across the North Atlantic and the North Sea. Records were obtained from a Doppler radar and wave buoys. The hindcast was performed with the WAVEWATCH III model (Tolman 2014) with high spectral resolution both in frequency and direction. A good general agreement was obtained for integrated parameters, but discrepancies were found to occur in spectral shapes. [ABSTRACT FROM AUTHOR]

Future wave climate projection is important for climate impact assessment of the coastal hazards and environment. In this study, monthly averaged wave heights are estimated by a linear multi-regression model using atmospheric data as explanatory variables. The present statistical model considers local atmospheric information (wind speed at 10 m height, sea level pressure) and large scale atmospheric information obtained from principal component analysis (PCA) of the global sea level pressure field. The representation of swell in the lower latitude is greatly improved by introducing the large scale atmospheric information from the PCA. The present statistical model was applied to the results of the Japan Meteorological Research Institute's Atmospheric General/Global Circulation Model (MRI-AGCM) climate change projection. The future change of wave heights shows an increase in the northern North Pacific Ocean and a decrease in the North Atlantic Ocean, middle latitude and tropics of the Pacific Ocean. [ABSTRACT FROM AUTHOR]

The results of studying sea-wave spectra in a wide wavelength range using high resolution (0.5-1.0 m) satellite optical imagery spectra and the results of measurements carried out from an oceanographic platform using string-wave recorders, stereo system, and drifting wave buoys are presented in this paper. The wave spectra retrieved from satellite imagery and sea-truth data have been compared. A comparison has shown the adequacy of the purposely developed retrieval methods. Power approximation indices for spatial spectra in the 0.04-5.0-m wavelength range have been found. It has been shown that the wave spectra measured experimentally by satellite-based and in-situ methods best approximate the Toba spectrum. [ABSTRACT FROM AUTHOR]

Widespread short-period internal wave (SPIW) activity in the White Sea has been revealed for the first time based on long-term (2009-2013) monitoring performed using satellite and in situ observations, and the statistical characteristics of these waves have been obtained. Two main regions where short-period waves constantly exist have been identified: the shelf area near the frontal zone at the boundary between the Basin and the Gorlo Strait and the shallow shelf area where the depths are about 30-50 m near Solovetskie Islands. Intense internal waves (IIWs), which are substantially nonlinear and are related to specific phases of a barotropic tide, are regularly observed near frontal zones. The wave height can reach half the sea depth and the wave periods vary from 7 to 18 min. [ABSTRACT FROM AUTHOR]

The Krishna-Godavari coastal region in east coast of India has a 525.15-km-long coastline with low-lying tidal mudflats, beaches, mangrove swamp, creek and tidal channels. Recently, the increasing frequency of tropical cyclones in the Bay of Bengal, i.e., Phylin and Hudhud in Andhra Pradesh coast, and the devastating impact of the 2004 tsunami in India increased the significance in assessing the vulnerability of the coastal lands to inundation and flooding, notably in the context of climate change-induced sea level rise. This study aims to estimate a coastal vulnerability index (CVI) for the coastal subregion of Krishna-Godavari delta and to use the calculated index to evaluate the vulnerability of 14 coastal talukas of the Krishna-Godavari delta region. This CVI is calculated by using four geological and three physical parameters characterizing the vulnerability of the study coastal region, including regional slope, coastal elevation, geomorphology, significant wave height, mean tidal range and relative sea level using different conventional and remotely sensed data. Using a composite coastal vulnerability index based on the relative risk rating of those parameters, each of the 14 coastal talukas was classified according to their vulnerability. The CVI results depict that coasts are least and most vulnerable to inundation, flooding and erosion of coastal lands where geological parameters are more efficient to CVI. The paper alerts to decision makers and planners to mitigate the natural disaster and manage the coastal zone and is a primary step toward prioritizing coastal lands for climate change adaptation strategies in the view of increased storminess and projected sea level rise. [ABSTRACT FROM AUTHOR]

Sea wind and sea state estimation by synthetic aperture radar (SAR) measurements is a topic of relevance both on the scientific and user side. The new European Space Agency (ESA) Sentinel-1 constellation is meant to support marine studies and ensure high-quality data. In this paper, we investigate the azimuth cut-off () sea wind speed and significant wave height retrieval approach by taking benefit of two sets of multi-look SAR images with incidence angles varying from 20° to 45°. The images have been co-located with sea surface wind measurements acquired by the scatterometer onboard the Chinese satellite HY-2A (HSCAT) and with the European Centre for Medium Range Weather Forecast (ECMWF) operational model output. This study is meant to analyse both the empirical dependency of SARon significant wave height () and wind speed (U). Several fitting geophysical model functions (-GMFs) are proposed and discussed. The results show thatis strongly correlated with the significant wave height in all sea state conditions, while the correlation with the wind speed is only high for fully developed sea states. The azimuth cut-off based significant wave height retrievals are compared with independent National Data Buoy Centre (NDBC) network observations, showing a root mean square difference of about 0.5 m. [ABSTRACT FROM PUBLISHER]

It is demonstrated that the greatest influence of the variations in the groupiness of storm waves in the Baltic Sea concerns the highest waves. The variations in the height of less high waves are defined by wind speed. It is revealed that the height of 3% of the highest waves depends on their bandwidth: higher and lower waves are characterized by the larger and smaller set of frequencies, respectively. The significant wave height does not almost depend on the bandwidth. It is found that the spectrum of storm waves in the southwestern part of the Baltic Sea has a multi-peak structure which reflects the complex structure of waves consisting of several wave systems. Envelopes and individual waves of different frequency ranges superimpose, and extreme waves are generated. The probability of occurrence of extreme waves is maximum at the moments of the maximum development of wave groupiness. [ABSTRACT FROM AUTHOR]

In this study, nadir altimeter radar measurements are used to improve wind speed and sea state information in coastal regions, more precisely the north Indian Ocean. A methodology is suggested to combine the Ku- and C-band radar measurements, their difference, the measured significant wave height (HS) parameter and its along-track gradient. A dimensionlessHSis used to recover empirical dependencies for fetch-limited wind wave development in this coastal region. As obtained, these simultaneous measurements can be efficiently combined to more precisely separate wind-related short-scale wave contributions from large-scale wave components, related to the local sea state degree of development. As demonstrated, this development helps to gain valuable insights concerning the use of altimeter measurements in coastal regions. [ABSTRACT FROM PUBLISHER]

The influence of wave-current interactions on time series of marine X-band radar backscatter maps at the mouth of the Columbia River (MCR) near Astoria, Oregon, is examined. The energetic wave environment at the MCR, coupled with the strong tidally forced currents, provides a unique test environment to explore the limitations in accurately determining the magnitude and vertical structure of upper-ocean currents from wavefield measurements. Direct observation in time and space of the wave-induced radar backscatter and supporting acoustic Doppler current profiler (ADCP) current measurements provide a rich dataset for investigating how currents shift the observed wave dispersion relationship. First, current extraction techniques that assume a specific current-depth profile are tested against ADCP measurements. These constrained solutions prove to have inaccuracies because the models do not properly account for vertical shear. A forward solution using measured current profiles to predict the wavenumber-Doppler shift relationship for the range of ocean waves sensed by the radar is introduced. This approach confirms the ocean wavefield is affected by underlying vertical current shear. Finally, a new inversion method is developed to extract current profiles from the wavenumber-dependent Doppler shift observations. The success of the inversion model is shown to be sensitive to the range of wavenumbers spanned by observed Doppler shifts, with skill exceeding 0.8 when wavenumbers span more than 0.1 rad m−1. This agreement when observations successfully capture the broadband wavefield suggests the X-band backscatter is a viable means of remotely estimating current shear. [ABSTRACT FROM AUTHOR]

Predetermination of background error covariance matrix B is challenging in existing ocean data assimilation schemes such as the optimal interpolation (OI). An optimal spectral decomposition (OSD) has been developed to overcome such difficulty without using the B matrix. The basis functions are eigenvectors of the horizontal Laplacian operator, pre-calculated on the base of ocean topography, and independent on any observational data and background fields. Minimization of analysis error variance is achieved by optimal selection of the spectral coefficients. Optimal mode truncation is dependent on the observational data and observational error variance and determined using the steep-descending method. Analytical 2D fields of large and small mesoscale eddies with white Gaussian noises inside a domain with four rigid and curved boundaries are used to demonstrate the capability of the OSD method. The overall error reduction using the OSD is evident in comparison to the OI scheme. Synoptic monthly gridded world ocean temperature, salinity, and absolute geostrophic velocity datasets produced with the OSD method and quality controlled by the NOAA National Centers for Environmental Information (NCEI) are also presented. [ABSTRACT FROM AUTHOR]

In design and operation of floating offshore structures, one has to avoid fatigue failures caused by action of ocean waves. The aim of this paper is to investigate the applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures. The applicability was investigated for Bluewaters' FPSO (Floating Production, Storage and Offloading) which had been turret moored at Sable field for half a decade. The waves were predicted as sea-state time series consisting of one wind sea and one swell. The predicted waves were compared with wave data obtained from ERA-interim and buoy measurements. Furthermore, the fatigue calculations were also carried out for main deck and side shell locations. It has been concluded that predicted fatigue damages of main deck using WaveWatch-III are in a very good agreement regardless of differences in predicted wind waves and swells caused by differences in wave system partitioning. When compared to buoy measurements, the model underestimates fatigue damages of side shell by approximately 30 %. The reason for that has been found in wider directional spreading of actual waves. The WaveWatch-III wave model has been found suitable for the fatigue assessment. However, more attention should be paid on relative wave directionality, wave system partitioning and uncertainty analysis in further development. [ABSTRACT FROM AUTHOR]

The high-frequency (HF) radar inversion algorithm for spectrum estimation (HIAS) can estimate ocean wave directional spectra from both dual and single radar. Wave data from a dual radar and two single radars are compared with in situ observations. The agreement of the wave parameters estimated from the dual radar with those from in situ observations is the best of the three. In contrast, the agreement of the wave parameters estimated from the single radar in which no Doppler spectra are observed in the cell closest to the in situ observation point is the worst among the three. Wave data from the dual radar and the two single radars are compared. The comparison of the wave heights estimated from the single and dual radars shows that the area sampled by the Doppler spectra for the single radar is more critical than the number of Doppler spectra in terms of agreement with the dual-radar-estimated wave heights. In contrast, the comparison of the wave periods demonstrates that the number of Doppler spectra observed by the single radar is more critical for agreement of the wave periods than the area of the Doppler spectra. There is a bias directed to the radar position in the single radar estimated wave direction. [ABSTRACT FROM AUTHOR]

An autonomous vessel, the Offshore Sensing Sailbuoy, was used for wave measurements near the Ekofisk oil platform complex in the North Sea (56.5º N, 3.2º E, operated by ConocoPhillips) from 6 to 20 November 2015. Being 100 % wind propelled, the Sailbuoy has two-way communication via the Iridium network and has the capability for missions of 6 months or more. It has previously been deployed in the Arctic, Norwegian Sea and the Gulf of Mexico, but the present study was the first test for wave measurements. During the campaign the Sailbuoy held position about 20 km northeast of Ekofisk (on the lee side) during rough conditions. Mean wind speed measured at Ekofisk during the campaign was 9.8 m/s, with a maximum of 20.4 m/s, with wind mostly from south and southwest. A Datawell MOSE G1000 GPS-based 2 Hz wave sensor was mounted on the Sailbuoy. Mean significant wave height ( H 1 min) measured was 3 m, whereas maximum H was 6 m. Mean wave period was 7.7 s, while maximum wave height, H , was 12.6 m. These measurements have been compared with non-directional Waverider observations at the Ekofisk complex. The agreement between the two data sets was very good, with a mean percent absolute error of 7 % and a linear correlation coefficient of 0.97. The wave frequency spectra measured by the two instruments compared very well, except for low H (∼1 m), where the motion of the vessel seemed to influence the measurements. Nevertheless, the Sailbuoy performed well during this campaign, and results suggest that it is a suitable platform for wave measurements in a broad range of sea conditions. [ABSTRACT FROM AUTHOR]

We present a comprehensive and critical review of work on the numerical modelling of swash zone processes between 2005 and 2015. A wide range of numerical models has been employed for the study of this region and, hence, only phase-resolving approaches (i.e., depth-averaged and depth-resolving models) are analyzed. The current advances in the modelling of swash zone processes are illustrated by comparing different numerical models against laboratory experiments of a dam-break-driven swash event. Depth-averaged and depth-resolving models describe well the swash flow for both coarse sand and gravel impermeable beach cases. Depth-averaged models provides a practical tool for engineering use, whereas depth-resolving models improve the flow description, especially for the backwash phase, with a significantly higher computational cost. The evolution and magnitude of bed shear stresses predicted by all models is reasonable when compared with laboratory estimates based on the log-law. However, differences between modelling approaches cannot be rigorously evaluated owing to the uncertainty in shear stress estimates while employing such approximation. Furthermore, small-scale processes, such as turbulence evolution, are investigated with depth-resolving models, finding differences between the two-dimensional and three-dimensional approaches. Numerical models allow us to investigate other processes such as beach morphology changes, the evolution of the turbulence coherent structures, and the infiltration/exfiltration effects on the swash flow. A discussion on the advantages and limitations of each model is presented. The future of swash zone modelling depends on the increase of the computational power and, more importantly, on the improvement of the current capability to obtain intra-wave measurements for model validation, calibration, and greater resolution of physical processes. [ABSTRACT FROM AUTHOR]

This study deals with winter storm-induced continental shelf waves (CSWs) in the northern South China Sea in winter 2009 using tidal gauge data and along-track satellite altimeter data. The results show that the periods of CSWs propagating along the coast from Kanmen to Shuidong are in bands of 62 and 133 h. The phase speeds are in a range from 8 to 13 m s −1 between Kanmen and Shantou, from 9 to 11 m s −1 between Shantou and Huizhou and from 10 to 15 m s −1 between Huizhou and Shuidong, respectively. Satellite altimeter captured along-track sea level anomaly during the CSW events. Further analysis using the theoretical cross-shore CSW modes to fit the along-track sea level anomaly data indicates that the first three wave modes play important roles during the CSW events and the first mode is a dominant component. [ABSTRACT FROM AUTHOR]

In ocean engineering designs, random extreme events are the most difficultly determined environmental load factors. Appearances of freak waves in the normal sea states are just such events. To reduce their potential destruction of marine structures, a forecast model is studied to predict whether freak waves occur in the wave propagation. In this model, the modified fourth-order nonlinear Schrödinger equation is employed as the deep-water wave model, which controls the evolution of complex wave envelopes. The measured wave train is set as its initial condition which needs to be changed into its corresponding complex wave envelope by use of the Hilbert transform method to be input into the wave model. During the evolution of complex wave envelope, its corresponding wave heights are estimated and compared with the definition of freak waves. If a freak wave is captured, its occurrence position and time are given. Three cases of observed, simulated and laboratory wave trains as initial conditions are performed to predict the generation of freak waves. Results show that measured wave trains can be simply and accurately input into this forecast model through the Hilbert transform method and this model can predict the generation of freak waves within some space and time in its traveling. In addition, larger groups than usual group height or length increase the probability of freak wave generation. This forecast model may provide marine activities with a safety warning in some open seas. [ABSTRACT FROM PUBLISHER]