Abstract
Lightning generates sound waves across a wide range of frequencies, including infrasonic waves below 20 Hz. Source mechanism for these low frequency pulses is still area for debate. Infrasound pulses detected after rapid changes of electrostatic field during the thunderstorm activity were analyzed. The measurements were done by large aperture array of absolute microbarometers located in the Western part of the Czech Republic. Distances between four measuring sites are in the range of 4–10 km. The infrasound source position was calculated from time delays between the rapid change of electrostatic field and infrasound signal arrival to the individual microbarometers assuming propagation of spherical waves from the source. Only cases with a sufficient signal-to-noise ratio on all four microbarometers were analyzed. The variation of sound speed with height due to temperature height profile was taken into account. For most of the analyzed cases, the calculated infrasound source position corresponds to the lightning location determined by European lightning detection network (EUCLID). The calculated height of infrasound source is most often 3–5 km.
Highlights
Thunderstorms and lightning are known from the dawn of mankind
One of the not fully explained phenomena is the generation of acoustic pulses in the infrasound frequency range that are observed in addition to the audible thunderclap
The source of infrasound is fast adiabatic expansion of the hot lightning channel as it is generally accepted for audible frequency range (Few, 1969; Assink et al, 2008; Lacroix et al, 2019)
Summary
Thunderstorms and lightning are known from the dawn of mankind They represent an important natural hazard for human beings, animals and technological systems. The source of infrasound is fast adiabatic expansion of the hot lightning channel as it is generally accepted for audible frequency range (Few, 1969; Assink et al, 2008; Lacroix et al, 2019). Another mechanism could be the pressure change caused by ohmic air heating by currents flowing from the charged area into the lightning channel (Few, 1985). The infrasound pulse is generated, according to this hypothesis, after removal of electric charge to the lightning channel, which leads to a sudden change of pressure
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