Igor Chunchuzov

Sound propagation through and scattering by internal gravity waves in a stably stratified atmosphere

A stably stratified atmosphere supports propagation of internal gravity waves (IGW). These waves result in highly anisotropic fluctuations in temperature and wind velocity that are stretched in a horizontal direction. As a result, IGW can significantly affect propagation of sound waves in nighttime boundary layers and infrasound waves in the stratosphere. In this paper, a theory of sound propagation through, and scattering by, IGW is developed. First, 3D spectra of temperature and wind velocity fluctuations due to IGW, which were recently derived in the literature for the case of large wave numbers, are generalized to account for small wave numbers. The generalized 3D spectra are then used to calculate the sound scattering cross section in an atmosphere with IGW. The dependencies of the obtained scattering cross section on the sound frequency, scattering angle, and other parameters of the problem are qualitatively different from those for the case of sound scattering by isotropic turbulence with the von K...

On acoustical impulse propagation in a moving inhomogeneous atmospheric layer

In the present work a solution is obtained by the method of normal modes, which describes the sound field of a point impulse source in the atmosphere with definite temperature and wind velocity profiles and ground impedance. This solution describes the impulse shape transformation in different directions relevant to wind velocity involving the low‐frequency case, when the ray approach becomes invalid. The impulse shape evolution during guided and antiguided propagation (in the shadow region) is in good qualitative agreement with the shape observed in the experiment. The change of the impulse shape in time is observed in the experiment during transition of the boundary atmospheric layer from a convective state to one with a stable temperature inversion. The experimental measurements and theoretical estimations show that the nearground acoustical waveguide is formed mainly due to wind stratification in the boundary layer. Solving of the direct problem also shows a principal possibility of inclined sounding ...

Acoustic pulse propagation through a fluctuating stably stratified atmospheric boundary layer

Mesoscale wind speed and temperature fluctuations with periods from 1 min to a few hours significantly affect temporal variability and turbulent regime of the stable atmospheric boundary layer (ABL). Their statistical characteristics are still poorly understood, although the knowledge of such statistics is required when modeling sound propagation through the stable ABL. Several field experiments have been conducted to study the influence of mesoscale wind speed fluctuations on acoustic pulse propagation through the stable ABL. Some results of these experiments are described in this paper. A special acoustic source was used to generate acoustic pulses by the detonation of an air-propane mixture with a repetition period 30 s. The mean wind speed and temperature profiles were continuously measured by Doppler sodar and temperature profiler, whereas mesoscale wind fluctuations were measured by anemometers placed on a 56-m mast. From the measurements of the pulse travel time fluctuations at different distances from the source, the statistical characteristics of the mesoscale wind fluctuations, such as frequency spectra, coherences, horizontal phase speeds and scales, have been obtained. Some of the obtained results are interpreted with the use of a recently developed model for the internal wave spectrum in a stably stratified atmosphere.

Modeling propagation of infrasound signals observed by a dense seismic network

The long-range propagation of infrasound from a surface explosion with an explosive yield of about 17.6 t TNT that occurred on June 16, 2008 at the Utah Test and Training Range (UTTR) in the western United States is simulated using an atmospheric model that includes fine-scale layered structure of the wind velocity and temperature fields. Synthetic signal parameters (waveforms, amplitudes, and travel times) are calculated using parabolic equation and ray-tracing methods for a number of ranges between 100 and 800 km from the source. The simulation shows the evolution of several branches of stratospheric and thermospheric signals with increasing range from the source. Infrasound signals calculated using a G2S (ground-to-space) atmospheric model perturbed by small-scale layered wind velocity and temperature fluctuations are shown to agree well with recordings made by the dense High Lava Plains seismic network located at an azimuth of 300° from UTTR. The waveforms of calculated infrasound arrivals are compared with those of seismic recordings. This study illustrates the utility of dense seismic networks for mapping an infrasound field with high spatial resolution. The parabolic equation calculations capture both the effect of scattering of infrasound into geometric acoustic shadow zones and significant temporal broadening of the arrivals.

Mesoscale variations in acoustic signals induced by atmospheric gravity waves.

The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on acoustic signal parameters are analyzed in the present study. From the measurements of acoustic travel time fluctuations (periods 1 min-1 h) with distant receivers, the temporal fluctuations of the effective sound speed and wind speed are retrieved along different ray paths connecting an acoustic pulse source and several receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal phase velocities, and spatial scales) are estimated. The capability of acoustic tomography in estimating wind shear near ground is shown. A possible mechanism describing the temporal modulation of the near-ground wind field by ducted internal waves in the troposphere is proposed.

Anisotropy in internal gravity waves in conditions of a stable nocturnal boundary layer

In July 2005 the Oboukhov Institute of Atmospheric Physics (OIAP) and the Leipzig Institute for Meteorology (LIM) conducted a joint experiment at Zvenigorod (Russia) using the OIAPs acoustic pulse sounding method and the acoustic travel time tomography of the LIM group. These were deployed simultaneously with SODAR and temperature profiler measurements of wind speed and temperature profiles used for monitoring the state of the lower atmosphere. Internal gravity waves (IGWs) in the stably stratified atmosphere were detected by means of cross-coherence analysis of the acoustic travel times. The acoustic receivers were placed in groups of three at several locations distributed within the measurement field. Two methods were employed for detecting coherent structures: first in the vertical direction along refracting ray paths with turning points in the atmosphere between 50 m to 300 m and second the pulse propagation along almost horizontal ray paths that connect pairs of source and receivers. In this way both horizontal and vertical information of the state of the atmosphere was monitored continuously during the experiment; this allowed both the detection of wave-like structures and the spatial and temporal characteristics of the effective sound speed fluctuations. From these fluctuations the anisotropy of the IGWs is deduced. Two measurement days are analysed in this study which revealed several anisotropic frequency domains caused by wave-like structures.

Infrasound and internal gravity waves generated by atmospheric storms

The recordings of infrasound and internal gravity waves (IGWs) obtained during 2015-2016 at infrasound station I43 IMS and a network of microbarographs installed by Obukhov Institute of Atmospheric Physics (OIAP) are presented. The OIAP network of microbarographs is capable of detecting simultaneously an infrasound at frequencies less than 3 Hz and IGWs with periods ranging from 5 min to 3 hr. It is shown that the low-frequency wave processes generated by atmospheric fronts retain high coherence (0.6-0.9) over the areas with horizontal dimensions of a few tens of km. It is found that after the passage of atmospheric front the internal wave trains were observed with the amplitudes considerably exceeding those of IGWs that were detected before the passage of the atmospheric front. The discrete periods of 35 min, 56 min, and 110 min were found in the frequency spectra of the observed wave trains. For these periods, the coherence between atmospheric pressure variations measured at different points reach local...

Using the acoustic-pulse conservation law in estimating the energy of surface acoustic sources by remote sounding

The atmospheric effect on the characteristics of infrasonic signals from explosions has been studied. New methods have been proposed to remotely estimate the energy of explosions using the data of infrasonic wave registration. One method is based on the law of conservation of acoustic pulse I, which is equal to the product of the wave profile area S/2 of the studied infrasonic signal and the distance to the source EI [kt] = 1.38 × 10–10 (I [kg/s])1.482. The second method is based on the relationship between the explosion energy and the dominant period T of the recorded signal, EТ [kt] =1.02 × (Т [s]2/σ)3/2, where σ is a dimensionless distance used for determining the degree of manifestation of nonlinear effects in the propagation of sound along ray trajectories. When compared to the conventional EW (Whitaker’s) relation, the advantage of the EI relation is that it can be used for pulsed sources located at an arbitrary height over the land surface and having an arbitrary form of the initial-pulse profile and for any type of infrasonic arrivals. A distinctive feature of the expression for EТ is that the atmospheric effect on the characteristics of recorded infrasonic signals is explicitly taken into account. These methods have been tested using infrasonic data recorded at a distance of 322 km from the sources (30 explosions caused by a fire that occurred at the Pugachevo armory in Udmurtia on June 2, 2011). For the same explosion, empirical relations have been found between energy values obtained by different methods: EI = 1.107 × EW, EТ = 2.201 × EI.

Internal Gravity Wave Perturbations and Their Impacts on Infrasound Propagation in the Atmosphere

The model of shaping of the 3-D and 1-D wavenumber spectra for the wind velocity and temperature fluctuations induced by atmospheric gravity waves is described here. Using the 3-D spectrum of gravity wave perturbations, the variances of the fluctuations of sound travel time along refracting ray paths and the azimuth of arrival of acoustic signals are estimated. These variances define the errors in localization of infrasound sources caused by gravity wave perturbations. The results of theory and numerical modeling of infrasound scattering from gravity wave perturbations are presented. With a recently developed infrasound probing method the vertical profiles of the horizontal wind velocity fluctuations in the upper stratosphere (height range is 30–52 km) and lower thermosphere (90–140 km) are retrieved. The method is based on analytic relation between scattered infrasound field in the shadow zone and the vertical profile of the layered inhomogeneities of the effective sound speed. The obtained results show a capability of the probing method in the retrieval of the detailed wind-layered structure in the stratosphere, mesosphere and lower thermosphere. The vertical wavenumber spectra of the retrieved vertical profiles of the wind velocity fluctuations in the upper stratosphere and their coherence functions are analyzed.

Simulating the Propagation of Infrasonic Waves and Estimating the Energy of the Chelyabinsk Meteoroid Explosion Observed on February 15, 2013

Results obtained from simulating the propagation of infrasonic waves from the Chelyabinsk meteoroid explosion observed on February 15, 2013, are given. The pseudodifferential parabolic equation (PDPE) method has been used for calculations. Data on infrasonic waves recorded at the IS31 station (Aktyubinsk, Kazakhstan), located 542.7 km from the likely location of the explosion, have been analyzed. Six infrasonic arrivals (isolated clearly defined pulse signals) were recorded. It is shown that the first “fast” arrival (F) corresponds to the propagation of infrasound in a surface acoustic waveguide. The rest of the arrivals (T1–T5) are thermospheric. The agreement between the results of calculations based on the PDPE method and experimental data is satisfactory. The energy E of the explosion has been estimated using two methods. One of these methods is based on the law of conservation of the acoustic pulse I, which is a product of the wave profile area S/2 of the signal under analysis and the distance to its source EI [kt] = 1.38 × 10–10 (I [kg/s])1.482. The other method is based on the relation between the energy of explosion and the dominant period T of recorded signal ET [kt] = 1.02 × (T [s]2/σ)3/2, where σ is the dimensionless distance determining the degree of nonlinear effects during the propagation of sound along ray trajectories. According to the data, the explosion energy EI,T ranges from 1.87 to 32 kt TNT.