Instrumental recording of electrophonic sounds from Leonid fireballs

Abstract

Electrophonic meteor sounds, heard simultaneously with the meteor appearance, are a longstanding problem due to their nonintuitive nature. Previous investigations have been undermined by lack of instrumental recordings. Here we present the first instrumental detection of electrophonic sounds obtained during the observation of 1998 Leonids from Mongolia. Two Leonid fireballs of brightness −6.5m and −12m produced short, low‐frequency sounds, which were simultaneously recorded by microphones in a special setup and heard by different observers. Simultaneous measurements of electromagnetic ELF/VLF radiation above 500 Hz did not reveal any signal correlated to the electrophonic event. The lack of signal was explained by the low frequency of electrophones. We show that physical characteristics of Leonid electrophones cannot be completely explained by existing theories and that further theoretical refinement and observational work is needed. Finally, we tentatively suggest the possibility of stronger than expected coupling of fireballs with atmospheric charge dynamics and ionosphere.

On the electrophonic generation of audio frequency sound by meteors

“…The Poynting flux corresponding to this magnetic field is a few times 10 −8 W/m 2 . This is comparable to the sound measurements made by Zgrablić et al []. More importantly, the threshold flux for human hearing is 10 −12 W/m 2 , so the efficiency of the electrophonics effect need only be ~0.1%.…”

“…The theoretical work presented here is based on experimental studies by Hawkins [], Keay [, ], Keay and Ostwald [], Keay [, ], Keay and Ceplecha [], Garaj et al [], Price and Blum [], and Zgrablić et al []. The Zgrablić et al [] article has many useful references.…”

“…The theoretical work presented here is based on experimental studies by Hawkins [1958], Keay [1980aKeay [ , 1980b, Keay and Ostwald [1991], Keay [1992aKeay [ , 1992b, Keay and Ceplecha [1994], Garaj et al [1999], Price and Blum [2000], and Zgrablić et al [2002]. The Zgrablić et al [2002] article has many useful references. Price and Blum [2000] measured the magnetic field on the ground during the 1999 Leonids event, which they reported as having an integrated ELF/VLF magnetic field of several picoteslas.…”

“…Earlier, Beech et al [1995] reported VLF detection due to fireball meteors. The sounds recorded by Zgrablić et al [2002] at around 50 Hz correspond to a sound energy flux of 10 À8 W/m 2 . For reference, the threshold for human hearing is 10 À12 W/m 2 [Durrant and Lovrinic, 1984].…”

Proton-induced halo formation in charged meteors

“…Radar observations of such high-altitude meteors indicate the importance of magnetic field and suggest the existence of new types of high-altitude meteors that are possibly a result of E-mail: dejan@iszd.hr (DV) some electrodynamic instability triggered by a meteor (Gao & Mathews 2015). Instrumental detection of anomalous meteor sounds, known as electrophones (Lamar & Romig 1964), also inspired speculations of a possible electrodynamic coupling between meteors and the ionosphere (Zgrablić et al 2002).…”