Propagation Of Acoustic-gravity Waves Research Articles

Propagation to the upper atmosphere of acoustic-gravity waves from atmospheric fronts in the Moscow region

Abstract. The paper uses experimental data of pressure variations on the Earth's surface during the passage of an atmospheric front recorded by a network of four microbarographs in the Moscow region. Applying these experimental data, empirical approximations of atmospheric pressure field oscillations are suggested. The obtained approximating surface pressure functions are used as the lower boundary condition for simulating the vertical propagation of acoustic-gravity waves from a source in the lower troposphere. Estimates of the amplitude of temperature disturbances in the upper atmosphere caused by acoustic-gravity waves from a propagating atmospheric front are obtained. For the amplitude of wave temperature disturbances, values of about 200 K are obtained. The amplitude of temperature disturbances in the upper atmosphere caused by background pressure fluctuations on the Earth's surface is estimated at 4–5 K.

Acoustic-gravity waves in a quiet region of the solar atmosphere

We study numerically the propagation of small-amplitude acoustic-gravity waves in a quiet region of the gravitationally stratified solar atmosphere. These waves are excited by a localized in-space periodic driver which acts in the vertical component of velocity at the bottom of the photosphere. Our aim is to study these waves and their period variations in space in 2D medium approximation. We collect the wave signals along few spatial directions to mimic line-of-sight (LOS) effects. The results of numerical simulations we performed reveal that the detected wave periods depend strongly on the LOS directions; above the driver, along the vertical direction, only acoustic waves with their periods smaller than about 300 s are free to propagate, while obliquely to the gravity action longer-period gravity waves can penetrate a quiet region of the solar atmosphere.

Correct Boundary Conditions for the High-Resolution Model of Nonlinear Acoustic-Gravity Waves Forced by Atmospheric Pressure Variations

Currently, an international network of operating high-resolution microbarographs was established to record wave-induced pressure variations at the Earth’s surface. Based on these measurements, simulations are performed to analyze the characteristics of waves corresponding to the observed variations of atmospheric pressure. Such a mathematical problem involves a set of primitive nonlinear hydrodynamic equations considering lower boundary conditions in the form of pressure variations at the Earth’s surface. Selection of upward propagating acoustic-gravity waves (AGWs) generated or reflected at the Earth’s surface requires the Neumann boundary conditions involving the vertical gradients of vertical velocity at the lower boundary. To analyze the correctness of the mathematical problem, linearized equations are used for small-surface wave amplitudes excited near the ground. Using the relation for wave energy, it is proven that the solution of the boundary problem based on the nondissipative approximation is uniquely determined by the variable pressure field at the Earth’s surface. The respective dissipative problem has also a unique solution with the appropriate choice of lower boundary conditions for temperature and velocity components. To test the numerical algorithm, solutions of the linearized equations for AGW modes are used. Developed boundary conditions are implemented into the model describing acoustic-gravity wave propagation from the surface atmospheric pressure source. Atmospheric waves propagating from the observed surface pressure variations to the upper atmosphere are simulated using the obtained algorithms and the computer codes.

Propagation of non-stationary acoustic-gravity waves at thermospheric temperatures corresponding to different solar activity

Numerical simulation of non-stationary nonlinear acoustic-gravity waves (AGWs) propagating from the surface wave source to the thermosphere reveals that their propagation conditions and parameters depend on changes in background temperature, density, composition, molecular viscosity and heat conduction caused by changes in solar activity (SA). At small wave source amplitudes, AGW amplitudes, momentum fluxes and wave accelerations of the mean flow are slightly larger at altitudes about 150 km at low SA because of smaller mean density and ρ0−1/2dependence of wave amplitudes at low dissipation. Larger kinematic coefficients of molecular viscosity and heat conduction lead to stronger decrease of wave amplitudes and momentum fluxes at altitudes above 150 km at low SA. At large amplitudes of surface wave excitation, AGW breaking and smaller-scale inhomogeneities appear at altitudes 100–150 km, which are stronger at low SA. Increased dissipation of breaking AGWs may produce wave-induced jet streams with velocities close to the wave horizontal phase speed and near-critical layers at altitudes 110–150 km, which dramatically decrease amplitudes and momentum fluxes of the primary AGW mode propagating from the surface wave source. The wave-induced horizontal wind becomes smaller above altitude of 150 km and allows growing amplitudes of the primary wave mode partially penetrating through the near-critical layer and of secondary AGW modes, possibly generating in the wave induced jet stream. The wave amplitude grows at altitudes higher than 150 km is larger at high SA due to smaller velocities of wave-induced mean wind and smaller molecular viscosity and heat conduction. Accelerations of the mean flow by dissipating AGWs are generally larger at low SA. This determines faster grows of wave-induced jet streams in time at low SA. In almost all simulated cases, velocities of the wave-induced mean flows are higher at low SA compared to high SA. Resulting SA impact at a given thermospheric altitude depends on competition between AGW amplitude increase due to smaller molecular dissipation and smaller energy transfer to the wind-induced mean flow and amplitude decrease caused by larger density and stronger reflection at higher SA.

Well-Posedness of a Problem of Propagation of Nonlinear Acoustic-Gravity Waves in the Atmosphere Generated by Surface Pressure Variations

Currently there are many international microbarograph networks for high-resolution recording of wave pressure variations on the Earth’s surface. This arouses interest in wave propagation in the atmosphere generated by atmospheric pressure variations. A full system of nonlinear hydrodynamic equations for atmospheric gases with lower boundary conditions in the form of wavelike pressure variations on the Earth’s surface is considered. Since the wave amplitudes near the Earth’s surface are small, linearized equations are used in the analysis of well-posedness of the problem. With the help of a wave energy functional method, it is shown that in the non-dissipative case the solution to the boundary value problem is uniquely determined by the variable pressure field on the Earth’s surface. The corresponding dissipative problem is well-posed if, in addition to the pressure field, appropriate conditions on the velocity and temperature on the Earth’s surface are given. In the case of an isothermal atmosphere, the problem admits analytical solutions that are harmonic in the variables x and t. A good agreement between the numerical and analytical solutions is obtained. The study shows that the temperature and density can rapidly vary at the lower boundary of the boundary value problem. An example of solving the three-dimensional problem with variable pressure on the Earth’s surface taken from experimental observations is given. The developed algorithms and computer programs can be used to simulate atmospheric waves generated by pressure variations on the Earth’s surface.

Disturbance in the lower ionosphere that accompanied the reentry of the Chelyabinsk cosmic body

The paper describes quasi-periodic and aperiodic variations in the phase and amplitude of radio waves of LF and VLF ranges, which accompanied the flight and explosion of the Chelyabinsk meteoroid. Quasi-periodic variations in the phase have been explained by the generation of acoustic-gravity waves in the atmosphere, which modulate the electron density in the ionosphere and the phase of radio waves. Aperiodic variations in the phase and amplitude of radio waves are associated with an increase in the electron density in the lower ionosphere (at altitudes of 65–70 km). This increase was most likely caused by the interactions of subsystems in the Earth–atmosphere–ionosphere–magnetosphere system or, more correctly, by the precipitation of high-energy electrons from the magnetosphere into the lower ionosphere, which was stimulated by the flight and explosion of a cosmic body. According to the estimates, the density of the flux of electrons with energies of 100 KeV should be on the order of 106 m–2 s–1.

Numerical study of heating the upper atmosphere by acoustic-gravity waves from a local source on the Earth's surface and influence of this heating on the wave propagation conditions

The propagation of acoustic-gravity waves (AGW) from a source on the Earth's surface to the upper atmosphere is investigated with methods of mathematical modeling. The applied non-linear model of wave propagation in the atmosphere is based on numerical integration of a complete set of two-dimensional hydrodynamic equations. The source on the Earth's surface generates waves with frequencies near to the Brunt-Vaisala frequency. The results of simulation have revealed that some region of heating the atmosphere by propagated upward and dissipated AGWs arises above the source at altitudes nearby of 200 km. The horizontal scale of this heated region is about 1000 km in the case of the source that radiates AGWs during approximately 1 h. The appearing of the heated region has changed the conditions of AGW propagation in the atmosphere. When the heated region in the upper atmosphere has been formed, further a waveguide regime of propagation of waves with the periods shorter the Brunt-Vaisala period is realized. The upper boundary of the wave-guide coincides with the arisen heated region in the upper atmosphere. The considered mechanism of formation of large-scale disturbances in the upper atmosphere may be useful for explanation of connections of processes in the upper and lower atmospheric layers.

Correctness of the problem of propagation of nonlinear acoustic-gravity waves in the atmosphere from pressure variations on the lower boundary

Correctness of the problem of propagation of nonlinear acoustic-gravity waves in the atmosphere from pressure variations on the lower boundary

Disturbances of the upper atmosphere and ionosphere caused by acoustic-gravity wave sources in the lower atmosphere

The results of observations of acoustic-gravity waves in the troposphere and the ionosphere at middle latitudes during periods of passage of the solar terminator are presented. Tropospheric observations were performed using a lidar. The frequency characteristics of variations of the tropospheric parameters are determined based on observations of the intensity of the scattered lidar signal. The characteristics of variations of the total electron content (TEC) in the atmosphere are determined from data collected by GPS navigation satellites. An analysis of the observational data showed that the spectrum of variations of the atmospheric and ionospheric parameters is indicative of acoustic-gravity waves (AGW) propagating from the lower atmosphere. Modeling studies of the vertical propagation of AGW from the Earth’s surface showed that such waves quickly (within ~15 min) reach altitudes of the upper atmosphere (~300 km). The refraction and dissipation of waves in the upper atmosphere produces perturbations of the background state of the atmosphere and gives rise to the waveguide propagation of infrasonic wave components. The observed manifestations of TEC disturbances caused by AGW propagating from the lower atmosphere can be explained by the diurnal variation of the altitude of the ionosphere and the waveguide propagation of infrasonic waves.

Acoustic-gravity waves in the Earth’s atmosphere generated by surface sources

The generation of acoustic-gravity waves and their propagation in the Earth’s atmosphere is analyzed numerically on the basis of a computer model of the stratified atmosphere with dissipation. Atmospheric and ionospheric wavelike disturbances from different surface sources such as earthquakes, explosions, seiches, temperature heating, and tsunamis are studied.

Verifications of the high-resolution numerical model and polarization relations of atmospheric acoustic-gravity waves

Abstract. Comparisons of amplitudes of wave variations of atmospheric characteristics obtained using direct numerical simulation models with polarization relations given by conventional theories of linear acoustic-gravity waves (AGWs) could be helpful for testing these numerical models. In this study, we performed high-resolution numerical simulations of nonlinear AGW propagation at altitudes 0–500 km from a plane wave forcing at the Earth's surface and compared them with analytical polarization relations of linear AGW theory. After some transition time te (increasing with altitude) subsequent to triggering the wave source, the initial wave pulse disappears and the main spectral components of the wave source dominate. The numbers of numerically simulated and analytical pairs of AGW parameters, which are equal with confidence of 95 %, are largest at altitudes 30–60 km at t > te. At low and high altitudes and at t < te, numbers of equal pairs are smaller, because of the influence of the lower boundary conditions, strong dissipation and AGW transience making substantial inclinations from conditions, assumed in conventional theories of linear nondissipative stationary AGWs in the free atmosphere. Reasonable agreements between simulated and analytical wave parameters satisfying the scope of the limitations of the AGW theory prove the adequacy of the used wave numerical model. Significant differences between numerical and analytical AGW parameters reveal circumstances when analytical theories give substantial errors and numerical simulations of wave fields are required. In addition, direct numerical AGW simulations may be useful tools for testing simplified parameterizations of wave effects in the atmosphere.

Exponential and local Lamb waves in the nonisothermal atmosphere as an obstacle to the acoustic-gravity disturbance propagation up to the ionosphere

In this study generalized Lamb waves in a nonisothermal atmosphere have been examined theoretically. Our results suggest that the pressure component of the Lamb wave decreases exponentially upwards near the layer with an extremum of sound speed. We find that local wave disturbances of the wave pressure component are formed in the resonance layer at which the horizontal phase velocity is equal to the sound speed. These resonance layers are the reason for a filtration of atmospheric disturbances. Such filtration is an obstacle to the acoustic-gravity wave propagation up to the ionosphere.

СПУТНИКОВЫЕ ИССЛЕДОВАНИЯ ИОНОСФЕРНЫХ ПРОЯВЛЕНИЙ РАСПРОСТРАНЕНИЯ АКУСТИКО-ГРАВИТАЦИОННЫХ ВОЛН

The response of the ionospheric plasma on the propagation of acoustic-gravity waves (AGW) studied at altitudes of 250 − 350 km using the satellite Dynamics Explorer 2 measurements. Wave perturbations are analyzed according to simultaneously measured data of temperature, concentration and velocity of neutral particles and ions at high and middle latitudes. The following features of ionospheric manifestations of acoustic-gravity waves have been established: 1) relative variations of temperature of neutral particles and ions are roughly the same for these latitudes, except for the regions of auroral ovals; 2) variations in total plasma concentration are antiphase to those in concentration of neutral particles, their relative amplitude being severatimes larger than the amplitude of neutral particles; 3) concentration of molecular ions is in phase with neutral particles;4) vertical velocity of the ions at high latitudes is consistent with that of neutral particles, thus showing their mutual movement along the magnetic field lines. In the high-latitude ionosphere, toseparate the ionospheric manifestations of acoustic-gravity waves from other types of disturbances, the simultaneous analysis of different parameters should be used. Key words: acoustic-gravity waves, moving ionospheric disturbances, auroral zone, ionosphere, atmosphere Manuscript submitted 13.05.2014 Radio phys. radio astron. 2014, 19(3): 206-216 REFERENCES 1. BURMAKA, V.P., TARAN, V. I., andCHERNOGOR, L. F., 2005. Results of the study of wave disturbances in the ionosphere by incoherent scattering. Uspehi sovremennoi radioelectroniki . no. 3, pp. 4–35 (in Russian). 2. LIZUNOV, G. V. and FEDORENKO, A. K., 2006. Atmospheric Gravity Waves Generation by Solar Terminator According to "Atmosphere Explorer-E" Satellite Data. Radio Phys. Radio Astron. , vol. 11, no. 1, pp. 49–62 (in Russian). 3. FEDORENKO, A. K., 2009. Determination Characteristics of Atmospheric Gravity Waves in the Polar Regions Using Mass-Spectrometer Satellite Measurements. Radio Phys. Radio Astron ., vol. 14, no. 3, pp. 254–265 (in Russian). 4. CARIGNAN, G. R., BLOCK, B. P., MAURER, J. C, HEDIN, A. E., REBER, C. A., and SPENCER, N. W., 1981.The neutral mass Spectrometron Dynamics Explorer. Space Sci. Instrum . vol. 5, pp. 429–441. 5. SPENCER, N. W., WHARTON, L. E., NIEMANN, H. B., HEDIN, A. E., CARIGNAN, G. R., and MAURER, J. C., 1981.The Dynamics Explorer wind and temperature spectrometer. Space Sci. Instrum. , vol. 5, pp. 417–428. 6. DUDIS, J. J. and REBER, C. A., 1976. Composition effects in thermospheric gravity waves. Geophys. Res. Lett ., vol. 3, No. 12, pp. 727–730. DOI: https://doi.org/10.1029/GL003i012p00727 7. RATCLIFFE, J. A., 1975. An Introduction to the Ionosphere and Magnetosphere . Moscow: Mir Publ. (in Russian). 8. BRYUNELLI, B. E. and NAMGALADZE, A. A., 1988. Physics of the Ionosphere . Moscow: Nauka Publ. (in Russian). 9. LYATSKY,W. B. and MALTSEV, Y. P., 1983. Magnetosphere-Ionosphere Interaction . Moscow: Nauka Publ. (in Russian).

Three-dimensional numerical simulation of nonlinear acoustic-gravity wave propagation from the troposphere to the thermosphere

Three-dimensional nonlinear breaking acoustic-gravity waves (AGWs) propagating from the Earth's surface to the upper atmosphere are simulated numerically. Horizontally moving periodical structures of vertical velocity on the Earth's surface are used as AGW sources in the model. The 3D algorithm for hydrodynamic equation solution uses finite-difference analogues of basic conservation laws. This approach allows us to select physically correct generalized wave solutions of hydrodynamic equations. The numerical simulation covers altitudes from the ground up to 500 km. Vertical profiles of the mean temperature, density, molecular viscosity, and thermal conductivity are specified from standard models of the atmosphere. Atmospheric waves in a few minutes can propagate to high altitudes above 100 km after activation of the surface wave forcing. Surfaces of constant phases are quasi-vertical first, and then become inclined to the horizon below about 100 km after some transition time interval. Vertical wavelengths decrease with time and tend to theoretically predicted values after times longer than several periods of the wave forcing. Decrease in vertical wavelengths and increase in AGW amplitudes can lead to wave instabilities, accelerations of the mean flow and wave-induced jet streams at altitudes above 100 km. AGWs may transport amplitude modulation of atmospheric wave sources in horizontal directions up to very high levels. Low wave amplitudes in the beginning of transition processes after activation of atmospheric wave sources could be additional reasons for slower amplitude grows with height compared to the nondissipative exponential growth predicted for stationary linear AGWs. Production of wave-induced mean jets and their superposition with nonlinear unstable dissipative AGWs can produce strong narrow peaks of horizontal speed in the upper atmosphere. This may increase the role of transient nonstationary waves in effective energy transport and variations of atmospheric parameters and gas admixtures in a broad altitude range.

Formation of large-scale disturbances in the upper atmosphere caused by acoustic gravity wave sources on the Earth’s surface

The results of a model study of the acoustic gravity wave (AGW) propagation from the Earth’s surface to the upper atmospheric altitudes have been considered. Numerical calculations have been performed using a nonhydrostatic model of the atmosphere, which takes into account nonlinear and dissipative processes originating when waves propagate upward. The model source of atmospheric disturbances has been specified in an area localized on the Earth’s surface. The disturbance source frequency spectrum includes harmonics at frequencies of 0.5ωg-1.5ωg (ωg is the Brunt-Vaisala frequency near the Earth’s surface). The calculations indicated that AGW propagation and dissipation over the source result in the fact that the region of large-scale spatial disturbances of the upper atmosphere mean state is formed at ∼200 km altitudes. This region substantially affects AGW propagation and results in waveguide propagation of AGWs with periods shorter than the Vaisala-Brunt period at the altitude of a disturbed atmosphere. The dissipation of AGWs propagating in such a waveguide results in a waveguide horizontal expansion. The extension of the disturbed region of the mean state of the upper atmosphere and, consequently, the waveguide length can reach ∼1000 km, if the AGW ground source operates for ∼1 h. The physical mechanism by which large-scale disturbances are formed in the upper atmosphere, based on the propagation and dissipation of AGWs with periods shorter than the Vaisala-Brunt period in the upper atmosphere, explains why these disturbances are rapidly generated and localized above AGW sources located on the Earth’s surface or in the lower atmosphere.

Modeling the ionospheric propagation of acoustic gravity waves from the Tohoku tsunami of 2011

The observations of the upper atmosphere after the severe Tohoku earthquake of March 11, 2011 are analyzed. The observations cover the Hawaii region and span the time interval from about 7 h after the main shock to about half an hour before the arrival of the tsunami wave generated this earthquake. We explore the factors that are responsible for the emergence of the ionospheric response, which comprises a series of waves propagating ahead of the tsunami. The contribution of the moving tsunami wave into the formation of such a pre-tsunami response is established by the numerical simulation of the equations of geophysical hydrodynamics with two-dimensional geometry.

Numerical modeling of seismic and acoustic-gravity waves propagation in an “Earth-Atmosphere” model in the presence of wind in the air

In this paper, an effective numerical algorithm for 2.5D seismic and acoustic-gravitational wave propagation is applied to a combined “Earth-Atmosphere” model in the presence of wind in the air. Seismic wave propagation in an elastic half-space is described by a system of first-order dynamic equations of elasticity theory. The propagation of acoustic-gravitational waves in the atmosphere in the presence of wind is described by the linearized Navier-Stokes equations. The algorithm is based on the integral Laguerre transform with respect to time, the finite integral Fourier transform with respect to a spatial coordinate combined with a finite difference method for the reduced problem.

Observed features of acoustic gravity waves in the heterosphere

According to measurements on the Dynamic Explorer 2 satellite, features of the propagation of acoustic gravity waves (AGWs) in the multicomponent upper atmosphere have been investigated. In the altitude range 250–400 km in wave concentration variations of some atmospheric gases, amplitude and phase differences have been observed. Using the approach proposed in this paper, in different gases, AGW variations have been divided into components associated with elastic compression, adiabatic expansion, and the vertical background distribution. The amplitude and phase differences observed in different gases are explained on the basis of analyzing these components. It is shown how to use this effect in order to determine the wave propagation, the vertical displacement of the volume element, the wave frequency, and the spatial distribution of the wave energy density.

Numerical modeling of the propagation of nonlinear acoustic-gravity waves in the middle and upper atmosphere

A numerical algorithm for modeling the vertical propagation and breaking of nonlinear acoustic-gravity waves (AGWs) from the Earth’s surface to the upper atmosphere is described in brief. Monochromatic variations in the vertical velocity at the Earth’s surface are used as an AGW source in the model. The algorithm for solving atmospheric hydrodynamic equations is based on three-dimensional finite-difference analogues of fundamental conservation laws. This approach selects physically correct generalized solutions to hydrodynamic equations. A numerical simulation is carried out in an altitude region from the Earth’s surface to 500 km. Vertical profiles of the background temperature, density, and coefficients of molecular viscosity and heat conduction are taken from the standard atmosphere models. Calculations are made for different amplitudes of lower-boundary wave forcing. The AGW amplitudes increase with altitude, and waves may break in the middle and upper atmosphere.

Numerical Modeling of the Propagation of Nonlinear Acoustic-Gravity Waves in the Middle and Upper Atmosphere

Numerical Modeling of the Propagation of Nonlinear Acoustic-Gravity Waves in the Middle and Upper Atmosphere