Search

Offshore wind farms are becoming an increasingly common feature in the marine environment as a renewable energy source. There is a growing body of evidence on the effects of wind farms on the seabed and its organisms. However, an important and understudied aspect of site development is the interaction of turbine foundations on the surrounding marine environment. Structures exert significant disturbance on tides, waves and currents; these are visible as optically-distinct, elongate wakes at the sea surface with elevated suspended particulate matter. Despite this, there is uncertainty on the mechanisms that lead to the visible manifestation of wakes at turbine foundations, primarily due to a lack of direct measurements. Here, in situ measurements along with a 15- year time series of satellite images of the Thanet offshore wind farm, located within the Thames Estuary, were used to investigate the formation of visible monopile wakes, and the effects these have on the surrounding water column. We show the optically distinct wakes are near-constant at Thanet; visible in >90% of all satellite images, yet no regional change in sea surface turbidity could be attributed to wind farm construction or operation. Monopile wake in situ water samples and acoustic Doppler current profiler (ADCP) backscatter measurements demonstrated colour change related to elevated sea surface sediment concentration. However, averaged water column measurements of suspended sediment within wakes, and upstream of monopiles, remained consistent. These measurements demonstrate that sediment was redistributed towards surface waters, rather than additional sediment becoming suspended in the wake. ADCP velocity measurements supported a mechanism of sediment lofting towards the surface, with enhanced vertically upwards flow recorded in wakes. [ABSTRACT FROM AUTHOR]

This study reports a moored array dataset (MASCS 1.0) consisting of five buoys and four moorings in the northern South China Sea during 2014–2015. The dataset includes measurements of sea surface meteorological data using two sets of instruments: sea surface waves recorded using a wave recorder, temperature and salinity from the surface to a depth of 400 m, and at 10 m and 50 m above the ocean bottom using conductivity, temperature, and depth (CTD) recorders. It also includes currents from the surface to a depth of 850 m measured using acoustic Doppler current profilers (ADCPs) and at 10 m, 50 m, and 100 m above the surface measured using current meters. Additional measurements were taken for sea surface radiation, air visibility, chlorophyll, turbidity and chromophoric dissolved organic matter at Buoy 3, which was located at the center of the moored array. The dataset captures the effects of tropical cyclones Rammasun, Kalmaegi, Fung-wong, and Hagupit on the moored array, as well as the transition from summer to winter monsoon in the northern South China Sea. The data reveal oceanic processes in the upper and bottom ocean and are valuable for further studies on air-sea interactions and ocean dynamics. All the data described here are made publicly available from https://zenodo.org/records/12635331 (Zhang et al. 2024). [ABSTRACT FROM AUTHOR]

Related literature has shown that internal waves (IWs) observed in the ocean are capable of producing secondary magnetic fields with a small signal-to-noise ratio due to the flow of dissolved salts. It can be difficult to characterize these signals since they are relatively weak, highly transient, and capable of being multi-modal. Using data collected by an array of magnetometers and acoustic Doppler current profilers, a technique called magnetic anomaly and particle velocity array correlator was developed for the detection of IWs. By using a combination of filtering techniques and a multi-variate correlation step, peak correlations above 90% were shown between the magnetic and water particle velocity records of potential IWs. [ABSTRACT FROM AUTHOR]

Bubble plumes play a significant role in the air–sea interface by influencing processes such as air–sea gas exchange, aerosol production, modulation of oceanic carbon and nutrient cycles, and the vertical structure of the upper ocean. Using acoustic Doppler current profiler (ADCP) data collected off the west coast of Ireland, we investigate the dynamics of bubble plumes and their relationship with sea state variables. In particular, we describe the patterns of bubble plume vertical extension, duration, and periodicity. We establish a power-law relationship between the average bubble penetration depth and wind speed, consistent with previous findings. Additionally, the study reveals a significant association between whitecapping coverage and observed acoustic volume backscatter intensity, underscoring the role of wave breaking in bubble plume generation. The shape of the probability distribution of bubble plume depths reveals a transition toward stronger and more organized bubble entrainment events during higher wind speeds. Furthermore, we show that deeper bubble plumes are associated with turbulent Langmuir number Lat ∼ 0.3, highlighting the potential role of Langmuir circulation on the transport and deepening of bubble plumes. These results contribute to a better understanding of the complex interactions between ocean waves, wind, and bubble plumes, providing valuable insights for improving predictive models and enhancing our understanding of air–sea interactions. Significance Statement: This research contributes to understanding bubble plume dynamics in the upper ocean and their relationship with sea state variables. The establishment of a power-law relationship between the bubble penetration depth and wind speed, along with the association between whitecapping coverage and acoustic backscatter intensity, contributes to improved predictive capabilities for air–sea interactions and carbon dioxide exchange. The identification of the potential influence of Langmuir circulation on bubble plume dynamics expands our understanding of the role of coherent circulations in transporting bubble plumes. Additionally, this study presents a clear methodology using commercial sensors such as an ADCP, which can be easily replicated by researchers worldwide, leading to potential advancements in our comprehension of bubble plume dynamics. [ABSTRACT FROM AUTHOR]

Processed and analyzed sea surface wave characteristics derived from an up-looking acoustic Doppler current profiler (ADCP) for the period 2016–2022 are presented as a dataset available from the public open-access repository of SEA scieNtific Open data Edition (SEANOE) at 10.17882/96904. The collected data include full two-dimensional wave fields, along with computed bulk parameters, such as wave heights, periods, and directions of propagation. The ADCP was mounted on the submerged Deep Levantine (DeepLev) mooring station located 50 km off the Israeli coast to the west of Haifa (bottom depth ∼1470 m). It meets the need for accurate and reliable in situ measurements in the eastern Mediterranean Sea as the area significantly lacks wave data compared to other Mediterranean sub-basins. The developed long-term time series of wave parameters contribute to the monitoring and analysis of the region's wave climate and the quality of wind–wave forecasting models. [ABSTRACT FROM AUTHOR]

Small, lightweight, and easy-to-deploy Global Positioning Satellite (GPS)-based miniature wave buoys (mini-buoys) are increasing in popularity. Most are deployed as Lagrangian drifters, so their utility for engineering applications, requiring a nearshore mooring, has remained in question. We evaluated the performance of five moored mini-buoys off the coast of Duck, North Carolina at Field Research Facility (FRF). We collected 8 months of data over two deployments; first near the FRF's 8-m array and then near a Datawell Waverider in 17-m depth. We deployed an Acoustic Doppler Current Profiler (ADCP) that measured waves and currents, and compared it to the nearby operational system as a performance benchmark for the mini-buoys. The mini-buoys performed well, with statistics similar to the benchmark for wave frequency spectra and spectral parameters, and they outperformed the benchmark on directional parameters. However, mini-buoy communication was sometimes interrupted by tilting or submersion, which manifested as low-frequency noise or drop-outs. If a mooring was taut, forced by winds or currents and exacerbated by tangled lines or shallower depths, then mini-buoys were more susceptible to communication issues. Overall, these issues were rare; thus, mini-buoys were found to be appropriate for many applications. [ABSTRACT FROM AUTHOR]

Processed and analyzed sea surface wave characteristics derived from an up-looking Acoustic Doppler Current Profiler (ADCP) for the period 2016-2022 are presented as a dataset. The collected data include full two-dimensional wave fields along with computed bulk parameters, such as wave heights, periods, and directions of propagation. The ADCP was mounted on the submerged Deep Levantine mooring station located 50 km off the Israeli coast to the west of Haifa (bottom depth ~1470m). It meets the need for accurate and reliable in situ measurements in the Eastern Mediterranean Sea, as the area significantly lacks wave data compare to other Mediterranean sub-basins. The developed long term timeseries of wave parameters allow for monitoring and analysis of the region's wave climate, as well as a deeper understanding of wind-wave generation mechanisms. [ABSTRACT FROM AUTHOR]

Turbulence in the ocean surface layer is forced by a mixture of buoyancy, wind, and wave processes that evolves over time scales from the diurnal scale of buoyancy forcing, through storm time scales, to the annual cycle. This study seeks a predictor for root-mean-square w (rmsw), a time and surface layer average of turbulent vertical velocity w measured by bottom-mounted vertical-beam acoustic Doppler current profilers, in terms of concurrently measured surface forcing fields. Data used are from two coastal sites, one shallow (LEO, 15-m depth) and one deeper (R2, 26-m depth). The analysis demonstrates that it is possible to predict observed rmsw with a simple linear combination of two scale velocities, one the convective scale velocity w * familiar from the atmospheric literature, the other a scale velocity wS representing combined wind and wave effects. Three variants are considered for this latter scale velocity, the wind stress velocity u * alone and two forms using both u * and US, a Stokes velocity characteristic of the surface wave field. At both sites, the two-parameter fit using u * alone is least accurate, while fits using the other two variants are essentially indistinguishable. At both sites, the coefficient multiplying w * is the same, within error bounds, and within the range of previous observations. At the deeper site, the coefficient multiplying the wind/wave scale velocity wS is approximately half that at the shallow site, a difference here attributed to difference in wave character. [ABSTRACT FROM AUTHOR]

Bubble plume penetration depths have been identified as a key parameter linking subsurface turbulent kinetic energy (TKE) dissipation rates and whitecaps. From data collected in the Atlantic sector of the Southern Ocean, nominally 50°S 40°W, bubble plume penetration depths were estimated from Acoustic Doppler Current Profiler measurements of the acoustic backscatter anomaly. Bubble presence at depth was corroborated using independent measurements of optical scattering. Here, an effective wavelength, observations of significant wave height and atmospheric forcing were used to scale penetration depths of breaking waves under open ocean conditions. The parameterization was developed assuming a correlation between the observed penetration depth and an estimate of the TKE dissipation rate enhancement under breaking waves. The effective wavelength was defined from the effective phase speed based on a momentum and energy balance across the atmospheric wave boundary layer and was considered to be the largest actively wind‐coupled wave and representative of large‐scale breaking for wave ages ranging from 15 to 35 (i.e., 15 ≤ 〈cp/u*〉 ≤ 35). This yields a dimensional penetration depth parameterization in terms of inverse wave age and the length scales under consideration. The parameterization captures the bubble plume penetration depth with stronger forcing leading to deeper injections, reaching up to 9 m. Both length scales are effective at defining the depth of a wave‐affected layer in terms of bubble presence with the effective wavelength better collapsing the data under mixed conditions with deeper plumes associated to larger fractional whitecap coverage. Plain Language Summary: The depth to which waves breaking at the ocean surface influence oceanic processes in the mixed layer, including the transfer of momentum, heat and gases between the atmosphere and ocean, is an ongoing and active area of research. Parameterizations and observations describing the vertical extent of wave‐driven effects, including whitecaps and vertical jets associated with Langmuir circulation, are relevant for numerical circulation models and our understanding of wave breaking and dissipation dynamics. Here, observations of atmospheric and oceanic conditions, principally wind, wave, and inferred bubble plume penetration depths collected in the Atlantic sector of the Southern Ocean were used to build a parameterization for estimating the vertical extent of bubble injections and for inferring the depth of the wave‐affected layer. These results suggest that wavelengths shorter than the dominant peak and significant wave heights properly weighted by atmospheric parameters are a good proxy for defining the extent of wave‐driven bubble transport. Key Points: The significant wave height and the effective wavelength were used to scale bubble penetration depths under open ocean conditionsBoth length scales successfully provide a penetration depth parameterization with the effective wavelength better collapsing the data [ABSTRACT FROM AUTHOR]

Internal waves are responsible for many important processes in the ocean environment (ocean ventilation, energy transfer from large-scale processes to turbulence, etc.). Our goal is to draw attention to the relatively little studied effect of internal waves on ships at sea. We encountered this effect many times while working on the study of internal waves in the shelf zone. The work was carried out from a yacht equipped with the "Rio Grande 600 kHz" ADCP, which makes it possible to measure both the parameters of internal waves and other important parameters of the medium. Two typical examples of the impact of internal waves on a yacht are given. One, when the yacht was at anchor and a train of soliton-like internal waves passed under it. The second, when the yacht was moving and passing over a train of internal waves. Internal waves passing under the moored yacht shifted its position synchronously with the periods of passing waves. A uniformly moving yacht, passing over a package of internal waves synchronously with the period of waves, alternately increased and decreased the speed of its movement. The described effect is explained by the impact on the vessel of the orbital currents of internal waves. Under our conditions, at heights of internal waves reaching 10–15 m, the ship's speed fluctuations reached 0.30 m/s, which was more than 10% of the ship's speed. [ABSTRACT FROM AUTHOR]

The structure and variability of the currents in the Timor Passage are studied based on the measurements from a subsurface mooring deployed in the center of the passage from September 2017 to December 2019. The annual mean currents are found to flow westward into the Indian Ocean in the upper 1,400 m, with a maximum velocity core at ∼50 m. The mean volume transport through the Timor Passage into the Indian Ocean is estimated to be −9.9 ± 1.0 Sv (1 Sv = 106 m3 s−1) in the upper 1,400 m with much of this transport concentrated in the upper 480 m (−8.9 Sv). This value contrasts with the estimate of −7.5 Sv above 1,890 m based on INSTANT measurements. The transport during the 2019 positive Indian Ocean Dipole event was only slightly larger than that during the 2018 normal year in the upper 480 m. The variability in the along‐strait velocity in the Timor Passage is dominated by an annual cycle in the upper 150 m and a semiannual cycle in the lower layer. The annual cycle in the upper layer is mainly driven by local monsoonal forcing. Downward energy propagation is observed below 200 m, which is shown to be mainly driven by remote Kelvin waves from the Indian Ocean. The transport variability through the Timor Passage is dominated by a semiannual cycle, associated with the semiannual circulation over the equatorial Indian Ocean, with the transport in the upper and lower layers largely canceling each other in the annual cycle. Plain Language Summary: Based on the INSTANT mooring measurements, the transport through the Timor Passage contributes a large portion of the transport of the Indonesian Throughflow (ITF). However, due to the scarcity of the observations, the transport and variability of the Timor currents have not been adequately studied. In this study, we show that the currents in the upper 150 m, measured by an acoustic Doppler current profiler moored at the valley center of the Timor Passage, feature strong annual harmonics associated with local monsoonal forcing. Semiannual harmonics below 200 m reveal upward phase propagation associated with remote forcing from the Indian Ocean. The transport variability through the Timor Passage features a stronger semiannual cycle in the upper 480 m instead of an annual cycle, as observed in the local annual winds, due to the mutual cancelation of the annual transports in the upper and lower layers. Thus, the baroclinic processes play an important role in producing the semiannual‐dominant variability of the ITF through the Timor Passage. The disclosed results are important for understanding the dynamics of the ITF connection between the Indian Ocean and the Indonesian seas. Key Points: Timor Passage currents, measured by a subsurface mooring, show strong annual and semiannual harmonics in the upper and lower layers, respectivelyUpward phase propagation of the currents below 200 m is observed, suggesting downward energy propagationThe total transport through the Timor Passage features a stronger semiannual cycle and a weak annual cycle [ABSTRACT FROM AUTHOR]

Application of Acoustic Doppler Current Profilers (ADCPs) in natural marine experiments makes it possible simultaneously to record currents and to observe internal waves, which allows one to make significant progress in the study of water dynamics on the sea shelf. During the studies carried out in the Sea of Japan, a new mechanism for the generation of internal waves on the shelf was found, which is associated with the collision of tidal currents approaching the coastal zone with alongshore coastal currents. Description of the main features of the process is given on the basis of measurements made with the Rio Grande 600 kHz current profiler. [ABSTRACT FROM AUTHOR]

Significant wave height (SWH) in shallow waters is assessed by generating two wave hindcasts; the first uses ERA-Interim wind fields and the second one from ERA5 to quantify the improvement of the ERA5 surface winds on the SWH representativeness, both in deep and shallow waters along the Chilean coastline. Additionally, wind field predictions from the Global Forecast System (GFS) were used to assess the representativeness of shallow waters. Oceanographic buoys were used to validate SWH in deep waters, while Acoustic Doppler Current Profiler (ADCPs) was equipped to measure waves in shallow waters. Energy spectrums coupling Wavewatch III and Simulating Waves Nearshore (SWAN) models were transferred to evaluate the performance of shallow water simulations. In general, the SWH from both wave hindcasts showed good performance. Nonetheless, those forced by ERA5 presented a better qualitative comparison of sea state temporal variability, which increased the correlation coefficients (>0.9), coefficients of determination (>0.8), and minor errors (RMSE, MAE, and BIAS) compared to oceanographic buoys and ADCPs. Additionally, in simulations forced by GFS, the temporal variability of the waves in shallow waters was successfully reproduced. Nevertheless, an increase in the RMSE, MAE, and BIAS error was statistically verified compared to ERAInterim and ERA 5. [ABSTRACT FROM AUTHOR]

Wave measurements from a new, low-cost, real-time wave buoy (Spotter) are investigated in a comparative study as part of a site characterization study at a wave energy candidate site at King Island, Tasmania, Australia. Measurements from the Sofar Ocean Spotter buoy are compared with concurrent measurements from a Teledyne RD Instrument (RDI) 1200 kHz Work Horse ADCP and two RBRsolo3 D wave16 pressure loggers. The comparison period between 8 August and 12 October 2019 provides both the shallowest and longest continuous published comparison undertaken with the Spotter buoy. Strong agreement was evident between the Spotter buoy and RDI ADCP of key wave parameters including the significant wave height, peak wave period, and mean wave direction, with the mean values of those parameters across the full deployment period agreeing within 3%. Surface wave spectra and directional spectra are also analyzed with good agreement observed over the majority of the frequency domain, although the Spotter buoy records approximately 17% less energy within a narrow frequency band near the peak frequency when compared to the RDI ADCP. Measurements derived from the pressure loggers routinely underestimated the significant wave height and overestimated the mean wave period over the deployment period. The comparison highlights the suitability of the Spotter buoy for low-cost wave resource studies, with accurate measurements of key parameters and spectra observed. [ABSTRACT FROM AUTHOR]

BRY SON ROBERTSON Director P ACIFIC MARINE ENERGY CENTER OREGON STA TE UNIVERSITY OREGON, U.S. Dr. Bryson Robertson first became involved in wave energy research by working on the deck of boats and throwing wave measurement buoys into the ocean. From there, he launched into a series of wave energy projects that focus on the responsible development and accelerated design processes for marine energy technologies, which will ultimately benefit coastal communities and mitigate climate changes. Today, she manages the marine renewable energy field work program of the Pacific Regional Institute for Marine Energy Discovery (PRIMED) where she spends most of her time planning, preparing, and executing deployments and recoveries of a fleet of wave-measurement buoys and waveand-tidal-measurement acoustic Doppler current profilers in the waters surrounding Vancouver Island. [Extracted from the article]

This study presents an overview of the main hydrodynamic features of the Alderney Race strait based on in situ measurements and twodimensional hydrodynamic model simulations. The strait encompasses a large amplitude of tidal properties (tidal range and tidal wave propagation) and particularly strong currents exceeding 5ms-1 with associated counter currents and gyres. Variations in depth, sea bottom roughness, coastal topography and current orientation around the La Hague Cape provide access to a large variety of original hydrodynamic regimes. Some are revealed as locations with a 0.4m drop in the mean sea level associated with strong average currents. A resonance effect associated with the offshore currents can also be observed close to the coasts. The 'St Martin whistle' occurs in a bay whose gyre centre oscillates with a reversal of the measured current every 5-7 min. The Alderney Race represents a particular area of interest for coastal hydrodynamic studies. The available in situ measurement datasets are rich with recordings of: sea levels; acoustic Doppler current profiler current profiles; surface radar currents; waves; dye experiments; surface and in-depth dissolved tracer surveys. Combined with hydrodynamic models, the complexity of this area can be further understood and knowledge of the hydrodynamic process and forcing parameters can be refined, which can be applied to other coastal areas. This article is part of the theme issue 'New insights on tidal dynamics and tidal energy harvesting in the Alderney Race'. [ABSTRACT FROM AUTHOR]

Near-inertial oscillation is an important physical process transferring surface wind energy into deep ocean. We investigated the near-inertial kinetic energy (NIKE) variability using acoustic Doppler current profiler measurements from a mooring array deployed in the tropical western Pacific Ocean along 130°E at 8.5°N, 11°N, 12.6°N, 15°N, and 17.5°N from September 2015 to January 2018. Spatial features, decay timescales, and significant seasonal variability of the observed NIKE were described. At the mooring sites of 17.5°N, 15°N, and 12.6°N, the NIKE peaks occurred in boreal autumn and the NIKE troughs were observed in boreal spring. By contrast, the NIKE at 11°N and 8.5°N showed peaks in winter and troughs in summer. Tropical cyclones and strong wind events played an important role in the emergence of high-NIKE events and explained the seasonality and latitudinal characteristics of the observed NIKE. [ABSTRACT FROM AUTHOR]

La Réunion Island in the southwest Indian Ocean is seasonally affected by austral swells among which some extreme events may have strong impacts on coastal infrastructures. The very limited number of sensors available on and around the island and in the whole SW Indian Ocean impedes any direct monitoring of the swell activity. In this study, we analyse direct observations of the ocean swell by combining terrestrial measurements of the microseismic noise with in situ oceanographic observations issued from two pressure gauges and an Acoustic Doppler Current Profiler (ADCP), together with swell numerical modelling. The reliability of the terrestrial seismic station to characterize the ocean activity in both the primary and secondary microseisms peaks (PM and SM, respectively), and also in the long period secondary microseismic peak (LPSM) for the case of La Réunion Island is presented and discussed here. By computing the hourly RMS of the PM and LP(SM) amplitudes, we establish a transfer function between the PM and (LP)SM amplitude and the maximum wave height, which appears to be valid for any PM and LPSM amplitudes >0.15 μm and >1.0 μm, respectively. The correlation coefficient between the PM amplitude and the wave height is >0.92. It suggests that the PM amplitude can be used as a robust proxy for the swell height and may help calibrating the wave heights from other independent observable. For some swell events, we observe LPSM that correlate well (>0.91) with the local wave height suggesting a generation by coastal swell reflection. From polarization and spectral analyses, directions and periods of swells are also well retrieved from seismic data. Finally, continuous measure of the SM amplitude shows that it can be used as precursor information for distant swells that may hit La Réunion Island a few days after their generation in the southern Indian Ocean. [ABSTRACT FROM AUTHOR]

The genetic algorithm (GA) model presented here provides specific JONSWAP parameters that can be used for wave modelling. This work describes a validated heuristic model based on GA, to select JONSWAP spectra parameters, regardless of water depth restrictions and sea state conditions. The identification of the JONSWAP spectra parameters is difficult, as the alpha and gamma coefficients have scattered distributions that modulate the spectral peak energy. In addition, the selection of alpha and gamma coefficients from in situ free surface records may be difficult and time-consuming, because of the amount of data and nonlinearities involved. The proposed model uses either in situ or numerically modelled wave data and has three main steps: (1) generation and crossover, (2) minimisation of the cost function ΔHs, defined as the minimum difference between the calculated artificial significant wave height and the in situ wave height (instrumented or modelled), and (3) mutation and natural selection. To apply the model, in situ wave data measured by an acoustic Doppler current profiler over 5.5 months was used in this research. The results show a high correlation (r2), of 0.95, between the best fitted curves of modelled spectra and measured data. [ABSTRACT FROM AUTHOR]

High-frequency (HF) ocean radar has the potential to observe sea ice, but this application has not been thoroughly investigated. In this article, we explore sea ice observation with HF radar (HFR) and develop a corresponding signal processing procedure. We derived sea ice radial velocities from raw HFR data and determined angular positions using the MUltiple SIgnal Classification (MUSIC) algorithm. Sea ice velocities were evaluated by comparison with measurements from moored acoustic Doppler current profilers (ADCPs) and a drifting buoy. The root-mean-square (rms) differences between the sea ice velocities obtained by HFR and the ADCPs decreased with increasing radar signal-to-noise ratio (SNR), implying that a high SNR was associated with accurate measurement of sea ice velocity. These results agree with previous validations of HFR ocean current observations. The sea ice pattern mapped by HFR is consistent with the simultaneous C-band microwave radar observations. In particular, the HFR captured the approach of the sea ice edge toward the coast. Sharp attenuation of the HF signal over high concentration sea ice resulted in missing and/or low-SNR data at ranges beyond the front edge of pack ice, in qualitative agreement with model estimates of attenuation. [ABSTRACT FROM AUTHOR]

Observational evidence demonstrates the signature of near‐inertial wave (NIW) trapping by a long‐lived westward propagating mesoscale anticyclonic eddy under normal atmospheric conditions. Cross‐eddy sections of density and shipboard acoustic Doppler current profiler data show the downward (upward phase) propagation of NIW packets with vertical wavelengths of 200 m within the eddy, and wave energy amplification in a critical vertical layer located near the base of the anticyclone. Elevated strain variance, enhanced turbulent kinetic energy dissipation rates obtained from a fine‐scale parameterization, and the occurrence of low (≤1) gradient Richardson numbers are consistent with turbulence production and mixing from 400 m to at least the maximum sampling depth of 725 m associated with the trapped NIWs. The observation of NIW packets near the eddy base at two different stages of the survey separated by 10 days and the persistence of low to moderate winds before and during the eddy sampling strongly suggest that our findings may be common in similar open‐ocean anticyclonic eddies under normal wind conditions. Plain Language Summary: Near‐inertial waves—or internal gravity waves with a frequency near the inertial frequency—are typically excited at the sea surface by variable wind stress forcing. These waves can be trapped and amplified at the base of mesoscale (horizontal scales of about 10–100 km) anticyclonic eddies, especially after storms or strong wind events, situations in which high near‐inertial energy is generated. In this article we present observational evidence of near‐inertial wave trapping during low to moderate wind conditions. We also show that these trapped waves lead to deep mixing near the base of the eddy. The observation of near‐inertial wave packets on two different dates and the low to moderate winds persistent during the survey suggest that our findings may be common in other similar open‐ocean eddies. Mesoscale anticyclonic eddies of the World Ocean may therefore act as deep mixing structures as they propagate westward. Key Points: Observational evidence demonstrates the signature of near‐inertial wave trapping near the base of a mesoscale anticyclonic eddy during low to moderate wind conditionsThe trapped near‐inertial waves produce low fine‐scale Richardson numbers and enhanced strain variance, suggesting turbulence productionEnhanced vertical mixing may presumably be found inside similar open‐ocean eddies under normal atmospheric conditions [ABSTRACT FROM AUTHOR]

High‐frequency measurements of waves, currents, and turbulence were made using the bottom‐mounted tripod equipped with the Nortek 6‐MHz acoustic Doppler velocimetry at eight mooring stations in the East China Shelf Seas. The observational data are analyzed to estimate the bottom drag coefficient and also the contributions from currents and waves. Variations of bottom drag coefficient caused by currents show no obvious relationship with water depth. Generally, the current‐induced drag coefficient decreases with the strengthening currents, and the wave‐induced drag coefficient increases with the enhancing waves. Synthesis analyses of the observational data reveal a scale relationship between the current‐induced drag coefficient and the turbulent Reynolds number and that between the wave‐induced drag coefficient and the bottom wave orbital velocity. The analyses show no significant impacts of waves on turbulent Reynolds stress, and the total bottom drag coefficient is the sum of that due to currents and waves. The empirical formula for bottom drag coefficient derived from this study may help to improve the simulation of tides, storm surges, and sediment transport in coastal seas. Plain Language Summary: Ocean floor exerts a frictional force on ocean currents, and this force is particularly important in coastal oceans. This force is difficult to measure directly and is usually parameterized using the near‐bottom currents and a bottom drag coefficient. In this study, we derive estimates of bottom drag coefficient from observed currents and turbulence at eight mooring stations in the East China Shelf Seas. The estimated bottom drag coefficient is not a constant. Empirical relationships are established to link the impacts of currents and waves on bottom drag coefficient to separate dynamic parameters, that is, the turbulent Reynolds number and the bottom wave orbital velocity. The total bottom drag coefficient can be taken as the sum of the two components. The empirical formula for bottom drag coefficient derived from this study may help to improve the simulation of tides, storm surges, and sediment transport in coastal seas. Key Points: Near‐bottom currents, waves, and turbulence were measured at eight mooring stations in the East China Shelf SeasThe estimated bottom drag coefficient shows significant variationsScale relationships are established to represent the impacts of currents and waves on bottom drag [ABSTRACT FROM AUTHOR]

A novel procedure based on filtering and interpolation approaches is proposed to estimate the sea state parameters, including significant wave height, peak wave direction, peak period, peak wavenumber, and peak wavelength in shallow waters using the X-band marine radars. The method compensates the distortions introduced by the radar acquisition process and the power decay of the radar signal along the distance applying image-enhancement techniques instead of empirical and semiempirical calibration methods that use signal-to-noise ratio and in situ measurements as external references. To determine the threshold value for the interpolation approach, the influence of the antenna height on shadowing modulation effects is examined through performing an analysis of variance (ANOVA) that uses data from two X-band radars deployed at 10 and 20 m above MSL. ANOVA results reveal that it is possible to explain the increment of intensities affected by shadowing throughout the distance using an adaptive threshold retrieved from a third-order polynomial function of the mean radar cross section (RCS). Finally, an X-band radar is installed at 13 m above MSL to test the proposed technique. During measurements, the wind and wave conditions varied, and the antenna-look direction remained constant. Errors for $H_{s}$ , $\theta _{p}$ , and $T_{p}$ calculated as the difference between estimated and true data show a mean bias and a relative value of 0.05 m (2.72%), 1.52° (5.94%), and 0.15 s (1.67%), respectively. The directional and wave energy spectra derived from radar estimates, acoustic wave and current, ADVs record, as well as JONSWAP formulation are presented to illustrate the improvement resulting from the proposed method over the frequency domain. [ABSTRACT FROM AUTHOR]

A series of Acoustic Doppler Current Profiler (ADCP) measurements moored along the equatorial and coastal wave-guide were used to evaluate the dynamics of the South Java Coastal Current (SJCC). 17-month (December 2008 to May 2010) data from the ADCP off South Java give some insights into the dynamics of the SJCC. The data reveal high variability in the upper 100 m depth, where the core of the SJCC is located. In addition, robust intraseasonal variations at period of 70 - 100 days dominate the SJCC variation. Consistent with previous studies, dynamics of the SJCC is strongly driven by the equatorial waves from the Indian Ocean. Due to a failure in ADCP measurement, the equatorial moorings only have a short overlapping period with the South Java mooring, from the boreal fall 2009 until spring 2010. Nevertheless, the data still exhibit coherence variations in which the strong eastward flow during the boreal fall 2009 and the spring 2010 that observed off South Java can be traced back to the equatorial region. Further analysis confirmed the important role of the remote winds from the equatorial Indian Ocean in affecting the SJCC variations through a generation of eastward propagating wind-forced equatorial Kelvin waves. Nevertheless, the contribution of the local wind forcing is not negligible in generating the SJCC variations. [ABSTRACT FROM AUTHOR]

Marine hydrokinetic energy technologies are approaching commercialization. However, one barrier to development is finding cost effective methods of conducting resource assessments, or easily measuring current speed and direction in high velocity tidal and river environments. Incumbent technologies for tidal energy resource assessment are typically variants of acoustic Doppler current profilers (ADCPs), but they are expensive to operate and there is risk to the equipment in high current locations. Research and development was therefore undertaken to design, build, and test a variable depth, long endurance, and cost-effective means of measuring tidal and river water current velocities. In conjunction with Mavi Innovations, the University of British Columbia developed a prototype two-point mooring sensor, which can be deployed in river or tidal environments over sustained periods in order to gather both water velocity and current direction data. The sensor was successfully deployed over two periods of approximately 24 hours during both a spring and neap tide at Mavi's tidal energy demonstration site at Blind Channel, British Columbia. Results of the deployments provided ample current speed and direction data to inform turbine developers of the tidal current regime at the site, and also offered some agreement with ADCP measurements done simultaneously. Test results broadly demonstrated good potential for the technology, particularly for smaller or remote projects where the cost or logistics of ADCP deployments are less feasible and where quickly accessible data are needed, without too much pre-deployment calibration or post-deployment formatting time. Operational challenges still remain for the buoy sensor, and various options for further development and testing are suggested in this paper, along with detailed discussion of the trial deployments, sensor design, construction, and calibration methods. [ABSTRACT FROM AUTHOR]

Distant swells generated by storms in the high latitudes (>40°) can impact islands and atolls of the Pacific Ocean far from their genesis locations. While common, they can also occasionally generate very high wave height (>5 m) at high period (>16 s) during several days. These rare mega-swells can damage distant human infrastructures in tropical islands by direct wave impacts, but also by the extreme elevation of the sea level in lagoons exposed to the incoming swell. The lagoon surge, and land flooding, resulting from these events can be catastrophic, especially for low-lying atolls. In July 2022, the hydrodynamic conditions during the third highest energy southern mega-swell of distant origin (55°S-150°W) impacting French Polynesia since 1996 could be monitored real time with an array of sensors (pressure, acoustic Doppler current profilers, temperature) previously deployed to study the physical environment of black pearl farms in Apataki Atoll (15.45°S, 146.35°W), a semi-open atoll of the Tuamotu Archipelago. This was a unique opportunity to characterize for the first time the hydrodynamics conditions before, during and after a mega-swell with measurements of lagoon and ocean water levels, incoming wave heights and periods on the oceanic forereef, current speeds and directions along the atoll rims and in the deep passes. The array of available sensors provided a real time spatial view of the transient conditions that the atoll experimented during the mega-swell event, that can complement the more traditional assessment carried out after similar events using sedimentologic and geomorphologic evidences. While the degree of protection offered by atolls in the south of Apataki have limited the impact, the significant wave height (up to 4.2 m), flows in the passes (with up to 6.4 knots outgoing currents) and a 0.5 m surge above the average lagoon level characterize a major event. Other atolls (e.g., Makemo) have experienced higher surges in similar events in 1996 and 2011, which confirms that assessment of risks induced by mega-swells should be specific to each atoll according to its position, exposure, geomorphology and the settlement of human infrastructures. • Pacific Ocean atolls are exposed and vulnerable to distant mega-swells. • Hydrodynamic conditions in atolls during mega-swells are poorly known. • In July 2022, an array of sensors in Apataki atoll captured these conditions. • Wave, surge & currents are described before, during & after the event. • Surge and damages were limited for Apataki, but remain highly atoll-dependent. [ABSTRACT FROM AUTHOR]

The shift towards salmon farming in more exposed locations has been an industry-wide trend for the last decade. Moving fish farms to locations with high water currents and waves can improve production by providing more stable temperatures and water quality, as well as reducing the negative environmental impacts of fish farming. This study investigates how waves affect the behavior of salmon from the same group, reared at different locations within a fish farm in standard circular sea cages. Using echosounders, DO (dissolved oxygen), temperature sensors and ADCP (Acoustic Doppler Current Profiler), we show that salmon avoid waves, swim below them and maintain their normal behavior. We also show that salmon behavior is related to the exposure of the cage, in the farm layout, to waves and currents. An integrated numerical model of fish and flexible sea cages is used to simulate the fish behavior under waves and currents and it able to reproduce the observed fish distributions in general. [ABSTRACT FROM AUTHOR]

Moh, T.; Cho, J.H.; Jung, S.-K.; Kim, S.-H., and Son, Y.B., 2018. Monitoring of the Changjiang River plume in the East China Sea using a wave glider. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 26–30. Coconut Creek (Florida), ISSN 0749-0208. Most water from the Changjiang River discharges into the East China Sea (ECS), and affects the sea's oceanographic environment, even near Jeju Island, Korea. However, most research conducted using vessels, buoys, and satellite systems has a limited capacity for continuous direct measurement over a wide area. To overcome these spatial and temporal limitations, an autonomous wave-powered glider equipped with a fluorometer, a conductivity-temperature-depth, and an acoustic Doppler current profiler was deployed. Over 34 days from August 19 to September 22 in 2016, the wave glider navigated 985 km in the ECS near Jeju Island, and sensed 34,500 continuous water columns every minute. The glider transmitted the data via the Iridium satellite communication system, even under severe weather conditions. The wave glider detected low salinity and high turbidity of the surface water southwest of Jeju Island. Comparison of the surface turbidity and back-scattered echo intensity revealed that the surface turbid water migrated from west to south of Jeju Island. It descended slightly through chaning of the mixed layer depth. The observations from this study suggest that wave gliders can provide reliable sensing and maneuvering capabilities for monitoring of the Changjiang River plume in the ECS. [ABSTRACT FROM AUTHOR]

In conducting a cross-shelf wave transformation experiment off the Atlantic coast of north Florida, a unique opportunity was exploited in which an Acoustic Doppler Current Profiler (ADCP) instrument was installed 30 km offshore at the exact location of one of the archive-nodes of a WAM-like wave hindcast model (OWI3G). A second ADCP was installed 550 m from shore. Approximately 53 days of directional wave spectra collected with the two ADCPs are used to (a) locally test the reliability of a subsequent update of the hindcast, (b) document the loss in energy as the waves crossed the broad, relatively shallow continental shelf between the two instruments, (c) test the ability of the SWAN (Gen2) nearshore wave transformation model to replicate the measurements taken in shallow water when driven by the offshore ADCP spectra, and (d) reassess the spectral transformation results when the offshore hindcast is used as input. In addition to direct comparison of the time series of frequency spectra and the directional distribution of energy, typical spectral parameters are each subjected to standard error tests. Results indicate that the offshore hindcast performs well in replicating significant wave height, fairly well for mean period, but not as reliably for peak period. Directional spreading in deeper water is generally well-represented, although vector mean direction is not, and is believed due to the proximity of the coast to the hindcast node. The nearshore model requires an order-of-magnitude reduction in bed roughness from its default value before agreement in wave energy at the nearshore ADCP can be achieved. Outcomes of the error tests for the hindcast-driven versus the ADCP-driven nearshore results (after roughness calibration) are quite similar, but nevertheless indicate that transformed wave period, wave direction, and directional spreading require improvement. [ABSTRACT FROM AUTHOR]

Internal solitary waves (ISWs) are ubiquitous phenomena in many coastal oceans, especially the northern South China Sea (SCS). They can pose a serious threat to the deep-water drilling platforms and other ocean engineering structures. In this paper, we describe a simple and economical early warning method by estimating ISW propagation speeds using the measurements by a single acoustic Doppler current profiler (ADCP). This method is based on the Korteweg-de Vries (KdV) equation. As an example, a set of observational data collected by mooring buoys at the Liwan block (19–20°N, 115–116°E) of the northern SCS are used to calculate the propagation speeds and directions of measured ISWs. The accuracy of estimated ISW propagation speeds is also tested by tracking the signals of ISWs using two ADCP moorings and it is found that the prediction deviation is less than 10%. The force and torque exerted by an ISW on a semisubmersible drilling platform are also estimated according to Morison’s equation and other empirical formulas, which can provide a reference for safety controls on offshore platforms. [ABSTRACT FROM AUTHOR]

Energetic near-inertial internal waves (NIWs) were observed on the continental slope of the northern South China Sea in September 2008. Characteristics of the observed near-inertial waves were examined based on current data recorded by a moored acoustic Doppler current profiler. Results of a simple slab model indicated that the NIWs were generated by the surface winds of Typhoon Hagupit. Following Hagupit's passage, the wave field was dominated by baroclinic NIWs. The near-inertial currents were surface-intensified with a maximum of 0.52 m/s but still reached 0.1 m/s at the depth of 210 m. Moreover, the near-inertial currents were clockwise-polarized and slightly elliptical. A depth-leading phase of the near-inertial currents was evident, which indicated downward energy propagation. However, the rotary vertical wavenumber spectra suggested that upward energy propagation also existed, which was consistent previous theoretical study. The frequency of the NIWs, modified by the positive background vorticity, was 0.714 2 cycles per day, which was 0.02 f higher than the local inertial frequency ( f). The near-inertial kinetic energy evolved exponentially and had an e-folding timescale of about 3 days. The vertical phase and group velocity were estimated to be 10 and 2.1 m/h, respectively, corresponding to a vertical wavelength of 340 m. The NIWs were dominated by the second mode with a variance contribution of >50%, followed by the third mode, while the first mode was insignificant. [ABSTRACT FROM AUTHOR]

During the observational period of our study, Typhoon Hagupit passed over the mooring site and induced strong near-inertial waves (NIWs), which provided an opportunity to investigate the interactions between internal tides (ITs) and NIWs. Based on the mooring data, we compared the current spectra during the typhoon period and non-typhoon period in the northern South China Sea, and found that the high-frequency waves (fD and fD) were evident during the former. Moreover, the observations of the current revealed that fD and fD occurred near the depth of strong vertical shear in the NIWs. In order to confirm the generation mechanism of fD and fD, we compared the positions of strong vertical shear in the NIWs and strong vertical velocity in the ITs. It was established that the vertical shear of the horizontal current of the NIWs and the vertical current of the ITs contributed to the generation of fD and fD. [ABSTRACT FROM AUTHOR]

The observational data of acoustic Doppler current profiler (ADCP) indicates that a suspected internal solitary wave packet (ISWP) consists of two depression waves in the northern South China Sea (SCS). This paper analyzes the current field features and propagation characteristics of the front and rear waves, calculates their propagation phase speeds and direction angels respectively, and demonstrates that the generation site of the suspected ISWP is Luzon Strait (LS).The our result shows that for the front wave, the height is 96m, the time period is 16min, the propagation phase speed is 1.04ms−1, the direction angel is 283.4°, and the wavelength is 1.0km; for the rear wave, the height is 80m, the time period is 14min, the propagation phase speed is 0.89ms−1, the direction angel is 299°, and the wavelength is 0.74km. The maximum horizontal velocity of the front wave is 1.1ms−1 in depth 106m below the sea surface, and the maximum shear is 0.030s−1 in the wave trough; the maximum horizontal velocity of the rear wave is 0.84ms−1 at the same depth and the maximum shear is 0.020s−1 in the wave trough as well. According to the data and theoretical analysis there is an interaction between the front and rear waves 17km to the direction of LS, showing that they were not generated during the same time interval. In this paper, our results may provide understanding the physical features and propagation characteristics of sequential internal solitary waves and their relationships. [ABSTRACT FROM AUTHOR]

The diel vertical migration (DVM) behaviors of zooplankton and micronekton vary among species in response to diverse ambient conditions. Based on the observed mean volumes of backscattering strength (MVBS), we studied the mean features and seasonal variations of DVM in the Andaman Sea. Nocturnal-ascent DVM pattern prevailed throughout the observation period, with a mean downward (upward) migratory speed of 3.85 (3.81) cm/s. The DVM in this area exhibited a 3-layer vertical structure. Between the surface nighttime residence and the daytime residence below 300 m, there was a weak subsurface daytime residence probably formed by the assemblage of migrants avoiding aerobic predators. The variations in lower margin depth of surface nighttime residence and the upper margin depth of subsurface daytime residence were consistent with the variation in oxycline depth, which is closely related to thermocline variations. Compared with the premonsoon season, the MVBS was weaker, but the DVM was more active during the summer monsoon season, corresponding to the water clarity trend. Overall, equatorial Kelvin waves and monsoon winds presumably dominated the seasonal variations in DVM by modulating sea water properties such as oxygen concentration and transparency. • The diel MVBS difference revealed a 3-layer DVM structure in the OMZ area of the AS. • Equatorial Kelvin wave modulated scattering layer depths by influencing the oxycline depth. • Low MVBS and active DVM in summer monsoon season was associated with variation in water clarity. [ABSTRACT FROM AUTHOR]

Instruments drifting at the ocean surface are quasi-Lagrangian, that is, they do not follow exactly the near-surface ocean currents. The currents measured by three commonly-used drifters (CARTHE, CODE and SVP) are compared in a wide range of sea state conditions (winds up to 17 m/s and significant wave height up to 3 m). Nearly collocated and simultaneous drifter measurements in the southwestern Mediterranean reveal that the CARTHE and CODE drifters measure the currents in the first meter below the surface in approximately the same way. When compared to SVP drogued at 15 m nominal depth, the CODE and CARTHE currents are essentially downwind (and down-wave), with a typical speed of 0.5–1% of the wind speed. However, there is a large scatter in velocity differences between CODE/CARTHE and SVP for all wind and sea state conditions encountered, principally due to vertical and horizontal shears not related to the wind. For the CODE drifter with wind speed larger than 10 m/s and significant wave height larger than 1 m, about 30–40% of this difference can be explained by Stokes drift. [ABSTRACT FROM AUTHOR]

The data of acoustic Doppler profilometers placed at the edge of the steep shelf of Oahu Island, Hawaii, are analyzed for the currents. The specific character of inertial oscillations is revealed in the region: strong elongation of inertial orbits, a large amount of anomalous (cyclonic) current rotation, and sharp weakening in the divergence layer of the background (low-frequency) oscillations, the strong variation of which results in significant deviations of the effective inertial frequency from its local geographical value. It is suggested that cyclonic rotation of the inertial currents is related to a strong decrease in the effective oscillation frequency of the oceanic waves on the shelf. [ABSTRACT FROM AUTHOR]

Acoustic Doppler current profilers (ADCPs) are the standard tool for measuring tidal currents at tidal stream energy sites; they are used to estimate several parameters, including turbulent kinetic energy (TKE). However, estimates of TKE from ADCPs are often swamped by wave action. We surmise that this bias can be detected as a data mode: to test this, we present an empirical orthogonal function (EOF) analysis of two months of TKE estimates from ADCP measurements at a tidal energy site with significant wave activity. The results of the analysis were compared with linear wave theory, using data from a wave buoy. The first data mode identified from EOF analysis agrees well with the wave bias predicted by linear theory, and the resulting decomposition of the data set into wave and turbulent components appears realistic. This decomposition is possible from ADCP data alone, and therefore offers a novel and widely applicable analysis technique for simultaneous assessment of turbulence and waves at highly-energetic tidal sites. The method can also be applied retrospectively to historical data sets. We also show that the decomposition can be improved by including higher EOF modes, but this requires an independent measurement of waves to determine the optimum number of modes. • Wave action introduces large biases into ADCP estimates of turbulent kinetic energy. • Wave and turbulent contributions to TKE estimates are decoupled statistically. • Method shown to work well for sufficiently strong waves. • Decoupling can be achieved with ADCP alone, but can be improved with extra data. [ABSTRACT FROM AUTHOR]

1. We present data with a high spatio-temporal resolution from a 72-h field survey in Bautzen Reservoir (Saxony, Germany). The aims of this survey were to observe hydrophysical processes during a period of unstable stratification in spring and investigate the effect of wind-induced internal waves on the vertical distribution of zooplankton. 2. Wind velocities up to 10 m s−1 caused a strong downwelling event of warm water at the sampling site and led to the generation of internal waves with an amplitude of 4 m. 3. The zooplankton community, which was dominated by Daphnia galeata, inhabited epilimnetic waters. Downwelling enlarged the thickness of the epilimnetic layer and, hence, led to high zooplankton abundances down to relatively deep water strata indicating lateral transport of zooplankton. As a consequence, area-specific zooplankton abundances increased considerably (max. fourfold) during downwelling. 4. We conclude that classical limnological field sampling, such as for monitoring purposes, can lead to severely biased estimates of zooplankton abundance due to the interfering effects of hydrophysical processes like internal waves. 5. Backscattering strengths measured by a simultaneously deployed Acoustic Doppler Current Profiler (600 kHz) were found to be correlated with estimated zooplankton abundances based on plankton samples. [ABSTRACT FROM AUTHOR]

In this paper, the advantages of shaping a non-conventional triple collocation-based calibration of a wave propagation model is pointed out. Illustrated through a case study in the Bagnoli-Coroglio Bay (central Tyrrhenian Sea, Italy), a multi-comparison between numerical data and direct measurements have been carried out. The nearshore wave propagation model output has been compared with measurements from an acoustic Doppler current profiler (ADCP) and an innovative low-cost drifter-derived GPS-based wave buoy located outside the bay. The triple collocation—buoy, ADCP and virtual numerical point—make possible an implicit validation between instrumentations and between instrumentation and numerical model. The procedure presented here advocates for an alternative "two-step" strategy. Indeed, the triple collocation technique has been used solely to provide a first "rough" calibration of one numerical domain in which the input open boundary has been placed, so that the main wave direction is orthogonally aligned. The need for a fast and sufficiently accurate estimation of wave model parameters (first step) and then an ensemble of five different offshore boundary orientations have been considered, referencing for a more detailed calibration to a short time series of a GPS-buoy installed in the study area (second step). Such a stage involves the introduction of an enhancement factor for the European Centre for Medium-Range Weather Forecasts (ECMWF) dataset, used as input for the model. Finally, validation of the final model's predictions has been carried out by comparing ADCP measurements in the bay. Despite some limitations, the results reveal that the approach is promising and an excellent correlation can be found, especially in terms of significant wave height. [ABSTRACT FROM AUTHOR]

Billson, O.J.; Russell, P.; Davidson, M.; Poate, T.; Amoudry, L.O., and Williams, M.E., 2020. In-situ observations of infragravity response during extreme storms on sand and gravel beaches. Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 382–386. Coconut Creek (Florida), ISSN 0749-0208. Infragravity waves (frequency = 0.005 – 0.05 Hz) play a key role in coastal storm impacts such as flooding and beach/dune erosion. They are known to dominate the inner surf zone on low-sloping sandy beaches during storms. However, in large wave conditions, their importance on different beach types, of variable swell and wind-waves dominance, is largely unknown. Here, a new dataset is presented comprising in-situ observations during storm wave conditions (significant wave height of 3.3 m, peak periods of 18 s and return periods up to 1 in 60 years) from two contrasting sites: a low-sloping sandy beach and a steep gravel beach. Wave measurements were collected seaward of the breakpoint by wave buoys and bed-mounted acoustic Doppler current profilers, and through the surf zone using arrays of pressure transducers. Wave spectra showed contrasting evolution from the shoaling zone to the inner surf zone at the two sites. At the sandy beach, gravity band energy dissipated gradually as depth reduced, while infragravity band energy simultaneously increased, resulting in strongly infragravity-dominated wave spectra in the inner surf zone. At the steep gravel site, a rapid drop in short wave energy was observed, with limited growth of infragravity energy so that inner surf zone spectra showed a low energy peak in the infragravity band. The normalized bed slope parameter indicated whether infragravity waves were generated by bound long wave release or breakpoint forcing, showing that the former (latter) was dominant on the sandy (gravel) beach. In spite of these differences, the shoreline wave spectra under storm wave conditions were infragravity-dominated on both the sandy and gravel beaches. [ABSTRACT FROM AUTHOR]

Full-ocean-depth observations of horizontal velocity, temperature and salinity along 68.5° W chiefly over the period October 2010–May 2014 are analyzed in conjunction with repeated shipboard acoustic Doppler current profiler (SADCP) upper-ocean velocity sections occupied upstream at 70.3° W and regional satellite-altimeter-based sea surface height (SSH) data to construct estimates of the time-averaged Gulf Stream velocity, property structures and transport. A stream-coordinate mean section is created from two moorings near 68.5° W where data are binned relative to distance from the Gulf Stream axis, rotated into along- and across-stream coordinates, and then averaged. Transport in the upper 600 m inferred from the moorings excluding times of large Stream axis curvature and Gulf Stream ring influences is 59.9 Sv (with 95% confidence bounds between 58.6 and 61.6 Sv). This is in good agreement with a mean constructed from the SADCP sections at 70.3° W. Relative to the mean field at 70.3° W, the velocity core of the time-averaged Stream at 68.5° W appears broader with weaker maximum speed, consistent with a companion analysis of the altimetric SSH data. The time-averaged full-ocean-depth transport inferred from the moorings is 102.1 Sv (with 95% confidence bounds between 99.1 and 106.3 Sv), which is stronger than the mean inferred from an ensemble of 10 full-depth lowered acoustic Doppler current profiler (LADCP) sections collected along the moored array. The 2010–2014 time-averaged Gulf Stream inferred from the moored observations is weaker by about 10% than the time-averaged full-ocean-depth transport reported for the late 1980s at the same location using similar procedures, with much of this difference arising from flows at depths greater than 1000 m. Satellite altimetry provides spatial and temporal context for these results and suggests that there are small-scale recirculation cells flanking the separated Gulf Stream west of the New England Seamount Chain. Gulf Stream transport, which includes throughput and recirculating components, appears to be more sensitive to changes in these recirculations at 68.5° W compared to 70.3° W. • In situ measures of subsurface velocity determine mean Gulf Stream strength. • In situ observations from the Line W and Oleander Programs are merged with altimetry. • The 2010–2014 full-depth Gulf Stream transport is 10% weaker than the 1988–1990 mean. • The detached Gulf Stream is flanked by local recirculation cells. • Regional differences are found in the temporal character of Gulf Stream SSH gradients. [ABSTRACT FROM AUTHOR]

Velocity measurements collected by an upward-looking acoustic Doppler current profiler were used to provide the first study of ambient turbulence in Alderney Race. Turbulence metrics were estimated at mid-depth during peak flooding and ebbing tidal conditions. The dissipation rate ε and the integral lengthscale (L) were estimated using two independent methods: the spectral method and the structure function method. The spectral method provided ε and (L) estimates with standard deviations twice lower than that obtained from the structure function method. Removal of wave and Doppler noise-induced bias when estimating the dissipation rate was shown to be a crucial step in turbulence characterization. It allowed for a significant refining in (L) estimates derived from the spectral and structure function methods of 35 % and 20 % respectively. The integral lengthscale was found to be 2–3 times the local water depth. It is considered that these findings could be valuable for current turbine designers, helping them optimizing their designs as well as improving loading prediction through the lifetime of the machines. • The first study of ambient turbulence in Alderney Race is provided. • Two independent methods are used to quantify turbulence metrics. • Removal of wave and Doppler noise-induced bias is a crucial step. • The integral lengthscale was found to be 2–3 times the local water depth. • Unique dataset of turbulence metrics computed at mid-depth are provided. [ABSTRACT FROM AUTHOR]

The 1.5° lat. x 3.5° lon. Levantine area south of Crete was surveyed for the first time in April 2016 with a combination of direct current measurements comprised by CTD-LADCP (Lowered Acoustic Doppler Current Profiler) grid casts and ship-track ADCP measurements in the upper 500 m, while a mooring was launched at the end of the continental slope and provided yearly current records at 700 m and 30 m off the bottom depth of 4300 m. Horizontal flow structures are mapped in the upper 1000 m via objective analysis of the direct current measurements depicting the Cretan Cyclone at the west, the Rhodes Gyre at the east and anticyclonic circulation in the middle due to Modified Atlantic Water in the upper 80 m and a thick, saline, warm mass extending from ~100 m to ~1500 m, possibly of Cretan origin. The bottom kinetic energy spectra have higher density values than those at 700 m. In the two-month energetic period of end/Jan.-to-end/Mar. 2017, topographic Rossby waves (TRW) with wavelength of ~42 km exist in the window of ~34-19 days with significant coherence between the near-bottom and the 700-m records. At the TRW spectral window, the motions are transverse and the direction of maximum velocity variance veers from nearly along isobaths ~20° (north-northeast) to ~45° (northeast) with decreasing period. The presence of TRWs in the specific time period within 2017 appears to be related to the lateral shifts of the Ierapetra Anticyclone over the sloping bottom of the continental margin. [ABSTRACT FROM AUTHOR]

Wind waves are of great importance in various fields of oceanography and engineering. Although they propagate along entire seas and oceans, due to the complexity and high costs in setting deep water measurements, they are mostly measured only in nearshore regions. The connection between deep sea wave conditions and nearshore ones is commonly done using wave propagation models. Nevertheless, due to the scarcity of deep water measurements, the validity of this process is seldomly tested. This work presents newly acquired data for investigating wave evolution from the deep sea far beyond the continental shelf to intermediate coastal waters. The deep water wave measurements were obtained using an upward-looking Acoustic Doppler Current Profiler (ADCP) mounted on a submerged buoy (35 m depth) in the East Mediterranean 50 km offshore Israel (bottom depth of 1500 m). To the best of our knowledge, it is the first time that such a deep sea measurement is carried out in the region. Another ADCP was deployed on the sea bed (26 m depth) 2 km offshore. During this campaign, a substantial storm ( H m 0 =6 m) was recorded simultaneously by both ADCPs. A wave evolution model accounting for triad and quartet interactions was employed for connecting the two measurements, in order to explain the differences between the two measurements with numerical estimations. A new methodology was developed for resolving spatial variability in the deep sea conditions by assimilating the deep water data into the output of an operational wave model for the Mediterranean Sea. This allowed forming appropriate boundary conditions for propagation of the wave field from deep to coastal waters. Model results show an importance of accounting for inhomogeneity of the wave field in deep water. Nevertheless, the measurements indicate that one cannot expect to fully resolve the exact wave spectra only by applying wave modeling. This emphasizes the importance of conducting such deep wave measurements. [ABSTRACT FROM AUTHOR]

The Réunion Island in the South-West Indian Ocean is often affected by austral or cyclonic swells that may have strong impacts on coastal infrastructures. The ReNovRisk project that started in 2017, developed by Météo-France and the University of La Réunion aims at improving cyclone forecasts in the South-West Indian Ocean, by better modelling atmosphere and ocean interactions and by increasing direct observations to better calibrate and validate the swell activity. In the present study, we first analyze the microseismic noise recorded by permanent and temporary seismic stations operating in La Réunion. Together with microseismic noise, we analyze data issued from oceanographic instruments deployed in coastal areas: pressures gauges, OSSI sensors (pressure and temperature) and Acoustic Doppler Current Profiler (ADCP) sensors from which wave height and water currents are derived. These sensors were operated during the period March-May 2017, September-October 2018 and will be deployed twice a year, in and outside of the lagoon, at a depth between 10 and 80 m, with an operational recording of 3 months. Our results for the austral swells occurring in March-May 2017 and September-October 2018 show that the swells measured on both sides of the reef have the same patterns, except that the amplitudes outside the lagoon are ten times higher than those inside. This demonstrates the major role of the coral reef in attenuating the swell and therefore the importance of preserving it to reduce coastal wave submersion hazards. The amplitude of the primary microseisms (0.05 Hz-0.1 Hz) display a good correlation (~0.95) with the swell height, confirming its generation by swell-coast interaction. Secondary Microseisms (SM) that develop within the storm at several thousands of km in the Austral Ocean reach the island 1-4 days before the swell hit the coast of La Reunion island, suggesting that SM monitoring may provide a robust way for predicting large swell events.During the cyclones, the PSD show that the microseismic noise levels in both the PM and SM frequency bands intensified. In the PM band, our results show that the amplitude of the microseismic noise depends on both the distance and the intensity of the cyclone. We observe a clear correlation between the swell height as provided by the WWIII model in the neighbourhood of La Réunion Island and the microseismic noise amplitude, indicating a coastal origin for the PM and confirming that the seismic noise amplitude may be used as a proxy of the swell height. SM is clearly visible for cyclone distance of ~1000 km. Following the arrival of the SM and depending on the cyclone-station distance, the swell hits the coast of the Island and generates the PM signal. This demonstrates that SM can be used to monitor the cyclone activity, but may also provide precursory information on swell arrival time and amplitude. [ABSTRACT FROM AUTHOR]

The Pentland Firth is located in the north of Scotland, between Caithness on the Scottish mainland and the Orkney islands to the north, and connects the North Atlantic Ocean on the west with the North Sea on the east. The phase lag of the tides results in a strong pressure gradient which drives very strong flows through the Pentland Firth. Flows can be as high as 5ms-1, commonly 2.5-3ms-1 and are strongly affected by the Spring/Neap cycle. The hydraulic current is the dominant feature but the existing geographical features (islands, headlands, etc) account for local tidal streaming. The net energy supply in the Pentland Firth comes from tidal forcing from the North Atlantic Ocean, but conditions can be further enhanced by weather systems sweeping in from the North Atlantic. It has been estimated that 50% of the UK tidal stream energy resource lies within it. (www.tidalstream.co.uk) There is a clear seasonal variability in the wave power resource, due mainly to the regular winter North Atlantic storms. Significant wave heights of over 5m have previously been recorded in the Firth in the autumn and winter months.Our recent study involved the monitoring of waves and currents in the Firth with a view to investigating any interaction between them and the potential effects this may have on marine energy production.An Acoustic Wave and Current Profiler (AWAC) and an Acoustic Doppler Current Profiler (ADCP) were deployed in the Pentland Firth for 2 periods of 15 weeks, approximately 1km north of Dunnet Head and an X-band radar located on the cliffs overlooking the deployment site was used at various times over these periods to monitor sea state behaviour over the wider area. The data obtained by all 3 instruments was correlated and used to characterise the hydrodynamic conditions at the western end of the Pentland Firth.The first deployment was from February to May 2018 and was expected to include Atlantic storm conditions. However, unusual weather patterns meant no such storms occurred throughout this period so a second deployment from Aug-Nov 2018 was carried out. Interesting wave patterns were observed during the 2 easterly weather fronts in March, with clear wave height modulation with tides, and these are being studied further. Sea temperature changes were also observed to follow tidal patterns, even down at seabed level. Two powerful storms occurred in the second deployment period with waves of over 11m measured (Hm0 over 6m). The data from October 2018 is being closely examined as particularly high waves occurred during this month, and connections with currents and tides are being investigated. The extent to which waves affect currents in the Pentland Firth and vice versa is only emerging, but further examination of the data is anticipated to lead to better understanding of wave-current interactions in an area rich in marine energy potential. [ABSTRACT FROM AUTHOR]