Atmospheric Acoustic-gravity Waves Research Articles

Ionospheric Perturbations after Stromboli Volcano Eruptions

Based on data from ground-based vertical sounding of the ionosphere, we analyze disturbances in the region of the maximum of the ionospheric F2-layer during the period of a strong eruption of the Stromboli volcano (Italy) in the form of two explosions in July and August 2019, as well as after the resumption of volcanic activity on October 9, 2022. As characteristics of the ionospheric response to these events, we research variations in the critical frequency of the F2-layer at the Giebilmann, Rome, and San Vito stations located near (no further than 450 km) the volcano. The measurement results indicate the influence on the ionosphere of atmospheric acoustic-gravity waves generated by volcanic activity and causing the appearance of long-lived disturbances in the ionosphere.

Multi‐Layer Evolution of Acoustic‐Gravity Waves and Ionospheric Disturbances Over the United States After the 2022 Hunga Tonga Volcano Eruption

AbstractThe Hunga‐Tonga Hunga‐Ha'apai volcano underwent a series of large‐magnitude eruptions that generated broad spectra of mechanical waves in the atmosphere. We investigate the spatial and temporal evolutions of fluctuations driven by atmospheric acoustic‐gravity waves (AGWs) and, in particular, the Lamb wave modes in high spatial resolution data sets measured over the Continental United States (CONUS), complemented with data over the Americas and the Pacific. Along with >800 barometer sites, tropospheric observations, and Total Electron Content data from >3,000 receivers, we report detections of volcano‐induced AGWs in mesopause and ionosphere‐thermosphere airglow imagery and Fabry‐Perot interferometry. We also report unique AGW signatures in the ionospheric D‐region, measured using Long‐Range Navigation pulsed low‐frequency transmitter signals. Although we observed fluctuations over a wide range of periods and speeds, we identify Lamb wave modes exhibiting 295–345 m s−1 phase front velocities with correlated spatial variability of their amplitudes from the Earth's surface to the ionosphere. Results suggest that the Lamb wave modes, tracked by our ray‐tracing modeling results, were accompanied by deep fluctuation fields coupled throughout the atmosphere, and were all largely consistent in arrival times with the sequence of eruptions over 8 hr. The ray results also highlight the importance of winds in reducing wave amplitudes at CONUS midlatitudes. The ability to identify and interpret Lamb wave modes and accompanying fluctuations on the basis of arrival times and speeds, despite complexity in their spectra and modulations by the inhomogeneous atmosphere, suggests opportunities for analysis and modeling to understand their signals to constrain features of hazardous events.

Multiyear variations of time-correlated mesoscale OH temperature perturbations near the mesopause at Maymaga, Tory and Zvenigorod

Ground-based observations of the natural hydroxyl (OH) nightglow at altitudes of 85–90 km are used for deriving the rotational temperature of excited OH, which is close to the neutral atmospheric temperature. For filtering of mesoscale perturbations, we use differences between pairs of measured values of OH rotational temperature separated with fixed time intervals in the range of 0.5–2 h. The filtering is applied for studying mesoscale variations of temperature near the mesopause according to the data of spectral OH nightglow measurements at observatories of Zvenigorod (56°N, 37°E.) in the years 2004–2016, Tory (52°N, 103°E) in 2012–2017 and Maymaga (63°N, 130°E) in 2000–2015. Monthly-mean values and variances of temperature disturbances with periods 0.7–8.2 h are determined. Semiempirical and statistical approaches are used to estimate and subtract variances of the instrumental dark current noise and uncorrelated in time fluctuations. Seasonal and interannual variations in standard deviations of correlated in time mesoscale perturbations of the OH rotational temperature at the considered observational sites are studied. They can give information about multiyear changes in the activity of atmospheric acoustic-gravity waves propagating through the OH layer near the mesopause.

The characteristics of the 2022 Tonga volcanic tsunami in the Pacific Ocean

Abstract. On 15 January 2022, an exceptional eruption of the Hunga Tonga–Hunga Ha'apai volcano generated atmospheric and tsunami waves that were widely observed in the oceans globally, gaining remarkable attention from scientists in related fields. The tsunamigenic mechanism of this rare event remains enigmatic due to its complexity and lack of direct underwater observations. Here, to explore the tsunamigenic mechanisms of this volcanic tsunami event and its hydrodynamic processes in the Pacific Ocean, we conduct statistical analysis and spectral analysis of the tsunami recordings at 116 coastal gauges and 38 deep-ocean buoys across the Pacific Ocean. Combined with the constraints of some representative barometers, we obtain the plausible tsunamigenic origins of the volcano activity. We identify four distinct tsunami wave components generated by air–sea coupling and seafloor crustal deformation. Those tsunami components are differentiated by their different propagating speeds or period bands. The first-arriving tsunami component with an ∼ 80–100 min period was from shock waves spreading at a velocity of ∼ 1000 m s−1 in the vicinity of the eruption. The second component with extraordinary tsunami amplitude in the deep ocean was from Lamb waves. The Lamb wave with a ∼ 30–40 min period radically propagated outward from the eruption site with spatially decreasing propagation velocities from ∼ 340 to ∼ 315m s−1. The third component with a ∼ 10–30 min period was probably from some atmospheric-gravity-wave modes propagating faster than 200 m s−1 but slower than Lamb waves. The last component with a ∼ 3–5 min period originated from partial caldera collapse with dimension of ∼ 0.8–1.8 km. Surprisingly, the 2022 Tonga volcanic tsunami produced long oscillation in the Pacific Ocean which is comparable with that of the 2011 Tohoku tsunami. We point out that the long oscillation is associated not only with the resonance effect with the atmospheric acoustic-gravity waves but more importantly with their interactions with local bathymetry. This rare event also calls for more attention to the tsunami hazards produced by an atypical tsunamigenic source, e.g. volcanic eruption.

Destructive Potential of Planetary Meteotsunami Waves beyond the Hunga Tonga–Hunga Ha‘apai Volcano Eruption

Abstract Worldwide tsunamis driven by atmospheric waves—or planetary meteotsunami waves—are extremely rare events. They mostly occur during supervolcano explosions or asteroid impacts capable to generate atmospheric acoustic-gravity waves including the Lamb waves that can circle the globe multiple times. Recently, such ocean waves have been globally recorded after the Hunga Tonga–Hunga Ha‘apai volcano eruption on 15 January 2022, but did not pose any serious danger to the coastal communities. However, this study highlights that the mostly ignored destructive potential of planetary meteotsunami waves can be compared to the well-studied tsunami hazards. In practice, several process-oriented numerical experiments are designed to force a global ocean model with the realistic atmospheric response to the Hunga Tonga–Hunga Ha‘apai event rescaled in speed and amplitude. These simulations demonstrate that the meteotsunami surges can be higher than 1 m (and up to 10 m) along more than 7% of the world coastlines. Planetary meteotsunami waves thus have the potential to cause serious coastal damages and even human casualties during volcanic explosions or asteroid impacts either releasing intense acoustic energy or producing internal atmospheric gravity waves triggering the deep-ocean Proudman resonance at a speed of ∼212 m s−1. Based on records of catastrophic events in Earth’s history, both scenarios are found to be realistic, and consequently, the global meteotsunami hazards should now be properly assessed to prepare for the next big volcanic eruption or asteroid impact even occurring inland.

Qualitative Analysis of a Hyperchaotic Lorenz-Stenflo Mathematical Model via the Caputo Fractional Operator

The Lorenz-Stenflo mathematical model describes a complex dynamical behavior related to atmospheric acoustic-gravity waves. In this study, qualitative analysis of the four-dimensional hyperchaotic Lorenz-Stenflo system via the Caputo fractional derivative is implemented. By using the Matignon stability criterion, the local stability analysis of the system showed that all the equilibrium points of the system are locally unstable. Calculation of the Lyapunov exponents along with the relevant bifurcation diagrams with respect to different fractional orders exposed the hyperchaotic dynamical behavior for the system. Bifurcation diagrams for all the four parameters in the system also showed the hyperchaotic nature of the Lorenz-Stenflo system. Different phase attractors of the system corresponding to different fractional derivatives and parameters are presented to specify the dynamical nature of the system. The Lorenz-Stenflo system showed sensitivity to initial conditions. The master and slave systems showed a strong correlation among themselves, as verified by graphs of time series solutions of the two systems.

On the Geomagnetic Field Line Resonance Eigenfrequency Variations during Seismic Event

In this paper, we report high statistical evidence for a seismo–ionosphere effects occurring in conjunction with an earthquake. This finding supports a lithosphere-magnetosphere coupling mechanism producing a plasma density variation along the magnetic field lines, mechanically produced by atmospheric acoustic gravity waves (AGWs) impinging the ionosphere. We have analysed a large sample of earthquakes (EQ) using ground magnetometers data: in 28 of 42 analysed case events, we detect a temporary stepwise decrease (Δf) of the magnetospheric field line resonance (FLR) eigenfrequency (f*). Δf decreases of ∼5–25 mHz during ∼20–35 min following the time of the EQ. We present an analytical model for f*, able to reproduce the behaviour observed during the EQ. Our work is in agreement with recent results confirming co-seismic direct coupling between lithosphere, ionosphere and magnetosphere opening the way to new remote sensing methods, from space/ground, of the earth seismic activity.

Complex Dynamical Behaviors of Lorenz-Stenflo Equations

A mathematical chaos model for the dynamical behaviors of atmospheric acoustic-gravity waves is considered in this paper. Boundedness and globally attractive sets of this chaos model are studied by means of the generalized Lyapunov function method. The innovation of this paper is that it not only proves this system is globally bounded but also provides a series of global attraction sets of this system. The rate of trajectories entering from the exterior of the trapping domain to its interior is also obtained. Finally, the detailed numerical simulations are carried out to justify theoretical results. The results in this study can be used to study chaos control and chaos synchronization of this chaos system.

Qualitative behaviors of the high-order Lorenz-Stenflo chaotic system arising in mathematical physics describing the atmospheric acoustic-gravity waves

The boundedness of chaotic systems plays an important role in investigating the stability of the equilibrium, estimating the Lyapunov dimension of attractors, the Hausdorff dimension of attractors, the existence of periodic solutions, chaos control, and chaos synchronization. However, as far as the authors know, there are only a few papers dealing with bounds of high-order chaotic systems due to their complex algebraic structure. To sort this out, in this paper, we study the bounds of a high-order Lorenz-Stenflo system arising in mathematical physics. Based on Lyapunov stability theory, we show that there exists a globally exponential attractive set for this system. The innovation of the paper is that we not only prove that this system is globally bounded for all the parameters, but also give a family of mathematical expressions of global exponential attractive sets of this system with respect to its parameters. We also study some other dynamical characteristics of this chaotic system such as invariant sets and chaotic behaviors. To justify the theoretical analysis, we carry out detailed numerical simulations.

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

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.

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.

Analysis of the Spatial Coherence of Short-Period Acoustic-Gravity Waves in the Atmosphere

Summary The coherence of atmospheric acoustic-gravity waves has been measured in the period range 10–100 s at the Large Aperture Microbarograph Array in south-eastern Montana. The acoustic-gravity waves observed were signals generated by presumed nuclear explosions. The decrease of coherence with increasing distance between pairs of microbarographs is less rapid in the direction of wave propagation than transverse to it. Variation of direction of arrival over a small range of azimuth (±5°) explains the spatial behaviour of coherence in the direction normal to the wave propagation; variation of phase velocity of ±10 ms-1 explains the behaviour along the direction of wave propagation. Both effects may be due to inhomogeneities in the atmosphere; the velocity variation may be due to the presence in the signal of several normal modes of acoustic- gravity waves, each travelling at a slightly different phase velocity in the range 300–330 ms-1.

Ionosphere F2-region under the influence of the evolutional atmospheric gravity waves in horizontal shear flow

The ambipolar diffusion equation for the height distribution of electron density in the ionospheric F2-layer is solved in the presence of neutral horizontal shear flow. By using this nonstationary solution the reaction of the F2-region electron density on the evolution of atmospheric acoustic–gravity waves (AGW) is investigated. The evolution of the AGW and the corresponding behaviour of the height distribution of the F2-region electron density are described by the characteristic time, t a, of transient development of shear waves in the horizontal shear flow. For long times t > t a, the gravity wave frequency tends to the isothermal Brunt–Väisälä frequency, which appears in the F2-layer as wavelike behaviour of h m F2 and N m F2 with periods close to 16–20 min, when the scale height of the neutral gas is H = 60 km. The shear wave, which is due to the presence of horizontal shear flow, gives sufficient changes of the height profile of electron density for times of t ⩽ t a.

Amplification/damping processes of atmospheric acoustic-gravity waves in horizontal winds with linear shear

The time-varying frequencies and amplification/damping rate (ADR) of atmospheric acoustic-gravity waves (AGW) in unbounded horizontal winds with linear shear (HWLS) in the linear approach is analytically obtained for the three-dimensional case. The numerical solutions for the temporal evolution of the AGW amplitudes point at the possibility of the energy transformation between the obtained acoustic, gravity and shear wave modes.

Some characteristics of atmospheric gravity waves observed by radio-interferometry

Abstract. Observations of atmospheric acoustic-gravity waves (AGWs) are considered through their effect on the horizontal gradient G of the slant total electron content (slant TEC), which can be directly obtained from two-dimensional radio-interferometric observations of cosmic radio-sources with the Nançay radioheligraph (2.2°E, 47.3°N). Azimuths of propagation can be deduced (modulo 180°). The total database amounts to about 800 h of observations at various elevations, local time and seasons. The main results are: a) AGWs are partially directive, confirming our previous results. b) The propagation azimuths considered globally are widely scattered with a preference towards the south. c) They show a bimodal time distribution with preferential directions towards the SE during daytime and towards the SW during night-time (rather than a clockwise rotation as reported by previous authors). d) The periods are scattered but are larger during night-time than during daytime by about 60%. e) The effects observed with the solar radio-sources are significantly stronger than with other radio-sources (particularly at higher elevations), showing the role of the geometry in line of sight-integrated observations.

The Los Alamos beacon receiver array

Describes radio receivers that monitor transmissions from beacons on geosynchronous satellites. The receivers can detect ionospheric perturbations of a 300-3000 s period in the electron density integrated from beacon to receiver, for amplitudes as low as (1-2)/spl times/10/sup 13/ m/sup -2/. Data are used in studies of atmospheric acoustic and acoustic-gravity waves. >

Mount St. Helens Eruption of 18 May 1980: Air Waves and Explosive Yield

Strong atmospheric acoustic-gravity waves were recorded by sensitive microbarographs and seismographs at large distances from the Mount St. Helens eruption of 18 May 1980. Wave signatures were similar to those of waves from large nuclear explosions. Independent theoretical and empirical analyses indicate that the explosive yield of the eruption was approximately 35 megatons.

Dynamics of severe storms through the study of thermospheric-tropospheric coupling.

Atmospheric acoustic-gravity waves associated with severe local thunderstorms, tornadoes, and hurricanes can be studied through the coupling between the thermosphere and the troposphere. Reverse group ray tracing computations of acoustic-gravity waves, observed by an ionospheric Doppler sounder array, show that the wave sources are in the neighborhood of storm systems and the waves are excited prior to the storms. It is suggested that the overshooting and ensuing collapse of convective turrets may be responsible for generating the acoustic-gravity waves observed. The results of this study also show that the study of wave-wave resonant interactions may be a potential tool for investigating the dynamical behavior of severe storm systems using ionospheric observations of atmospheric acoustic-gravity waves associated with severe storms.

Phase memory and additional memory in W. K. B. solutions for wave propagation in stratified media

For a wave travelling obliquely in a stratified inhomogeneous medium the W. K. B. solution contains a phase memory term that expresses the cumulative change of complex phase as the wave propagates. This memory may have two parts. One is the familiar phase memory displayed in all cases. The other is an additional memory that has recently been shown to be important for radio waves in an anisotropic ionosphere, but it is not present for an isotropic ionosphere. The subject is examined here for some other types of wave in geophysics and atmospheric physics. It is shown that there can be an important additional memory for atmospheric acoustic gravity waves, and a small additional memory in some other cases including seismic waves when Coriolis force is allowed for, and electromagnetic waves in a stratified optically active but isotropic medium. For magnetohydrodynamic waves there is additional memory if a gravitational field is present, but not otherwise.

Interpretation of the phase velocity dispersion of observed F-region waves

An attempt is made to explain the observed dispersion of F-region waves by means of atmospheric acoustic-gravity waves, taking into account the effects of thermal conduction, viscosity, and ion drag. Acoustic-gravity waves of a given period then have an attenuation minimum at a certain horizontal phase velocity, and it is assumed that those waves having the lowest attenuation predominate. With this assumption, the dispersion of the horizontal phase velocity observed at night, and the dispersion of the vertical phase velocity can be explained. A similar interpretation of horizontal phase velocities observed near sunrise or sunset fails.