Third-generation Wave Model Research Articles

Simulated Directional Wave Spectra of the Wind Sea and Swell under Typhoon Mangkhut

A third-generation wave model is driven by the synthetic wind field combined with the revised Holland wind and surface wind product from the National Centers for Environmental Prediction (NCEP). The temporal and spatial characteristics of the wind waves and swell during the typhoon are studied, as well as the responses of their wave energy spectra to the source terms. The results show that the typhoon waves have a more complicated asymmetric structure than the wind field, and the maximum significant wave height is always located on the right side of the direction along which the typhoon is moving, where wind waves are dominant, due to the extended fetch. The nonlinear wave–wave interaction helps to redistribute the energy of the wind seas at a high frequency to the remotely generated swells at a low frequency, ensuring that the typhoon wave’s energy spectrum remains unimodal. This process occurs in regions without extended fetch, and a similar continued downshift in frequency as the wave–wave interaction occurs for the wind input as well when the waves outrun the typhoon, due to the nonlinear coupling between the wind and growing swells.

The operational CMEMS wind wave forecasting system of the Black Sea

ABSTRACT Accurate wind wave data is essential for ship navigation, safety at sea, and offshore energy production. Access to real-time and forecast wave data, with quality metrics, is vital for operational services. The Copernicus Marine Environment Monitoring Service (CMEMS) operational wave forecasting system of the Black Sea relies on the third-generation WAve Model (WAM). It offers a 1-day hindcast and 10-day forecast at 2.5 km spatial and 1-hour temporal resolutions. The model is driven by ECMWF IFS010 winds as well as surface currents and sea surface heights from a hydrodynamic model. The model's validation against satellite and buoy data indicates good overall performance. For two-year satellite significant wave heights, error statistics include a root mean square difference (RMSD) of 27 cm, a bias of – 16 cm, a scatter index of 0.22, and a correlation coefficient of 0.93. Wave buoy comparisons show a RMSD of 1.09 s for the TM02 period and a 30.5° standard deviation of the mean direction. The model performs well during storm events and provides reliable wave forecasts for up to four days, despite slightly underestimating the significant wave height. The driving wind fields generally perform well, but assessments reveal shortcomings along the coasts.

Study on the tropical cyclone-generated waves after ensemble-based assimilation of multi-mission satellite altimeters

The third-generation wave model, WAVEWATCH III, is adopted for numerical simulation during the 2020 Atlantic Hurricane Season (AHS). This study examines the effects of data assimilation using significant wave height (SWH) from six satellite altimeters, notably the CRYOSAT-2, JASON-3, SENTINEL-3A, SENTINEL-3B, HY-2B, and CFOSAT. Two packages of wind input and wave dissipation (ST4 and ST6) are compared during 22 tropical cyclones, revealing that ST4 is better suited for farshore regions, while ST6 is more appropriate for nearshore areas. Additionally, satellite assimilation has the potential to enhance the predictive capabilities of wave models using diverse parameterization schemes. In farshore regions characterized by high sea conditions and distances less than 200 km from satellite data, a significant reduction in Root Mean Squared Error (RMSE) is evident in assimilation experiments, with the degree of improvement escalating as more satellite altimeters are assimilated. Moreover, when model simulations display substantial negative biases, the assimilation of additional altimeters effectively rectifies these biases. However, in nearshore areas, substantial enhancements resulting from increased satellite data assimilation are observable only when the distance to the nearest satellite data is less than 50 km. Future assimilation endeavors should contemplate the inclusion of in-situ observations from nearshore sites.

Wave Energy Assessment for the Atlantic Coast of Morocco

This study estimates wave energy for the Moroccan Atlantic coast using SWAN, a third-generation wave model, covering a period of 30 years, from 1991 to 2020. The model is forced by the wind from the ERA-5 reanalysis dataset and uses boundary conditions generated by the WAVEWATCH III model. The significant wave height and period are used to obtain wave energy, which is analyzed at a regional scale. The mean wave energy density within the domain is assessed to be about 20 kW/m. Five specific locations are evaluated along the coast in order to determine the most energetic ones. The most energetic area of the Moroccan Atlantic coast is located at the center, between the cities of Agadir and Essaouira. Finally, the performance of six different wave energy converters is assessed through their power matrix for each of the five locations.

Estimating waves via measured ship responses

Optimisation of energy efficiency and operational performance as well as assessment of safety levels and emissions of marine operations require detailed information about the acting wave system. It is possible—with an analogy to classical wave buoys—to estimate the directional wave spectrum by processing sensor measurements of wave-induced responses (e.g., motions and structural responses) from a ship. Compared to other sources of wave data (e.g., buoys, satellites, third-generation wave models), estimation concepts using the ship itself as a buoy provide the wave spectrum at the exact spatio-temporal point, potentially increasing accuracy and with minimal associated cost. This paper gives an overview of the technology, discusses associated uncertainties, and highlights new developments made for estimating waves via measured ship responses.

THE WAVE CLIMATE OF SOUTH-EAST AUSTRALIA AND FUTURE WAVE PROJECTION BY THE END OF 21ST CENTURY

In this study, high-resolution unstructured ocean wave datasets based on a third-generation wave model (WAVEWATCH III, WW3) were developed for south-east Australia. Through this study, we aim to understand the wave climate based on hindcast model datasets and develop future wave projections by the end of the 21st century.

AUTOMATIC WAVE MODEL CALIBRATION USING SURROGATE MODELS

Alonso and Solari (2017) presented an approach for the automatic calibration of a third-generation wave model, using the significant wave height error as the objective function. Alonso and Solari (2021) extended the methodology, incorporating a spectral error as the objective function and the use of the maximum dissimilarity algorithm to minimize the number of sea states used for calibration without losing representativeness. It was found that the use of the spectral error does not necessarily guarantee an improvement in Hs results. Furthermore, calculation times were still too long for the general application of the method. The objective of this work is twofold: (1) to introduce the use of surrogate models in the automatic calibration algorithm to speed up computation times, and (2) to explore a wide spectrum of objective functions for model calibration.

Evolution Wave Condition Using WAVEWATCH III for Island Sheltered Area in the South China Sea

Wave conditions around islands in the South China Sea (SCS) are of significant interest due to their importance for marine operations and coastal engineering. Understanding and accurately predicting wave characteristics in this region are crucial. In this study, the third-generation wave model WAVEWATCH III is employed to examine wave conditions around islands in the SCS. According to the water depth and significant wave height, the sea state around the island was classified into two categories: typhoon sea state and moderate sea state. Several popular wind input–dissipation source terms (ST2, ST4 and ST6) are used to assess the typhoon sea state and the moderate sea state separately. The results are validated by field wave data. ST4 and ST6 show good performance in significant wave height for moderate sea states, while ST2 is good at the mean wave period. For the typhoon sea state, ST2 gives the best results in significant wave height with larger correlation coefficients and a smaller RMSE. The above results provide valuable insights into the effects of different source terms on the accuracy of wave simulations for different sea states. The spatial distribution of the significant wave heights is also demonstrated with ST2, which may be useful for assessing the wave conditions of marine structures from the large scale of the SCS to the island scale of the Yongle Atoll.

Global 3-hourly wind-wave and swell data for wave climate and wave energy resource research from 1950 to 2100

Ocean wave climate, including wind waves and swells, is essential to human marine activities and global or regional climate systems, and is highly related to harnessing wave energy resources. In this study, a global 3-hourly instantaneous wave dataset was established with the third-generation wave model MASNUM-WAM and wind forcings derived from the products of the First Institute of Oceanography-Earth System Model version 2.0, the climate model coupled with wave model, under the unified framework of the Coupled Model Intercomparison Project phase 6. This dataset contains 17 wave parameters, including the information associated with wave energy and spectral shape geometries, from one historical (1950–2014) simulation and three future (2015–2100) scenario experiments (ssp125, ssp245, and ssp585). Moreover, all the parameters can be accessed separately in the form of wind waves and swells. The historical results show that the simulated wave characteristics agree well with satellite observations and the ERA5 reanalysis products. This dataset can provide the community with a unique and informative data source for wave climate and wave energy resource research.

Time Variation Trend of Wave Power Density in the South China Sea

Based on the third-generation wave model WAVEWATCH-III (WW3), this paper analyzes the changing trend of wave power density (WPD) in the South China Sea, which can provide necessary references for the development and utilization of wave energy resources in the future. In this study, multi-platform cross-calibrated (CCMP) wind data was used to drive WW3 to calculate the WPD of the South China Sea. The Mann-Kendall (MK) algorithm can be used to determine the mutation of WPD, and the accuracy of the CCMP wind was verified. Next, the time distribution of WPD is analyzed for the whole sea area and dominant sea area of the South China Sea, and on this basis, the dominant sea area for the development of wave energy resources in the South China Sea was studied. The results are as follows: (1) Extreme weather has a significant impact on the change of WPD in the South China Sea, and this change is likely due to the effect of extreme weather on sea temperature. (2) Dongsha Islands has the highest annual WPD value and has the greatest impact on the overall trend change of the South China Sea. (3) Integrated wave energy exploitability and safety and technology perspectives, the waters around Taiwan Strait are more suitable as the primary site for energy conversion.

Assessment of WAVEWATCH-III in Wind Wave Modeling of the Xisha Islands

The Xisha islands is a unique area where offshore structures can be utilized as exploration bases in the remote sea. Forecasting of sea state parameters is critical for the design and operation of offshore structures. The goal of this work is to establish an effective operational model to simulate wind waves in the Xisha Islands based on the third-generation wave model WAVEWATCH-III. During the process, two significant difficulties are highlighted and addressed: grid modeling optimization and physical source terms assessment. Typhoon-induced waves using different grid modeling techniques and physical parameterizations were modeled and evaluated using buoy measurements near islands and reefs. It was found that the unstructured triangular grid had a better performance than the other grid options in complex terrain environments like the Xisha Islands. The ST2 source-term package can provide efficient and accurate results in significant wave heights than the other source-term packages in the South China Sea.

Research on the influential characteristics of asymmetric wind fields on typhoon waves

The East China Sea is an ocean region with frequent typhoons, typhoons are also the main reason for inducing typhoon waves. The complexity of typhoon waves is closely related to the complexity of typhoon wind field. In previous studies, symmetrical wind field models or superimposed wind field models were usually used to simulate typhoon waves. However, the actual wind fields are asymmetric, and the asymmetry is affected by many factors. Therefore, three wind field models are used to simulate the wind field of Typhoon Muifa that moved through the East China Sea. Moreover, the abovementioned wind field models are used to drive the third-generation wave model SWAN to simulate the wave field and wave spectrum of Typhoon Muifa. Studies show that the values generated by the asymmetric wind field model are most consistent with the actual measurement data. This is especially the case if the typhoon center is closer to the station. The accuracy of the typhoon waves simulated using the asymmetric wind field model is better than that of the other two wind field models. The asymmetric wind field can reflect the asymmetric characteristics of the typhoon well. The substantial wave heights on the right side of typhoon’s path are substantially higher than those on the left side of path. Additionally, the maximum wave spectral density and total energy of waves as simulated by the asymmetric wind field are both larger than those of the other two wind field models. Thus, the asymmetric wind field model is more suitable for the numerical simulation of typhoon waves in the East China Sea.

Study on wave attenuation on a coral reef flat in SCS by in-situ measurement and simulation

There has been no quantitative assessment of the wave attenuation coefficient on the coral reef flat in South China Sea (SCS) previously. Based on MIDAS DWR (Directional Wave Recorder), an in-situ experiment was carried out on a coral reef flat of Yongle Atoll, SCS. Waves and currents were measured at several locations on the reef flat, which were used to estimate wave attenuation due to bottom friction. A spectral wave model based on the action density balance equations is proposed to solve the wave attenuation coefficients on the coral reef flat, which can consider influence of currents. The wave attenuation coefficients due to bottom friction on the coral reef flat were found to be one order of magnitude greater than that recommended in most spectral wave models. Additionally, numerical simulation using a third-generation wave model SWAN was carried out. The simulation results verify in turn that the bottom friction plays a predominant role in the wave attenuation on the coral reef flat. It also captures the main characteristic of wave directional spectra with high precision. The study of the wave attenuation characteristics near islands and reefs will lay a foundation for the mechanism of wave propagating near islands and reefs.

Storm Wave Characteristics during Typhoons Maysak and Haishen on the East and South Coasts of Korea

Seo, S.-C.; Kim, H.-J.; Hwang, T., and Lee, W.-D., 2023. Storm wave characteristics during Typhoons Maysak and Haishen on the east and south coasts of Korea. Journal of Coastal Research, 39(1), 129–142. Charlotte (North Carolina), ISSN 0749-0208. Typhoons Maysak and Haishen, the ninth and tenth typhoons of 2020, ravaged the Korean Peninsula within an interval of only 4 to 5 days. In the vicinity of the peninsula, these two typhoons exhibited unusual northward movement paths as they made landfall on the south coast of Korea and exited off the east coast. The storm waves caused by these typhoons damaged a number of structures along the east and south coasts, particularly by overtopping and flooding. In this study, storm waves were estimated by applying the wind fields caused by Typhoons Maysak and Haishen in the third-generation wave model Simulation WAves Nearshore (SWAN), and results were verified through a comparison with wave observation data. The storm wave characteristics were analyzed mainly based on the east and south coasts, which were damaged by high waves that accompanied the typhoons. In addition, the deep-water design wave specifications around the Korean Peninsula revised in 2019 were compared with the storm waves that occurred during Typhoons Maysak and Haishen as calculated by the SWAN model. Consequently, during the onslaughts of Typhoons Maysak and Haishen, storm waves corresponding to more than 90% of the deep-water design wave heights for the 50 year return period were estimated at grid points on the East Sea and Ulleungdo Island of Korea.

Numerical Investigation Of The Uncertainty Of Typhoon Wave Parameters Retrieval Using HF Radar

The aim of this study was to identify the sources of uncertainties of typhoon wave field monitoring using HF radar and to quantitatively assess the bias of the wave parameters, such as significant wave height and mean period, retrieved under various conditions. The strategy was to apply a purely numerical simulation of the Doppler-range spectra and then compare the estimation results to the target. For the quantitative investigation, a numerical test-bed was established. The test-bed was used to simulate the Doppler spectra based on Barrick’s (1972) theory by using the input of the directional wave spectra. The typhoon wave spectra were hindcasted using a third-generation wave model. Initially, the uncertainty source from Barrick’s theory was identified when comparing the deviations of the estimation results obtained from the idealized case of steady and homogenous fields. The accuracy of the wave height and the mean period was found to be significantly influenced by the angle between the radar-looking direction and the wave direction. Furthermore, two conceptual numerical experiments were designed to evaluate the uncertainties owing to the rotation and the translation of the typhoon wind fields, respectively. The first design focussed on the upper-right quadrant around the maximum wind radius of the typhoon using a virtual radar network that moved along with the typhoon. The second one was a more realistic design in that the virtual radar stations were located on the coastline. The scatter index of the wave height estimated from the second design was found to be approximately twice larger than that obtained using the first design. It was 25% larger for the uncertainty of the mean period. This demonstrated that except for the error from theory, the uncertainty of the estimated wave parameters in type 1 was influenced by the change in the wave generated by the wind field, while that of type 2 was affected by the complicated typhoon wavefield, including the mixed wind waves and swells. The results showed that the error of 0.02 of the scatter index in the case of the wave height could be identified even when no system noise was considered. This error was attributed to the simplification of the coupling coefficient and the weighting function in Barrick’s theory. The error was direction dependent and non-negligible. For the typhoon cases, the heterogeneity and rapid changes in the spatial distribution of the wavefield under the influence of the rotating wind fields were the challenging

Study on the influence range of tropical cyclones on ocean waves

Extreme waves forced by extreme winds, such as tropical cyclones, pose a great threat to ocean and coastal structures. Therefore, the study on the influence range of tropical cyclones on ocean waves is crucial in the engineering community. In this study, the comparative advantages of different wind input and dissipation schemes available in the third-generation wave model, WAVEWATCH III, are explored in most of the China Seas, where tropical cyclones frequently occur, including the Yellow Sea, East China Sea and northern South China Sea. Compared with buoy observations, the effects of 6 parameterization schemes of input and dissipation source terms on the simulated tropical cyclone-generated waves show that the simulation with the parameterization ST6-4.18 performs well, especially during strong wind. Analyzing the simulated wave fields forced by 90 tropical cyclones, the influence ranges of tropical cyclones on ocean waves are derived, performing along the left and right sides of the tropical cyclone track. The resulting formulas can be used to screen out the tropical cyclone-generated wave for studying the extreme wave and predict the influence of tropical cyclones on waves in the engineering area before the tropical cyclone approaches.

Performance of different input and dissipation packages in WAVEWATCH III model during tropical cyclones

Ocean surface waves exposed to extreme weather conditions, such as tropical cyclones (TCs), are critical environmental forces acting on the coastal and offshore structures. Therefore, it is necessary to investigate the applicability of the third-generation wave model WAVEWATCH III for simulated waves in the China Seas, where TCs are frequent. This study compares different packages of wind input and wave dissipation (ST1, ST2, ST3, ST4, and ST6) during five TCs with significant wave heights (SWHs) and wave spectra in the Yellow Sea, East China Sea, and South China Sea. The results show that ST6 performs best in the simulation of the SWHs, presenting the only positive deviation, with a normalized mean bias of 1.76%. ST2 systematically underestimates the large SWHs due to insufficient wind input from the spectra. However, the suitability of the packages varies in different sea conditions. ST6 is preferred in extreme wave simulations during TCs, ST4 performs best under the weak influence of TCs, and ST2 has the best performance in calm sea conditions.

Energy assessment of potential locations for OWC instalation at the Portuguese coast

This work aims to determine the exploitable wave energy resource at five potential sites close to harbour protection facilities at the Portuguese coast, namely at the Azores archipelago, at Madeira Island and at Sines, on the coast of mainland Portugal. For that purpose, a third-generation wave model SWAN is used to transfer the offshore estimates of sea wave conditions to those points over the last 40 years. Sea states and wind fields are provided by the climate reanalysis datasets ERA5. Using sea states as boundary conditions and wind fields as forcings in the numerical domains of the SWAN model, the sea states were propagated shoreward, in order to estimate and analyse the wave conditions in the regions of interest. By combining the average energy flux per unit length of wave front and the probability of occurrence of each sea state, the average exploitable annual energy per unit length of wave crest can be computed. The variability of this energy flux is analysed since it is of paramount importance for the efficiency of Wave Energy Converters (WEC). This assessment showed that the best location for the installation of dual-chamber OWC devices is at the Azores archipelago.

Future variability of wave energy in the Gulf of Oman using a high resolution CMIP6 climate model

There is a worldwide compromise toward increasing the proportion of renewable energy in future electricity production to mitigate the impacts of greenhouse gases. This study explores the sustainability of wave energy resources in the northern part of the Gulf of Oman, considering the impact of climate change using a Shared Socio-economic Pathway (SSP5-8.5) representing a high increase in CO2 concentration by 2100. Near-surface wind speed dataset from a high-resolution CNRM (CNRM-CM6-1-HR) global climate model was employed to force a third-generation wave model. A novel statistical bias-correction technique was developed based on Weibull distribution to generate high-resolution input wind for the wave model, and various criteria were employed to assess the sustainability of the wave energy in the study area. Comparing future projections of wave energy under SSP5-8.5 with those of historical simulations demonstrated the sustainability of the wave resources in the study area. The methodology of utilizing multiple criteria assessments, including accessibility, availability, and exploitable storage of wave energy predicts an increase ranging from 21 to 45% in the future wave power under a high emission scenario.

Numerical study of the effect of current on waves in the Agulhas Current Retroflection

The generation of extreme waves in the Agulhas Current Retroflection as the result of strong wave-current interaction is examined. High-resolution simulations with two third-generation wave models are performed considering ocean surface currents for two years and six months. The study is made with high-resolution SWAN (Simulating Waves Nearshore) nested grids which use the boundary conditions from the outer WAM (Wave Advanced Modeling) grid. Surface current velocities of mesoscale eddies influence surface wave properties and wave energy. The effects of the current speed on the wave spectral shapes are explored inside the eddies and in their vicinity. The numerical results show that in the interior of the eddies the extreme wave parameters can reach high values as well as the probability of occurrence of abnormal waves.