Three-Dimensional Characterization of a Coastal Mode-Water Eddy from Multiplatform Observations and a Data Reconstruction Method

Coastal mesoscale eddies are important oceanic structures partially responsible for regulating ocean-shelf exchanges. However, their description and characterization are challenging; observations are often too scarce for studying their physical properties and environmental impacts at the required spatio-temporal resolution. Therefore, models and data extrapolation methods are key tools for this purpose. Observations from high-frequency radar, one satellite and two gliders, are used here to better characterize the three-dimensional structure of a coastal mode-water eddy from a multiplatform approach in the southeastern Bay of Biscay in spring 2018. After the joint analysis of the observations, a three-dimensional data reconstruction method is applied to reconstruct the eddy current velocity field and estimate the associated water volume transport. The target eddy is detected by surface observations (high-frequency radar and satellite) for two weeks and presents similar dimensions and lifetimes as other eddies studied previously in the same location. However, this is the first time that the water column properties are also observed for this region, which depicts a mode-water eddy behavior, i.e., an uplift of the isopycnals in the near-surface and a downlift deeper in the water column. The reconstructed upper water column (1–100 m) eddy dynamics agree with the geostrophic dynamics observed by one of the gliders and result in cross-shelf inshore (offshore) volume transports between 0.04 (−0.01) and 0.15 (−0.11) Sv. The multiplatform data approach and the data reconstruction method are here highlighted as useful tools to characterize and three-dimensionally reconstruct coastal mesoscale processes in coastal areas.

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Characterization of 3D coastal mesoscale structures and transports from multiplatform observations and a data reconstruction method

10.5194/egusphere-egu21-14304 ◽

2021 ◽

Author(s):

Ivan Manso ◽

Anna Rubio ◽

Gabriel Jordà ◽

Jeffrey Carpenter ◽

Lucas Merckelbach ◽

...

Keyword(s):

Particle Density ◽

3D Structure ◽

Hf Radar ◽

Water Volume ◽

Coastal Processes ◽

Data Reconstruction ◽

Reconstruction Method ◽

Mode Water ◽

Mesoscale Structures

<p>The role of coastal mesoscale variability in the modulation of surface along-shelf and cross-shelf exchanges in the SE Bay of Biscay has been demonstrated by several works, from land-based and satellite observations, including high resolution current fields from high-frequency (HF) radars. However, the characterization of physical processes and associated transports at subsurface levels from observations remains a challenge since observations are often too scarce to offer the required spatio-temporal resolution and coverage. In addition to the numerical modelling, the use of methods to reconstruct three-dimensional (3D) current fields from the combination of multiplatform data offers an alternative approach for the study of 3D properties of mesoscale coastal processes, and an improved background to explore bio-physical interactions. Studying the physical properties of coastal mesoscale structures at subsurface levels, where primary production and plankton concentration peak, is key to understand the coupling between physical and biological processes. In this work, we use a previously validated data-reconstruction method and different CMEMS products (coastal simulations, observations from HF radar, satellite, mooring) and glider data, to better characterize the 3D structure of a coastal mode-water eddy and its associated water volume transport. Different Lagrangian properties (maps of particle density, residence times, Lagrangian eddy kinetic energy) obtained at surface and subsurface levels provide a new insight into the water volume transports associated with the main coastal processes in the area.</p>

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Near-surface scattering effects observed with a high-frequency phased array at Pinyon Flats, California

Bulletin of the Seismological Society of America ◽

10.1785/bssa0880061548 ◽

1998 ◽

Vol 88 (6) ◽

pp. 1548-1560

Author(s):

Frank L. Vernon ◽

Gary L. Pavlis ◽

Tom J. Owens ◽

Dan E. McNamara ◽

Paul N. Anderson

Keyword(s):

Surface Wave ◽

Wave Field ◽

Particle Motion ◽

High Frequency ◽

Body Wave ◽

Three Dimensional ◽

Wave Guide ◽

Surface Scattering ◽

Near Surface ◽

Frequency Wave

Abstract Analysis of data collected by a high-frequency array experiment conducted at Pinyon Flat in southern California provides strong evidence that the high-frequency wave field from local earthquakes at this hard-rock site are strongly distorted by near-surface scattering. The seismic array we deployed consisted of 60, 2-Hz natural frequency, three-component sensors deployed in a three-dimensional array. Two of the sensors were located in boreholes at 150 and 275 m depth. The other 58 sensors were deployed in an areal array above these boreholes. Thirty-six of these were deployed in a 6-by-6 element grid array with a nominal spacing of 7 m centered over the borehole sensors. The remaining 22 seismometers were laid out in two 11-element linear arrays radiating outward from the grid. Coherence calculations reveal a rapid loss of coherence at frequencies over 15 Hz at all but the shortest length scales of this array. Three-dimensional visualization techniques were used to closely examine the spatial stability of particle motions of P and S waves. This reveals systematic variations of particle motion across the array in which the particle motion tracks tilt drastically away from the backazimuth expected for an isotropic medium. These variations, however, are frequency dependent. Below around 8 Hz, the particle motions become virtually identical for all stations. At progressively higher frequencies, the wave-field particle motion becomes increasingly chaotic. Frequency-wave-number analysis of these data provide quantitative measures of the same phenomena. We find that direct wave f-k spectra are bathed in a background of signal-generated noise that varies from 10 to 30 dB down from the direct arrival signal. This signal-generated noise appears to be nearly white in wavenumber indicating the wavelength of this “noise” on the scale of tens of meters and less. Refraction measurements we made on two lines crisscrossing the array reveal that the weathered layer velocities are highly variable and define a very strong wave guide. Measured surface P-wave velocities varied from 400 to 1300 m/sec, and velocities at depth of approximately 15 m varied from 1600 to 2700 m/sec. Previous measurements in the boreholes showed that the intact granite below about 65 m depth has a velocity of approximately 5400 m/sec. These results demonstrate the extreme velocity contrast and degree of velocity heterogeneity of the near surface at this site. We conclude that all the observations we made can be explained by strong scattering of incident body-wave signals into a complex mishmash of body-wave and surface-wave modes in this heterogeneous near-surface wave guide.

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Surface currents in the Alderney Race from high-frequency radar measurements and three-dimensional modelling

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2019.0494 ◽

2020 ◽

Vol 378 (2178) ◽

pp. 20190494 ◽

Cited By ~ 2

Author(s):

G. Lopez ◽

A.-C. Bennis ◽

Y. Barbin ◽

A. Sentchev ◽

L. Benoit ◽

...

Keyword(s):

High Frequency ◽

Current Model ◽

Three Dimensional ◽

Surface Current ◽

Tidal Energy ◽

Phase Lag ◽

Surface Currents ◽

Entire Study ◽

High Frequency Radar ◽

Radar Measurements

Two weeks of high-frequency radar measurements collected at the Alderney Race are compared with the results of a three-dimensional fully coupled wave–current model. Spatial current measurements are rare in this site, otherwise well investigated through modelling. Thus, the radar measurements offer a unique opportunity to examine the spatial reliability of numerical results, and can help to improve our understanding of the complex currents in the area. Comparison of observed and modelled surface current velocities showed a good agreement between the methods, represented by root mean squared errors ranging from 14 to 40 cm s −1 and from 18 to 60 cm s −1 during neap and spring tides, respectively. Maximum errors were found in shallow regions with consistently high current velocities, represented by mean neap and spring magnitudes of 1.25 m s −1 and 2.7 m s −1 , respectively. Part of the differences between modelled and observed surface currents in these areas are thought to derive from limitations in the k-epsilon turbulence model used to simulate vertical mixing, when the horizontal turbulent transport is high. In addition, radar radial currents showed increased variance over the same regions, and might also be contributing to the discrepancies found. Correlation analyses yielded magnitudes above 0.95 over the entire study area, with better agreement during spring than during neap tides, probably because of an increase in the phase lag between radar and model velocities during the latter. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

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Three-dimensional exchange flows in a semi-enclosed bay: Numerical simulations and high frequency radar observations

Estuarine Coastal and Shelf Science ◽

10.1016/j.ecss.2018.05.027 ◽

2018 ◽

Vol 210 ◽

pp. 26-35 ◽

Cited By ~ 2

Author(s):

X. Flores-Vidal ◽

S. González-Montes ◽

R. Zertuche-Chanes ◽

I. Rodríguez-Padilla ◽

C.L. Marti ◽

...

Keyword(s):

Numerical Simulations ◽

High Frequency ◽

Three Dimensional ◽

Radar Observations ◽

Exchange Flows ◽

High Frequency Radar ◽

Enclosed Bay

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On the Performance of High Frequency Radar in the Western Mediterranean During the Record-Breaking Storm Gloria

Frontiers in Marine Science ◽

10.3389/fmars.2021.645762 ◽

2021 ◽

Vol 8 ◽

Cited By ~ 3

Author(s):

Pablo Lorente ◽

Jue Lin-Ye ◽

Manuel García-León ◽

Emma Reyes ◽

Maria Fernandes ◽

...

Keyword(s):

High Frequency ◽

Mixed Layer Depth ◽

Three Dimensional ◽

Surface Current ◽

Western Mediterranean ◽

Ocean Model ◽

Transport Processes ◽

Instantaneous Rate ◽

High Frequency Radar ◽

The Impact

Storm Gloria (January 19–24, 2020) hit the NW Mediterranean Sea with heavy rainfall, strong easterly winds, and very high waves, causing structural damages and 13 fatalities. The low-lying Ebro Delta (ED) region was severely inundated, ruining rice fields and seaside promenades. A variety of Copernicus Marine Environment Monitoring Service (CMEMS) modeling and observational products were jointly used to examine the fingerprint of Gloria and the response of the upper oceanic layer. According to the results, Gloria can be interpreted as a high-impact once-in-a-decade metocean event where various historical records were beaten. The 99th percentile of several parameters (wind speed, significant wave height, wave period, and surface current velocity), derived from long-term observational time series, was persistently exceeded. The atmospheric surge, albeit not negligible, exerted a secondary role in ED. The ability of a high-frequency radar deployed in this region (HFR-ED) to characterize the striking features of the storm was quantified from both waves and circulation aspects. Consistent radar current observations were subsequently compared against the 5-day-ahead forecast of CMEMS Iberia-Biscay-Ireland (IBI) regional ocean model to determine, from an Eulerian perspective, the strengths and shortcomings in its predictive capabilities. Time-averaged maps of surface circulation, superimposed with fields of Instantaneous Rate of Separation (IROS), were derived to resolve flow features and identify areas of elevated particles dispersion, respectively. The mean and P99 values of IROS almost doubled the historical statistics in the vicinity of the northern Ebro hemidelta. Although IBI predicted moderately well basic features of the storm-induced circulation, results suggests that coastal transport processes, likely modulated by wave-current interactions, were not fully captured. Furthermore, current estimations from other two radar systems, overlooking immediate choke points like the Ibiza Channel and the Strait of Gibraltar, evidenced Gloria’s remote-effect in the anomalous circulation patterns observed, that altered the usual water exchanges between adjacent sub-basins. Finally, three-dimensional outcomes from IBI were used to elucidate the impact of this moving storm at different depth levels. Data analyses illustrated that Gloria caused a large increase in kinetic energy and a significant deepening of the mixed layer depth.

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Using Artificial Neural Networks for the Estimation of Subsurface Tidal Currents from High-Frequency Radar Surface Current Measurements

Remote Sensing ◽

10.3390/rs13193896 ◽

2021 ◽

Vol 13 (19) ◽

pp. 3896

Author(s):

Max C. Bradbury ◽

Daniel C. Conley

Keyword(s):

Neural Network ◽

Neural Networks ◽

Water Column ◽

High Frequency ◽

Least Squares Method ◽

Accurate Determination ◽

Surface Current ◽

Training Data ◽

Prediction Ability ◽

High Frequency Radar

An extensive record of current velocities at all levels in the water column is an indispensable requirement for a tidal resource assessment and is fully necessary for accurate determination of available energy throughout the water column as well as estimating likely energy capture for any particular device. Traditional tidal prediction using the least squares method requires a large number of harmonic parameters calculated from lengthy acoustic Doppler current profiler (ADCP) measurements, while long-term in situ ADCPs have the advantage of measuring the real current but are logistically expensive. This study aims to show how these issues can be overcome with the use of a neural network to predict current velocities throughout the water column, using surface currents measured by a high-frequency radar. Various structured neural networks were trained with the aim of finding the network which could best simulate unseen subsurface current velocities, compared to ADCP data. This study shows that a recurrent neural network, trained by the Bayesian regularisation algorithm, produces current velocities highly correlated with measured values: r2 (0.98), mean absolute error (0.05 ms−1), and the Nash–Sutcliffe efficiency (0.98). The method demonstrates its high prediction ability using only 2 weeks of training data to predict subsurface currents up to 6 months in the future, whilst a constant surface current input is available. The resulting current predictions can be used to calculate flow power, with only a 0.4% mean error. The method is shown to be as accurate as harmonic analysis whilst requiring comparatively few input data and outperforms harmonics by identifying non-celestial influences; however, the model remains site specific.

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Three-dimensional reconstruction of the 40S ribosomal subunit from rabbit reticulocytes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100128961 ◽

1987 ◽

Vol 45 ◽

pp. 936-937

Author(s):

Neng-Yu Zhang ◽

Terence Wagenknecht ◽

Michael Radermacher ◽

Tom Obrig ◽

Joachim Frank

Keyword(s):

Three Dimensional ◽

Ribosomal Subunit ◽

Uranyl Acetate ◽

Reconstruction Method ◽

Single Exposure ◽

Electron Dose ◽

Ribosomal Subunits ◽

40S Ribosomal Subunit ◽

Dimensional Reconstruction ◽

Rabbit Reticulocytes

We have reconstructed the 40S ribosomal subunit at a resolution of 4 nm using the single-exposure pseudo-conical reconstruction method of Radermacher et al.Small (40S) ribosomal subunits were Isolated from rabbit reticulocytes, applied to grids and negatively stained (0.5% uranyl acetate) in a manner that “sandwiches” the specimen between two layers of carbon. Regions of the grid exhibiting uniform and thick staining were identified and photographed twice (magnification 49,000X). The first micrograph was always taken with the specimen tilted by 50° and the second was of the Identical area untilted (Fig. 1). For each of the micrographs the specimen was subjected to an electron dose of 2000-3000 el/nm2.Three hundred thirty particles appearing in the L view (defined in [4]) were selected from both tilted- and untilted-specimen micrographs. The untilted particles were aligned and their rotational alignment produced the azimuthal angles of the tilted particles in the conical tilt series.

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ИССЛЕДОВАНИЯ АКУСТИЧЕСКИХ ХАРАКТЕРИСТИК ВЕРХНЕГО СЛОЯ МОРЯ МЕТОДОМ МНОГОЧАСТОТНОГО АКУСТИЧЕСКОГО ЗОНДИРОВАНИЯ

Podvodnye issledovaniia i robototehnika ◽

10.37102/24094609.2020.31.1.006 ◽

2020 ◽

Author(s):

V.A. Bulanov ◽

I.V. Korskov ◽

A.V. Storozhenko ◽

S.N. Sosedko

Keyword(s):

High Frequency ◽

Wave Motion ◽

High Spatial Resolution ◽

Wind Waves ◽

Acoustic Parameter ◽

Sea Surface ◽

Near Surface ◽

Acoustical Properties ◽

Acoustic Spectroscopy ◽

Sea Bottom

Описано применение акустического зондирования для исследования акустических характеристик верхнего слоя моря с использованием широкополосных остронаправленных инвертированных излучателей,устанавливаемых на дно. В основу метода положен принцип регистрации обратного рассеяния и отраженияот поверхности моря акустических импульсов с различной частотой, позволяющий одновременно измерятьрассеяние и поглощение звука и нелинейный акустический параметр морской воды. Многочастотное зондирование позволяет реализовать акустическую спектроскопию пузырьков в приповерхностных слоях моря,проводить оценку газосодержания и получать данные о спектре поверхностного волнения при различных состояниях моря вплоть до штормовых. Применение остронаправленных высокочастотных пучков ультразвукапозволяет разделить информацию о планктоне и пузырьках и определить с высоким пространственным разрешением структуру пузырьковых облаков, образующихся при обрушении ветровых волн, и структуру планктонных сообществ. Участие планктона в волновом движении в толще морской воды позволяет определитьпараметры внутренних волн спектр и распределение по амплитудам в различное время.This paper represents the application of acoustic probingfor the investigation of acoustical properties of the upperlayer of the sea using broadband narrow-beam invertedtransducers that are mounted on the sea bottom. Thismethod is based on the principle of the recording of thebackscattering and reflections of acoustic pulses of differentfrequencies from the sea surface. That simultaneouslyallows measuring scattering and absorption of the soundand non-linear acoustic parameter of seawater. Multifrequencyprobing allows performing acoustic spectroscopy ofbubbles in the near-surface layer of the sea, estimating gascontent, and obtaining data on the spectrum of the surfacewaves in various states of the sea up to a storm. Utilizationof the high-frequency narrow ultrasound beams allows us toseparate the information about plankton and bubbles and todetermine the structure of bubble clouds, created during thebreaking of wind waves, along with the structure of planktoncommunities with high spatial resolution. The participationof plankton in the wave motion in the seawater columnallows determining parameters of internal waves, such asspectrum and distribution of amplitudes at different times.

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