Jean-L. RAULT F6AGR
IMO (International Meteor Organization) Radio Commission 1. Introduction
For many years, credible meteor observers have reported some shooting stars producing various acoustic noises at the moment they were appearing.
However, knowing that the speed of sound in our atmosphere is around 340 meters per second and that fireballs generally appear at altitudes around 90 km, the sounds associated to the fireballs should be delayed by several hundreds of seconds.
To explain these anomalous sounds appearing simultaneously with meteors, Keay (1980) proposed that some ELF/VLF (extremely low frequency / very low frequency) electromagnetic energy could be radiated by the decaying meteor and then transduced into audible sounds at the observer location. This ELF/VLF high speed vector is supposed to explain the observed simultaneity of sound and meteor light.
A Global Electrophonic Fireball Survey performed by Vincovic et al. (2002) suggests that the electrophonic meteors, as Keay named them, produce a very wide family of hissing, swishing, rustling, buzzing, whooshing or … crackling sounds.
Keay’s theory states that trapping and twisting the earth magnetic field lines in the turbulent wake of the largest meteors and then releasing them suddenly could be the reason for producing high power ELF/VLF radiation in the 100 Hz to 10 kHz range.
Breech & Foschini (1994) explained that the Keay’s theory was only able to explain the long duration noises such as hisses and other high-pitched whistles, but not the pops, tics and other claps which were often reported. They developed their own “space charge model” theory which states that some sharp shock waves occurring in the meteor trail plasma could induce some sudden electrical field transients.
Several tentatives for recording such electrophonic phenomenons, using microphones, video cameras and VLF receivers were performed these last decades (see bibliography).
In fact, due to extreme rareness of the electrophonic phenomenon, instrumentally recorded electrophonic meteor data are very scarce and not statistically convincing.
The purpose of the present experiment, “Searching for ELF/VLF meteors signatures” is simply to verify, by means of statistical analysis of coincidences between radio and meteors events and by spectral analysis of the candidate VLF radio events, that some meteors entering the Earth atmosphere are really radiating some detectable ELF/VLF electromagnetic energy.