Propagation Of Acoustic-gravity Waves Research Articles

A linearized coupled model of acoustic-gravity waves and the lower ionosphere at Mars

Highly variable ionospheric structures were recently detected on Mars using spacecraft measurements. Acoustic-gravity waves (AGWs) could be the underlying mechanism. Studying the response of the Martian ionosphere to AGWs could provide us with an important understanding of the neutral wave--ionospheric coupling processes. We developed a linearized wave model to explore the plasma--neutral coupling driven by AGWs in the lower ionosphere of Mars. This model can describe the propagation and dissipation of AGWs in a realistic atmosphere and is the first of its kind to incorporate plasma behaviors associated with photochemistry and electromagnetic fields. We adopted a full-wave model as the first part of our coupled model to delineate wave propagation in a realistic atmosphere. The second part of our model consists of the governing equations describing the plasma behaviors. Therefore, our model not only replicates the result of the full-wave model, but can also be used to investigate the wave-driven variations in the plasma velocity and density, electromagnetic field, and thermal structures. Our model results reveal that ions are mainly dragged by neutrals and oscillate along the wave phase line below sim 200 km altitude. Electrons are primarily subject to gyro-motion along the magnetic field lines. The wave-driven distinct motions among charged particles can generate the perturbed electric current and electric field, further contributing to localized magnetic field fluctuations. Major charged constituents, including electrons, O$^ $, O$_ $, and CO$_ $, have higher density amplitudes when interacting with waves of larger periods. The presence of photochemistry leads to a decrease in the plasma density amplitude, and there exists a moderate correlation between the density variations of plasma and those of neutrals. Our numerical results indicate that the wave-driven variations range from several percent to sim 80<!PCT!> in the plasma density and from sim 0.2<!PCT!> to 17<!PCT!> in the magnetic field, values that are consistent with the spacecraft observations. Further calculations reveal that the wave-induced plasma--neutral coupling can heat the neutrals yet cool the plasmas. Electrons are cooler than ions in the coupling process. The wave-driven heating by neutral--ion collisions exceeds that by neutral--electron collisions but tends to be lower than the wave dissipative heating and photochemical heating. Our model has potential applications in studying the AGW-driven variable ionospheric structures and can be used for other planets.

Propagation of Acoustic-Gravity Waves in Inhomogeneous Wind Flows of the Polar Atmosphere

Propagation of Acoustic-Gravity Waves in Inhomogeneous Wind Flows of the Polar Atmosphere

ABOUT ONE PROPERTY OF THE DISPERSION EQUATION FOR LATITUDINAL ACOUSTIC-GRAVITATIONAL WAVES

Acoustic-gravity waves are an example of processes that largely determine the dynamics of the Earth’s atmosphere. This is due to the fact that the sources of these waves are located throughout the height of the atmosphere, from the very “bottom”, where earthquakes, volcanic emissions, tsunamis, tornadoes, etc., occur, and to the very “top”, where perturbations of the solar wind, magnetic storms, and precipitation of particles in high latitudes are active. All these phenomena lead to the active energy exchange between all layers of the Earth’s atmosphere and the interaction of wave disturbances of significantly different scales — from several thousand kilometers to several hundred meters, and this — to the appearance and development of processes of convection and turbulence in the environment. It seems that only nonlinear processes should dominate under such conditions. To a large extent, it is true, but at the same time, observations indicate that in many cases in the process of propagation of acoustic-gravity waves (AGW), the effects can be comprehensively described within the framework of the linear approximation of perturbation theory and well-developed theory of oscillations. At the same time, when creating models of the process, it turned out to be appropriate to use sufficiently justified physical approximations, such as isothermality of the atmosphere, its unlimitedness in the horizontal direction and compressibility in the vertical direction. Taking into account the real scales of the AGW, it is possible to neglect the curvature of the Earth’s surface and consider it locally flat at any point of the surface and use the Cartesian coordinate system X, Y, Z in the calculations. To describe the environment, it makes sense to use non-dissipative hydrodynamics and in an equilibrium state — the hydrostatic equilibrium equation and barometric equation. The above-mentioned approximations and the mathematical apparatus of the theory of oscillations and the theory of differential equations allow when studying the initial system of equations describing the dynamics of AGW, to obtain a dispersion equation in the form of a polynomial of the fourth degree relative to the angular frequency of rotation as a function of the normalized wave vector of disturbance k  (AGW). AGW spectrum is a spectrum of the atmosphere’s own oscillations in the form ( ) k  , and its obtaining can be considered as the final solution to the initial problem if we ignore the obvious influence on the AGW spectrum of the angular frequency of rotation of the atmosphere , which must necessarily be present in the dispersion equation due to the influence of the Coriolis force. The formal reason for the absence of the components of the vector  in the dispersion equation (DE) is the fact that the | |   is a minimum of two orders of magnitude smaller than the characteristic rotation frequency of the atmosphere 0 , which is equal to the acoustic cutoff frequency. At the same time, the improvement of modern atmospheric observation equipment places increases the requirements for the accuracy of DE model solutions. In this sense, the resolution of DE in the work [Cheremnykh O. K. et al. Kinematics and Phys. Celestial Bodies. 2020. 36, № 2. P. 64—78] can be considered as a “zero-order” solution with a small parameter 0    | |/  . In addition, according to the method of obtaining, this solution is approximate. By definition, the solution obtained in the work [Cheremnykh O. K. et al. Kinematics and Phys. Celestial Bodies, 2022. 38, № 3. P. 121—131] by taking into account terms   0 in the modified DE is more accurate. But it is also approximate, although more accurate. In this work, we study in detail the dispersion equation for latitudinal AGW. The need for such consideration, as will be shown, is a consequence of the structure of this equation, namely the presence of a linear frequency term in it. Preliminary analysis showed that existing mathematical methods do not provide an unambiguous solution to this equation. This suggests the need to study possible solutions of the equation in terms of their coincidence with previously obtained ones for some partial cases. Such research allows us to choose the right decision. In the proposed study, we have shown that the Euler-Lagrange method allows, under certain additional conditions, to obtain an exact solution of the modified equation for AGW in closed analytical form.

Approximation of Small Amplitude Waves Short in Vertical in the Atmosphere Taking Into Account the Average Wind

Using the method of different scales, formulas for the hydrodynamic fields of acoustic-gravity waves (AGWs) with vertical wavelengths small compared to the scales of changes in the background temperature and wind fields are derived. These formulas are equivalent to the conventional WKB approximation, but explicitly include the vertical gradients of the background fields. The conditions for the applicability of the obtained formulas for describing the propagation of AGWs from the troposphere to the thermosphere are formulated and analyzed. The absence of singular points (critical levels) in the equations for wave modes in the analyzed height range is one of the conditions for the applicability of approximate formulas. For the wind from the empirical HWM model, singular points are often located below 200 km and are typical for internal gravity waves (IGWs), with lengths of the order of 10 km. As the wavelength increases, the number of singular points decreases. For IGWs with scales on the order of 300 km or more, there are usually no singular points. It is shown that IGWs with periods of less than 20 min propagating upward from tropospheric heights usually have one turning point in the altitude range from 100 to 130 km. The obtained formulas are useful, in particular, for parametrization of AGW effects in numerical models of atmospheric dynamics and energy.

Modeling of infrasonic and acoustic-gravity wave propagation, nonlinear evolution, and observable effects

Mechanical disturbances associated with hazardous events—e.g., earthquakes, explosions (volcanic or man-made)—and severe weather – generate broad spectra of infrasound and acoustic-gravity waves (AGWs). These wave signals may provide diagnostic insight into the processes that generated them. They are routinely detected as fluctuations in atmospheric pressure, measured at ground or from balloon-borne platforms; at lower frequencies (<1 Hz), and where they may attain sufficient amplitudes at high altitudes, they may also be measured via the fluctuations that they impose in densities of layered species throughout the atmosphere and ionosphere. Thus, they provide complementary remote sensing opportunities, where waves and their effects, especially above and surrounding larger sources, may be diagnosed as they propagate. We review recent progress and techniques for high-fidelity modeling and simulation, to capture the propagation and evolution of low-frequency infrasound and AGWs throughout the atmosphere, from 0–500 km altitude (from surface to exobase). Strategies to (1) efficiently extend model simulation domains well into the diffusive thermosphere, to (2) connect models of atmospheric dynamics to those for other measurable processes (e.g., the ionosphere), and to (3) construct simulations that extend from source processes to specific remote sensing methodologies are discussed.

The Influence of the Earth’s Atmosphere Rotation on the Spectrum of Acoustic-Gravity Waves

It was shown in a recent study [11] that taking into account the rotation of the Earth’s atmosphere leads to the appearance of a new region of evanescent waves with a continuous frequency spectrum on the diagnostic diagram of acoustic-gravity waves. The region is located below the lower limit of gravity waves, which is equal to $$2\Omega $$ for all wavelengths, where $$\Omega $$ is the angular frequency of the atmospheric rotation. This result was obtained for high-latitude regions of the atmosphere in which one can be limited to considering only the vertical component of the Earth’s rotation frequency. This paper shows that taking into account both components of the vector $$\vec {\Omega }$$ of the atmospheric rotation frequency $$\vec {\Omega }$$ —horizontal, $$\Omega \cos \varphi ,$$ where $$\varphi $$ is the local latitude, and vertical, $$\Omega \sin \varphi $$ —the dominant role in the acoustic-gravity wave propagation is played by the vertical component. It is shown that the horizontal component leads to a negligible modification of the boundaries of the regions of acoustic and gravity waves on the diagnostic diagram. It is also shown that the vertical component of the frequency affects most strongly the lower limit of gravity waves, which depends on the latitude of the observation site for all wavelengths and is equal to 2 $$\Omega \sin \varphi $$ .

Influence of the Earth’s atmosphere rotation on the spectrum of acoustic-gravity waves

It was shown in a recent paper by Cheremnykh et al. (Advances in Space Research, 2022) that taking into account the rotation of the Earth's atmosphere leads to the appearance of a new region of evanescent waves with a continuous frequency spectrum on the diagnostic diagram of acoustic-gravity waves. The region is located below the lower limit of gravity waves, which is equal $2\Omega$ at all wavelengths, where $\Omega$ is the angular frequency of the atmosphere rotation. This result was obtained for high-latitude regions of the atmosphere, in which we can limit ourselves to considering only the vertical component of the Earth's rotation frequency. In the proposed paper we show that taking into account both components of the vector of the atmosphere rotation frequency $\overrightarrow{\Omega}$ - horizontal, $\Omega\cos\varphi$ , and vertical, $\Omega\sin\varphi$, where $\varphi$ is the Earth`s latitude, the dominant role in the acoustic-gravity waves propagation is played by the vertical component. It is shown that the horizontal component leads to an insignificant modification on the diagnostic diagram of the boundaries of the areas of acoustic and gravity waves, which can be neglected. Also shown that the strongest vertical component of the frequency affects the lower limit of gravity waves, which depends at all wavelengths on the latitude of the observation site and is equal to $2\Omega\sin\varphi$.

The effect of compressed ice-shelf on acoustic-gravity wave propagation in a compressible ocean having elastic bottom

Acoustic-gravity wave propagation under a compressed ice-shelf is mathematically modelled under the assumption of small ice-shelf deflection, linearised compressible water wave theory, and ocean floor elasticity. The dispersion relation associated with the acoustic-gravity modes is derived. Special cases of the free surface gravity wave motion with a rigid and elastic bottom, and flexural-gravity wave motion with rigid ocean bottom are approximated by utilising the dispersion relation. The effect of ice-shelf thickness and compressive stress on the propagation speed is investigated for different acoustic-gravity modes. The pressure distribution along the water column and the ice-shelf due to different acoustic-gravity modes are illustrated. While ice thickness significantly alters the phase speed and pressure distribution, the compressive force generally has a negligible effect on the phase speed of acoustic-gravity modes. However, the compression has significant effect on the pressure distribution. A separate treatment for relatively low frequencies shows a significant impact of the compressive force on the spatial pressure distribution. The dominance of the leading acoustic-gravity modes on different physical characteristics is evident from their graphical representations. An orthogonality property for the depth-dependent functions of the velocity potential in the water region is established along with a few approximate forms. This mathematical model can be treated as a more general one that can unify several well-established models of acoustic-gravity wave propagation.

Thermospheric disturbances caused by the propagation of acoustic-gravity waves from the lower atmosphere during a solar eclipse

The paper studies disturbances of the upper thermosphere caused by the vertical propagation of acoustic-gravity waves (AGW) from the lower atmosphere during the solar eclipse on March 20, 2015. The experimentally obtained data on pressure variations near the Earth’s surface during the solar eclipse on March 20, 2015 over Kaliningrad ( 54 ° N , 20 ° E ) are used as the source of waves. The calculation results showed that the passage of a solar eclipse is accompanied by an increase in wave activity in the lower atmosphere in the AGW range with periods of ~ 4–20 min. In the thermosphere, at altitudes of ~ 200 km, disturbances are formed due to the dissipation of AGWs coming from the lower atmosphere. These disturbances have characteristic periods of ~ 50 min and propagate in opposite direction to the movement of the solar eclipse region along the Earth’s surface. The obtained characteristic features of disturbances in the upper atmosphere are in qualitative agreement with the results of observations of ionospheric disturbances during a solar eclipse.

IMPACT OF METEOROLOGICAL STORMS ON THE E-REGION OF THE IONOSPHERE IN 2017–2018

The paper presents the results of observations of the sporadic Es layer during the period of meteorological disturbances in Kaliningrad in October 2017 and 2018 under quiet geomagnetic conditions. During the meteorological storms (October 29–30, 2017 and October 23–24, 2018), significant changes occurred in the dynamics of the Es-layer critical frequency. Observations of atmospheric and ionospheric disturbances in the Kaliningrad region show that the delay between the ionospheric response and the moment of maximum disturbances in atmospheric parameters is about 3 hours. These phenomena at the heights of the E-region might have been caused by propagation of acoustic-gravity waves generated by convective processes in the lower atmosphere during periods of a meteorological storm. Intensification of turbulent processes in the lower thermosphere leads to an increase in the atmospheric density and, accordingly, to higher recombination rates. This leads to a rapid decrease in the concentration of ions and, consequently, to a decrease in the critical frequency of the sporadic layer below the sensitivity threshold of ionosondes.

Влияние метеорологических штормов на область Е ионосферы в 2017–2018 гг

The paper presents the results of observations of the sporadic Es layer during the period of meteorological disturbances in Kaliningrad in October 2017 and 2018 under quiet geomagnetic conditions. During the meteorological storms (October 29–30, 2017 and October 23–24, 2018), significant changes occurred in the dynamics of the Es-layer critical frequency. Observations of atmospheric and ionospheric disturbances in the Kaliningrad region show that the delay between the ionospheric response and the moment of maximum disturbances in atmospheric parameters is about 3 hours. These phenomena at the heights of the E-region might have been caused by propagation of acoustic-gravity waves generated by convective processes in the lower atmosphere during periods of a meteorological storm. Intensification of turbulent processes in the lower thermosphere leads to an increase in the atmospheric density and, accordingly, to higher recombination rates. This leads to a rapid decrease in the concentration of ions and, consequently, to a decrease in the critical frequency of the sporadic layer below the sensitivity threshold of ionosondes.

Acoustic-gravity wave propagation characteristics in three-dimensional radiation hydrodynamic simulations of the solar atmosphere.

There has been tremendous progress in the degree of realism of three-dimensional radiation magneto-hydrodynamic simulations of the solar atmosphere in the past decades. Four of the most frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D and MURaM. Here we test and compare the wave propagation characteristics in model runs from these four codes by measuring the dispersion relation of acoustic-gravity waves at various heights. We find considerable differences between the various models. The height dependence of wave power, in particular of high-frequency waves, varies by up to two orders of magnitude between the models, and the phase difference spectra of several models show unexpected features, including ±180° phase jumps. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

Generation of magnetic field in the low-latitude ionosphere by tsunami wave

The travel of a tsunami wave is accompanied by generation of geomagnetic field perturbation and acoustic-gravity wave (AGW) propagating into the ionosphere. We consider a mechanism of electric current generation by the tsunami wave in the ocean and ionosphere. The electric current in the ocean is generated by motion of conducting seawater in geomagnetic field, and in the conducting ionosphere it is generated by AGW propagation from the atmosphere. The electric current in the ionosphere may be greater than in the seawater due to exponential increase of amplitude of the upward-propagating AGW. The equations of magnetic field in the “ocean-atmosphere-ionosphere” model in the inclined magnetic field were derived. The spatial distribution of the magnetic field perturbation in the atmosphere and ionosphere was calculated. It is shown that the electric current in the ionosphere significantly changes the geomagnetic field perturbation. An influence of the geomagnetic field inclination on its perturbation is analyzed. Our results demonstrate a possibility of satellite monitoring of tsunami wave based on recording electromagnetic field in the middle and low latitudes.

Influence of Vertical Heterogeneity of Atmospheric Temperature on the Propagation of Acoustic-Gravity Waves

A new approach to the study of acoustic-gravity waves in the Earth’s atmosphere in the presence of vertical temperature inhomogeneity is proposed. Using this approach, the local AGW dispersion equation was obtained for the atmosphere with a small vertical temperature gradient. The modification of the acoustic and gravitational regions of freely propagating AGWs on the spectral plane $$\left( {\omega ,{{k}_{x}}} \right)$$ depending on the temperature gradient was investigated. It is shown that the acoustic and gravitational regions approach each other with a positive temperature gradient, while the distance between them increases with a negative gradient. On the spectral plane, the indicators of the location of the acoustic and gravitational regions of freely propagating AGWs are the dispersion curves of the non-divergent and inelastic horizontal wave modes. The possibility of overlapping the acoustic and gravitational regions of AGWs in a nonisothermal atmosphere was investigated.

Influence of vertical heterogeneity of the atmosphere temperature on the propagation of acoustic-gravity waves

A new approach to the study of acoustic-gravity waves (AGW) in the Earth’s atmosphere in the presence of a vertical temperature inhomogeneity is proposed. Using this approach, the local AGW dispersion equation is obtained for an atmosphere with a small vertical temperature gradient. The modification of acoustic and gravitational regions of freely propagating AGWs on the spectral plane is studied depending on the temperature gradient. It is shown that, the acoustic and gravitational regions approach each other with a positive temperature gradient and the distance between them increases with a negative gradient. On the spectral plane, the dispersion curves of non-divergent and anelastic horizontal wave modes are the indicators of location of the acoustic and the gravitational regions of freely propagating AGWs. The possibility of overlapping the acoustic and the gravitational regions of AGWs in non-isothermal atmosphere is investigated.

Meteorological Storm Influence on the Ionosphere Parameters

This paper presents the observations of ionospheric parameters in Kaliningrad (54° N, 20° E) during a meteorological storm in the Baltic Sea during October 2017 and 2018. Analysis of the total electronic content (TEC) during the storm showed that perturbations of the TEC values from the median can reach two standard deviations of the value. For the critical frequency of the F2 layer, it was 1.5–1.6 times the standard deviations. On days of a meteorological storm, significant changes were noted in the dynamics of the E-layer’s critical frequency. The reasons for the occurrence of the observed phenomena were due to the propagation of acoustic-gravity waves generated by convective processes in the lower atmosphere during periods of a meteorological storm. Spectral analysis of TEC variations revealed an increase in the amplitudes of ionospheric variations 10–16 min over the area of a meteorological storm. The analysis allowed us to conclude that ionospheric perturbations during the meteorological perturbation were caused by increased acoustic-gravity wave (AGW) generation processes in the lower atmosphere. The most likely cause of negative ionospheric disturbances were processes associated with the dissipation of AGW propagating from the area of a meteorological storm and increased turbulence in the lower thermosphere.

Simulation of Propagation of Acoustic-Gravity Waves Generated by Tropospheric Front Instabilities into the Upper Atmosphere

A numerical model of the propagation of acoustic-gravity waves excited by pressure fluctuations on the Earth’s surface is developed. Propagation of acoustic-gravity waves generated by instabilities of tropospheric fronts into the upper atmosphere is simulated. The experimental data on atmospheric pressure variations during 2016 year registered on a net of four microbarographs located in the Moscow region are processed. A case of very significant pressure fluctuations (up to 30 times larger than the average level) is selected, which were caused by an atmospheric front arrival. Observed surface pressure field variations for this field were approximated and used as the lower boundary condition for simulating the vertical wave propagation. The numerical simulations showed that just after the boundary source activation, the infrasonic waves in the upper atmosphere may have amplitudes of perturbations of temperature up to 100 K, and horizontal velocity up to 60 m/s. Internal gravity waves come into the upper atmosphere later and far horizontally away from the wave source. The influence of the limited dimensions of the computational domain on the simulation results is investigated. The conditions at the horizontal boundaries of the computational domain, which allow the runaway of waves beyond the domain are proposed. The frequency spectrum of waves in the non-isothermal atmosphere is analyzed.

Vertical Propagation of Acoustic Gravity Waves from the Lower Atmosphere during a Solar Eclipse

This paper presents the results of the analysis of a numerical experiment on the generation of acoustic gravity waves (AGWs) in the lower atmosphere and their propagation into the upper atmosphere. The observed variations in atmospheric pressure during the passage of a solar eclipse on March 20, 2015, over Kaliningrad (54° N, 20° E) are considered the be a wave source. The calculation results showed that the passage of a solar eclipse is accompanied in the lower atmosphere by an increase in wave activity in the AGW range with periods of ~4–20 min. In the upper atmosphere, at altitudes of ~200 km, disturbances are formed due to the dissipation of AGWs coming from the lower atmosphere; these disturbances propagate with characteristic periods of ~50 min. The propagation direction of these disturbances was opposite to the propagation direction of the solar eclipse region along the Earth’s surface. The results of the numerical experiment are in qualitative agreement with the results of observations of ionospheric disturbances during the solar eclipse on March 20, 2015.

Vertical propagation acoustic-gravity waves from atmospheric fronts into the upper atmosphere

Using experimental observations of atmospheric pressure variations on the Earth’s surface recorded with a network of 4 microbarographs located in the Moscow region during the passage of an atmospheric front, empirical approximations of oscillations of atmospheric pressure field were constructed. The obtained approximating functions were used as the lower boundary condition for the numerical simulation of acoustic-gravity wave propagation to the upper atmosphere from the source in the lower troposphere. Estimates of the amplitude of temperature disturbances in the upper atmosphere caused by iacoustic gravity waves from the atmospheric front are given. The obtained estimates for the temperature disturbance amplitude take values around 170 K. The amplitude of temperature disturbances in the upper atmosphere, caused by background variations of pressure on the Earth's surface, is estimated at 4-5 K.

Vertical Propagation of Acoustic-Gravity Waves from Atmospheric Fronts into the Upper Atmosphere

Vertical Propagation of Acoustic-Gravity Waves from Atmospheric Fronts into the Upper Atmosphere