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.

This paper is devoted to the study of the characteristics of internal waves in the Kara Sea and their interaction with the atmosphere, in particular, their influence on the turbulent momentum and heat fluxes in the surface layer of the atmosphere. The direction and horizontal velocity of propagation of short-period internal waves in the Kara Gates Strait are calculated. Cross spectra of mesoscale fluctuations of water temperature at the sea surface, at depths of 10 and 20 m, and meteorological parameters at a height of 22 m are analyzed. Common spectral maxima at periods characteristic of the trapped internal gravity modes propagating in the thermocline layer and atmospheric gravity modes in the stably stratified layer of the lower troposphere are revealed. A possible mechanism of influence of the observed gravity modes in the thermocline layer on mesoscale fluctuations of meteorological parameters (with periods from 10 min to several hours) and turbulent fluxes of momentum and apparent and latent heat in the surface layer of the atmosphere is proposed.

In this paper, we study tropospheric wind velocity fluctuation spectra measured both along horizontal aircraft tracks over Greenland and along inclined aircraft tracks during their ascents and descents. This study is done based on the analysis of the global and long-term high-resolution dataset of meteorological parameters measured by civil aircrafts. The transition from the Nastrom-Gage spectrum with a slope of -5/3 in the horizontal scale-range of 6–200 km to a steeper part of the spectrum at shorter scales is analyzed. Based on the results of wind measurements along 82 inclined trajectories of airplanes during their ascent and descent in the troposphere, the vertical wave number spectra of wind velocity fluctuations measured along these trajectories as a function of height (hereinafter referred to as inclined spectra) were obtained. From the obtained horizontal and inclined spectra of the wind velocity fluctuations their anisotropy (the ratio of horizontal-to-vertical scale) is estimated. The obtained spectra are interpreted using models of 3-D and 1-D (horizontal and vertical) wavenumber spectra of the wind velocity fluctuations. The tropospheric vertical wave number spectra of anisotropic wind velocity fluctuations obtained from the aircraft measurements during ascents and descents (altitudes 5–10 km) are compared to the vertical wave number spectra of the wind velocity fluctuations in the stratosphere and mesosphere retrieved from the infrasound signals generated by ground-based explosions and volcanic eruptions. The general physical mechanism of formation of the fine layered structure of wind velocity for both the stably-stratified layers of the troposphere and the stratosphere-mesosphere is discussed.

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 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 derivation of a nonlinear Burgers-type equation for acoustic waves within the ray approximation for an inhomogeneous moving dissipative atmosphere is presented. The equation is applied to investigate the propagation of three-dimensional infrasonic waves, without using significant computational resources. By means of solving the obtained equation, the shapes of infrasonic signals recorded at distances of 295 km and 305 km from the explosion with energy of 30 kt THT were calculated. The observation point at the distance of 295 km (Tsimlyansk) was located in the western direction from the source. At this place, infrasonic signals were recorded corresponding to the sound propagation in the stratospheric and thermospheric acoustic waveguides. The presence of both two stratospheric and two thermospheric rays falling into the same observation point on the Earth's surface is a wave propagation feature result here. The recorded signals in Tsimlyansk also have a complex structure, both for stratospheric and thermospheric infrasonic arrivals. The registration point at a distance of 305 km (Saratov) was located north of the source. For this point, the calculations showed the presence of only thermospheric rays. The calculation results are compared with experimental data. A satisfactory agreement between the calculated and experimental data was obtained for both observation points in Saratov and Tsimlyansk. The calculated data in Tsimlyansk include manifestation features of the multipath structure of infrasound propagation and agree with the complex structure of infrasound signals recorded in Tsimlyansk.

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.

The structure and characteristics of the internal wave field (coherence, frequency spectra, phase velocities, dispersion of velocity fluctuations) observed in an ocean frontal zone on the shelf-slope east of the island of Malta is studied. Using spectral and coherence analysis of temporal temperature variations measured by two thermistor chains 7 km apart the near-inertial internal gravity waves (NIWs) were detected, and their wavelengths and trace velocities were estimated. The temperature, salinity and density front that existed during the measurement period and the bottom irregularities of island’s shelf are both proposed to be the sources of the observed NIWs and internal waves of different periods. The mechanism of formation of the frequency spectrum of the observed internal wave field is proposed. By analyzing the effect of advection of internal waves by an alternating current induced by all the internal waves the observed periodic change of the sign of the trace velocity of the internal waves is explained.

This study uses low-frequency, inaudible acoustic waves (infrasound) to probe wind and temperature fluctuations associated with breaking gravity waves in the middle atmosphere. Building on an approach introduced by Chunchuzov et al., infrasound recordings are used to retrieve effective sound-speed fluctuations in an inhomogeneous atmospheric layer that causes infrasound backscattering. The infrasound was generated by controlled blasts at Hukkakero, Finland and recorded at the IS37 infrasound station, Norway in the late summers 2014 - 2017. Our findings indicate that the analyzed infrasound scattering occurs at mesospheric altitudes of 50 - 75 km, a region where gravity waves interact under non-linearity, forming thin layers of strong wind shear. The retrieved fluctuations were analyzed in terms of vertical wave number spectra, resulting in approximate kz-3 power law that corresponds to the “universal“ saturated spectrum of atmospheric gravity waves. The kz-3 power law wavenumber range corresponds to vertical atmospheric scales of 33 - 625 m. The fluctuation spectra were compared to theoretical gravity wave saturation theories as well as to independent wind measurements by the Saura medium-frequency radar near Andøya Space Center around 100 km west of IS37, yielding a good agreement in terms of vertical wavenumber spectrum amplitudes and slopes. This suggests that the radar and infrasound-based effective sound-speed profiles represent low- and high-wavenumber regimes of the same “universal“ gravity wave spectrum. The results illustrate that infrasound allows for probing fine-scale dynamics not well captured by other techniques, suggesting that infrasound can provide a complementary technique to probe atmospheric gravity waves.

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).

This paper studies a possible mechanism for the formation of spiral structures around a submesoscale eddy (Rossby number Ro ~ 5) detected on September 22, 2017, by a Sentinel-1 synthetic aperture radar (SAR) image of an ocean area in the Mozambique Channel (Africa). We present a calculation of wave crest shapes of trapped internal waves in a stably stratified ocean thermocline that are generated due to advection by the eddy current of its turbulent density and velocity inhomogeneities. The shapes of the simulated internal wave crests compare well with the shape of the spiral bands in the eddy image, thereby supporting our hypothesis that eddies can generate internal waves. The parameters (variations in the intensity of a reflected radar signal and their spectra and horizontal periods) of the banded spiral structure are also analyzed for a second submesoscale eddy with a diameter of about 5 km detected in the image from September 25, 2017, and having an opposite direction of circulation of the current inside the eddy as compared to the current inside the eddy in the image from September 22, 2017.

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 results of study of temporal variations of the characteristics of infrasound and internal gravity waves (amplitudes, coherences, grazing angles, azimuths and horizontal phase speeds) detected during a passage of warm and cold fronts through the networks of microbarometers installed in the Moscow region and Armenia (city Talin) are presented. Infrasound radiated during periods of weather changes is an almost continuous background against which infrasound monitoring of explosions in the atmosphere is carried out. The significant differences were observed in the characteristics of infrasound from warm and cold fronts. Such differences must be taken into account when detecting infrasound precursors of atmospheric storms. A possible aerodynamic mechanism for the generation of infrasound caused by the turbulent air flow around the geometric irregularities of the surface of meteorological front is proposed.

Some results on modeling and observation of infrasound propagation in the atmosphere in a presence of mesoscale and anisotropic wind velocity and temperature fluctuations are presented. The theoretical model of infrasound scattering from anisotropic wind velocity and temperature inhomogeneities of the atmosphere is developed. With this model, the appearance of the stratospheric, mesospheric, and thermospheric arrivals of the infrasound signals in the acoustic shadow zones is explained. The analytic relation between the wave field of the scattered infrasound signal and the vertical profile of the effective sound speed fluctuations is obtained. Using this relation, the vertical profiles of the fluctuations within the upper stratosphere (25-55 km) and the lower thermosphere (105-140 km) were retrieved from the waveforms and travel times of the signals recorded in the acoustic shadow zones. The theoretical frequency spectrum of the infrasound wavefield reflected from the fine-scale layered structure of the atmosphere is obtained and compared with the spectra of the observed stratospheric arrivals.

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.

Recently, it has been shown for the first time by observations that an anticyclonic mesoscale eddy can generate internal waves (wavelengths of 0.4 to 1 km) that carry energy away from the eddy. In the present study, we investigate a possible mechanism for generating internal waves near the edge of a submesoscale eddy. The study was motivated by airborne infrared imagery that shows curved thermal bands (wavelengths ∼70 m) near the edge of a 1-km-diameter cyclonic eddy. We hypothesize that these bands represent internal wave wakes generated by turbulent perturbations having scales of a few tens of meters that are advected along the eddy’s thermal perimeter. An analytical theory is developed to investigate this for an idealized perturbation advected by a circular current. Calculations show that, for a reasonable choice of parameter values, an internal wave wake develops around the eddy that has spiral-like phase lines resembling the orientations and wavelengths of the field observations. The general validity of our proposed mechanism should be verified with further studies.

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.