A numerical model for ocean ultra-low frequency noise: Wave-generated acoustic-gravity and Rayleigh modes

Ardhuin, Fabrice; Lavanant, Thibaut; Obrebski, Mathias; Marié, Louis; Royer, Jean‐Yves; Deü, Jean-François; Howe, Bruce M.; Lukas, Roger; Aucan, Jérôme

doi:10.1121/1.4818840

Cited by 29 publications

(35 citation statements)

References 43 publications

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“…This projection of the model onto the observation space has the advantage of taking into account the complex effect of ocean wave directionality. However, it assumes that this directionality is well reproduced by the model, which is generally the case for the wave periods longer than 6 s that we use here (Ardhuin et al, ; Peureux & Ardhuin, ).…”

Section: Data Sets and Model Setupmentioning

confidence: 99%

Sea State Trends and Variability: Consistency Between Models, Altimeters, Buoys, and Seismic Data (1979–2016)

et al. 2019

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Wave hindcasts of long time series (>30 years) have been instrumental in understanding the wave climate. However, it is still difficult to have a consistent reanalysis suitable for study of trends and interannual variability. Here we explore the consistency of a wave hindcast with independent observations from moored buoys, satellite altimeters, and seismic data. We use the Climate Forecast System Reanalysis (CFSR) winds to drive a wave model since extreme events are generally well captured. Unfortunately, the original CFSR winds are not homogeneous in time. We systematically modify this wind field in time and space to produce a wave field that has homogeneous differences against the Globwave/SeaStateCCI altimeter wave height database. These corrections to the winds and resulting waves are validated using independent buoy and microseism data. We particularly use seismic data in the dominant double‐frequency band, around 5‐s period, that are generated by opposing waves of equal frequencies. The seismic data confirms that our correction of time‐varying biases is consistent, even in remote and undersampled region such as the Southern Ocean where the original CFSR biases are strongest. Our analysis is performed on monthly time series, and we expect the monthly statistics to be better suited for climate studies. Remaining issues with time consistency of reanalysis products and associated wave hindcasts are further discussed.

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Section: Data Sets and Model Setupmentioning

confidence: 99%

Sea State Trends and Variability: Consistency Between Models, Altimeters, Buoys, and Seismic Data (1979–2016)

et al. 2019

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“…It is a matter of fact that below the seafloor, a layer of sediments lies between ocean and crust. Ardhuin et al [] and Gualtieri [] show, by using two different methods, that a sedimentary layer may strongly affect this site effect.…”

Section: The Seafloor Sediment Effectmentioning

confidence: 99%

On the shaping factors of the secondary microseismic wavefield

et al. 2015

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Seismic noise in the period band 3–10 s is known as secondary microseism, and it is generated at the ocean surface by the interaction of ocean gravity waves coming from nearly opposite directions. In this paper, we investigate the seismic content of the wavefield generated by a source at the ocean surface and three of the major wavefield shaping factors using the 2‐D spectral element method: the ocean‐continent boundary, the source site effect, and the thickness of seafloor sediments. The seismic wavefield recorded on the vertical component seismograms below the seafloor is mainly composed of the fundamental mode and the first overtone of Rayleigh waves. A mode conversion from the first overtone to the fundamental mode of Rayleigh waves occurs at the ocean‐continent boundary. The presence of a continental shelf at the ocean‐continent boundary produces a negligible effect on land‐recorded seismograms, whereas the source site effect, i.e., the source location with respect to the local ocean depth and sediment thickness, plays the major role. A source in shallow water mostly enhances the fundamental mode of Rayleigh waves, whereas a source in deep water mainly enhances the first overtone of Rayleigh waves. Land‐recorded long‐period signals (T > 6 s) are mostly due to deep water sources, whereas land‐recorded short‐period signals (T < 6 s) are due to sources in relatively shallow water, located close to the shelf break. Seafloor sediments around the source region trap seismic waves reducing the amplitude of land‐recorded signals, especially at long periods (T > 6 s).

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“…The AGWs signal, however, is at the order of 10 kPa, which is easy to measure (e.g., the MODE experiment that measures the pressure fluctuation on the deep-sea floor by Brown et al, 1975). This simple example shows that AGWs may be responsible for the low-frequency oceanic noise on the seabed (e.g., Ardhuin et al, 2013).…”

Section: Acoustic-gravity Waves In Deep Oceanmentioning

confidence: 99%

Wavemaker theories for acoustic–gravity waves over a finite depth

Tian

Kadri

2017

J Eng Math

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Acoustic-gravity waves (hereafter AGWs) in ocean have received much interest recently, mainly with respect to early detection of tsunamis as they travel at near the speed of sound in water which makes them ideal candidates for early detection of tsunamis. While the generation mechanisms of AGWs have been studied from the perspective of vertical oscillations of seafloor and triad wave-wave interaction, in the current study we are interested in their generation by wave-structure interaction with possible implication to the energy sector. Here, we develop two wavemaker theories to analyze different wave modes generated by impermeable (the classic Havelock's theory) and porous (porous wavemaker theory) plates in weakly compressible fluids. Slight modification has been made to the porous theory so that, unlike the previous theory, the new solution depends on the geometry of the plate. The expressions for three different types of plates (piston, flap, delta-function) are introduced. Analytical solutions are also derived for the potential amplitude of the gravity, acoustic-gravity, evanescent waves, as well as the surface elevation, velocity distribution, and pressure for AGWs. Both theories reduce to previous results for incompressible flow when the compressibility is neglected. We also show numerical examples for AGWs generated in a wave flume as well as in deep ocean. Our current study sets the theoretical background towards remote sensing by AGWs, for optimized deep ocean wave-power harnessing, among others.

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A numerical model for ocean ultra-low frequency noise: Wave-generated acoustic-gravity and Rayleigh modes

Cited by 29 publications

References 43 publications

Sea State Trends and Variability: Consistency Between Models, Altimeters, Buoys, and Seismic Data (1979–2016)

Sea State Trends and Variability: Consistency Between Models, Altimeters, Buoys, and Seismic Data (1979–2016)

On the shaping factors of the secondary microseismic wavefield

Wavemaker theories for acoustic–gravity waves over a finite depth

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