Lightning characterization through acoustic measurements

Gallin, Louis-Jonardan; Rénier, Mathieu; Gaudard, Eric; Farges, Thomas; Marchiano, Régis; Coulouvrat, François

doi:10.1121/1.4831383

Cited by 3 publications

(3 citation statements)

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“…Acoustic reconstructions turned out even better in the lower part of the lightning channel, when the acoustic station is in the vicinity of the flash (less than 20 km). In particular, atmospheric effects are neglected, and sound propagation is assumed straight line in a homogeneous atmosphere at the constant temperature (Gallin, , Chapter 4, Figure 4.2) measured on the ground, so that the reference sound speed is c 0 =340 m/s. Ray tracing methods including realistic atmospheric profiles of temperature and velocity did not show a significant improvement in this particular case (see Gallin et al, , appendix B) and even provided a poorer quality result.…”

Section: Methodsmentioning

confidence: 99%

Acoustical Measurement of Natural Lightning Flashes: Reconstructions and Statistical Analysis of Energy Spectra

et al. 2018

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Twenty-seven natural flashes of three thunderstorms which occurred during October 2012 in Southern France are acoustically reconstructed and analyzed in the [0.1 − 180]-Hz frequency bandwidth and the [0.3−20]-km distance range. A 50-m triangular array of four recalibrated microphones sampled at 500 Hz has been used for the recording. A novel method of separation of return strokes from intracloud discharges within the acoustical signal is detailed and systematically applied. It shows the possibility to separate nearby cloud-to-ground (CG) events or nearby and distant CGs of the same flash. The separation method yields a total of 36 return stroke signals and spectra, along with some intracloud signals. The combination of reconstruction, separation, and frequency analysis provides new insights on the origin of thunder infrasound, showing unambiguously that thunder infrasound originate dominantly from return strokes. Apart from the higher amplitude of CGs, no clear difference between intracloud and CG spectra is observed. No sharp frequency peaks can be put into evidence. The spectral variability with distance is highlighted, especially for the total acoustic energy and the center frequency and bandwidth. A link between acoustic energy and impulse charge moment change is also found, though only by a small number of data.The description of these two mechanisms explaining the infrasonic and audible acoustic content of thunder has been summarized by Few (1995). Regarding the audible content, the sudden core heating (25,000-30,000 K) just after the electric discharge produces a chain of strong shock waves along the lightning channel. The time dependence of pressure within the lightning channel was estimated by Orville (1968a) from the first measured time resolved optical spectra (Orville, 1968b), with peak overpressure exceeding 80 kPa. Based on a radiation thermodynamical model, Hill (1971) could simulate such values, with even higher shock amplitudes for shorter times (see his Figure 5). The different steps to switch from strong shock waves to weak shock waves and finally to acoustic waves are developed by Few (1969). Theory for self similar strong shock wave was proposed by Taylor (1950) for point sources and Lin (1954) for line sources and then numerically extended to transition and weak shock regimes by Brode (1955) for spherically symmetric shocks. The cylindrical symmetry was described by Plooster (1970). An empirical match between strong and weak shock theories has been applied to lightning by Jones et al. (1968) assuming a rectilinear channel. However, lightning channel tortuosity has been observed optically by Hill (1968), who proposed a mean value of 16 ∘ deflection of one segment to the next. Synthesizing these previous studies, Few et al. (1967) andFew (1969) assumed that the transition between strong and weak shocks takes place approximately in the same range of distances as the transition between cylindrical and spherical divergence. This distance is called relaxation radius. Indeed,

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Section: Methodsmentioning

confidence: 99%

Acoustical Measurement of Natural Lightning Flashes: Reconstructions and Statistical Analysis of Energy Spectra

et al. 2018

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“…Given the complexity of the physics to be taken into account, numerical simulations of atmospheric propagation have necessarily been based on simplified approaches. Ray tracing (Rogers & Gardner 1980;Lonzaga et al 2015;Sabatini et al 2016b;Scott, Blanc-Benon & Gainville 2017), normal modes (Waxler 2002(Waxler , 2004Bertin, Millet & Bouche 2014; and oneway models (Lingevitch, Collins & Siegmann 1999;Ostashev et al 2001;Le Pichon, Ceranna & Vergoz 2012;Gallin et al 2014) have been the most commonly used techniques. Albeit computationally efficient, they are not able to account for all the aforementioned physical phenomena.…”

Section: Numerical Modelling Of Infrasound Propagationmentioning

confidence: 99%

Three-dimensional direct numerical simulation of infrasound propagation in the Earth’s atmosphere

et al. 2018

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A direct numerical simulation of the three-dimensional unsteady compressible Navier–Stokes equations is performed to investigate the infrasonic field generated in a realistic atmosphere by an explosive source placed at ground level. To this end, a high-order finite-difference method originally developed for aeroacoustic applications is employed. The maximum overpressure and the main frequency of the signal recorded at 4 km distance from the source location are about 4000 Pa and 0.2 Hz, respectively. The atmosphere is parametrized as a vertically stratified medium, constructed by specifying vertical profiles of the temperature and the horizontal wind which reproduce measurements. The computation is carried out up to 140 km altitude and 450 km range. The goal of the present paper is twofold. On the one hand, the feasibility of using a direct numerical simulation of the three-dimensional fluid dynamic equations for the detailed description of long-range propagation in the atmosphere is proven. On the other hand, a physical analysis of the infrasonic field is realized. In particular, great attention is directed towards some important phenomena which are not taken into account or not well predicted by classical propagation models. To begin with, the present study clearly demonstrates that the weakly nonlinear ray theory may lead to an incorrect evaluation of the waveform distortion of high-amplitude waves propagating towards the lower thermosphere. In addition, signals recorded in the shadow zones are investigated. In this regard, the influence on the acoustic field of temperature and wind inhomogeneities of length scale comparable with the acoustic wavelength is analysed. The role of diffraction at the thermospheric caustic is finally examined and it is pointed out that the amplitude of the source may have a strong impact on the length of the shadow zone.

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“…Existing sonic boom propagation models that account for turbulence effects [11][12][13][14][15][16] are either based on the nonlinear KZK parabolic equation [17][18][19] or the nonlinear FLHOWARD equation. 20,21 These models are one-way propagation models and were, thus, formulated to only account for diffracted signals but not backscattered signals. 20 As with electromagnetic waves, the random fluctuation in a turbulence field does not only lead to acoustic forward scattering but also backscattering.…”

Section: Introductionmentioning

confidence: 99%

Multiple scattering theory for modeling sonic booms in atmospheric turbulence

Lonzaga

2023

The Journal of the Acoustical Society of America

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Sonic booms are often modeled using Burgers equations accounting for dominant propagation effects. Scattering effects of turbulence, however, have not been incorporated into such equations, although these effects are ubiquitous in measured sonic booms. This paper formulates the mean scattering effects, including backscattering, using multiple scattering theory and ensemble averaging. It obtains an acousto-turbulence interaction energy representing the interaction of an acoustic wavefield with a turbulence field. The interaction energy gives rise to a scattering wavenumber, a complex-valued correction to the free-space wavenumber. The scattering wavenumber leads to a dispersion and attenuation of the mean waveform due to backscattering, and can be obtained from a derived exact solution. An existing Burgers equation is extended to include the scattering effects of turbulence as an additional linear term. Numerical simulations of an N-wave and a low boom show that the mean scattering effects lead to shock thickening in the mean waveforms as well as reduce the peak amplitudes and total energy contents. The energy reduction is less severe in the low boom than in the N-wave and is dependent on the variance, correlation length, and thickness of the turbulence field.

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Lightning characterization through acoustic measurements

Abstract: Table des matières 4.7.2 Capacité des mesures acoustiques à reconstruire les parties des décharges de faible altitude .

Cited by 3 publications

References 55 publications

Acoustical Measurement of Natural Lightning Flashes: Reconstructions and Statistical Analysis of Energy Spectra

Acoustical Measurement of Natural Lightning Flashes: Reconstructions and Statistical Analysis of Energy Spectra

Three-dimensional direct numerical simulation of infrasound propagation in the Earth’s atmosphere

Multiple scattering theory for modeling sonic booms in atmospheric turbulence

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