Average Significant Wave Height Research Articles

Spatial trend analysis of significant wave heights in the Kara Sea

Over the past decades, the extent of sea ice in the Arctic, including the Kara Sea, has been diminishing. This phenomenon has a direct impact on wind waves as the increased expansion of ice-free water influences wave height. Furthermore, alterations in the ice cover also lead to modifications in atmospheric circulation, necessitating a concurrent analysis of wind and waves to refine the understanding of their interrelationships. In this study, wave modeling data were employed using the WAVEWATCH III model and NCEP/CFSR/CFSv2 reanalyzes. Calculations were performed on a non-structural computational grid. The grid covers the Barents and Kara Seas, as well as the entire northern part of the Atlantic Ocean. The spatial resolution varies from ~ 700 m for the coastal zone of the Kara Sea, to ~ 20 km in the open part of the Kara Sea, covering the period from January 1, 1979 to December 31, 2021. Subsequently, average significant wave heights (SWH), maximum SWH, and the 95th percentile of SWH were computed for each grid node on both monthly and yearly basis. The annual values were analyzed for trends and their significance. Calculations were conducted for both the entire period and ice-free period. Positive trends in annual mean values were observed throughout the sea, with the maximum trend occurring near the boundary with the Barents Sea, barely exceeding 0.2 m/10 years. The northern and northeastern parts of the sea were characterized by significant positive trends of the maximum SWH values. Maximum trend values for the 95th percentile of SWH were also evident in the northern part of the Kara Sea. For the ice-free period, maximum trend values were notable for both the annual mean and the 95th percentile of SWH in the northern part of the sea (maximum trend values are approximately 0.25 m/10 years and 0.5 m/10 years, respectively). Significant positive trends in the annual mean SWH were characteristic of the southern part of the sea, while the largest and significant trends for maximum wave heights were observed in the northeast. The assessment of the contribution of wind and ice regimes to the variability of wind waves remains a subject of discussion.

Spatiotemporal variability of wave climate in the Gulf of Riga

Basic properties of wind wave climate in the Gulf of Riga, the Baltic Sea, are evaluated based on modelled wave fields, instrumentally measured and historical visually observed wave properties. Third-generation spectral wave model SWAN is applied to the entire Baltic Sea for 1990–2021 with a spatial resolution of 3 nautical miles (nmi, about 5.5 km) forced by the wind field of ERA5, to the Gulf of Riga and its entrance area with a resolution of 1 nmi (about 1.85 km), and to nearshore areas of this gulf with a resolution of 0.32 nmi (about 600 m). The calculations are performed for an idealised ice-free climate. Wave properties are represented by 36 directional and 32 frequency bins. The simulations are complemented by five sessions of instrumental measurements in the 2000s and two sets of historical visual wave observations from the island of Ruhnu and the Sõrve Peninsula for 1954–2011. Predominantly representing fetch-limited windseas, the wave climate in the gulf is milder and more intermittent than in the open Baltic Sea. The average significant wave height is mostly in the range of 0.6–0.8 m and peaks at 0.82 m inside the gulf. Typical wave periods are shorter than in the Baltic proper. The spatial pattern of wave heights, with higher wave intensity in the northern and eastern parts of the basin, follows anisotropy in wind conditions. Interannual variations are highly synchronised in different parts of the gulf. Their magnitude is less than 10% of the long-term average wave height. No long-term trend has been found in significant wave height and no distinct decadal variation exists inside the gulf.

MODELLED AND OBSERVED IMPACT OF THE APRIL 2021 SOUTHERN OCEAN STORM

Wind-wave extreme events are a major driver of coastal erosion (Lowe et al., 2010). As such, accurate estimates of metocean extremes are crucial to implement efficient and resilient coastal defense strategies. Global wave reanalysis datasets are commonly used to estimate wind and wave statistical properties for coastal engineering purposes. However, despite the impressive accuracy of such datasets in representing average significant wave height conditions (global biases against observations of less than 5 cm), models usually underestimate metocean extremes (Cavaleri et al. 2009; Cavaleri et al., 2020). To obtain an understanding of model performance under extreme conditions, we focus on a single storm event generated in the Southern Ocean on April 7th, 2021.

Statistical characteristics of sea surface waves derived from buoy measurements in the eastern Guangdong offshore water

The wave characteristics of the eastern Guangdong offshore water were quantified based on 1-year wave observations at a water depth of 60 m. This study statistically analyzed the observed wave characteristics and quantified the variations of the wave parameters and spectrum due to Super Typhoon Mangkhut. Results showed that the dominant and strong wave directions in the northeastern South China Sea were north-eastern and eastern, respectively. The average significant wave height was in the range of 0.7–2.4 m. During Super Typhoon Mangkhut, the maximum wave height and period were 11.3 m and 10–12 s, respectively, and peak spectral density mainly varied between 0.06 and 0.1 Hz. Results of this study can provide a basis for offshore engineering design and are of great significance for marine forecasting and disaster prevention and reduction.

Spatial and temporal variation of nearshore significant wave height in the Three Gorges Reservoir, China

The study of wave characteristic changes is critical for understanding the role of wave erosion in the shoreline erosion of reservoirs and its subsequent impact on environmental pollution. This study utilizes RBRvirtuoso D-wave-pressure-based wave gauges to make in situ observations of the nearshore significant wave height (SWH) in the Three Gorges Reservoir. The differential and impact factors affecting the SWH under varying water levels, in the main and tributary streams, and shoreline sections are analyzed. This research also investigates the alteration of the frequency distribution of the SWH. The findings indicate that the average SWH increases as the water level increases, reaching 1.2 cm, 1.5 cm, and 1.9 cm for water levels of 150 m, 165 m, and 175 m, respectively, with a SWH frequency distribution curve that becomes increasingly smooth. The average SWH in the mainstream is 2.9 times larger than that in the tributaries, with the former having a smoother frequency distribution curve. The average SWHs in different shoreline sections are inconsistent at the same water level, with the Badong (downstream) section near the Three Gorges Dam exhibiting a significantly higher average SWH than the Zhongxian (midstream) section further from the dam. When shipping activities intensify, there is often a marked increase in the magnitude of the SWH. The SWH in narrower reservoir sections is significantly greater than that in wider sections, with average measurements of 2.2 cm and 1.4 cm, respectively. Fluctuations of the water level, shipping activities, and other factors in the Three Gorges Reservoir have a significant impact on the alteration of the nearshore SWH, and changes in the SWH from low to high water levels may result in changes in both the spatial and temporal patterns of shoreline erosion. These alterations can, in turn, affect sediment and nutrient transport, potentially exacerbating environmental pollution issues.

Offshore wave climate of the Great Barrier Reef

The Great Barrier Reef (GBR) is the largest coral reef system on earth, with ecological and scientific importance for the world and economic and iconic value for Australia. However, the characterisation of its offshore wave climate remains challenging because of its remoteness and large dimensions. Here, we present a detailed analysis of the offshore wave climate of the GBR, unveiling the details of both modal conditions and extreme events. We used a calibrated satellite radar altimeter dataset (spanning from 1985 to 2018) to quantify wave climate, assess the influence of climate drivers, and analyse the wave conditions generated by tropical cyclones at three main regions of the GBR (northern, central, and southern). Our results indicate average significant wave heights of 1.6 m, 1.5 m, and 1.7 m for the northern, central, and southern GBR, respectively. The modal wave climate exhibits substantial seasonality, particularly in the northern region with dry season wave heights up to twofold larger than during wet season. The northern and central wave climates show decreasing wave height and wave energy trends over the last 33 yrs, whilst the southern region remains stable. Consistent with prior studies, we found that the wave climate in the southern region is modulated by the El Niño-Southern Oscillation and the southern annular mode, with influence additionally extending to the central region. Analysis of the extreme waves generated by tropical cyclones revealed they generate large, long period waves, frequently above 7 m, resulting in wave power up to 32-fold higher than median conditions.

Nearshore Wave Energy Resource Assessment for Off-Grid Islands: A Case Study in Cuyo Island, Palawan, Philippines

Electrifying off-grid and isolated islands in the Philippines remains one of the challenges that hinders community development, and one of the solutions seen to ensure energy security, energy access and promote a low-carbon future is the use of renewable energy sources. This study determines the nearshore wave energy resource during monsoon seasons in Cuyo Island using a 40-year wave hindcast and 8-year on-site wind speed data as inputs to develop a high-resolution wave energy model using SWAN and assesses its annual energy production through matching with wave energy devices. The results show that the average significant wave height (Hs), peak period (Tp) and wave power density (Pd) during a northeast monsoon are Hs = 1.35 m, Tp = 4.79 s and Pd = 4.05 kW/m, respectively, while a southwest monsoon, which is sheltered by the mainland, results in Hs = 0.52 m, Tp = 3.37 s and Pd = 0.34 kW/m. While the simulated model was observed to overestimate the significant wave height (bias = 0.398, RMSE = 0.54 and SI = 1.34), it has a strong relationship with the “observed values” (average r = 0.9). The annual energy production for Wave Dragon, Archimedes Wave Swing and Seawave Slot-Cone Generator are highest at 1970.6 MWh, 2462.04 MWh, 62.424 MWh and 4099.23 MWh, respectively.

Wind–wave characterization and modeling in the Azores Archipelago

Wind–wave characterization and modeling around a group of islands can have significant challenges due to strong diffraction, shoaling, and reflection. In this work, the wind–wave climate of the Azores archipelago (North Atlantic Ocean) is characterized based on wave buoy measurements recorded between 2012 and 2021 at five different locations with water depth ranging from 80 to 110 m. Moreover, wave measurements during four storms of extratropical origin and two storms of tropical origin are analyzed in detail. Due to identified island shadow effects, the average significant wave height (Hs) ranged between 1.50 m (S. Miguel island) and 1.86 m (Graciosa island) in the south and north of the archipelago, respectively. Under storm conditions, shadow effects can lead to differences up to approximately 7 m in Hs between the north and south of the archipelago. The ability to simulate the local wave conditions by an unstructured WAVEWATCH III model covering the north Atlantic with high resolution around the Azores Archipelago is analyzed. In addition, the model performance and scalability on two different High Performance Computing environments are analyzed considering different numerical schemes and parallelization algorithms.

An Appraisal of CFOSAT Wave Spectrometer Products in the South China Sea

AbstractThe China‐France ocean satellite (CFOSAT) has obtained synchronized observations of sea winds and sea waves for the first time in the world, providing accurate data support for the study of swells. In this paper, the accuracy of key parameters and the wave spectrum of CFOSAT surface waves investigation and monitoring (SWIM) L2 data are analyzed and evaluated using a spatial‐temporal matching criterion. The accuracies of the significant wave height (SWH), spectrum peak period (Tp) and dominant azimuth (Azi) are 0.76 m, 2.89 s and −24.02°, respectively, in the coastal area of the South China Sea (SCS) and 0.30 m, 0.97 s and 13.02° in the offshore area of the SCS. Calculated based on CFOSAT SWIM data, the annual average SWH of mixed waves in the SCS is 1.47 m, and 80% of them are between 0.5 and 3 m. There are high value areas in the central, northeastern and southwestern parts of the SCS. The average annual SWH of swells is 0.93 m, and 99% of swells are less than 2 m. A high swell SWH also exists in the central part of the SCS.

Modeling wave climates and wave energy attenuation in marsh terrace environments in the northern Gulf of Mexico

Marsh terracing is a coastal restoration technique that has been implemented in Louisiana and Texas for almost 30 years. Marsh terraces are segmented ridges of soil built in inland coastal ponds for the objectives of creating new marsh, disrupting fetch, and dissipating wind-driven wave energy, which causes marsh erosion. Despite widespread implementation, no numerical modeling studies have been conducted to understand the effect of terraces on wave climate in marsh environments. The objectives of this study were to: 1) simulate wave climates in marsh terrace fields using the Simulating WAves Nearshore (SWAN) model and evaluate the agreement between modeled and observed wave conditions and 2) assess the effectiveness of marsh terraces at reducing significant wave height by comparing wave climates in terraced sites with hypothetical unterraced sites. The SWAN model was used to simulate wind-waves at two terrace fields in coastal Louisiana. Model validation was performed using data collected with in situ wave instruments and wind data measured by NOAA stations located 25 km to the east and 62 km to the northeast of the study area. Results from this study modeled and measured small (0.03–0.14 m) and high–frequency waves (0.80–1.29 s) in the marsh terrace fields. Model validation revealed agreement between modeled and observed data, particularly for significant wave height and direction. Additionally, a comparison of wave climates in terraced and unterraced marsh environments indicated an average significant wave height reduction of 45% (min:18%, max: 84%) when terraces were present. Overall, the model was able to evaluate wave climates in marsh terrace fields and assess the effectiveness of this restoration technique in reducing significant wave height. The model's performance in this low energy and complex environment (shallow water, nonlinear shoreline, marsh fragmentated) is encouraging given the lack of research assessing wave parameters in marsh terrace environments.

Analysis of the Caribbean wave climate for wave energy harvesting

In this study, the design requirements for a regional wave energy converter are identified from the analysis of 10 years of spectral data provided by nine buoys located across the Caribbean. It indicated that the average significant wave height and wave period in the Caribbean is 1.62 m and 5.91 s, respectively, while the average total theoretical power capable of being absorbed from a wave energy converter is 7.4 kilowatts per meter of surface waves. Devices should be designed to withstand a significant wave height of 19.0 ± 2.8 meters (95% confidence) for a 1 in 100 year return wave. This was determined by performing various extreme wave analyses. Additionally, a design life of 30 years for a device would have a probability of exceedance regarding this return wave as 26%. Using two-dimensional wave spectra analysis for the resource study, the overall spectral width, directionality coefficient and direction of the maximum directionally resolved wave power for the region are determined to be 0.172, 0.74 and 42°, respectively. It is expected that the combination of these information would improve the viability of a wave energy industry in the Caribbean and advance technological development.

Sand-mud transition dynamics at embayed beaches during a typhoon season in eastern China

Sand-mud transition (SMT) is an important boundary of the beach system, and its location and evolution have been increasingly studied in recent years. This study focuses on the location and migration of SMTs and their influencing factors on three representative embayed beaches on the east coast of Zhujiajian Island, Zhejiang Province, China, characterized by different levels of human interventions. Beach topographies, surficial sediment characteristics and nearshore hydrodynamic data were obtained through three field campaigns carried out during the early, middle and late stages of the 2019 typhoon season. This typhoon season included four typhoons with nearshore significant wave height Hs exceeding 3.71 m, and maximum Hs of 6.77 m (Super Typhoon Lekima). Results show that the three beaches were all impacted by the high-energy wave conditions, although with some different behaviors. Sediments of the three beaches all coarsened with worse sorting during the typhoon season, with the nearshore surficial sediments showing similar patterns. The SMTs of the three beaches were stable or migrated seaward during the typhoon season. During the typhoon season, offshore SMT migration was positively correlated with the beach profile volumetric loss at three embayed beaches in this study. The SMTs of beaches with less human intervention are more stable during typhoon season. By including 12 additional embayed beaches of eastern China in our analysis, we found that the SMT offshore distance increases with increasing nearshore average significant wave height, increasing headland offshore extent and decreasing tidal range. Our study suggests that SMT is a relevant indicator of beach sediment stability, which can help to increase the understanding of embayed beach dynamics and to guide coastal management and planning during typhoon seasons at such embayed beaches.

Evolution of a nourished sand beach under low wave energy in Thailand

Sand beaches are essential for coastal tourism in Thailand, but erosion narrowed some beaches significantly over the years. Pattaya is a famous resort near Bangkok in the upper Gulf of Thailand. The Pattaya beach is microtidal with the average tidal range of 1.5 m. The average significant wave height is 0.2 m and the wave energy is low. The beach was widened by placing 130 m3/m of medium sand along the shoreline length of 2.8 km between two terminal groins constructed in 2018. The bathymetry and topography were measured in 2015, 2019, and 2020. Approximately 14% of the placed sand in the water depth less than 2 m was lost after one year, as may be expected for nourished beaches. The bathymetry change in the water depth of 2-4 m varied alongshore. The sand volume change in this offshore zone beyond the surf zone was as large as that in the landward sand placement zone. The assumption of negligible profile changes seaward of a closure depth is not applicable to this beach during 2015-2020.

Predicting water turbidity in a macro-tidal coastal bay using machine learning approaches

Water turbidity is of particular importance for diffusion and migration of nutrients and contaminants, biological production, and ecosystem health in coastal turbid areas. The estimation of water turbidity is therefore significant for studies of coastal dynamics. Many factors influence turbidity in complex and nonlinear ways, making accurate estimations of turbidity a challenging task. In this study, three machine learning models, Artificial Neural Networks (ANN), Genetic Programming (GP), and Support Vector Machine (SVM) are developed for better estimation and prediction of the tidally-averaged sea surface turbidity. The observational data of tides and waves at a macro-tidal coastal bay, Jiangsu coast, China are used as model inputs. Through data reduction, it is found that tidal average sea surface turbidity is most determined by the average tidal range of the two preceding tidal cycles (2 and 3 tidal periods before the present one, respectively) and the tidal average significant wave height of the present tidal cycle of turbidity. These three machine learning models all show successful estimations of turbidity, and comparisons of the optimized models indicate that ANN shows the best performance and GP helps to provide physically meaningful predictors. This study provides an example of developing a predictive machine learning algorithm with a limited dataset (94 tidal cycles). The generality of the present predictors can be reinforced with much more data from a variety of coastal environments.

滨海湿地消浪服务空间分布特征——以上海市崇明岛为例

全球气候变化增加了滨海地区遭受侵蚀、风暴潮等灾害的风险，利用自然湿地的消浪功能增强海岸防护是当前研究的热点，但目前对消浪服务的空间分布评估研究相对匮乏。以上海市崇明岛环岛滨海湿地为例，结合GIS与Kobayashi指数形式波高衰减模型评估常规状态下湿地消浪服务的空间分布特征。结果显示，大、小潮升条件下，崇明环岛湿地消波的平均高度分别为0.94、0.54 m与效度分别为83.6%、60.4%，消波高度的空间分布表现为南岸小于北岸，消波效度的空间分布在小潮升时与消波高度相似，而大潮升时南岸的消波效度有明显提升。物理环境与生物因素空间分布及其相互作用的异质性，导致消浪服务的空间分布也具有空间异质性。实际参与消波的断面宽度与不同景观消波服务的评估结果表明，一个断面的所有景观并非都参与到消浪过程中，即使在大潮升时期，不同岸段景观的平均参与度不足71%。潮高与波高的增加并不会使参与消波的景观规模成对应比例的增加，说明消波服务在空间上具有明显的非线性特征。研究可为滨海湿地生态修复空间规划、基于生态系统的海岸带管理、自然资本核算提供科技支撑。;Global coastal zone is faced with the challenge of increasing threats from sea level rise, coastal erosion and storm surge as the result of climate change. To improve the adaptability of the coastal area to climate change, many scientists proposed to incorporate wetlands wave attenuation service into conventional coastal protection schemes, despite the knowledge gap of the spatial distribution of such service. In this study, we incorporated an exponential wave propagation model into GIS, and simulated the spatial distribution of the wave attenuation service of the coastal wetlands in Chongming island, Yangtze Estuary, under two normal scenarios (spring rise and neap rise). The results showed that coastal wetlands could reduce average significant wave heights up to 0.94 m and 0.54 m, accounting for 83.6% and 60.4% of their incoming wave heights under spring rise and neap rise, respectively. In either case, wave height reduced by the wetlands on the southern coast of Chongming island was lower than that on the northern coast. The spatial characteristics of wave attenuation rate was similar to that of the reduced wave height under neap rise. Compared to the neap rise scenario, wave attenuation rate of the wetlands along the southern coast of Chongming island showed a significant improvement under spring rise. The spatial heterogeneity of the wave attenuation service can be explained by the spatial patterns of coastal physical and biotic factors as well as their interactions. Not the whole transects of vegetation contributed to wave attenuation, even under spring rise scenario. Only a part of the transects, 70.8% in average, were engaged in wave attenuation under spring rise. This result indicates that the increased height of tide and wave may not induce the corresponding proportion increase in the width of ecosystem involved in dissipating waves due to the non-linear feature of ecosystems' wave attenuation service in space. This study can provide important support for coastal wetland restoration, ecosystem-based coastal management, and natural capital accounting.

Temporal Variability of the Wind Wave Parameters in the Baltic Sea in 1979–2018 Based on the Numerical Modeling Results

Purpose. The aim of the paper is to identify possible trends in the wave climate dynamics in the Baltic Sea, and to analyze statistical significance of the coefficients of these trends based on the results of their numerical modeling for 1979–2018. Methods and Results. The simulations for 1979–2018 (40 years) were carried out on an irregular grid using the MIKE 21 SW spectral wave model. The wind forcing was preset according to the ERA-Interim reanalysis data. The model was calibrated and validated against the data of wave buoys located in the northern and southern parts of the Baltic Sea. Based on the calibrated model, the wind wave parameters were calculated for the whole Baltic Sea area from 1979 to 2018 with the interval 1 hour. These parameters became the initial data for estimating temporal variability of the wind wave heights in the Baltic Sea for 40 years. The simulation results obtained on the irregular grid were interpolated to the regular one. It permitted to construct the maps of distribution of the maximum and average (for the 40-year period) significant wave heights in the Baltic Sea. The time trends for the average annual significant wave height values were revealed, and statistical significance of the coefficients of these trends was estimated. Conclusions. The average annual values of the significant wave heights over almost the whole Baltic Sea area for 1979–2018 (40 years) tend to decrease with the rate not exceeding 2–3 cm (2–3 %) per 10 years. The highest rate reduction is observed in the southeastern part of the Baltic Sea, the lowest – in the Gulf of Bothnia and the Gulf of Finland. Interannual variability of the average annual significant wave heights and the changes along the trend during the entire 40-years period are of the same order.

Vremennáya izmenchivost' parametrov vetrovykh voln v Baltiyskom more za period 1979-2018 godov po rezul'tatam chislennogo modelirovaniya

Purpose . The aim of the paper is to identify possible trends in the wave climate dynamics in the Baltic Sea, and to analyze statistical significance of the coefficients of these trends based on the results of their numerical modeling for 1979–2018. Methods and Results . The simulations for 1979–2018 (40 years) were carried out on an irregular grid using the MIKE 21 SW spectral wave model. The wind effect was preset according to the ERA-Interim reanalysis data. The model was calibrated and validated against the wave buoys’ data in the northern and southern parts of the Baltic Sea. Based on the calibrated model, the wind wave parame-ters were calculated for the whole Baltic Sea area from 1979 to 2018 with the interval 1 hour. These parameters became the initial data for estimating temporal variability of the wind wave heights in the Baltic Sea for 40 years. The simulation results obtained on the irregular grid were interpolated to the regular one. It permitted to construct the maps of distribution of the maximum and average (for the 40-year period) significant wave heights in the Baltic Sea. The time trends for the average annual significant wave height values were revealed, and statistical significance of the coefficients of these trends was estimated. Conclusions. The average annual values of the significant wave heights over almost the whole Baltic Sea area for 1979–2018 (40 years) tend to decrease with the rate not exceeding 2–3 cm (∼2–3%) per 10 years. The highest rate reduction is observed in the southeastern part of the Baltic Sea, the lowest – in the Gulf of Bothnia and the Gulf of Finland. Interannual variability of the average annual signifi-cant wave heights and the changes of its trend in course of the 40-year period are of the same order.

Interannual Variability of the Wind-Wave Regime Parameters in the Black Sea

Purpose. The paper is aimed at studying climatic trends in variability of the average annual and average monthly fields of significant wave heights of the mixed and wind seas, swell and the wind speeds in the Black Sea region. Methods and Results. Based on the MIKE 21 SW numerical model, the significant wave heights’ fields of the mixed and wind seas, and also swell were obtained for the period from 1979 to 2018. Long-term wind velocity changes were analyzed using the ERA-Interim reanalysis data for the same period. Linear climatic trends in the average annual and average monthly variability of the significant wave heights and the average wind speeds were evaluated by the statistical methods. Conclusions. The main feature of climatic variability of the significant wave height fields in the Black Sea is the pronounced spatial heterogeneity. In the western part of the sea, decrease in storm activity is observed. The eastern part is characterized by increase of the average significant wave heights. Statistically significant positive trends in fluctuations of the significant wave heights are observed in the coastal area from the Crimea southeast coast to the Georgia coast. Over the past 40 years, swell waves have intensified near the Turkish coast (to the east of Sinop) and near the Kerch Strait. The largest increase of the average monthly heights of mixed waves is observed in the eastern part of the sea in March and amounts 0.5–0.6 cm/year. This corresponds to increase of the average wind speeds by 0.025 m/s/year. In November, decrease of storm activity is observed in the western part of the sea that is expressed in diminution of the monthly average values of the significant wave heights by 0.8 cm/year. Decrease of the average annual wave heights by 0.08 cm/year is observed in the southwestern part of the Black Sea. On the contrary, the whole eastern part of the sea is subject to the increased storm activity accompanied by growth of the average annual wave heights in the fields of the mixed and wind seas by 0.10–0.15 cm/year. The above-mentioned features reflect climatic variability of the average wind speeds, which are characterized by wind weakening in the western part of the sea (0.010–0.015 m/s/year) and its amplification in the sea eastern part (0.015–0.020 m/s/year).

Mezhgodovaya izmenchivost' parametrov rezhima vetra i volneniya Chernogo morya

Purpose. The paper is aimed at studying climatic trends in variability of the average annual and aver-age monthly fields of significant wave heights of the mixed and wind waves, swell and the wind speeds in the Black Sea region. Methods and Results . Based on the MIKE 21 SW numerical model, the significant wave heights’ fields of the mixed and wind waves, and also swell were obtained for the period from 1979 to 2018. Long-term wind velocity changes were analyzed using the ERA-Interim reanalysis data for the same period. Linear climatic trends in the average annual and average monthly variability of the significant wave heights and the average wind speeds were evaluated by the statistical methods. Conclusions. The main feature of climatic variability of the significant wave height fields in the Black Sea is the pronounced spatial heterogeneity. In the western part of the sea, decrease in storm activity is observed. The eastern part is characterized by increase of the average significant wave heights. Statistically significant positive trends in fluctuations of the significant wave heights are observed in the coastal area from the Crimea southeast coast to the Georgia coast. Over the past 40 years, swell waves have intensified near the Turkish coast (to the east of Sinop) and near the Kerch Strait. The largest increase of the average monthly heights of mixed waves is observed in the eastern part of the sea in March and amounts 0.5–0.6 cm/year. This corresponds to increase of the average wind speeds by ~0.025 m/s/year. In November, decrease of storm activity is observed in the western part of the sea that is expressed in diminution of the monthly average values of the significant wave heights by 0.8 cm/year. Decrease of the average annual wave heights by ~0.08 cm/year is observed in the south-western part of the Black Sea. On the contrary, the whole eastern part of the sea is subject to the in-creased storm activity accompanied by growth of the average annual wave heights in the fields of the mixed and wind waves by 0.10–0.15 cm/year. The above-mentioned features reflect climatic variabil-ity of the average wind speeds, which are characterized by wind weakening in the western part of the sea (0.010–0.015 m/s/year) and its amplification in the sea eastern part (0.015–0.020 m/s/year).

Analysis of Typhoon-Induced Waves along Typhoon Tracks in the Western North Pacific Ocean, 1998–2017

In this study, Version 5.16 of the WAVEWATCH-III (WW3) model is used to simulate parameters of typhoon-generated wave fields in the Western North Pacific Ocean during the period 1998–2017. From a database of more than 300 typhoons, typhoon tracks are partitioned into six groups by their direction of motion and longitude of recurvature track. For typhoons that recurve east of 140° E, or track toward mainland Asia, regions of high significant wave height (SWH) values are separated by a minimum in SWH near 30° N. Partitioning SWH into wind sea and swell components demonstrates that variations in typhoon tracks produce a much stronger signal in the wind sea component of the wave system. Empirical orthogonal function (EOF) analysis is used to compute the four leading modes of variation in average SWH simulated by the WW3 model. The first EOF mode contributes to 17.3% of the total variance; all other modes contribute less than 10%. The first EOF mode also oscillates on an approximately 1-year cycle during the period 1998–2017. Overall, typhoon-induced wave energy dominates north of 30° N. Temporal analysis of the leading principal component of SWH indicates that (a) the intensity of the wave pattern produced by westward-tracking typhoons decreased during the last 20 years, and (b) typhoons that recurve east of 140° E and those that track westward toward southeast Asia are largely responsible for the decadal variability of typhoon-induced wave distribution.