A method for recognizing infrasound acoustic signals for two types of sources based on the analysis of the shape of their wavelet spectra is proposed. The idea of constructing this form is based on the principal component method. Morphological image analysis methods are used to search for characteristic areas. The proposed method makes it possible to effectively solve the problem of multiclass classification of acoustic signals.

The results of airborne measurements and statistical characteristics of mesoscale fluctuations of wind velocity, temperature, and concentrations of gas constituents at different heights of a stably stratified troposphere are presented. The measurements were carried out in September 2022 in the Arctic region of Russia with the aircraft laboratory Tu-134 "Optik." The obtained spectra and structure functions of the fluctuations are interpreted with the theoretical model of formation of the spectrum of mesoscale wind velocity and temperature fluctuations described in the paper. The presence at high wavenumbers of a steep section in the obtained horizontal wavenumber spectra of the fluctuations of wind velocity and greenhouse gas concentration with a slope close to -3 is discussed. The fluctuation spectra along different slanted tracks of the aircraft crossing the tropospheric layer between altitudes of 1 and 9 km are also obtained and analyzed with the theoretical model.

The results of studying the influence of internal gravity waves (IGWs) on the spatiotemporal variability of atmospheric pressure and wind velocity in the lower troposphere using a triangular network of three microbarographs and an antihail acoustic cannon installed in Talin (Armenia) are presented. By coherent analysis of pressure fluctuations measured at different points, IGWs generated by thunderstorm fronts about 5–6 h before the passage of the fronts over the network of microbarographs have been detected. The regularities of changes in phase speeds and propagation directions of IGWs as thunderstorm precursors with time are studied. The possibility of IGW monitoring in the troposphere by measuring temporal fluctuations of the travel time of acoustic pulses along the ray-paths connecting the antihail cannon with spatially separated acoustic receivers has been demonstrated. Vertical profiles of wind velocity fluctuations in certain layers of the lower troposphere up to a height of 800 m have been retrieved from the shapes and travel times of acoustic pulses having a shock front and scattered by anisotropic fluctuations of wind velocity and temperature in the stably stratified lower troposphere. Owing to the high vertical resolution (on the order of 1 m) of the method of pulsed acoustic sounding of the lower troposphere used here, the vertical spectra of anisotropic fluctuations of wind velocity in the range of short vertical scales, from one to tens of meters, are obtained for the first time and theoretically interpreted.

The features of the propagation of nonlinear pulsed acoustic disturbances in the atmosphere are considered. Data are presented on the experimental observation of shock front formation and the transition of a shock wave into a low-intensity acoustic wave with transformation of the pulse shape and broadening of the front at distances greater than 1000 km under both spherical and cylindrical propagation conditions. The influence of Kelvin–Helmholtz instability during rapid gas compression on the formation of the shock front structure is discussed. Under atmospheric conditions, such instability significantly affects dissipative processes in the air and forms the front of a nonlinear wave.

The data of measurements of air temperature profiles in the atmospheric boundary layer (ABL) during the total solar eclipse on March 29, 2006, in Kislovodsk and at the High-Mountain Scientific Station (HMSS) on the central shadow line are presented. The solar eclipse lasted from 2:08 p.m. to 4:27 p.m. local time; the total phase of the eclipse began at 3:15 p.m. and lasted 2 min 32 s. In developing the results we obtained in our previous work, we compared the data on air temperature profiles at two points, Kislovodsk and the HMSS. The influence of local conditions has been studied. It is shown that local conditions significantly affect both the amplitude of atmospheric pressure pulsations caused by a solar eclipse and their phase, as well as the nature of the change in the spectral density of air temperature with height in the range of periods corresponding to the duration of the solar eclipse. Based on the measurements of temperature profiles, the fluctuations of the atmospheric pressure difference at the level of the earth’s surface and at a certain height up to which the temperature profiles were measured equal to 600 m, were reconstructed, caused by a solar eclipse, in coordinates: height–time has different trajectories in the case of Kislovodsk and the HMSS. The difference in the trajectories of air temperature minima in Kislovodsk and at the HMSS determines both different delays in pressure minima relative to the beginning of the eclipse and time delays between surface pressure fluctuations at observation points as a whole. Also, a new method is proposed for determining the speed of ascending air currents using data on the altitude dependence of the time of reaching a minimum in temporal temperature variations caused by a solar eclipse. The changes in the spectral density of air are compared with height, the amplitude of the reconstructed atmospheric pressure pulsations in Kislovodsk and at the HMSS, and the speed of ascending air currents.

The paper deals with studying the influence of air pressure fluctuations on the health of patients. Since August 2008, the Obukhov Institute of Atmospheric Physics of Russian Academy of Sciences and the Central Clinical Hospital of the Russian Academy of Sciences (CCH RAS) observed air pressure fluctuations with a simultaneous registration of patients who were urgently hospitalized to the CCH RAS and classified as weather-sensitive. Weather-sensitive patients included patients diagnosed with myocardial infarction, angina, hypertension, extrasystole, stroke, and cerebrovascular disease. The data on 6078 patients over a four-year period (January 1, 2009-November 31, 2012) were processed. The results have shown an increase in the cases of patients' hospitalization with an enhancement of the external effects of air pressure.

Avalanches are a dangerous natural phenomenon that has a significant negative impact on infrastructure facilities located on the territory of North Ossetia. Avalanches cause damage to settlements and tourist infrastructure, communication routes, power lines and forestlands. More often than others, highways suffer from avalanches, blockages on which lead to long breaks in traffic. The need to create monitoring systems to assess and promptly predict the consequences of possible emergencies caused by avalanches, the interface of such systems with local warning systems of federal executive authorities has been repeatedly discussed at various levels of government, but so far, there are no existing avalanche danger monitoring systems in the Russian Federation. The Geophysical Survey of the Russian Academy of Sciences has been conducting experiments for several years to register avalanches with the help of infrasound sensors. To register the signals, various configurations of infrasound groups consisting of three sensors set apart in space were used. As a result of the experiments, recordings of infrasound signals were obtained at various distances from the avalanche hearth. The possibility of reliable isolation and identification of infrasound signals caused by avalanches at a distance of up to 10 km is shown. Conclusions are drawn about the high efficiency of the infrasound method for recording avalanche facts. The results obtained made it possible to develop a technique for automatic detection of signals generated by avalanches, to develop an optimal configuration for building a system for continuous monitoring of avalanche activity in the North Caucasus.

A new decomposition method (decomposition into N and U-waves) of infrasonic signals corresponding to partial reflection of N-wave sounding pulses from anisotropic atmospheric layers and recorded in areas of geometric shadow at large distances from explosions and volcanic eruptions is presented. The decomposition method makes it possible to determine the vertical gradients of the effective sound speed (sound speed plus wind speed in the direction of propagation) that are not available for determination by other methods.

A model of atmospheric pressure signal propagation from the eruption of the Hunga–Tonga—Hunga–Haʻapai volcano (hereafter abbreviated as Tonga) is proposed. The model is used to explain some peculiarities in the changes in the wave form of the observed signal with increasing distance from the volcano. The model is based on the solution of the linearized Korteweg de Vries (KDV) equation, which describes the change in the wave form of the Lamb wave as a function of distance from the source. We compare the observed and model signals obtained as a superposition of the Lamb wave and the acoustic modes calculated for three infrasound stations (IS22, IS24, and IS30). The energy of the volcanic eruption is estimated from the pressure amplitude and characteristic duration of the signal recorded at one of the infrasound stations closest to the volcano (IS24).

A model of propagation of an atmospheric pressure signal from the eruption of the Hunga Tonga−Hunga Haʻapai volcano is proposed. This model is used to explain some patterns in the change in the form of the observed signal with an increase in the distance from the volcano. It is based on the solution of the linearized Korteweg–de Vries (KdV) equation, which describes the change in the Lamb wave form as a function of the distance from a source. We compare the observed and model signals obtained as a superposition of the Lamb wave and acoustic modes calculated for three infrasound stations (IS22, IS24, and IS30). The energy of the volcanic eruption is estimated using the fluctuation amplitude of the atmospheric pressure and the characteristic duration of the signal recorded at the infrasound stations closest to the volcano.

The influence of wind velocity and temperature stratification in the upper stratosphere on the waveform of the infrasound signal received at a distance of 2398 km from the epicenter of the powerful explosion in Beirut that occurred on August 4, 2020 is studied using ray trace and pseudo-differential parabolic equation (PDPE) methods. Given a high temporal variability of the wind velocity in the stratopause predicted by the European Centre for Medium-Range Weather Forecasts model, it is assumed that within the stratopause layer, the increase in effective sound speed with increasing height is very small, on the order of 1 m/s. When modeling propagation of the signal from the explosion, the presence of a fine-scale layered structure of wind velocity and temperature in the real atmosphere was also taken into account. Accounting for the scattering of infrasound by strongly anisotropic (layered) inhomogeneities of the effective sound speed allowed us to explain the appearance of "fast" stratospheric arrivals, their time durations, the time period between successive arrivals (about 110 s), and the waveform of the entire observed signal.

The generation and propagation of waves from model tropospheric meteorologic heat sources are theoretically studied. The processes of gas heating/cooling in water phase transitions at tropospheric altitudes are assumed to be the wave sources. In an analytical part of the study, equations are derived which describe the generation and propagation of acoustic and internal gravity waves separately. It is shown that powers of partial sources of acoustic and internal gravity waves always approximately coincide, regardless of wave frequencies, and the generation of internal gravity waves cannot occur without the generation of acoustic waves, and vice versa. Explicit analytical expressions are obtained for the generated waves. Due to resonant properties of the atmosphere, the high-frequency sources generate predominantly acoustic waves. The low-frequency sources generate mainly internal gravity waves if the sources work long enough for the resonance properties of atmosphere to be manifested. Using numerical experiments, the issue of error is investigated which is introduced if a tropospheric source is replaced with a surface one in which the pressure fluctuations on the surface are the recorded pressure fluctuations caused by the tropospheric source. It is shown that, if a tropospheric source operates at the infrasonic wave frequencies, then the wave patterns generated in the upper atmosphere from the tropospheric source and from the surface pressure fluctuations are almost identical. In the case of a tropospheric source operating at frequencies of internal gravity waves, the amplitude of waves from the surface pressure may be overestimated no more than twice. It is shown that, based on pressure fluctuations on the Earth’s surface, some corrected surface pressure source can be constructed which takes into account the phase shifts of interfering waves that propagate into the upper atmosphere. This provides a significant improvement in the simulation of waves from meteorological sources based on data on atmospheric pressure fluctuations.

The characteristics of acoustic-gravity waves (waveforms, time durations, amplitudes, azimuths and horizontal phase speeds) from the eruption of the Hunga-Tonga-Hunga-Hapai volcano detected at different infrasound stations of the Infrasound Monitoring System and at a network of low-frequency microbarographs in the Moscow region are studied. Using the correlation analysis of the signals at different locations, six arrivals of signals from the volcano, which made up to two revolutions around the Earth, were detected. The Lamb mode of acoustic gravity waves from the volcano eruption is identified and the effect of this mode on generation of tsunami waves and variation of aerosol concentration is studied. The energy released from an underwater volcano into the atmosphere is estimated from the parameters of the Lamb wave and compared with the energy released from the most powerful nuclear bomb of 58 Mt TNT.

The data of measurements of atmospheric pressure fluctuations together with measurements of air temperature profiles in the surface layer of the atmosphere during the total solar eclipse on March 29, 2006 in Kislovodsk on the central line of the shadow are presented. The total phase of the eclipse began at 15:15 local time and lasted 2 min 32 s. According to the measurements of temperature profiles, the fluctuations of the atmospheric pressure difference at the level of the Earth's surface and at a certain height to which the temperature profiles were measured were restored. The recovered fluctuations were compared with atmospheric pressure fluctuations recorded by a microbarograph, as well as with pressure fluctuations during the solar eclipse in Tynda, in the Amur region, on July 31, 1981. It is shown for the first time that temporary changes in vertical profiles of air temperature in the surface layer of the atmosphere caused by a solar eclipse make the main contribution to the pulsation of atmospheric pressure at ground level.

The main characteristics (coherences, phase velocities, propagation directions, characteristic periods, and amplitudes) of wave disturbances in the field of pressure and wind speed in the troposphere caused by the solar terminator (ST) moving relative to the Earth are studied. A coherent analysis of pressure variations measured by infrasound microbarographs of the stations IS26 (Germany), IS37 (Norway), and IS43 (Russia) making a triangle with sides of about 2000 km in size is used to detect wave disturbances from the ST. With such a large triangle, it is possible to isolate acoustic-gravity waves of high coherence with ST azimuths and propagation velocities against the background of much slower internal gravity waves (IGWs) from meteorological fronts. Wind speed and atmospheric pressure fluctuations are measured with sodars and microbarographs located in the region of Moscow and forming a small triangle with side lengths from 7 to 60 km. The distributions of the number of signal arrivals over azimuths and horizontal phase speeds are obtained. An explanation is given for the presence of dominant azimuths and phase speeds of internal gravity waves in the small triangle.

Infrasound parameters (amplitudes, coherences, grazing angles, azimuths, and horizontal phase speeds) derived during the passage of warm and cold fronts through the networks of microbarometers in the cities of Dubna and Moscow are presented. The significant differences observed in the temporal variations of the parameters of infrasound from warm and cold fronts are discussed. Such differences must be taken into account when detecting infrasound precursors of atmospheric storms. A possible mechanism for the generation of infrasound by the turbulent airstream flowing around the geometric irregularities of the meteorological front is proposed. The observed effect of internal gravity waves on the parameters of infrasound and its frequency spectrum is explained.

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.