Infrasound pulses from lightning and electrostatic field changes: Observation and discussion

Abstract

[1] Narrow (~1-2 s) infrasound pulses that followed, with~11 to~50 s delays, rapid changes of electrostatic field were observed by a microbarometer array in the Czech Republic during thunderstorm activity. A positive pressure fluctuation (compression phase) always preceded decompression; the compression was usually higher than the decompression. The angles of arrival (azimuth and elevation) were analyzed for selected distinct events. Comparisons of distances and azimuths of infrasound sources from the center of microbarometer array with lightning locations determined by the European Cooperation for Lighting Detection lightning detection network show that most of the selected events can be very likely associated with intracloud (IC) discharges. The preceding rapid changes of electrostatic field, their potential association with IC discharges, and high-elevation angles of arrival for near infrasound sources indicate that an electrostatic mechanism is probably responsible for their generation. It is discussed that distinguishing the relative role of thermal and electrostatic mechanism is difficult and that none of the published models of electrostatic production of infrasound thunder can explain the presented observations precisely. A modification of the current models, based on consideration of at least two charged layers, is suggested. Further theoretical and experimental investigations are however needed to get a better description of the generation mechanism.

Location and analysis of acoustic infrasound pulses in lightning

“…In addition to audible acoustic signals, some cloud‐to‐ground (CG) and most intracloud (IC) lightning flashes produce infrasonic acoustic signals below 20 Hz which are not audible by humans. Numerous observations of the infrasound produced by lightning show discrete pulses characterized by an initial compression followed by a rarefaction with amplitude in the range of 0.05–5 Pa and spectral peak in the range of 0.2–2 Hz [e.g., Bohannon et al , ; Bohannon , ; Balachandran , ; Assink et al , ; Chum et al , ].…”

Acoustic detection, tracking, and characterization of three tornadoes

“…These features are typical of the data from the three storms analyzed. The sources of these high-level transients are not certain, but they could be thunder or the tornado interacting with objects on the ground (Chum et al, 2013). Closer inspection reveals that the relative time of onset of these acoustic events with respect to the sensor locations indicates that several of the events occurred in the direction of the tornado, but some of them did not.…”

Atmospheric infrasound observed during intense convective storms on 9–10 July 2011

“…Liszka (2008) also describes signals of short duration and of limited extent of arrival azimuth that were generated by distant cloud-to-ground discharges and adds that cloudto-cloud discharges can produce signals of duration up to 30 s arriving from extended gradually changing azimuths. Chum et al (2013) observed narrow infrasound pulses of duration of 1-2 s that occurred 11-50 s after rapid changes of electrostatic field at the site of microbarograph measurements. The pulses always had a form of compression followed by a decompression phase.…”

“…For cloud-to-cloud (CC) discharges the efficiency is lower. Rough estimates give about 70-80% (Chum et al, 2013).…”