Depth-integrated equation for hydro-acoustic waves with bottom damping

2015 ◽  
Vol 766 ◽  
Author(s):  
Ali Abdolali ◽  
James T. Kirby ◽  
Giorgio Bellotti
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Model Equation ◽  
Low Frequency ◽  
3D Models ◽  
Sediment Layer ◽  
Sea Bed ◽  
Weakly Compressible ◽  
Acoustic Wave Generation

AbstractWe present a depth-integrated equation for the mechanics of generation, propagation and dissipation of low-frequency hydro-acoustic waves due to sudden bottom displacement in a weakly compressible ocean overlying a weakly compressible viscous sediment layer. The model is validated against a full 3D computational model. Physical properties of these waves are studied and compared with those for waves over a rigid sea bed, revealing changes in the frequency spectrum and modal peaks. The resulting model equation can be used for numerical prediction in large-scale domains, overcoming the computational difficulties of 3D models while taking into account the role of bottom dissipation on hydro-acoustic wave generation and propagation.

scholarly journals A shallow water analogue of asymmetric core-collapse, and neutron star kick/spin

2011 ◽  
Vol 7 (S279) ◽  
pp. 134-137
Author(s):  
Thierry Foglizzo ◽  
Frédéric Masset ◽  
Jérôme Guilet ◽  
Gilles Durand
Keyword(s):  
Neutron Star ◽  
Shallow Water ◽  
Acoustic Waves ◽  
Large Scale ◽  
Massive Stars ◽  
Core Collapse ◽  
Hydraulic Jumps ◽  
Core Collapse Supernova ◽  
Accretion Shock

AbstractMassive stars end their life with the gravitational collapse of their core and the formation of a neutron star. Their explosion as a supernova depends on the revival of a spherical accretion shock, located in the inner 200km and stalled during a few hundred milliseconds. Numerical simulations suggest that the large scale asymmetry of the neutrino-driven explosion is induced by a hydrodynamical instability named SASI. Its non radial character is able to influence the kick and the spin of the resulting neutron star. The SWASI experiment is a simple shallow water analog of SASI, where the role of acoustic waves and shocks is played by surface waves and hydraulic jumps. Distances in the experiment are scaled down by a factor one million, and time is slower by a factor one hundred. This experiment is designed to illustrate the asymmetric nature of core-collapse supernova.

scholarly journals Contribution of low-frequency climatic–oceanic oscillations to streamflow variability in small, coastal rivers of the Sierra Nevada de Santa Marta (Colombia)

2019 ◽  
Vol 23 (5) ◽  
pp. 2379-2400 ◽  
Author(s):  
Juan Camilo Restrepo ◽  
Aldemar Higgins ◽  
Jaime Escobar ◽  
Silvio Ospino ◽  
Natalia Hoyos
Keyword(s):  
Energy Spectrum ◽  
Sierra Nevada ◽  
Large Scale ◽  
Low Frequency ◽  
Maximum Power ◽  
Simultaneous Occurrence ◽  
Atmospheric Processes ◽  
Low Frequency Oscillations ◽  
Streamflow Variability

Abstract. This study evaluated the influence of low-frequency oscillations, that are linked to large-scale oceanographic–atmospheric processes, on streamflow variability in small tropical coastal mountain rivers of the Sierra Nevada de Santa Marta, Colombia. We used data from six rivers that had > 32 years of complete, continuous monthly streamflow records. This investigation employed spectral analyses to (1) explore temporal characteristics of streamflow variability, (2) estimate the net contribution to the energy spectrum of low-frequency oscillations to streamflow anomalies, and (3) analyze the linkages between streamflow anomalies and large-scale, low-frequency oceanographic–atmospheric processes. Wavelet analyses indicate that the 8–12-year component exhibited a quasi-stationary state, with a peak of maximum power between 1985 and 2005. These oscillations were nearly in phase in all rivers. Maximum power peaks occurred for the Palomino and Rancheria rivers in 1985 and 1995, respectively. The wavelet spectrum highlights a change in river variability patterns between 1995 and 2015, characterized by a shift towards the low-frequency oscillations' domain (8–12 years). The net contribution of these oscillations to the energy spectrum was as high as 51 %, a value much larger than previously thought for rivers in northwestern South America. The simultaneous occurrence of hydrologic oscillations, as well as the increase in the amplitude of the 8–12-year band, defined periods of extremely anomalous wet seasons during 1989–1990, 1998–2002 and 2010–2011, reflecting the role of low-frequency oscillations in modulating streamflow variability in these rivers. Cross-wavelet transform and wavelet coherence revealed high common powers and significant coherences in low-frequency bands (>96 months) between streamflow anomalies and Atlantic Meridional Oscillation (AMO), Pacific Decadal Oscillation (PDO) and the Tropical North Atlantic Index (TNA). These results show the role of large-scale, low-frequency oceanographic–climate processes in modulating the long-term hydrological variability of these rivers.

scholarly journals Seismic time-frequency spectral decomposition by matching pursuit

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. V13-V20 ◽  
Author(s):  
Yanghua Wang
Keyword(s):  
Frequency Spectrum ◽  
Acoustic Waves ◽  
Large Scale ◽  
Matching Pursuit ◽  
Low Frequency ◽  
Gas Reservoir ◽  
Adaptive Wavelet ◽  
Redundant Dictionary ◽  
Time Frequency ◽  
Wavelet Selection

A seismic trace may be decomposed into a series of wavelets that match their time-frequency signature by using a matching pursuit algorithm, an iterative procedure of wavelet selection among a large and redundant dictionary. For reflection seismic signals, the Morlet wavelet may be employed, because it can represent quantitatively the energy attenuation and velocity dispersion of acoustic waves propagating through porous media. The efficiency of an adaptive wavelet selection is improved by making first a preliminary estimate and then a localized refining search, whereas complex-trace attributes and derived analytical expressions are also used in various stages. For a constituent wavelet, the scale is an important adaptive parameter that controls the width of wavelet in time and the bandwidth of the frequency spectrum. After matching pursuit decomposition, deleting wavelets with either very small or very large scale values can suppress spikes and sinusoid functions effectively from the time-frequency spectrum. This time-frequency spectrum may be used in turn for lithological analysis—for instance, detection of a gas reservoir. Investigation shows that the low-frequency shadow associated with a carbonate gas reservoir still exists, even high-frequency amplitudes are compensated by inverse-[Formula: see text] filtering.

scholarly journals 3D Numerical Simulation of Hydro-Acoustic Waves Registered during the 2012 Negros-Cebu Earthquake

Geosciences ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 300
Author(s):  
Claudia Cecioni ◽  
Alessandro Romano ◽  
Giorgio Bellotti ◽  
Paolo De Girolamo
Keyword(s):  
Acoustic Signal ◽  
Acoustic Waves ◽  
Sea Water ◽  
Three Dimensional ◽  
The Philippines ◽  
Pressure Waves ◽  
Sea Bed ◽  
Weakly Compressible ◽  
Waves Propagation ◽  
Underwater Acoustic Signal

The paper investigates on the hydro-acoustic waves propagation caused by the underwater earthquake, occurred on 6 February 2012, between the Negros and Cebu islands, in the Philippines. Hydro-acoustic waves are pressure waves that propagate at the sound celerity in water. These waves can be triggered by the sudden vertical sea-bed movement, due to underwater earthquakes. The results of three dimensional numerical simulations, which solve the wave equation in a weakly compressible sea water domain are presented. The hydro-acoustic signal is compared to an underwater acoustic signal recorded during the event by a scuba diver, who was about 12 km far from the earthquake epicenter.

Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part I: Barotropic Critical Region

2006 ◽  
Vol 63 (8) ◽  
pp. 1965-1981 ◽  
Author(s):  
G. Rivière ◽  
A. Joly
Keyword(s):  
Critical Region ◽  
Large Scale ◽  
Sudden Change ◽  
Storm Track ◽  
Low Frequency ◽  
Reanalysis Data ◽  
Deformation Field ◽  
Extratropical Cyclones ◽  
Exit Region

Abstract By using new theoretical results on perturbation growth in spatially and temporally complex quasigeostrophic flows, this paper investigates the role of the large-scale deformation field on extratropical cyclones and especially on their explosive growth in the jet-exit region. Theoretical ideas are tested by decomposing the atmospheric flow into a high- and a low-frequency part and by analyzing four-dimensional variational data assimilation (4DVAR) reanalysis data of the Fronts and Atlantic Storm-Track Experiment (FASTEX) during February 1997 as well as reanalysis data for the end of December 1999. Regions where the low-frequency deformation magnitude is greater than the absolute value of the low-frequency vorticity are shown to correspond to regions where synoptic disturbances at the same level tend to be located. These regions in the upper troposphere are intrinsically related to the horizontal inhomogeneities of the low-frequency large-scale upper-tropospheric jet but cannot be detected by looking separately at the deformation or vorticity. Transitions from one such large-scale region to the next furthermore can be accompanied by a sudden change of the dilatation axes orientation: this combination defines a barotropic critical region (BtCR). Reasons why a BtCR is a specific place where barotropic development is likely to occur are exposed. Two very differently located BtCR regions in two apparently similar zonal-like weather regimes are shown to be the preferred regions where synoptic eddies tend to cross the jet from the south to the north. BtCRs are also special regions where constructive association between barotropic and baroclinic processes is favored, indeed constrained to cooperate. This is illustrated through the detailed analysis of the last growth stage of Intensive Observation Period 17 (IOP17) of FASTEX. It happens precisely around a BtCR area located in the jet-exit region. Two processes explain this IOP17 development; one involves the barotropic generation rate resulting from the low crossing the BtCR and the other one is baroclinic interaction, which is strongly maintained far away from the baroclinicity maximum because of the new favorable baroclinic configuration resulting from the first process.

The Role of Streamwise Vorticity in the Control of Impinging Jets

2003 ◽  
Author(s):  
F. S. Alvi ◽  
H. Lou ◽  
C. Shih
Keyword(s):  
Velocity Field ◽  
Shear Layer ◽  
Acoustic Waves ◽  
High Speed ◽  
Feedback Loop ◽  
Large Scale ◽  
Field Measurements ◽  
Impinging Jets ◽  
Streamwise Vorticity

Supersonic impinging jets produce a highly unsteady flowfield leading to very high dynamic pressure loads on nearby surfaces. In earlier studies, we conclusively demonstrated that arrays of supersonic microjet, 400 μm in diameter, effectively disrupted the feedback loop inherent in high-speed impinging jet flows. This feedback disruption results in significant reductions in the adverse effects associated with such flows. In this paper, by primarily using detailed velocity field measurements, we examine the role of streamwise vorticity in order to better understand the mechanisms behind this control scheme. The velocity field measurements clearly reveal the presence of well-organized, streamwise vortices with the activation of microjets. This increase in streamwise vorticity is concomitant with a reduction in the azimuthal vorticity of the primary jet. We propose that the streamwise vorticity is mainly a result of the redirection of the azimuthal vorticity, which leads to a weakening of the large-scale structures in the primary jet. The appearance of strong vortices in the shear layer near the nozzle exit due to microjets further weakens the spatial coherence of the coupling between the acoustic waves and shear layer instability, while thickening the jet shear layer. All these effects are thought to be collectively responsible for the efficient disruption of the feedback loop using microjets.

scholarly journals Large-scale numerical modeling of hydro-acoustic waves generated by tsunamigenic earthquakes

2015 ◽  
Vol 15 (3) ◽  
pp. 627-636 ◽  
Author(s):  
C. Cecioni ◽  
A. Abdolali ◽  
G. Bellotti ◽  
P. Sammarco
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Early Warning Systems ◽  
Computationally Efficient ◽  
Significant Information ◽  
Tsunami Early Warning ◽  
Earthquake Scenarios ◽  
Weakly Compressible ◽  
Tsunami Early Warning Systems ◽  
Pressure Perturbations

Abstract. Tsunamigenic fast movements of the seabed generate pressure waves in weakly compressible seawater, namely hydro-acoustic waves, which travel at the sound celerity in water (about 1500 m s−1). These waves travel much faster than the counterpart long free-surface gravity waves and contain significant information on the source. Measurement of hydro-acoustic waves can therefore anticipate the tsunami arrival and significantly improve the capability of tsunami early warning systems. In this paper a novel numerical model for reproduction of hydro-acoustic waves is applied to analyze the generation and propagation in real bathymetry of these pressure perturbations for two historical catastrophic earthquake scenarios in Mediterranean Sea. The model is based on the solution of a depth-integrated equation, and therefore results are computationally efficient in reconstructing the hydro-acoustic waves propagation scenarios.

scholarly journals Large-scale numerical modeling of hydro-acoustic waves generated by tsunamigenic earthquakes

2014 ◽  
Vol 2 (7) ◽  
pp. 4629-4658 ◽  
Author(s):  
C. Cecioni ◽  
A. Abdolali ◽  
G. Bellotti ◽  
P. Sammarco
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Sea Water ◽  
Early Warning Systems ◽  
Computationally Efficient ◽  
Significant Information ◽  
Tsunami Early Warning ◽  
Earthquake Scenarios ◽  
Sea Bed ◽  
Tsunami Early Warning Systems

Abstract. Tsunamigenic fast movements of the sea-bed generate pressure waves in weakly compressible sea water, namely hydro-acoustic waves, which travel at the sound celerity in water (about 1500 m s−1). These waves travel much faster than the counter part long free-surface gravity waves and contain significant information on the source. Measurement of hydro-acoustic waves can therefore anticipate the tsunami arrival and significantly improve the capability of tsunami early warning systems. In this paper a novel numerical model for reproduction of hydro-acoustic waves is applied to analyze the generation and propagation in real bathymetry of these pressure perturbations for two historical catastrophic earthquake scenarios in Mediterranean Sea. The model is based on the solution of a depth-integrated equation and therefore results computationally efficient in reconstructing the hydro-acoustic waves propagation scenarios.

scholarly journals Evolution of the 2006–2007 El Niño: the role of intraseasonal to interannual time scale dynamics

2008 ◽  
Vol 14 ◽  
pp. 219-230 ◽  
Author(s):  
M. J. McPhaden
Keyword(s):  
El Niño ◽  
Time Scale ◽  
Large Scale ◽  
El Nino ◽  
Low Frequency ◽  
Enso Cycle ◽  
Interannual Time Scale ◽  
Unusual Behavior ◽  
Factors Affecting

Abstract. We describe development of the 2006–2007 El Niño, which started late, ended early and was below average strength. Emphasis is on the interplay between large scale, low frequency (i.e., seasonal-to-interannual time scale) deterministic dynamics and episodic intraseasonal wind forcing in the evolution of the event. Efforts to forecast the El Niño are reviewed, with discussion of factors affecting its predictability. Perspectives on the contemporaneous development of an Indian Ocean Dipole Zonal Mode event in 2006 and possible influences of global warming on the ENSO cycle, which exhibited unusual behavior in the first decade of the 21st century, will also be presented.

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