Variability Of Significant Wave Height Research Articles

A Comparison of Multiple Approaches to Study the Modulation of Ocean Waves Due To Climate Variability

AbstractUsing multiple approaches, the modulation of climate variability on global ocean waves from 1981 to 2020 is investigated based on a wave hindcast model forced by ERA5 winds. These climate variabilities include El Niño–Southern Oscillation (ENSO), Antarctic Oscillation (AAO), Arctic Oscillation (AO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and Indian Ocean Dipole. Linear regression and composite analysis results indicate that El Niño‐induced low‐pressure systems in December–February (DJF) generate energetic waves in the Pacific Ocean. Positive AAO events are associated with the southward movement of westerlies in the Southern Hemisphere and thus produce long‐period Southern Ocean swell that impacts the South Pacific Ocean. In the Northern Hemisphere, positive AO is associated with strengthening winds which generate larger waves around the Icelandic region. An empirical orthogonal function approach was further undertaken to study interannual variability of significant wave height (Hs) anomalies. In DJF, mode 1 marks the impacts of ENSO and PDO in the Pacific Ocean and AO in the North Atlantic Ocean. Mode 2 is controlled by AO, which is characterized by a dipole pattern in the North Atlantic Ocean. Mode 3 describes the AAO footprints in the Southern Ocean and the eastern Pacific Ocean. In June–August, the leading mode is influenced by AAO and AMO. Mode 2 indicates the importance of ENSO and PDO which exhibit opposite patterns in the Pacific Ocean sector of the Southern Ocean. Finally, a wavelet coherence analysis is conducted on the principal components and climate indexes, which shows their respective evolutions over the time–frequency domain.

Analysis of Spatial and Temporal Criteria for Altimeter Collocation of Significant Wave Height and Wind Speed Data in Deep Waters

This paper investigates the spatial and temporal variability of significant wave height (Hs) and wind speed (U10) using altimeter data from the Australian Ocean Data Network (AODN) and buoy data from the National Data Buoy Center (NDBC). The main goal is to evaluate spatial and temporal criteria for collocating altimeter data to fixed-point positions and to provide practical guidance on altimeter collocation in deep waters. The results show that a temporal criterion of 30 min and a spatial criterion between 25 km and 50 km produce the best results for altimeter collocation, in close agreement with buoy data. Applying a 25 km criterion leads to slightly better error metrics but at the cost of fewer matchups, whereas using 50 km augments the resulting collocated dataset while keeping the differences to buoy measurements very low. Furthermore, the study demonstrates that using the single closest altimeter record to the buoy position leads to worse results compared to the collocation method based on temporal and spatial averaging. The final validation of altimeter data against buoy observations shows an RMSD of 0.21 m, scatter index of 0.09, and correlation coefficient of 0.98 for Hs, confirming the optimal choice of temporal and spatial criteria employed and the high quality of the calibrated AODN altimeter dataset.

On the role of wave climate temporal variability in bias correction of GCM-RCM wave simulations

This work presents the performance analysis of a multi-model ensemble of wave climate projections in the Mediterranean Sea against hindcast data. The wave projections were developed with the numerical model Wavewatch III forced by surface wind fields of 17 EURO-CORDEX GCM-RCMs providing time series of the main wave parameters on a 3-h and 10-km resolution. The performance of the wave GCM-RCM simulations during the baseline period (1979–2005) was assessed by means of the deterministic metrics RMSE and Bias. Different bias correction methodologies were analyzed by means of the application of the widespread Empirical Quantile Mapping method considering different time periods of significant wave height in order to analyze the ability of the bias-correcting methods to capture the different wave climate temporal scales ranging from storm events, monthly, seasonal and interannual variability. The results show that the use of the EQM method for the full-time series without taking into account other timescales, can lead to increased biases in some regions and seasons and that the use of time-dependent bias-correction techniques leads to an improved accurate characterization of biases considering the interannual temporal variability of significant wave height. More specifically the use of the EQM method for monthly data provides a good performance in capturing the correlation and interannual temporal variability of wave climate.

Spatial and Temporal Variability of Significant Wave Height and Wave Direction in the Yellow Sea and East China Sea

Spatial and Temporal Variability of Significant Wave Height and Wave Direction in the Yellow Sea and East China Sea

Variability of the coastal currents, waves and wind surge along the shore of the South-Eastern Baltic (Kaliningrad Oblast, Russian Federation)

The coastline of the Kaliningrad Oblast is an area of the South-East Baltic, which continues from the Vistula Spit to the Curonian Spit via Sambia Peninsula. The coastline has been subject to severe erosion over the past years. The goal of the paper is to analyse whether the alongshore variations of the storm surge water level, field of waves and currents are the reason for the erosion alongshore variability. The numerical simulations were carried out using the quasi-stationary approach for the model wind. The offshore wave breaking distance and the non-linear dependence between wind surge and wind speed were estimated for four typical coastline sites. The alongshore velocity on most of the coastline was enough powerful to transport the fine, medium and coarse sands. West, northern-west and north winds were defined as the most dangerous for coastal erosion. The convergence and divergence of alongshore currents as well as the vortex zones were identified for each wind direction. The results were used to analyse the alongshore current velocity, wind surge, and significant wave height variability against the shore erosion characteristics. The hypothesis that the places of convergence and divergence of alongshore currents correspond to the accumulative and erosion zones was not confirmed with one exception on the western shore of the Sambia Peninsula. Three options were supposed to explain the absence of correlation between the monitoring results on coastal erosion and modelled hydrodynamic conditions: the studied shore has not had enough free sand to demonstrate the typical behaviour of dissipative shores; the erosion characteristics depend on the very local conditions which were not resolved by numerical model; the main erosion has happened at the short term event basis when waves reach the shore at the background of a general Baltic Sea high-water level and is not a result of the general alongshore distribution of waves, wave surge and current characteristics.

VARIABILITY ANALYSIS OF SIGNIFICANT WAVE HEIGHTS AND WIND WAVES IN RIAU ARCHIPELAGO SEA PART ALKI 1

The Riau Archipelago Sea is part of the Indonesian Archipelago Sea Lane (ALKI) 1, with a very high intensity of crossing ships. Analysis of surface wind speed and significant wave height is the most important for the safety and performance of offshore shipping. This research aims to study wave characteristics and wind speed by identifying the main factors that affect significant wave height and surface wind speed. Dominant factors that affect significant wave height and wind speed are needed to decide on the safest path and the best time before crossing in ALKI-1. Temporal and spatial analysis of the seasonal variability of significant wave height and wind speed using ECMWF data for 18 years. The data used are significant wave height data and wind speed every 6 hours during the period 2000 – 2018. Three observation points are used for temporal analysis, it is found that significant wave height and wind speed are influenced by two main factors, namely MJO and Monsoon. Maximum significant wave height and wind speed that occurs in the SON period for points 3 and the DJF period at points 1 and 2. MJO affects directly from phases one to eight for observation points 1, 2, and 3. The 4, 7, and 8 MJO phases affect the value of wave height and wave speed significantly, and the 1, 2, and 5 MJO phases affect wave height and wind speed weakly.
 Keywords: ALKI 1, MJO, MJO phase, Monsoon, Significant wave height, Wind speed.

Seasonal Variability of Waves Within the Indonesian Seas and Its Relation With the Monsoon Wind

The previous studies have simulated the variability of the wave within the Indonesian seas which showed that the variability of wave follows the seasonal pattern. However, their analysis only consider the influence of local wind forcings. The bias and error of their simulated wave were also unclear. In the present study, we investigate the variability of wave within the Indonesian seas and its relation with the surface wind speed using the combination of reanalysis and remote sensing data with high accuracies. We split the analysis into swell and wind wave to obtain the influence of local and remote wind forcings. We show that at the inner seas (i.e., the South China Sea, Java Sea, Flores Sea, Banda Sea and Arafura Sea), the variability of significant wave height (SWH) is majorly influenced by the variability of the speed of monsoon wind. The maximum SWH during Northwest monsoon (NWM) season is located at the South China Sea while during Southeast monsoon (SEM) season is at Arafura Sea. This indicates that the wind wave (sea) is dominant at the inner seas. At the open seas (i.e., Pacific Ocean and Indian Ocean) the variability of SWH less corresponds to the the speed of monsoon wind. The remote wind forcings control the wave variability in the open ocean area. This indicates that swell is dominant at the open seas. In general, the magnitude of SWHswell is also more than SWHsea within the Indonesian seas.

Surface Gravity Waves and Their Role in Ocean‐Atmosphere Coupling in the Gulf of Mexico

AbstractThis study provides an overview of the surface gravity wave dynamics in the Gulf of Mexico (GoM) using numerical simulations. The focus is on the effects of ocean currents on waves, and the geographic distribution of wave statistics and parameters related to the role of waves on both sides of the ocean‐atmosphere interface. Simulations are performed using the Simulating WAves Nearshore (SWAN) model with and without coupling with the Regional Ocean Modeling System (ROMS) model within the Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) framework. In the GoM, currents alter the climatological significant wave heights by up to 0.18 m (±15%), reducing wave heights in the southwestern GoM and generally increasing wave heights in other regions. In two instantaneous snapshots representing the Loop Current variability in terms of its northward extension into the GoM, significant wave heights are modulated by as much as 0.30 m (±35%) by the currents. Probability density of wave height modulation covers a wider range of values and is skewed toward positive values over the eastern flank of the Loop Current. In winter, spring, and fall, swell fraction of wave energy increases from east to west in the GoM and reaches as high as 0.8 in the southwestern GoM, off the coast of Mexico. The dominance of swell in this region combined with weak wind results in a higher prevalence of the wave‐driven wind regime throughout the year. The interannual variability of significant wave height and swell fraction shows signals of major storms in the GoM.

Interannual wave climate variability in the Taiwan Strait and its relationship to ENSO events

This study investigated the interannual wave climate variability in the Taiwan Strait (TS) and its relationship to the El Nino-Southern Oscillation (ENSO) phenomenon using a high-resolution numerical wave model. The results showed the interannual variability of significant wave height (SWH) in the TS, which exhibits significant spatial and seasonal variations, is typically weaker than the seasonal variability. The standard deviation of the interannual SWH anomaly (SWHA) showed similar spatial variations in the TS throughout the year, being largest in the middle of the strait and decreasing shoreward, except in summer, when there was no local maximum in the middle of the TS. Further analyses proved the interannual wave climate variability in the TS is controlled predominantly by tropical cyclone activities in summer and by the northeasterly monsoon winds in winter. Furthermore, the interannual SWHA in the TS was found correlated highly negatively with the ENSO phenomenon. This relationship mainly derives from that during the northeasterly monsoon seasons. During the northeasterly monsoon seasons in El Nino (La Nina) years, the negative (positive) SWHA in the TS derives from weakened (strengthened) northeasterly monsoon winds induced by a lower-tropospheric anomalous anticyclone (cyclone) over the western Pacific Ocean and the South China Sea. During the southwesterly monsoon season in El Nino (La Nina) years, however, the SWH in the TS tends to increase (decrease) anomalously because of intensified (weakened) TC activities over the western North Pacific Ocean and adjacent seas.

Storm waves focusing and steepening in the Agulhas current: Satellite observations and modeling

Strong ocean currents can modify the height and shape of ocean waves, possibly causing extreme sea states in particular conditions. The risk of extreme waves is a known hazard in the shipping routes crossing some of the main current systems. Modeling surface current interactions in standard wave numerical models is an active area of research that benefits from the increased availability and accuracy of satellite observations. We report a typical case of a swell system propagating in the Agulhas current, using wind and sea state measurements from several satellites, jointly with state of the art analytical and numerical modeling of wave-current interactions. In particular, Synthetic Aperture Radar and altimeter measurements are used to show the evolution of the swell train and resulting local extreme waves. A ray tracing analysis shows that the significant wave height variability at scales <~100 km is well associated with the current vorticity patterns. Predictions of the WAVEWATCH III numerical model in a version that accounts for wave-current interactions are consistent with observations, although their effects are still under-predicted in the present configuration. From altimeter measurements, very large significant wave height gradients are shown to be well captured, and also associated with the current vorticity patterns at global scale.

Interannual variability of significant wave height in the northern South China Sea

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.

Evaluation of XBeach performance for the erosion of a laboratory sand dune

A new set of laboratory data is used to investigate the bathymetry change of a steep sand dune exposed to waves and high water levels, and subsequently compared to the results of numerical simulations using XBeach. Bichromatic wave boundary conditions are used to simulate a combined short-wave and long-wave field for two water level elevations corresponding to collision with the dune face, and overwashing of the dune crest. In the collision regime case, episodic slumping due to the undercutting of the dune results in sudden erosional events followed by long periods of wave-driven reshaping at the dune toe. In the overwash regime case, morphological changes are faster and sediment transport rates are higher.The XBeach model was used to simulate wave-driven erosion of the dune at the two water levels observed in the laboratory. The model was not able to precisely recreate the cross-shore spatial variability of significant wave height observed in the experiments, however near-bed wave-orbital and mean current velocities were in good agreement with observations. Following rapid initial adjustment, the model results were in agreement with measured dune morphology at successive times. XBeach was sensitive to several parameters that control the rate of erosion including the critical avalanching slope under water, the threshold water depth and the sediment transport formulation, and performed well after careful selection of the best combination of these parameters. Overall, the model predictions were in better agreement with laboratory observations for dune erosion in the overwash regime case than the collision regime case.

Seasonally Variation of Significant Wave Height for 25 Year Period Based on JMA/MRI-AGCM3.2 Wind Climate Data

The global ocean wave climate has long been of interest to the ocean engineering community because of the need for accurate operational wave data for applications such as vessel design, design of offshore and coastal structures or naval operations. Recently, there has been a major interest in wave climate changes as a result of global warming. Therefore, studies on predicting the effect of global warming on ocean wave climate are required. The objectives of this study are to analyze the accuracy and variability of global significant wave height hindcast for the 25 year period 1979-2003. This study describes the 25 year global significant wave height simulation derived from the Japan Meteorology Agency/Meteorology Research Institute (JMA/MRI)-AGCM3.2 wind climate data. The wind climate data were input into ocean wave model WAM with a global grid of spacing 1o in latitude by 1o in longitude. In situ wind and wave data sets from National Data Buoy Center (NDBC)-National Oceanic and Atmospheric Administration (NOAA) database were used to evaluate the hindcast accuracy. The validation showed good agreement both wind and waves data. The wave hindcast analysis show that the seasonal variability of significant wave height in the Northern Hemisphere is greater than in the Southern Hemisphere. Meanwhile, most of the equatorial regions are in calm condition all year.

Subseasonal Prediction of Significant Wave Heights over the Western Pacific and Indian Ocean Region

Abstract The bias and skill of multi-week predictions of significant wave height (SWH) in the western Pacific and Indian Ocean (WP–IO) region are investigated. The WaveWatch III (WW3) model is forced with daily 10-m winds from the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), retrospective forecasts (CFSR). Reforecasts using January and May initial conditions for the period 1999–2009 are considered. The main features of the climatological mean 10-m winds in weeks 1–4 are well captured by CFSv2, although the magnitude of the bias increases with lead time over much of the region in both the January and May cases. The CFSv2–WW3 system similarly captures the magnitude and spatial structure of SWH in weeks 1–4 well in both cases; however, the magnitude of the positive biases increases with lead time over the Southern Ocean (SO), the South China Sea, and the northwestern Pacific region in the January cases, and over SO in the May cases. The magnitude of the SWH variability grows weaker with lead time over SO, which may be related to the weaker interannual variability of 10-m winds in weeks 1–4 over S0 in CFSR. During the first two forecast weeks, the temporal anomaly correlation skill of SWH is significantly higher than it is during weeks 3 and 4 in the WP–IO region. Based on a categorical forecast verification, the CFSv2–WW3 can predict rare events at these lead times.

Assessing Wave Climate Variability along with Large-Scale Climate Indices on the U.S. West Coast

AbstractWave 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 Nino 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.

Analysis of the influence of ENSO phenomena on wave climate on the central coastal zone of Rio de Janeiro (Brazil)

This paper evaluates the influence of the El Nino - Southern Oscillation on the wave climate variability in the central region of Rio de Janeiro's coastal zone. The regional climate of the area was characterized using the WAVEWATCH III wave data model, obtained from NOAA, organized as a 35 year time series (1979-2013). These data were validated for the study area and a characterization and analysis performed by focusing on years with occurrence of strong El Nino/La Nina events. The correla- tion between the interannual variability of significant wave height and Oceanic Nino Index showed a slight reduction in sig- nificant wave height during El Nino years and the opposite pattern during La Nina years, with a lag of four months. This de- crease could be attributed to the intensification of the South Atlantic High with a corresponding increase in the occurrence of subtropical jets during periods of El Nino. This weather change causes the blocking of cold fronts in the southern region of Brazil and the consequent reduction in the percentage of waves from the south along the southeast coast.

Monthly Variations of Global Wave Climate due to Global Warming

Over recent years, ocean wave climate change due to global warming has attracted a lot of attention not only coastal and offshore engineer but also stakeholders in the marine industry. There is a wide range of application in ocean environment that require information on ocean wave climate data, such as ships design, design of offshore platforms and coastal structures or naval industry. In this research, monthly variation in significant wave height is studied using MRI-AGCM3.2 wind climate data for 25 year period from 1979-2003. The 25 year significant wave height simulation derived from JMA/MRI-AGCM wind climate data. The JMA/MRI-AGCM climate data were input into WAM model. The results showed that the monthly variability of significant wave height in the Northern Hemisphere is greater than in the Southern Hemisphere. Meanwhile, most of the equatorial regions are in calm condition all year.

Hindcast of extreme sea states in North Atlantic extratropical storms

This study examines the variability of freak wave parameters around the eye of northern hemisphere extratropical cyclones. The data was obtained from a hindcast performed with the WAve Model (WAM) model forced by the wind fields of the Climate Forecast System Reanalysis (CFSR). The hindcast results were validated against the wave buoys and satellite altimetry data showing a good correlation. The variability of different wave parameters was assessed by applying the empirical orthogonal functions (EOF) technique on the hindcast data. From the EOF analysis, it can be concluded that the first empirical orthogonal function (V1) accounts for greater share of variability of significant wave height (Hs), peak period (Tp), directional spreading (SPR) and Benjamin-Feir index (BFI). The share of variance in V1 varies for cyclone and variable: for the 2nd storm and Hs V1 contains 96 % of variance while for the 3rd storm and BFI V1 accounts only for 26 % of variance. The spatial patterns of V1 show that the variables are distributed around the cyclones centres mainly in a lobular fashion.

Variabilidade temporal da posição dos bancos arenosos da praia do Cassino (RS): uma análise através de imagens de vídeo

As praias constituem sistemas dinâmicos onde ondas, marés, correntes e ventos interagem com sedimentos resultando em complexos processos hidro e morfodinâmicos, sendo os bancos arenosos uma das feições mais comuns nesses ambientes. O principal objetivo do presente trabalho foi analisar a variabilidade temporal da posição dos bancos da praia do Cassino (RS) com base em observações de alta resolução espaço-temporal utilizando técnicas de vídeo imageamento. A base de dados utilizada compreende o período entre abril de 2005 até abril de 2007. Os resultados indicam que a praia do Cassino é formada por um sistema de múltiplos bancos, com ocorrência mais comum de três bancos. Em especial foi registrado um evento de surgimento de um banco a partir da divisão do banco intermediário, acompanhado da gradual migração do banco externo costa afora até seu desaparecimento. Durante este processo a praia apresentou quatro bancos. As séries de dados indicaram diferentes componentes temporais, entre elas a subsazonal, a sazonal, a mensal e a semanal, sendo que esta última demonstrou maior representatividade na variabilidade total dos dados, apresentando ainda correlação significativa com a variabilidade diária da altura das ondas.

Parameterization of bottom friction under combined wave-tide action in the Hooghly estuary, India

A comprehensive knowledge of the wave climate is an essential pre-requisite for practical applications in coastal and near-shore region. In coastal areas the dominant dissipative mechanism appears to be bottom friction where the relative strength depends on bottom characteristics, sediment type and bottom ripple geometry. The present state-of-art version SWAN wave model uses three popular formulations for dissipative mechanism due to bottom interaction. The bottom friction coefficient as in SWAN cannot be a constant and needs to be tuned based on prevailing hydrodynamic conditions when applied for a tidal dominant region. A combined wave-current interaction study should take into account varying water levels, reversal of current system and associated shear on the sea-bed. The present work reports on development of a new resistance law for bottom friction under the combined action of waves and currents. This new formulation has been implemented in the SWAN model and further its implication on variability of significant wave height for the Hooghly estuary located in the Bay of Bengal, East coast of India was investigated by comparison with ENVISAT satellite measurement. Based on this study, it could be ascertained that new friction formulation has potential for wind-wave modeling studies in near-shore and coastal waters.