On the Possible Infrasound Generation by Sprites

Energetic electrons accelerated by electric fields in thunderstorms are assumed to be responsible for generation of luminous phenomena at altitudes above 30 km, so called sprites. If the generation of light in these phenomena is associated with local heating, it may also be expected that low frequency acoustic waves will be generated. Due to the cylindrical structure of the source the most of the acoustic energy will be radiated close to the horizontal plane along the entire height of the source. The infrasound form these phenomena is therefore unlikely to be detected immediately beneath the source. The search for infrasonic signals from the high altitude luminous phenomena was carried out during the recent years using data from the infrasonic networks operated by the Swedish Institute of Space Physics. During the night of May 26–27 1995, when a severe thunderstorm area passed over the Golf of Bothnia, it was possible to identify signals, most probably generated by sprites. The infrasonic observations made during that night are described in the present report. Similar, chirp-like signals were observed during some other occasions at Swedish stations during the recent years.