Wind-driven Waves Research Articles

Variability and Sources of the Internal Wave Continuum Examined from Global Moored Velocity Records

AbstractEnergy for ocean turbulence is thought to be transferred from its presumed sources (viz., the mesoscale eddy field, near-inertial internal waves, and internal tides) to the internal wave continuum, and through the continuum via resonant triad interactions to breaking scales. To test these ideas, the level and variability of the oceanic internal gravity wave continuum spectrum are examined by computing time-dependent rotary spectra from a global database of 2260 current meter records deployed on 1362 separate moorings. Time series of energy in the continuum and the three “source bands” (near-inertial, tidal, and mesoscale) are computed, and their variability and covariability examined. Seasonal modulation of the continuum by factors of up to 5 is seen in the upper ocean, implicating wind-driven near-inertial waves as an important source. The time series of the continuum is found to correlate more strongly with the near-inertial peak than with the semidiurnal or mesoscale. The use of moored internal-wave kinetic energy frequency spectra as an alternate input to the traditional shear or strain wavenumber spectra in the Gregg–Henyey–Polzin finescale parameterization is explored and compared to traditional strain-based estimates.

Horizontal energy flux of wind-driven intraseasonal waves in the tropical Atlantic by a unified diagnosis

AbstractIntraseasonal waves in the tropical Atlantic Ocean have been found to carry prominent energy that affects interannual variability of zonal currents. This study investigates energy transfer and interaction of wind-driven intraseasonal waves using single-layer model experiments. Three sets of wind stress forcing at intraseasonal periods of around 30 days, 50 days and 80 days with a realistic horizontal distribution are employed separately to excite the second baroclinic mode in the tropical Atlantic. A unified scheme for calculating the energy flux, previously approximated and used for the diagnosis of annual Kelvin and Rossby waves, is utilized in the present study in its original form for intraseasonal waves. Zonal velocity anomalies by Kelvin waves dominate the 80-day scenario. Meridional velocity anomalies by Yanai waves dominate the 30-day scenario. In the 50-day scenario, the two waves have comparable magnitudes. The horizontal distribution of wave energy flux is revealed. In the 30-day and 50-day scenarios, a zonally alternating distribution of cross-equatorial wave energy flux is found. By checking an analytical solution excluding Kelvin waves, we confirm that the cross-equatorial flux is caused by the meridional transport of geopotential at the equator. This is attributed to the combination of Kelvin and Yanai waves and leads to the asymmetric distribution of wave energy in the central basin. Coastally-trapped Kelvin waves along the African coast are identified by along-shore energy flux. In the north, the bend of the Guinea coast leads the flux back to the equatorial basin. In the south, the Kelvin waves strengthened by local wind transfer the energy from the equatorial to Angolan regions.

Field study of wave reflection from permeable rubble mound breakwater of Chabahar Port

The present study analyzes the field measurements of the reflective response of a permeable rubble mound breakwater encountered with a bimodal wave regime. The coexistence of sea and swell wind-driven waves during the measurement program provided directional spreading wave realizations for subsequent bulk and frequency-dependent wave reflection analysis. The directional wave data were acquired near the primary breakwater of Chabahar Port within 28 days, including 643 bursts using an AWAC wave recorder. The available formulae for wave reflection coefficient were evaluated against this data set. Results showed that the equations proposed by Postma (1989) and Zanuttigh and Van der Meer (2007) are in general agreement with the observations of the present study. However, the accuracy of reflection coefficient predictions was improved by developing two new alternative formulations. It was realized that the frequency reflective response differs between sea and swell prevailing conditions. The reflection coefficient decreases drastically within high sea wave predominant periods for the harmonics higher than peak frequency. However, reflection coefficients of high harmonics reduced slightly within swell domination periods. The frequency-dependent reflection coefficients can be even higher than unity due to energy transfer amongst other wave harmonics.

Investigating typhoon impact on SSC through hourly satellite and real-time field observations: A case study of the Yangtze Estuary

The variation in suspended sediment concentration (SSC) has an important impact on the protection of estuarine shoal wetlands and the maintenance of waterways. Typhoons (tropical cyclones), one of the most severe meteorological disasters, frequently occur along the southeastern coasts of China and substantially affect the spatial-temporal distribution of SSC in the Yangtze Estuary. In this study, the spatial-temporal distribution of SSC was observed at high frequency through hourly geostationary satellite remote sensing during four typhoon events, namely, Typhoons Damrey/Saola (August 2012), Soulik (July 2013), Matmo (July 2014) and Dujuan (September 2015). Such observation is difficult to achieve through in situ approaches due to the unsafe working conditions created by typhoon winds. Moreover, wind speed, wave height and period, and bottom shear stress (BSS) data combined with turbidity data were used to analyze the causes of typhoon-induced SSC variations. The results indicated that the average wind-driven significant wave height during typhoons was 2.1-fold higher than that in pre-typhoon periods. In the lower mouth of the Yangtze Estuary and in Hangzhou Bay, the SSC increased by 0.14–0.33 g/L, whereas in the upper mouth, the SSC was less affected by wind. The significant increase in SSC persisted for 1–2 days following typhoon transit. With the assistance of the FVCOM model, it was observed that the enhanced wave-current dynamics and increased BSS during the typhoons were the main reasons for the sharp increase in SSC. Moreover, it was inferred from the satellite images that sediment exchange occurs between channels and shoals during a typhoon, which affects the SSC distribution for up to one month.

Experimental study on the evolution of mechanically generated waves mixed with space non-uniform wind-driven waves

This study experimentally investigates the evolution of mechanically generated waves mixed with wind-driven waves. The pre-existing wind-driven waves are time stable and space non-uniform during the tests. Empirical formulations for fetch laws of dimensionless wave energy and peak frequency of wind-driven waves at the laboratory scale are given. Experimental results show that the characteristics of mixed waves are affected by the variations in wind speed, fetch, wave period, and wave height. At small fetches, both waves are generally inhabited after mixing. With increasing fetch, the energy of the generated waves is enhanced at a large wave steepness level. When the frequency gap between the two wave types is small, mixed waves tend to have a chaotic wave evolution. However, the changes in the two types of waves are small when the frequency gap between the two waves is large. A frequency lock-in phenomenon of the wind-driven waves at high-order waves of the generated waves is found in the regular wave tests at large wave steepness levels. Such a phenomenon does not exist in present irregular wave tests. With increasing fetch, the spectrum of mixed waves downshifts at the beginning and upshifts at a large fetch.

Benthic Community Responses to the Filling of a Hurricane-Induced Barrier Island Inlet

Rodil, I.F.; Long, Z.T.; Fegley, S.R.; Rodriguez, A.B., and Peterson, C.H., 2021. Benthic community responses to the filling of a hurricane-induced barrier island inlet. Journal of Coastal Research, 37(3), 601–610. Coconut Creek (Florida), ISSN 0749-0208.In September 2003, Hurricane Isabel created a new tidal inlet through Hatteras Island, a barrier island of North Carolina (U.S.A.). Within two months, the breach was filled with sand dredged from nearby areas. Subsequent ecological response of the benthic macroinvertebrate communities to the filling differed on shores on opposite sides of the island. Thus, the filled area on the high-energy sandy beach exhibited convergence in community composition and abundance with a nearby reference area within 30 months, whereas the filled area on the lower-energy sound shoreline still possessed a depauperate benthos. The high volume of long-shore sediment transport documented along the ocean beaches of Hatteras Island probably acted quickly to transport benthic macrofauna to the fill along with natural beach sediments, and thereby activating a rapid ecological response of the beach community. The beach community was dominated by annual macroinvertebrate species, which could account for mixing from nearby areas in the rapid macrofauna community response. In contrast, the Pamlico Sound shoreline experiences only local wind-driven waves and modest long-shore currents likely insufficient to import macrobenthos readily. Infrequent passive transport of macrobenthos and persistence of defaunated sediment habitats nearby probably slowed the macrofauna community response on the sound-shore side. Management intervention through habitat restoration would be recommended in the less dynamic sound shore environment compared to the high-energy ocean beach where ecological responses of the invertebrate community occurred rapidly.

Projected incremental changes to extreme wind-driven wave heights for the twenty-first century

Global climate change will alter wind sea and swell waves, modifying the severity, frequency and impact of episodic coastal flooding and morphological change. Global-scale estimates of increases to coastal impacts have been typically attributed to sea level rise and not specifically to changes to waves on their own. This study provides a reduced complexity method for applying projected extreme wave changes to local scale impact studies. We use non-stationary extreme value analysis to distil an incremental change signal in extreme wave heights and associate this with a change in the frequency of events globally. Extreme wave heights are not projected to increase everywhere. We find that the largest increases will typically be experienced at higher latitudes, and that there is high ensemble model agreement on an increase (doubling of events) for the waters south of Australia, the Arabian Sea and the Gulf of Guinea by the end of the twenty-first century.

Manifestation of surfactant films in underwater solar path images: numerical experiment

This paper continues a series of studies on using underwater solar path imagery (USPI) to retrieve characteristics of wind-driven waves and their variations in the field of near-surface hydrophysical processes under the influence of surfactant films. Research is based on previously developed mathematical models of USPI and its statistical moments, the Elfouhaily spectrum of wind-driven waves, the Ermakov model of wave damping by a thin film, and the Cox-Munk result for a thick oil film. A high sensitivity of two statistical moments of USPI to variations of wind-wave conditions and viscoelastic characteristics of oil films was shown. The presented examples demonstrated 20%-40% narrowing of the statistically average image (the first statistical moment) for thin films and more than 2 times narrowing for thick films. The film presence also leads to significant changes in the autocorrelation function of USPI. The characteristic scales and magnitudes of changes in the considered statistical moments fit into the ranges of values that can be recorded in practice using even inexpensive video cameras. At the same time, there are cases in which these moments are close. For example, for a clean sea surface in weak winds and for a surface covered by a thin film in stronger winds. These cases can be distinguished by analyzing a series of instant images. As an example, a series of real underwater images demonstrating changes in the glint structure with the surfactant film spot passing through the observed sea surface area were analyzed. This example is intended to help researchers to distinguish cases of wind weakening and a surfactant film presence.

Sensitivity analysis for wind-driven significant wave height model in SWAN: A Sunda Strait case

Sunda Strait is one of the most important straits in Indonesia since it connects two major islands of Indonesia as well as two oceans. Due to its high importance, it is essential to have a well understanding of significant wave height within the strait. However, there are currently no long-term significant wave data from buoy records in Indonesia. The available fine-resolution meteorology-oceanography (metocean) data around the Sunda Strait is also not as fine as other locations in the world. Therefore, hydrodynamic modelling is essential to obtain significant wave data that completely covers the strait. The aim of this study was to perform a sensitivity analysis based on Sunda Strait SWAN significant wave height model In the research, we performed a sensitivity analysis on a significant wave height SWAN model using various spatial resolution of wind forcing from the ECMWF ERA5 database. The analysis is essential to obtain the coarsest acceptable metocean data for modelling. Our result shows that higher spatial resolution of wind forcing gives better agreement with the ERA 5 wave data. For the Sunda Strait case, we recommend using no coarser than 0.5 degrees of spatial wind forcing resolution. However, we also found that the modelling result, along with models from past studies, still underestimates the reported wave height data in extreme conditions.

Quantifying interior coastal marsh degradation at two North Carolina marshes

Marshes along the coast of North Carolina are currently at risk due to ongoing land loss, and as they are highly productive waterways, understanding the processes driving land loss is critical. By focusing on two marshes adjacent to waterways — Roanoke Marsh, south of Manns Harbor, and Mackay Island National Wildlife Refuge — we created a dataset of land loss rates from 1983 to 2016, both within the marsh interior (due to expanding ponds) and on the outer edge of the marsh (coastal retreat). We investigated the hypothesized primary driver behind the interior pond expansion (wind-driven waves in the pond interior) and the coastal edge retreat of the marsh (wind-driven waves within Currituck Sound). The total land area lost over the 34- year study period was 1.49 km2 and 2.32 km2 on Roanoke Marsh and Mackay Island, respectively. The percentage of total land lost due to internal pond expansion was 60% in Roanoke Marsh and 44% in Mackay Island. Internal pond expansion is at least of equal importance to outer coastal retreat for net land loss in these coastal marshes. The local wind has a dominant direction from the north-northwest with more energetic winds during the winter. However, the wind directions and direction of pond expansion do not appear to be correlated. This may be because the winds are bimodal and drive expansion in multiple directions. In addition, there is subsidence in this portion of North Carolina that may be an additional factor contributing to the pond area expansion.

Vertical handover in heterogeneous networks using WDWWO algorithm with NN

ABSTRACT In heterogeneous networks, Vertical Handover (VH) plays a vital consequence of customer mobility as they have a high impact on networking performance like delay, throughput and call block probability. Even in the presence of various existing works, VH management exhibit certain drawbacks like method complexity, difficult network modelling and inaccurate handover. Thus, a hybrid methodology is proposed in this work which can provide accurate VH and considerable reduction in working complexity. Here, a combination of Deep Residual Neural (DRN) and Wind-Driven Water Wave Optimisation (WDWWO) is introduced to perform VH. Accurate prediction of Received Signal Strength (RSS) is a difficult task for mobile users while moving from one network to another. In order to tackle this situation, DRN is used with WDWWO based weight optimisation, hence the name Optimised DRN (ODRN). Almost every networking parameters like bandwidth, delay, throughput, velocity, BER, SNR, energy consumption, monetary cost and data traffic are included in ODRN modelling. The proposed work is implemented in NS2 platform and resultant performances like energy consumption, RSS, throughput, packet delivery ratio, packet loss, handover failure rate, algorithm convergence and latency are compared with conventional methods of D-TOPSIS, FIS-ENN and F-AHP.

Sea spray aerosol concentration modulated by sea surface temperature

Natural aerosols in pristine regions form the baseline used to evaluate the impact of anthropogenic aerosols on climate. Sea spray aerosol (SSA) is a major component of natural aerosols. Despite its importance, the abundance of SSA is poorly constrained. It is generally accepted that wind-driven wave breaking is the principle governing SSA production. This mechanism alone, however, is insufficient to explain the variability of SSA concentration at given wind speed. The role of other parameters, such as sea surface temperature (SST), remains controversial. Here, we show that higher SST promotes SSA mass generation at a wide range of wind speed levels over the remote Pacific and Atlantic Oceans, in addition to demonstrating the wind-driven SSA production mechanism. The results are from a global scale dataset of airborne SSA measurements at 150 to 200 m above the ocean surface during the NASA Atmospheric Tomography Mission. Statistical analysis suggests that accounting for SST greatly enhances the predictability of the observed SSA concentration compared to using wind speed alone. Our results support implementing SST into SSA source functions in global models to better understand the atmospheric burdens of SSA.

Coupled influence of pH and dissolved organic carbon on the immobilization of phosphorus by lanthanum-modified zeolite

Wind-driven waves and currents in shallow lakes frequently trigger the resuspension of sediments in the photic layer, which is characterized with a high pH and high dissolved organic carbon (DOC) concentration. The mechanism of phosphorus-inactivating agents (PIAs) immobilizing phosphorus under the coupled influence of pH and DOC is not clarified, and the applicability of PIAs in eutrophic shallow lakes is thus still doubtful. We found that, under the coupled influence of pH and DOC, the uptake of phosphate by LMZ was affected mainly by pH at low DOC concentrations and by DOC at high DOC concentrations. A high pH (9.3) and high DOC concentration (24.7 mg/L) greatly increased the release of phosphorus from sediment to water. However, the addition of LMZ substantially reduced the P concentrations in water, mainly via capture of dissolved inorganic phosphorus. The results of the reversibility of the adsorption of phosphates and DOC showed that phosphate had much higher affinity than DOC towards LMZ. The phosphate once adsorbed on LMZ was resistant to release when exposed to conditions of either a high pH (9.5), high DOC concentration (250 mg/L) or both; i.e., only <5% of the adsorbed phosphate is releasable. Therefore, we proposed that, to avoid the coupled influence of pH and DOC in the photic layer of eutrophic shallow lakes, LMZ could be applied in multiple low doses in the season when the growth of algae is minimal (a low pH and low DOC concentration).

Comparative Assessment of Different Modelling Schemes and Their Applicability to Inland Small Reservoirs: A Central Europe Case Study

Sustainable landscape management involve also water reservoir management. The demand of their reconstruction represents a good opportunity for redesigning hydrotechnical structures and their parameters using recent methods and models. The estimation of wind-driven waves on small water reservoirs and their effects on water reservoir structures rarely are applied, although it is an important part of the dam height calculation. The analysis of wave run-up on the upstream face of the dam was performed by means of the Slovak Technical Standard (STN), Coastal Engineering Manual (CEM), Shore Protection Manual (SPM) and model designed by American Society of Agricultural and Biological Engineers (ASABE). The estimations of the wave characteristics differ depending on the model; wave height (H13%) within the range 0.32–0.56 m, wave period 1.32–2.11 s and run-up (R2%) 0.84–1.68 m under conditions of design wind speed 25 m·s−1. Results obtained by CEM, SPM models predict lower values than STN and ASABE models. Since the height difference between the dam crest and still water level in the reservoir is only 0.90 m, we can expect overtopping of the crest by waves after the critical wind speed is exceeded.

Forecasting Remote Atmospheric Responses to Decadal Kuroshio Stability Transitions

AbstractBased on observational estimates and global ocean eddy-resolving coupled retrospective initialized predictions, we show that Kuroshio Extension variability affects rainfall variability along the west coast of North America. We show that the teleconnection between the current undulations and downstream rainfall can lead to improved subseasonal to seasonal predictions of precipitation over California, and we demonstrate that capturing these teleconnections requires coupled systems with sufficient ocean resolution (i.e., eddy-resolving), especially over time scales longer than one season. The improved forecast skill is diagnosed in terms of 35 years of retrospective initialized ensemble forecasts with an ocean eddy-resolving and an ocean eddy-parameterized coupled model. Not only does the ocean eddy-resolving model show sensitivity to Kuroshio Extension variability in terms of western North America precipitation, but the ocean eddy-resolving forecasts also show improved forecast skill compared to the ocean eddy-parameterized model. The ocean eddy-parameterized coupled model shows no sensitivity to Kuroshio Extension variability. We also find near-decadal variability associated with a progression of a lower-tropospheric height dipole around the North Pacific and how these height anomalies lead to wind-driven Rossby waves that affect the eddy activity in the Kuroshio Extension with a time lag on the order of four years. This decadal-scale variability (~10 years) opens the possibility of multiyear predictability of western North American rainfall.

Rogue waves associated with resonant slow sloshing waves spontaneously excited in wind-driven water wave turbulence

Rogue wave events (RWEs), rare uncertainly emerging localized events with extreme amplitudes, widely exist in various nonlinear wave media. Past laboratory studies on RWEs of water surface waves have mainly focused on mechanically excited waves but to a lesser extent on waves solely excited by wind, which also have a large number of degrees of freedom. In this work, we experimentally demonstrate the laboratory observation of RWEs in a wind-driven water surface wave system after the transition to the steady wave turbulent state by increasing averaged wind speed. The spatiotemporal water surface height evolution is measured using diffusive light photography. It is found that RWEs uncertainly emerge in traveling bursts with high frequency large-amplitude fluctuations and irregular burst amplitude. The associated spontaneous slow periodic wave is identified as the resonant slow sloshing wave selected by the water tank with a finite length and spontaneously excited under turbulence. The surface wind speed modulation by the oscillating surface height of the sloshing wave in the small fetch region is proposed as the source for the excitations of sequential large amplitude bursts. The burst envelope shape deterioration through further turbulent wind and water wave interactions as bursts propagate downstream causes the non-Gaussian water surface height histogram with a highly stretched tail, contributed by the uncertain generation of RWEs in irregular bursts in the middle fetch region.

Surface viscous stress over wind-driven waves with intermittent airflow separation

Abstract

ЭВОЛЮЦИОННОЕ РАЗВИТИЕ И СОВРЕМЕННОЕ СОСТОЯНИЕ ОЗЕРА НЕРО ПО ДАННЫМ АНАЛИЗА САПРОПЕЛЯ

The paper presents the characteristics of sapropel based on the results of analysis of samples collected at 21 stations in Lake Nero. Its current state is assessed based on hydrophysical and hydrochemical parameters. A layer-by-layer (0–10, 30–40 and 60–70 cm) granulometric composition of stratigraphic cores made it possible to compare the evolutionary development of the lake corresponding to the periods 100, 300–400 and 600–800 years ago. It is found that natural hydrodynamic processes (wind-driven waves and wind-driven currents) cause erosion and mixing of the surface (0–10 cm) polluted sapropel layer with clean underlying horizons and carry pollutants absorbed on suspended particles outside the lake. The approach used made it possible to identify the ways of a shallow lake ecosystem formation and outline promising directions

Intermittent disturbance benefits colony size, biomass and dominance of Microcystis in Lake Taihu under field simulation condition

Wind-driven wave disturbance is one of the environmental factors that shapes the formation of Microcystis blooms. Here we present data on the effect of different disturbance modes (continuous vs intermittent disturbances) on colony size, biomass and dominance of Microcystis in Lake Taihu under field conditions. Small submersible pumps were used to simulate different disturbance modes at turbulent dissipation rate (ε) of 2.98 × 10−6 m2 s–3. Our results show that the mean colony sizes of Microcystis in intermittent and continuous disturbance group were 1.94 and 1.23 times that of the control group, respectively. The mean densities of Microcystis in intermittent and continuous disturbance group were 4.23 and 2.91 times that of the control group, respectively. The mean proportion of Microcystis to total algae abundance in control group and continuous disturbance group changed from 78.3% at beginning of the experiment to 4.5% and 9.1% at the end of the experiment. However, the proportion of Microcystis to total algae cells in intermittent disturbance group was 65.7–94.3% during the whole experiment. The results demonstrated intermittent disturbances favored colony morphology, biomass and dominance of Microcystis. Our results suggested that intermittent disturbance benefited the formation of Microcystis bloom and was important in the development of predictive models for toxic cyanobacterial blooms under changing climates in shallow lakes.

Sand transport in the northeastern Caribbean characterized by wind-wave-current data

Sand transport around the northeastern Caribbean Virgin Islands (VI) is studied using global data-assimilation products and satellite measurements; with a focus on seasonal and event characteristics in the period 2002–2019. A review of applied research and a local statistical analysis indicate that currents accompanied by waves and wind mixing are capable of scouring near-shore sand bars.VI area (18.4–18.6N, 65.5–64.5W) time series analysis offer insights on the processes underlying suspended sediment concentrations estimated by 5 km resolution MODIS and VIIRS satellite red-band radiance. The winter season peak in turbidity derives from trade wind-driven waves and currents that reach critical thresholds to mobilize and transport the coarse sands. Instead of wave height, wave steepness and mixed layer depth are applied as coefficients to HYCOM3 near-surface currents, to create a multi-variate sand transport index. Statistical regression shows that a strengthened North Atlantic anticyclone and associated winter trade winds in the VI archipelago results in surface cooling and a deep mixed layer, making steep waves and westward currents more effective in sand transport.The leading case of satellite red-band radiance followed many months after the passage of tropical cyclones in September 2017. A sustained spell of intense trade winds in February 2018 induced 3 m waves of 3% steepness and near-surface currents up to 0.5 m/s. Rapid sea level oscillations >0.05 m suggest that long-period waves joined local wind-waves to mobilize coarse sands within a mixed layer >50 m deep. The plume of sand exhibited composite VIIRS red-band radiance of 0.1 W m−2 μm−1 sr −1; supplying coarse light-colored sands to downstream Caribbean islands.This study has universal application to near-shore sand transport by demonstrating the use of a high-resolution multi-variate index from freely available global data-assimilation products. Given rising sea levels, beach erosion and limited field data, such an index is an essential tool in coastal management.