Variation Of Wave Height Research Articles

Ocean Waves and Teleconnection Patterns in the Northern Hemisphere

Abstract Understanding long-term, ocean wave climate variability is important to assess climate change impacts on coastal and ocean physics and engineering. Teleconnection patterns can represent wave climate variability in the context of climate change. The objective of this study is to identify how large-scale spatial distributions of wave heights vary on a monthly basis and how they are influenced by various teleconnection patterns using reanalysis datasets. The wave height climate responses to teleconnection patterns in the eastern part of the North Pacific and North Atlantic are more sensible than in the corresponding western parts. The dominant spatial patterns of monthly averaged wave height variability in winter were obtained by empirical orthogonal function analysis. The three dominant patterns in the North Pacific and North Atlantic are similar. It is remarkable that one of the three dominant patterns, a band-shaped pattern, exhibits a strong relation to the teleconnection pattern in each ocean. The band-shaped pattern for the North Pacific was investigated in detail and found to be related to the west Pacific (WP) pattern. Where and how each teleconnection pattern influences wave climate becomes apparent especially during winter.

Wind-Wave Characteristics and Climate Variability in the Indian Ocean Region Using Altimeter Data

The significant wave height and wind speed derived for the period 1993–2010 from altimeter data sets over the Arabian Sea, Bay of Bengal, and the Indian Ocean categorized as six zones has been analyzed. The average variation of both significant wave height and wind speed is found to be almost stable for the period of study. The study reveals that the average wind speed increases by about 6cm/sec/year during monsoon and post monsoon in the southern Indian Ocean. The distribution of wind and waves was studied in the context of seasonal variations. In addition, the average inter-annual and intra-annual variations along with the statistical parameters such as standard deviation, and root mean square wave height for the six zones are also reported in this paper.

Wave climate simulation for southern region of the South China Sea

This study investigates long-term variability and wave characteristic trends in the southern region of the South China Sea (SCS). We implemented the state-of-the art WAVEWATCH III spectral wave model to simulate a 31-year wave hindcast. The simulation results were used to assess the inter-annual variability and long-term changes in the SCS wave climate for the period 1979 to 2009. The model was forced with Climate Forecast System Reanalysis winds and validated against altimeter data and limited available measurements from an Acoustic Wave and Current recorder located offshore of Terengganu, Malaysia. The mean annual significant wave height and peak wave period indicate the occurrence of higher wave heights and wave periods in the central SCS and lower in the Sunda shelf region. Consistent with wind patterns, the wave direction also shows southeasterly (northwesterly) waves during the summer (winter) monsoon. This detailed hindcast demonstrates strong inter-annual variability of wave heights, especially during the winter months in the SCS. Significant wave height correlated negatively with Nino3.4 index during winter, spring and autumn seasons but became positive in the summer monsoon. Such correlations correspond well with surface wind anomalies over the SCS during El Nino events. During El Nino Modoki, the summer time positive correlation extends northeastwards to cover the entire domain. Although significant positive trends were found at 95 % confidence levels during May, July and September, there is significant negative trend in December covering the Sunda shelf region. However, the trend appears to be largely influenced by large El Nino signals.

파력발전장치 설계를 위한후포 연안의 파랑 분석 및 스펙트럼 추정

There exist various types of the WEC (Wave Energy Converter), and among them, the point absorber is the most popularly investigated type. However, it is difficult to find examples of systematically measured data analysis for the design of the point absorber type of power buoy in the world. The study investigates the wave load acting on the point absorber type resonance power buoy wave energy extraction system proposed by Kweon et al. (2010). This study analyzes the time series spectra with respect to the three-year wave data (2002.05.01~2005.03.29) measured using the pressure type wave gage at the seaside of north breakwater of Hupo harbor located in the east coast of the Korean peninsula. From the analysis results, it could be deduced that monthly wave period and wave height variations were apparent and that monthly wave powers were unevenly distributed annually. The average wave steepness of the usual wave was 0.01, lower than that of the wind wave range of 0.02-0.04. The mode of the average wave period has the value of 5.31 sec, while mode of the wave height of the applicable period has the value of 0.29 m. The occurrence probability of the peak period is a bi-modal type, with a mode value between 4.47 sec and 6.78 sec. The design wave period can be selected from the above four values of 0.01, 5.31, 4.47, 6.78. About 95% of measured wave heights are below 1 m. Through this study, it was found that a resonance power buoy system is necessary in coastal areas with low wave energy and that the optimal design for overcoming the uneven monthly distribution of wave power is a major task in the development of a WEF (Wave Energy Farm). Finding it impossible to express the average spectrum of the usual wave in terms of the standard spectrum equation, this study proposes a new spectrum equation with three parameters, with which basic data for the prediction of the power production using wave power buoy and the fatigue analysis of the system can be given.

An Inner-Shelf Wave Forecasting System for the U.S. Pacific Northwest

Abstract An operational inner-shelf wave forecasting system was implemented for the Oregon and southwest Washington coast in the U.S. Pacific Northwest (PNW). High-resolution wave forecasts are useful for navigational planning, identifying wave energy resources, providing information for site-specific coastal flood models, and having an informed recreational beach user group, among other things. This forecasting model is run once a day at 1200 UTC producing 84-h forecasts. A series of nested grids with increasing resolution shoreward are implemented to achieve a 30-arc-second resolution at the shelf level. This resolution is significantly higher than what the current operational models produce, thus improving the ability to quantify the alongshore variations of wave conditions on the PNW coast. Normalized root-mean-squared errors in significant wave height and mean wave period range from 0.13 to 0.24 and from 0.13 to 0.26, respectively. Visualization of the forecasts is made available online and is presently being used by recreational beach users and the scientific community. A series of simulations, taking advantage of having a validated shelf-scale numerical wave model, suggests that neither dissipation due to bottom friction nor wind generation is important in the region at this scale for wave forecasting and hindcasting when considering bulk parameters as opposed to the processes of refraction and shoaling. The Astoria and McArthur Canyons; the Stonewall, Perpetua, and Heceta Banks; and Cape Blanco are significant bathymetric features that are shown to be capable of producing alongshore variability of wave heights on the shelf.

Bayesian hierarchical modelling of North Atlantic windiness

Abstract. Extreme weather conditions represent serious natural hazards to ship operations and may be the direct cause or contributing factor to maritime accidents. Such severe environmental conditions can be taken into account in ship design and operational windows can be defined that limits hazardous operations to less extreme conditions. Nevertheless, possible changes in the statistics of extreme weather conditions, possibly due to anthropogenic climate change, represent an additional hazard to ship operations that is less straightforward to account for in a consistent way. Obviously, there are large uncertainties as to how future climate change will affect the extreme weather conditions at sea and there is a need for stochastic models that can describe the variability in both space and time at various scales of the environmental conditions. Previously, Bayesian hierarchical space-time models have been developed to describe the variability and complex dependence structures of significant wave height in space and time. These models were found to perform reasonably well and provided some interesting results, in particular, pertaining to long-term trends in the wave climate. In this paper, a similar framework is applied to oceanic windiness and the spatial and temporal variability of the 10-m wind speed over an area in the North Atlantic ocean is investigated. When the results from the model for North Atlantic windiness is compared to the results for significant wave height over the same area, it is interesting to observe that whereas an increasing trend in significant wave height was identified, no statistically significant long-term trend was estimated in windiness. This may indicate that the increase in significant wave height is not due to an increase in locally generated wind waves, but rather to increased swell. This observation is also consistent with studies that have suggested a poleward shift of the main storm tracks.

Recent Studies on Wind Seas and Swells in the Indian Ocean: A Review

Winds and waves data measured at a few locations along the west coast of India as well as wave model results were analysed to study the wave characteristics in the deep as well as nearshore regions during different seasons. During fair weather season, we can observe distinct and systematic diurnal variation in wave height and wave period, especially, simultaneous increase in wave height and decrease in wave period with increase in local wind speed. This is due to superimposition of wind seas generated by the sea breeze system with the pre-existing swells. The swells observed in the Arabian Sea are from SW direction during SW monsoon season and from SW/SSW and NW directions during both pre-monsoon and post-monsoon seasons. The NW swells which occur during Shamal events show distinct characteristics such as an increase in wave height, decrease in swell period and a common propagation direction (northwest) for wind seas and swells. Also the swells generated at 400 S, propagate in the north Indian Ocean, and enter the Bay of Bengal without affecting the Arabian Sea. Fine resolution winds (say, MM5 or WRF) are necessary to understand the effect of land-sea breeze system on wind-sea generation in the coastal regions. Here, we review the recent work on wind seas and swells in the Indian Ocean and coastal regions that we have carried out using measured wave data and model results.

Surf Zone States and Energy Dissipation Regimes — A Similarity Model

A similarity parameter is derived to describe surf zone dissipation using the classical energy dissipation model for surf zone bores. This parameter can also be interpreted as a relative beach slope parameter, βγ, and, for shallow water sinusoidal waves, is the ratio of the local beach slope and the local wave steepness (H/L). βγ = 1 defines the boundary between two different energy dissipation regimes. Conditions with βγ < 1 represent over-dissipative conditions, where the classical bore dissipation model provides more dissipation than that required for depth-limited waves (constant H/h) to be maintained. Conditions with βγ > 1 represent under-dissipative conditions, where the bore model provides insufficient dissipation for depth-limited conditions to occur. Conditions with βγ = 1 at the breakpoint lead to locally saturated but not depth-limited surf. Hence, the new similarity parameter distinguishes between saturated and unsaturated surf conditions. Based on this bore dissipation model, an analytical model for the wave height transformation of monochromatic waves on planar beaches is derived. The cross-shore variation in wave height obtained from this model show different functional forms; concave upward for over-dissipative conditions and convex upward for under-dissipative conditions. Further, the analytical model shows that depth-limited conditions within the inner surf zone are not possible with this bore dissipation model and the model assumptions. Additional work is required to determine if this parameter is a useful predictor of other surf zone characteristics. Highlights: We derive a similarity parameter to describe surf zone dissipation. The similarity parameter defines the boundary of two dissipation regimes. The parameter distinguishes between saturated and unsaturated surf conditions. The classical bore dissipation model cannot predict depth-limited wave heights on a plane beach.

Wave‐current interactions in a wave‐dominated tidal inlet

Wave‐current interactions play a major role in the dynamics of shallow tidal inlets. This study investigates these interactions at a natural inlet, with a strong focus on current‐induced changes on wave propagation. The analysis of hydrodynamic data collected at the Albufeira lagoon, Portugal, revealed spatiotemporal variations of water levels and wave heights along the inlet, attributed to wave‐current interaction processes. We compared the simulations of a coupled wave‐circulation modeling system, computed with and without waves, and propagated with and without current feedback. The wave‐induced setup inside the lagoon represented 7%–15% of the offshore significant wave height. The accuracy of the wave's predictions improved when current feedback was included. During ebb, the currents increased the wave height at the mouth of the inlet (up to 20%) and decreased the wave height in the inlet (up to 40%), due to current‐induced refraction, steepness dissipation, and partial blocking. During flood, the currents decreased the wave height in the inlet (up to 10%) and increased the wave height at the exterior parts of the ebb shoal (up to 10%), due to current‐induced refraction. These effects significantly attenuate seaward sediment fluxes during ebb and contribute to the sediment accretion in the inlet.

완도 해역의 해수면 조건에 따른 파랑 변형 특성

The aim of this study was estimated the characteristics of the wave propagation by the water level conditions using a numerical modeling method at the Wando sea area. For three cases numerical simulation on the condition of incident and incoming of the deepwater design wave and the season normal wave, the spatial distribution of the incident wave at study area were investigated. And the calculated numerical modeling results were compared with measured field wave data. According to on-site wave data measured for 18 days, the range of the significant wave height and period were 0.10~1.14 m, 4.35~8.74 sec, respectively, and the maximum wave height were 0.15~1.66 m. From the results of numerical model for offshore design wave incident, the wave height attacked from Southern-East direction at this study area were over maximum 10.5 m because of rapidly change of water depth. Numerical modeling by three water level conditions of Approxmate Lowest Low Water Level(Approx. L.L.W), Mean Sea Level(M.S.L) and Approximate Highest High Water Level(Approx. H.H.W) were practiced. From the results for the case of Approx. H.W.L, variations of wave height at the back area of islands were about 1.6 m at maximum value for the case of deepwater design wave incoming. The significant wave heights of winter season were bigger than summer under normal wave condition, the incident wave height over 5.5 m decreased by shielding effect of islands. The change of maximum wave height at summer season were distinct than winter and was about 1.2 m and 0.8 m, respectively.

Random wave runup and overtopping a steep sea wall: Shallow-water and Boussinesq modelling with generalised breaking and wall impact algorithms validated against laboratory and field measurements

A semi-implicit shallow-water and Boussinesq model has been developed to account for random wave breaking, impact and overtopping of steep sea walls including recurves. At a given time breaking is said to occur if the wave height to water depth ratio for each individual wave exceeds a critical value of 0.6 and the Boussinesq terms are simply switched off. The example is presented of waves breaking over an offshore reef and then ceasing to break as they propagate inshore into deeper water and finally break as they run up a slope. This is not possible with the conventional criterion of a single onset of breaking based on rate of change of surface elevation which was also found to be less effective generally. The runup distribution on the slope inshore of the reef was well predicted. The model is tested against field data for overtopping available for Anchorsholme, Blackpool and corresponding 1:15 scale wave flume tests. Reflection of breaking waves impacting a steep sea wall is represented as a partial reversal of momentum flux with an empirically defined coefficient. Offshore to nearshore significant wave height variation was reasonably predicted although nearshore model spectra showed distinct differences from the experiments. The breaking wave shape described by a shape parameter was also not well represented as might be expected for such a simple model. Overtopping agreement between model, field and flume was generally good although repeatability of two nominally identical flume experiments was only within 25%. Different distributions of random phase between spectral components can cause overall overtopping rates to differ by up to a factor of two. Predictions of mean discharge by EurOtop methods were within a factor of two of experimental measurements.

Wave–current interaction: Effect on the wave field in a semi-enclosed basin

The effect on waves of the Wave–Current Interaction (WCI) process in the semi-enclosed Gulf of Venice (northern region of the Adriatic Sea) was investigated using the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) modeling system. COAWST relies on the ocean model ROMS (Regional Ocean Modeling System), the wave model SWAN (Simulating WAves Nearshore), and the CSTMS (Community Sediment Transport Modeling System) routines. The two-way data transfer between circulation and wave models was synchronous via MCT (Model Coupling Toolkit), with ROMS providing: current field, free surface elevation, and bathymetry to SWAN. For coupling, the 3-D current profiles were averaged using a formulation which integrated the near-surface velocity over a depth controlled by the spectral mean wavenumber. COAWST system was implemented on a parent grid (with horizontal resolution of 2.0km) covering the whole Adriatic Sea with one-way nesting to a child grid resolving the northern area (Gulf of Venice) at a resolution of 0.5km. The meteorological forcings provided by the operational meteorological model COSMO-I7 (a mesoscale model developed in the framework of the COSMO Consortium) were used to drive the modeling system in the period bracketing September 2010–August 2011. The adopted winds and the simulated waves were compared with observations at the CNR-ISMAR Acqua Alta oceanographic tower, located off the Venice littoral. Wave heights and sea surface winds were also compared with satellite-derived data. The analysis of WCI was performed on the child grid over the winter season (January–March 2011) with particular focus on the waves generated by prevailing and dominant winds blowing on the Adriatic Sea: Bora and Sirocco. Due to the variable wind direction with respect to the ocean current direction different effects on WCI were depicted, showing that within the northern Adriatic Sea the ocean–wave interactions are strongly dependent on the wind forcing direction. Further investigations reveal that, when applied to intense storms, the effect of coupling on waves results in variations of significant wave height up to 0.6m, with some areas experiencing significant increase/decrease of wave spectral energy for opposite/following currents respectively.

Potential impact of climate change at five Japanese beaches

Yoshida, J., Udo, K., Takeda, Y., and Mano, A., 2013. Potential impact of climate change at five Japanese beachesCoastal erosion caused by sea level rise is a serious problem over the world. Future sea level rise will almost certainly accelerate through the 21st century. Although its extent remains uncertain, some predictions expect the increase to be between up to 30 and 180 cm by 2100 (Nicholls and Cazenave, 2010). Several studies show that sea level rise is responsible for long-term beach erosion. Moreover, change of wave height and non-climate-related processes such as ground subsidence amplify coastal vulnerability associated with climate change. It is a pressing issue to predict shoreline change considering the fact that 10% of the global population lives in the coastal regions within 10 m elevation. This study estimates the potential impact of climate change in terms of the effects of: sea level rise; wave height variation; and land subsidence by comparing the past coastline evolutions at five beaches in Japan. The past long-term shoreline change was found to be related to coastal protection measures according to Japan's national policy (Coast Act). Notable erosion was resulted from the construction of coastal facilities that blocked coastal sand drift and the decrease of sediment supply from rivers caused by dam building from 1950 to 1990. Since 1990, shoreline has relatively unchanged because some measures, such as beach nourishment, groins and detached breakwaters, have worked to conserve sand beaches. The estimation results showed that shoreline would retreat over 15 m due to sea level rise and up to 5 m due to wave height variation at the five beaches by 2100. Projection of ground subsidence is uncertain because its rate varies depending on natural forces and human activities. This study suggests that sea level rise would have much greater impact on beach erosion compared with wave height variation and ground subsidence.

Extending the observed Baltic Sea wave climate back to the 1940s

ABSTRACT Soomere, T., 2013. Extending the observed Baltic Sea wave climate back to the 1940s. Systematic visual wave observations have been performed since 1946 at numerous locations on the eastern coast of the Baltic Sea. The records of wave height that mostly exist since 1954 are reconstructed back to 1946 using the high correlation (about 0.85) between the wave height and qualitative measures of sea state, and a linear regression between these quantities at Ventspils and Liepaja (Kurzeme Peninsula, Latvia). The analysis confirms the well-known properties of the Baltic Sea wave fields such as a relatively low overall wave intensity, short wave periods at the nearshore, high spatio-temporal variations in the average wave height and a strong evidence of decadal-scale changes. A part of the relevant changes are in counterphase for the southern and the northern Baltic Sea. There has been a relatively rapid decrease in the average wave height in the eastern Baltic Sea from the end of 1940s until ~1970, and a...

東シナ海における波高の極値の再評価

Based on shallow water wave hindcastings for a 65-year period of historical typhoons and a 100,000-year period of simulated typhoons, extremes of wave heights in the East China Sea are discussed. Main findings are 1)variation of the 100-year return wave height in the sea is less than ±5% for a 10-year extension of the data period, in cases where the maximum of the wave heights is around 16 m; 2)the location-dependent largest wave height generated by the historical typhoons ranges from 60 to 80 % of the probable maximum(pmx) wave height estimated for simulated typhoons; and 3)the 100-year return wave height in local areas around Kabashima close to the Goto Islands changes from 15 m at offshore points to 10 m at onshore points, which is more than 2 m greater than the previous estimate.

茨城県鉾田海岸の季節的海浜地形変動と潜突堤の効果検討

On the Hokota coast facing the Pacific Ocean, beach changes have occurred in response to the seasonal variation in wave direction and wave height. Aerial photographs were taken to investigate shoreline changes around Nos. 23 and 29 artificial headlands. Numerical simulation using the BG model improved by Noshi et al. (2009) was carried out. The seasonal changes in beach topography and grain size of bed materials were reproduced. Furthermore, beach changes when submerged groins were extended offshore of Nos. 23 and 29 artificial headlands were predicted.

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.

PIV MEASUREMENTS OF PARTICLE VELOCITIES AND TRAJECTORIES FOR INTERNAL WAVES PROPAGATING IN A TWO-LAYER FLUID ON A SLOPING BOUNDARY

Some characteristics of internal waves propagating in a two-layer fluid on a sloping bottom were investigated experimentally using particle image velocimetry (PIV) that was originally developed to express the velocity field in a two-dimensional area. Two dimensional vector distributions of velocity were estimated at several phases during one wave cycle. The method of characteristics was adapted to calculate the interfacial displacement and water particle trajectory. In addition, the variations of wave speed, wave height and wave setup from deepwater to shallow-water regions by an imaging technique were compared with those by a wave dissipation model based on the radiation stress concept. These attempts proved the ability of the imaging technique to accurately measure both temporal and spatial variations of some physical quantities due to the propagation of internal waves. The PIV technique was applied to the prediction of Lagrangian velocity in a Eulerian scheme. The measured particle path was compared with the positions found theoretically by the method of characteristics.

3-D WAVE FIELD AROUND SUBMERGED BREAKWATER

Methods for designing submerged breakwaters are still being developed, particularly in respect of the 3D nature of wave-breakwater interaction. Many of the available design tools are inefficient as they are not able to provide any information on the spatial distribution of the wave field around breakwaters, and cannot therefore guarantee reliability and accuracy for the engineer. There is thus a need for an engineering design tool with the ability to model spatial variation of wave height. This paper proposes a method based on machine learning algorithms for predicting the nearshore wave field behind a submerged breakwater that includes both 2D and 3D effects. The proposed numerical model has been validated by various scales of laboratory data. Comparisons reveal the ability of the proposed model to predict the wave field around submerged breakwater.

Forecasting space–time variability of wave heights in the Bay of Bengal: a genetic algorithm approach

The present work employs a genetic algorithm to carry out wave height forecasting in the Bay of Bengal. The use of empirical orthogonal function analysis allows the spatial extending of the forecast to the entire basin. The chaotic nature of the process limits the horizon of usable forecasts to 48 h in advance. Statistical evaluation of the quality of forecast leads to encouraging results. A major advantage of this method is that, once the forecast equations are derived, they can be used directly without the necessity of having a numerical wave model as an intermediate step.