Transmission of acoustic-gravity waves through gas–liquid interfaces

2012 ◽  
Vol 709 ◽  
pp. 313-340 ◽  
Author(s):  
Oleg A. Godin ◽  
Iosif M. Fuks
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Paper Analysis ◽  
Liquid Interfaces ◽  
Power Flux ◽  
Acoustic Gravity Waves ◽  
Restoring Forces ◽  
Anomalous Transparency ◽  
Diffraction Effects

AbstractIt was demonstrated recently that gas–liquid interfaces, which are usually almost perfect reflectors of acoustic waves, become anomalously transparent, and the power flux in the wave transmitted into the gas increases dramatically, when a compact sound source in the liquid approaches the interface within a fraction of the wavelength (Godin, Phys. Rev. Lett., vol. 97, 2006b, 164301). Powerful underwater explosions and certain natural sources, such as underwater landslides, generate very low-frequency waves in water and air, for which fluid buoyancy and compressibility simultaneously serve as restoring forces. In this paper, analysis of sound transmission through gas–liquid interfaces is extended to acoustic-gravity waves (AGWs) and applied to the air–water interface. It is found that, as for sound, the interface becomes anomalously transparent for sufficiently shallow compact sources of AGWs. Depending on the source type, the increase of a wave power flux into gas due to diffraction effects can reach several orders of magnitude. The physical mechanisms responsible for the anomalous transparency are discussed. Excitation of an interface wave by a point source in the liquid is shown to be an important channel of AGW transmission into the gas, which has no counterpart in the case of sound.

scholarly journals Nonlinear interaction between acoustic gravity waves

1996 ◽  
Vol 14 (3) ◽  
pp. 304-308 ◽  
Author(s):  
P. Axelsson ◽  
J. Larsson ◽  
L. Stenflo
Keyword(s):  
Gravity Waves ◽  
Nonlinear Interaction ◽  
Low Frequency ◽  
Resonant Interaction ◽  
Coupling Coefficients ◽  
Symmetric Form ◽  
Frequency Limit ◽  
Acoustic Gravity Waves

Abstract. The resonant interaction between three acoustic gravity waves is considered. We improve on the results of previous authors and write the new coupling coefficients in a symmetric form. Particular attention is paid to the low-frequency limit.

scholarly journals Time-Dependent Propagation of Tsunami-Generated Acoustic–Gravity Waves in the Atmosphere

2020 ◽  
Vol 77 (4) ◽  
pp. 1233-1244 ◽  
Author(s):  
Yue Wu ◽  
Stefan G. Llewellyn Smith ◽  
James W. Rottman ◽  
Dave Broutman ◽  
Jean-Bernard H. Minster
Keyword(s):  
Internal Waves ◽  
Gravity Waves ◽  
Acoustic Waves ◽  
Early Stage ◽  
Vertical Displacement ◽  
Inverse Laplace Transform ◽  
Acoustic Gravity Waves ◽  
Numerical Inverse Laplace Transform ◽  
Wave Development

Abstract Tsunami-generated linear acoustic–gravity waves in the atmosphere with altitude-dependent vertical stratification and horizontal background winds are studied with the long-term goal of real-time tsunami warning. The initial-value problem is examined using Fourier–Laplace transforms to investigate the time dependence and to compare the cases of anelastic and compressible atmospheres. The approach includes formulating the linear propagation of acoustic–gravity waves in the vertical, solving the vertical displacement of waves and pressure perturbations numerically as a set of coupled ODEs in the Fourier–Laplace domain, and employing den Iseger’s algorithm to carry out a fast and accurate numerical inverse Laplace transform. Results are presented for three cases with different atmospheric and tsunami profiles. Horizontal background winds enhance wave advection in the horizontal but hinder the vertical transmission of internal waves through the whole atmosphere. The effect of compressibility is significant. The rescaled vertical displacement of internal waves at 100-km altitude shows an arrival at the early stage of wave development due to the acoustic branch that is not present in the anelastic case. The long-term displacement also shows an O(1) difference between the compressible and anelastic results for the cases with uniform and realistic stratification. Compressibility hence affects both the speed and amplitude of energy transmitted to the upper atmosphere because of fast acoustic waves.

scholarly journals Traveling ionospheric disturbances triggered by the 2009 North Korean underground nuclear explosion

2015 ◽  
Vol 33 (1) ◽  
pp. 137-142 ◽  
Author(s):  
X. Zhang ◽  
L. Tang
Keyword(s):  
Acoustic Waves ◽  
High Frequency ◽  
Ionospheric Disturbance ◽  
Low Frequency ◽  
Ionospheric Disturbances ◽  
Underground Nuclear Explosion ◽  
Dual Frequency ◽  
International Gnss Service ◽  
Acoustic Gravity Waves ◽  
Traveling Ionospheric Disturbances

Abstract. Underground nuclear explosions (UNEs) can induce acoustic-gravity waves, which disturb the ionosphere and initiate traveling ionospheric disturbances (TIDs). In this paper, we employ a multi-step and multi-order numerical difference method with dual-frequency GPS data to detect ionospheric disturbances triggered by the North Korean UNE on 25 May 2009. Several International GNSS Service (IGS) stations with different distances (400 to 1200 km) from the epicenter were chosen for the experiment. The results show that there are two types of disturbances in the ionospheric disturbance series: high-frequency TIDs with periods of approximately 1 to 2 min and low-frequency waves with period spectrums of 2 to 5 min. The observed TIDs are situated around the epicenter of the UNE, and show similar features, indicating the origin of the observed disturbances is the UNE event. According to the amplitudes, periods and average propagation velocities, the high-frequency and low-frequency TIDs can be attributed to the acoustic waves in the lower ionosphere and higher ionosphere, respectively.

scholarly journals Electromagnetic oscillations of the Earth's upper atmosphere (review)

2010 ◽  
Vol 28 (7) ◽  
pp. 1387-1399 ◽  
Author(s):  
A. G. Khantadze ◽  
G. V. Jandieri ◽  
A. Ishimaru ◽  
T. D. Kaladze ◽  
Zh. M. Diasamidze
Keyword(s):  
Gravity Waves ◽  
Geomagnetic Field ◽  
Large Scale ◽  
Low Frequency ◽  
Planetary Waves ◽  
Upper Atmosphere ◽  
Acoustic Gravity Waves ◽  
Weakly Ionized ◽  
General Dispersion ◽  
Electromagnetic Oscillations

Abstract. A complete theory of low-frequency MHD oscillations of the Earth's weakly ionized ionosphere is formulated. Peculiarities of excitation and propagation of electromagnetic acoustic-gravity, MHD and planetary waves are considered in the Earth's ionosphere. The general dispersion equation is derived for the magneto-acoustic, magneto-gravity and electromagnetic planetary waves in the ionospheric E- and F-regions. The action of the geomagnetic field on the propagation of acoustic-gravity waves is elucidated. The nature of the existence of the comparatively new large-scale electromagnetic planetary branches is emphasized.

Wentzel–Kramers–Brillouin approximation for atmospheric waves

2015 ◽  
Vol 777 ◽  
pp. 260-290 ◽  
Author(s):  
Oleg A. Godin
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
Ad Hoc ◽  
Berry Phase ◽  
Boussinesq Approximation ◽  
Internal Gravity Waves ◽  
Wkb Approximation ◽  
Approximation Properties ◽  
Atmospheric Waves ◽  
Acoustic Gravity Waves

Ray and Wentzel–Kramers–Brillouin (WKB) approximations have long been important tools in understanding and modelling propagation of atmospheric waves. However, contradictory claims regarding the applicability and uniqueness of the WKB approximation persist in the literature. Here, we consider linear acoustic–gravity waves (AGWs) in a layered atmosphere with horizontal winds. A self-consistent version of the WKB approximation is systematically derived from first principles and compared to ad hoc approximations proposed earlier. The parameters of the problem are identified that need to be small to ensure the validity of the WKB approximation. Properties of low-order WKB approximations are discussed in some detail. Contrary to the better-studied cases of acoustic waves and internal gravity waves in the Boussinesq approximation, the WKB solution contains the geometric, or Berry, phase. The Berry phase is generally non-negligible for AGWs in a moving atmosphere. In other words, knowledge of the AGW dispersion relation is not sufficient for calculation of the wave phase.

scholarly journals Spectra of Acoustic-Gravity Waves in the Atmosphere with a Quasi-Isothermal Upper Layer

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 818
Author(s):  
Sergey P. Kshevetskii ◽  
Yuliya A. Kurdyaeva ◽  
Nikolai M. Gavrilov
Keyword(s):  
Gravity Waves ◽  
Evolution Operator ◽  
Mathematical Problem ◽  
Cutoff Frequency ◽  
Lower Boundary ◽  
Low Frequency ◽  
Acoustic Gravity Waves ◽  
Wide Range ◽  
Different Altitudes ◽  
Wave Modes

In this paper, we study, in theoretical terms, the structure of the spectrum of acoustic-gravity waves (AGWs) in the nonisothermal atmosphere having asymptotically constant temperature at high altitudes. A mathematical problem of wave propagation from arbitrary initial perturbations in the half-infinite nonisothermal atmosphere is formulated and analyzed for a system of linearized hydrodynamic equations for small-amplitude waves. Besides initial and lower boundary conditions at the ground, wave energy conservation requirements are applied. In this paper, we show that this mathematical problem belongs to the class of wave problems having self-adjoint evolution operators, which ensures the correctness and existence of solutions for a wide range of atmospheric temperature stratifications. A general solution of the problem can be built in the form of basic eigenfunction expansions of the evolution operator. The paper shows that wave frequencies considered as eigenvalues of the self-adjoint evolution operator are real and form two global branches corresponding to high- and low-frequency AGW modes. These two branches are separated since the Brunt–Vaisala frequency is smaller than the acoustic cutoff frequency at the upper boundary of the model. Wave modes belonging to the low-frequency global spectral branch have properties of internal gravity waves (IGWs) at all altitudes. Wave modes of the high-frequency spectral branch at different altitudes may have properties of IGWs or acoustic waves depending on local stratification. The results of simulations using a high-resolution nonlinear numerical model confirm possible changes of AGW properties at different altitudes in the nonisothermal atmosphere.

scholarly journals Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment

2017 ◽  
Vol 35 (1) ◽  
pp. 53-70 ◽  
Author(s):  
Yuriy G. Rapoport ◽  
Oleg K. Cheremnykh ◽  
Volodymyr V. Koshovy ◽  
Mykola O. Melnik ◽  
Oleh L. Ivantyshyn ◽  
...  
Keyword(s):  
Acoustic Wave ◽  
Gravity Waves ◽  
Acoustic Waves ◽  
Difference Frequency ◽  
Sound Waves ◽  
Acoustic Gravity Waves ◽  
Active Experiment ◽  
The Difference ◽  
The Impact ◽  
Sound Generator

Abstract. We develop theoretical basics of active experiments with two beams of acoustic waves, radiated by a ground-based sound generator. These beams are transformed into atmospheric acoustic gravity waves (AGWs), which have parameters that enable them to penetrate to the altitudes of the ionospheric E and F regions where they influence the electron concentration of the ionosphere. Acoustic waves are generated by the ground-based parametric sound generator (PSG) at the two close frequencies. The main idea of the experiment is to design the output parameters of the PSG to build a cascade scheme of nonlinear wave frequency downshift transformations to provide the necessary conditions for their vertical propagation and to enable penetration to ionospheric altitudes. The PSG generates sound waves (SWs) with frequencies f1 = 600 and f2 = 625 Hz and large amplitudes (100–420 m s−1). Each of these waves is modulated with the frequency of 0.016 Hz. The novelty of the proposed analytical–numerical model is due to simultaneous accounting for nonlinearity, diffraction, losses, and dispersion and inclusion of the two-stage transformation (1) of the initial acoustic waves to the acoustic wave with the difference frequency Δf = f2 − f1 in the altitude ranges 0–0.1 km, in the strongly nonlinear regime, and (2) of the acoustic wave with the difference frequency to atmospheric acoustic gravity waves with the modulational frequency in the altitude ranges 0.1–20 km, which then reach the altitudes of the ionospheric E and F regions, in a practically linear regime. AGWs, nonlinearly transformed from the sound waves, launched by the two-frequency ground-based sound generator can increase the transparency of the ionosphere for the electromagnetic waves in HF (MHz) and VLF (kHz) ranges. The developed theoretical model can be used for interpreting an active experiment that includes the PSG impact on the atmosphere–ionosphere system, measurements of electromagnetic and acoustic fields, study of the variations in ionospheric transparency for the radio emissions from galactic radio sources, optical measurements, and the impact on atmospheric aerosols. The proposed approach can be useful for better understanding the mechanism of the acoustic channel of seismo-ionospheric coupling.

Perturbation of low-frequency underwater acoustics by gravity waves

2000 ◽  
Vol 411 ◽  
pp. 305-324
Author(s):  
I. CHAMPY-DOUTRELEAU ◽  
D. EUVRARD ◽  
C. HAZARD
Keyword(s):  
Free Surface ◽  
Gravity Waves ◽  
Acoustic Waves ◽  
Small Amplitude ◽  
Low Frequency ◽  
Dirichlet Condition ◽  
Difficult Problem ◽  
Second Order ◽  
Convolution Product ◽  
Scattering Problems

A body immersed in an ocean of large depth is assumed to vibrate and to radiate a time-harmonic acoustic field of small amplitude in the presence of gravity waves of small amplitude. Assuming both waves to have lengths of the same order (which in practice corresponds to very low acoustic frequencies) it is shown that the diffraction of acoustic waves by the corrugated free surface generates a second-order acoustic pressure field p2. The computation of p2 involves a difficulty: a non-homogeneous Dirichlet condition to be satisfied on the mean free surface up to infinity which implies the absence of any clear indication about the condition that should be imposed at infinity to have a well-posed problem. In order to get an insight into this difficult problem the simple case of a point source is studied. We first judiciously choose one solution and then show it is the physical solution using a limiting-amplitude procedure. Coming back to the general case of a vibrating body the calculation of p2 is split into two successive steps: the first one consists in computing an explicit convolution product via numerical methods of integration, the second one is a standard radiation problem that is solved using a method coupling a Green integral representation and finite elements. A peak of the second-order pressure appears just above the vibrating body.The same concepts also apply to other second-order scattering problems, such as the sea-keeping of weakly immersed submarines.

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