Mean Wave Height Research Articles

Analysis of sea conditions for manned submersible operation in Southwest Indian Ocean

The southwest Indian Ocean is an important area for deep-sea investigation and exploration. In this paper, the spatial distribution and temporal variation characteristics of wave elements in the sea area were analyzed by using the high resolution reanalysis data (ERA) from the European Center, the optimal path set of tropical cyclones provided by the Joint Warning Center (JTWC) and the global ocean circulation model (OFES). The results show that the monthly mean effective wave height in the southwest Indian Ocean is relatively large, ranging from 3.5m to 5.5m. the wave season is relatively stable, with the highest mean wave height in winter and the lowest mean wave height in summer; The frequency of tropical cyclones is higher in summer and autumn and lower in winter; The most suitable operation time of manned submersible in the southwest Indian Ocean is from November to march of the next year, and other time needs to select good sea conditions for operation.

Control of dissipative rogue waves in nonlinear cavity optics: Optical injection and time-delayed feedback.

We investigate and review the formation of two-dimensional dissipative rogue waves in cavity nonlinear optics with transverse effects. Two spatially extended systems are considered for this purpose: the driven Kerr optical cavities subjected to optical injection and the broad-area surface-emitting lasers with a saturable absorber. We also consider a quasi-two-dimensional system (the two dimensions being space and time) of a fiber laser describing the complex cubic-quintic Ginzburg-Landau equation. We show that rogue waves are controllable by means of time-delayed feedback and optical injection. We show that without delayed feedback, transverse structures are stationary or oscillating. However, when the strength of the delayed feedback is increased, all the systems generate giant two-dimensional pulses that appear with low probability and suddenly appear and disappear. We characterize their formation by computing the probability distribution, which shows a long tail. Besides, we have computed the significant wave height, which measures the mean wave height of the highest third of the waves. We show that for all systems, the distribution tails expand beyond two times the significant wave height. Furthermore, we also show that optical injection may suppress the rogue wave formation in a semiconductor laser with a saturable absorber.

The characteristics of wind waves in Lake Chaohu in 2018

基于实测数据，利用验证良好的SWAN风浪模型开展了2018年巢湖风浪变化及分布特征研究.巢湖2018年平均有效波高和波周期分别为0.16 m和1.22 s，整体春季风浪大，秋季风浪小.月均最大值出现在4月，分别为0.22 m和1.36 s，月均最小值出现在11月，分别为0.11 m和1.06 s，变化幅度分别为最大值的52%和22%.月均值整体中巢湖最大，东巢湖次之，西巢湖最小.巢湖月最大有效波高和波周期主要出现在东巢湖或中巢湖，各值月间差异显著，最大变化幅度分别为最大值的61%和27%.不同湖区计算的月均有效波高和波周期较大值分布范围所占湖区的比例不同，中巢湖与东巢湖较大，西巢湖最小.不同月份及湖区较大有效波高出现的时间占比是不一致的，9-11月份时间占比较小，将有利于蓝藻水华的出现.;In this study, the wind-wave model SWAN was used to simulate the characteristics of variations and distributions of wind waves in Lake Chaohu for the year 2018. The model was calibrated and evaluated using observational data. Results suggest that the annual mean significant wave height and wave period of Lake Chaohu during 2018 were 0.16 m and 1.26 s, respectively. The wind wave was strong in spring and weak in autumn. The monthly mean values exhibit great variations. The largest monthly values of 0.22 m and 1.36 s were obtained in April, while these values were 0.11 m and 1.06 s in November, which were the lowest during 2018 and whose variation ranges were 52% and 22% of the maximum values, respectively. Among different lake basins, monthly mean wave height in the east basin and central basin were the highest, followed by the west basin. The highest value of monthly maximum significant wave height and wave period appeared in the east basin or the central basin. The values of monthly maximum significant wave height and wave period varied significantly during different months, whose variation ranges were 61% and 27% of the maximum values, respectively. The distribution ratio of the high values of monthly significant wave height and wave period computed by model in different lake zones were large in the east basin or central basin, but it was small in the west basin. The proportion of time when the high significant wave height appeared was different during different months in different lake zones, and it was small from September to November, which would be beneficial to the emergence of cyanobacteria blooms.

Morphological Variability of Phorcus lineatus (da Costa, 1778) Shells along the Coast of Portugal and the Significance of the Environment on Shell Morphology

Phorcus lineatus (da Costa, 1778) is a marine intertidal gastropod occurring in the Eastern Atlantic, from Northern Ireland and Wales to Mauritania. Along the Portuguese continental coast, it displays marked shell variability. Northern shells have a worn spire, but southern specimens display good preservation. At most sites, the majority of shells show no umbilicus, but at sites scattered along the coast, most shells display a distinct or conspicuous umbilicus. In order to understand these discrepancies, I carried out analyses of the mean grain size of the beach sand where live animals were collected and estimations of the annual mean wave height near the sampling sites by using Portuguese Institute for Sea and Atmosphere (IPMA) forecasts. Sampling, experiments and data loading were carried out in the period 2012–2015. Whereas no direct correlation was found between umbilicus prominence, shell size and studied environmental variables, abrasion and wear of the spire were found to be primarily dependent upon sea wave height and on beach sand grain size. It was concluded that current malacological literature, particularly field guides, sub-represent the morphological diversity of P. lineatus shells omitting eroded shells, and that worn shells occur along the distribution range of this species. Abrasion and wear of P. lineatus shells appear to increase with increasing sea wave height, and also with increasing beach sand grain size, reflecting the intensity of the hydrodynamics at a local scale.

Reliability-based analysis of Lázaro Cárdenas breakwater including the economical impact of the port activity

A formulation to assess the reliability and cost of a breakwater, including the economical impact of port operations, is proposed. The limit state function is the stability performance of the core elements and aleatory uncertainties on the wave height and the weight of these elements are considered. Also, epistemic uncertainty on the modeling of the mean wave height is introduced and its impact on the results is appraised by sensitivity analysis.The formulation identifies percentiles for the breakwater reliability providing an opportunity to make conservative decisions by taking into account specific percentiles of the reliability index as an improvement of the traditional consideration of the mean value. Also, target values of the breakwater reliability are calculated from the minimum expected life-cycle cost. In addition, a curve of the breakwater initial cost vs. reliability is proposed, as a tool towards the optimal decision making on design and maintenance. Reliability calculations are performed via FOSM (First Order Second Moments) approximation and MCS (Monte Carlo simulations techniques), the cost of consequences include potential fatalities and the economic loss of maritime and port activities. It is found, for a case study, that the reliability index through FOSM is 2.37, underestimated due to the linear approximation, whereas for MCS the index is 3.7. Sensitivity analysis showed that epistemic uncertainty on the mean wave height and on the core elements mean weight has significant impact on the breakwater reliability index. However, the standard deviation of the core elements weight has a minor impact on these index.

Ocean Wind Wave Climate Responses to Wintertime North Atlantic Atmospheric Transient Eddies and Low-Frequency Flow

AbstractAtmospheric transient eddies and low-frequency flow contributions to the ocean surface wave climate in the North Atlantic during boreal winter are investigated (1980–2016). We conduct a set of numerical simulations with a spectral wave model (WAVEWATCH III) forced by decomposed wind fields derived from the ERA-Interim reanalysis (0.7° horizontal resolution). Synoptic-scale processes (2–10-day bandpassed winds) are found to have the largest impact on the formation of wind waves in the western midlatitudes of the North Atlantic along the North American and western Greenland coasts. The eastern North Atlantic is found to be influenced by the combination of low-frequency forcing (>10-day bandpassed winds) and synoptic processes, contributing up to 60% and 30% of the mean wave heights, respectively. Midlatitude storm track variability is found to have a direct relationship with wave height variability along the eastern and western margins of the North Atlantic, implying an association between cyclogenesis over the North American eastern seaboard and wave height anomalies in the eastern North Atlantic. A change in wave height regimes defined using canonical correlation analysis is reflected in changes to their wave height distribution shapes. The results highlight the important role of transient eddies for the ocean surface wave climatology in the midlatitudes of the eastern North Atlantic both locally and through association with cyclone formation in the western part of the basin. These conclusions are presented and discussed particularly within the context of long-term storm track shifts projected as a possible response to climate warming over the coming century.

The Cape Point wave record, extreme events and the role of large-scale modes of climate variability

Situated on the southwestern coast of South Africa, Cape Point is directly impacted by ocean surface waves generated by midlatitude cyclones in the westerly wind belt. Severe swell events have a huge impact on coastal communities, infrastructure and maritime operations. We use the long term Council for Industrial and Scientific Research (CSIR) Cape Point Waverider buoy data and WaveWatch III model data together with atmospheric reanalysis data to investigate the role of the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) and their associated adjustments of cyclone tracks and intensities on the variability and extreme events of the Cape Point wave record. During austral summer (DJF), when the waves are generally smaller and more southerly, SAM and ENSO tend to result in robust responses: a negative (positive) SAM tends to result in bigger (smaller) more westerly (southerly) waves, while a positive (negative) ENSO results in bigger (smaller) waves from a more westerly (southerly direction). The mean austral (JJA) winter waves do not respond coherently to either SAM or ENSO. A shift in the wave characteristics between periods 1980–1992 and 1994–2006 is clear. The waves become smaller and more southerly during the latter period. This shift is associated with the shift to a more coherently out of phase relationship between SAM and ENSO, dominated by a positive SAM and negative ENSO, that amplifies the wave response, giving rise to smaller waves from a more southerly direction. During summer months there is a significant reduction in not only the mean wave heights, but also the extreme wave heights between the two periods, while during winter months there is only a significant change in the mean wave direction that becomes more southerly during the latter period. During a positive ENSO and negative SAM combination, the summer extreme wave heights tend to be more westerly while the inverse combination does not produce a robust result. Finally, we show that during summer months a positive (negative) ENSO leads to more frequent extreme wave events. On the other hand, a positive (negative) SAM leads to less (more) frequent extreme wave events during winter months.

Wave climate analysis in the ice-free waters of Kara Sea

Sea surface waves in the Kara Sea can vigorously generate and grow owing to the increasing ice cover reduction in recent years. This study aims to quantitatively determine the wave climate in the ice-free waters of Kara Sea based on the ECMWF ERA-Interim dataset. Wave parameters, such as the mean and extreme significant wave heights (SWH), periods (MWP), and their trends, roses and co-occurrences are adequately investigated. The optimal years from 2005 to 2018 are chosen when the summer ice-free extent continuously maintains at the maximum. Results reveal that the SWH and MWP are slightly higher in September than in August. The largest waves predominantly occur in the zone of 77∘N-79∘N and 67∘E-80∘E. The temporal linear trends of SWH and MWP are estimated but not statistically significant in most zones. The mean SWH and MWP remain stable with small fluctuations, while the extreme ones show a noticeable interannual variation. In addition, roses of SWH and MWP indicate that in the northern zone directions from SSW to NNW are predominant, while in the southern zone ones from NW to NE are prevalent. Moreover, the co-occurrences of simultaneous SWH and MWP are put forward. The SWH of 0.5–2.5 m with MWP of 4–7 s largely occur in the northern zone, while the SWH of 0.5–2 m with MWP of 3–6 s mainly appear in the southern zone.

Quality control of marine big data—a case study of real-time observation station data in Qingdao

Offshore waters provide resources for human beings, while on the other hand, threaten them because of marine disasters. Ocean stations are part of offshore observation networks, and the quality of their data is of great significance for exploiting and protecting the ocean. We used hourly mean wave height, temperature, and pressure real-time observation data taken in the Xiaomaidao station (in Qingdao, China) from June 1, 2017, to May 31, 2018, to explore the data quality using eight quality control methods, and to discriminate the most effective method for Xiaomaidao station. After using the eight quality control methods, the percentages of the mean wave height, temperature, and pressure data that passed the tests were 89.6%, 88.3%, and 98.6%, respectively. With the marine disaster (wave alarm report) data, the values failed in the test mainly due to the influence of aging observation equipment and missing data transmissions. The mean wave height is often affected by dynamic marine disasters, so the continuity test method is not effective. The correlation test with other related parameters would be more useful for the mean wave height.

Growth of wave height with retreating ice cover in the Arctic

Quantitative relationships between retreating ice cover and the intensification of surface waves in the Arctic Ocean are studied. Wave data are produced by twelve-year (2007—2018) hindcasts of summer melt seasons (from May to September) and numerical tests with WAVEWATCH III. When a viscoelastic wave-ice model and a spherical multiple-cell grid are applied, simulated wave heights agree with available buoy data, altimeter data and previous simulations. Then, with the model data, we find that changes in mean significant wave height of the whole Arctic are dominated by changes in surface winds when the ice extent is larger than 9.4 × 106 km2. If the ice extent retreats from 9.4 × 106 km2, the model predicts that the mean significant wave height will increase by approximately 0.07 m (106 km2)−1 with comparable contributions from both increasing effective fetch and wind speed. For seven Arctic subregions, modeled significant wave height and probabilities of occurrence of large waves (significant wave height > 2 m, 3 m and 4 m) are shown positively correlated with the latitude of ice edge, and for modeled wind sea fraction, it is negatively correlated. With these results, we show the transition of surface waves from wind wave dominated to swell dominated in most of the Arctic sea areas with retreating ice cover. Assuming that the ice-free period occurs in September, the simulations show that mean wave height of the Arctic Ocean will increase to approximately 1.6 m with much more large waves. It implies that there will be a higher growth rate of wave height (m (km2)−1) if the minimum ice extent continues to reduce in the future.

Estimation of Significant Wave Height of Near-Range Traveling Ocean Waves Using Sentinel-1 SAR Images

Synthetic aperture radar (SAR) is a valuable tool to observe many oceanographic parameters of the ocean surface. The significant wave height (H s or SWH), defined as the mean wave height of the highest one-third of waves, can be estimated using indirect relations between SAR-derived and the actual ocean wave spectra. However, multilook SAR imaging of ocean surface waves is highly affected by degraded azimuthal resolution and the random shift of scattered elements as the waves propagate off the SAR range direction. Therefore, the azimuthal displacement is found to be very low when near-range travelling ocean waves with narrow band spectrum are imaged. In this study, an improved algorithm is developed to directly estimate the significant wave height of ocean waves that propagate in the near-range direction using SARSAR imagery. The slope of the NRCS with respect to the radar wave incidence angle is derived from SAR images using an iterative scheme. A total of 69 SAR images from Sentinel-1A and 1B from 2016 to 2017, acquired near Hawaii, and in situ wave data from nearby National Data Buoy Center buoys are used to estimate H s and validate the improved algorithm. Results show that the algorithm performs well in estimating SWH under low to moderate wind forcing conditions (4-10 ms -1 ). The accuracy of the SWH estimation decreases under high-wind-speed and wind-wave-dominant conditions.

Coastal Vulnerability Mapping using Remote Sensing and GIS Techniques in Tuticorin Coast of Tamil Nadu, India

The southern part of the Indian peninsula of Tamil Nadu coast is potentially more vulnerable to hazards. This research aims to classify the coastal vulnerable zones of the Tuticorin, Tamil Nadu using Coastal Vulnerability Index (CVI). The multi-spectral satellite data of Landsat series was used for shoreline change analysis from 1978 to 2017. The Digital Shoreline Analysis System (DSAS) software extension was used to calculate the shoreline rate-of-change statistics from multiple historic shoreline positions developed by the United States Geological Survey. The study reveals significant erosion and accretion demarcated based on DSAS computed values along the coastal stretch. The six physical variables characterizing the vulnerability of the coast, including the geomorphology, shoreline change rate (m/yr), coastal slope (deg), relative sea-level change (mm/yr), mean wave height (m) and mean tide range (m). The geomorphology map was created using Landsat OLI satellite data in 1: 50,000 scale. The Shoreline change rate was calculated using temporal satellite data. Based on the CVI value, low vulnerable to very high vulnerable areas were identified. Besides, Vembar, Periyasamypuram, Vaippar, Kallurni, Pattanamarudur areas were identified in erosion. The Muttayyapuram coast has accretion by the consequence of sediment transport from the Thamiraparani estuary. The coastal zones are highly fragile for dynamic nature and resource. The sources of anthropogenic and natural processes are accelerating the erosion and accretion along the coast. Hence the vulnerability map prepared for the southeast coast of India and it can be most helpful for stakeholders and future coastal disaster mitigation and management.

Variability of the Nearshore Wave Climate in the Eastern Part of the Black Sea

The variability in nearshore wave climate of the eastern part of the Black Sea was studied based on 38 years of wave hindcast data from spectral wave modelling for the period from 1979 to 2016. Correlation analysis has revealed the spatial inhomogeneity within the region on the short timescale from a few hours to one day, with the southern part being more homogeneous than the northern one. The variability of annual mean wave heights in these two regions were compared using wavelet correlation analysis. The wave climate variability at four chosen locations subject to wave modelling was correlated with climate indices (NAO, AO, AMO, PDO and EA/WR) on the following timescales: 20–30, 10–17 and 4–7 years. Despite the fact that the selected periods of fluctuations of average annual wave heights are almost the same for the chosen locations due to changes in climatic indices, a decrease or increase in amplitudes of the same frequency (multi-annual and decennial) can occur in antiphase even within the same coast. Such behavior is probably caused by complex inhomogeneous wind conditions near the coast. Fluctuations of annual mean wave heights of southern and northern coasts correlate with teleconnection patterns in antiphase on multi-decadal periods of about 20–30 years. To conclude, the nearshore wave climate variability of the eastern part of the Black Sea is inhomogeneous and therefore it can be divided at least into three regions: northeastern, northwestern and southern.

Spatial variations in the Caspian Sea wave climate in 2002–2013 from satellite altimetry

The core properties of the wave climate and its changes in the Caspian Sea are established in terms of the annual mean significant wave height and its regional changes in 2002-2013 based on the outcome of the satellite altimetry mission JASON-1. Remotely estimated wave heights are validated against properties of the empirical distribution of instrumentally measured wave heights in the southern Caspian Sea and monthly averages of visually observed wave heights at three locations. A correction for systematic differences leads to very good correspondence between monthly averaged in situ and satellite data with a typical root mean square difference of 0.06 m. The average significant wave height in the Caspian Sea is 0.5-0.7 m in the northern basin of the sea, around 1.2 m in large parts of the central and southern basins and reaches up to 1.8 m in the northern segment of the central basin. The basin-wide average wave intensity varied insignificantly in the range of 1.02-1.14 m in 2002-2013. These estimates overestimate the wave heights by about 30% because low wave conditions are ignored. Substantial and statistically significant changes in the wave height occurred in certain areas. The wave height decreased by 0.019 +- 0.007 m/yr in the eastern segment of the central basin and by 0.04 +- 0.04 m/yr in the western segment of the southern basin. These changes can be explained by an increase in the frequency of westerly winds at the expence of southerly winds. Both basin-wide and regional extreme wave heights exhibit large interannual variations but do not show any significant trend. The patterns of changes in mean and extreme wave height are different. The average wave height has increased while the extreme wave height has decreased in the eastern segment of the southern basin.

A Study on Shipments of Swimming Crab Using Negative Binomial Regression Model

본 연구는 해양기상관측자료인 평균 풍속, 평균 기압, 평균 상대습도, 평균 기온, 평균 수온, 평균 최대파고, 평균 유의파고, 최고 유의파고, 최고 최대파고, 평균 파주기, 최고 파주기 등의 요인들이 꽃게의 출하건수에 미치는 영향을 음이항 회귀모형을 통해 확인하고 모형적합을 시도하였다. 염분과 수온이 갑각류의 성숙 및 산란에 영향을 미치며, 특히 수온은 성장에 관여하는 대사 작용에 영향을 끼친다고 알려져 있고 최근 지구온난화로 인해, 얼음이 녹으면서 바다의 유의, 최대, 평균파고와 파주기, 그리고 수온까지 영향을 미치고 있어 꽃게 출하건수를 예측하는데 있어 중요한 변수라고 생각할 수 있다. 분석결과 꽃게의 출하건수에 영향을 주는 요인은 평균 풍속, 평균 기압, 평균 상대습도, 평균 해수온도, 최대 파고, 평균 파주기, 최대 파주기로 결정되었다. 꽃게의 출하건수는 평균 풍속, 평균 기압, 평균 상대습도, 평균 해수온도, 평균 파주기가 높을수록 증가하는 경향을 보이고 있고, 최대 파고, 최대 파주기가 낮을수록 꽃게의 출하건수는 증가하는 경향을 보이고 있었다.The purpose of this paper is to analyse the effect of ocean weather factors on shipments of swimming crab. We use the data of data portal and ocean weather factors (mean wind velocity, mean atmospheric pressure, mean relative humidity, mean air temperature, mean water temperature, mean maximum wave height, mean significant wave height, maximum significant wave height, maximum wave height, mean wave period, maximum wave period). We did statistical analysis using Poisson regression analysis and negative binomial regression analysis. As the result of study, important factors influential in the shipments of swimming crab turn out to be mean wind velocity, mean atmospheric pressure, mean relative humidity, mean water temperature, maximum wave height, mean wave period and maximum wave period. the shipments of swimming crab increases as mean wind velocity, mean atmospheric pressure, mean relative humidity, mean water temperature increases or mean wave period increase. However, as maximum wave height, maximum wave period decreases, the shipment of swimming crab increases.

BASIN-SCALE MODEL FOR PREDICTING MARSH EDGE EROSION

Recent attempts to relate marsh edge retreat rate to wave power have met varying levels of success. Schwimmer (2001) correlated wave power to marsh boundary retreat rates over a five-year period along sites within Rehoboth Bay, Delaware, USA. Marani et al. (2011) derived a linear relationship between volumetric retreat rate and mean wave power density using Buckingham’s theorem of dimensional analysis. Leonardi and Fagherazzi (2015) added an exponential function to the Schwimmer (2001) equation to account for variability in soil resistance and mean wave height. These equations factor in soil type, water elevation, vegetation, and macrofauna through field-calibrated empirical constants, i.e., they are not explicitly considered. Consequently, the existing capability of predicting marsh edge erosion rate as a function of wave power and soil and vegetation properties is rather limited for engineering applications. For instance, Allison et al. (2017) show that without taking the marsh platform, soil, and vegetation into account, the relationships between marsh edge erosion rates and wave power on a basin or coastal-wide scale are not strong enough statistically to serve as a useful predictive model. The objective of this study is to develop a more robust marsh edge erosion model by characterizing the shear strength, wave power, and retreat rates in Terrebonne Bay, Louisiana.

WAVE CLIMATE VARIABILITY AND RELATED CLIMATE INDICES

Climate change is highly expected to give significant impact on coastal hazards and environment. The future projections of wave climate under global warming scenarios have been carried out and shows changes in wave heights depending on the regions (e.g., Hemer et al., 2013). Beside the long-term trends of wave climate, annual to decadal changes are also important to understand variability. For example, the North Atlantic Oscillation (NAO) is highly correlated to monthly mean wave height along the western European coast. However, variability of wave climate is not well understood over the globe, quantitatively. Additionally, the standard coastal engineers regard stationary process for wave environment for solving coastal problems. This study analyzes global wave climate variability for the last half century based on principal component analysis of atmospheric forcing (sea surface winds U10 and sea level pressure P) and wave hindcast.

FUTURE WAVE PROJECTION DURING THE TYPHOON AND WINTER STORM SEASON

IPCC’s AR5 stated that it is more likely than not that the frequency of tropical cyclones (TCs) will decrease and that the intensity of TCs will increase over the Western North Pacific in the late 21st century. Until now, many researchers have tried to project wave climate according to various climate change scenario (Hemer et al., 2013). Most studies focus on the change of mean and extreme wave heights. These indices are important to evaluate the effects on coastal structures in terms of natural disaster prevention. However, the effect of climate change on wave conditions induced by extreme events is still vague. The aim of this study is to evaluate the effects of future climate change on wave conditions from one-month simulations including periods of extreme events based on the pseudo-warming method (Sato et al., 2007) with the most recent IPCC scenario.

Future Wave Conditions of Europe, in Response to High‐End Climate Change Scenarios

AbstractChanges in future North Atlantic storminess will impact upon wave conditions along the European coasts, with implications for coastal erosion, overtopping, and flood risk. In this study we make a detailed analysis of historic and future wave conditions around the European Atlantic coast, making projections out to the year 2100 under Representative Concentration Pathways 4.5 and 8.5 future emissions scenarios. A decrease in mean significant wave height of the order 0.2 m is projected across most of the European coast. Increases in the annual maximum and 99th percentile wave height as large as 0.5–1 m are observed in some areas but with a more complex spatial pattern. An increase in waves to the north of Scotland is also observed, mainly caused by a reduction in sea ice. We generate a set of coastal wave projections at around 10‐km resolution around continental Europe, Ireland, and the British Isles. Widening of the probability density function (PDF) is observed, suggesting an increased intensity of rare high wave events in the future. The emergent signal of a reduced mean wave height is statistically robust, while the future changes in extreme waves have a wider confidence interval. An assessment of different extreme waves metrics reveals different climate change response at very high percentiles; thus, care should be taken when assessing future changes in rare wave events.

Characteristics of global waves based on the third-generation wave model SWAN

Long-term wave data at a global scale are crucial for the studying characteristics of global waves, such as spatial distributions and extreme waves. These characteristics play significant roles in the design, construction, installation and operation activities of marine structures. Because of the limited resolution and coverage of instrumental measurements, the global wave hindcast is widely used. To develop this hindcast, the Simulating WAves Nearshore (SWAN) model is forced with the ERA-Interim wind database from 1979 to 2017 with a resolution of 0.25° in both longitude and latitude. The hourly wave parameters, such as the significant wave height and the mean period, are validated against buoy measurements over the Northwest Pacific Ocean, the Northeast Pacific Ocean and the Northwest Atlantic Ocean. Based on the 39-year simulated results, the spatial distributions of mean and maximal significant wave heights are analysed for all 39 years, every decade, 4 seasons, 12 months and special years; extreme waves are studied at the global scale and at every computational point.