A very bright fireball observed over New South Wales in 1978 produced anomalous sounds clearly audible to some of the observers. An investigation of the phenomenon indicates that bright fireballs radiate considerable electromagnetic energy in the very-low-frequency (VLF) region of the spectrum. A mechanism for the production of VLF emissions from the highly energetic wake turbulence of the fireball is proposed. Trials with human subjects revealed a very extended range of thresholds for the perception of electrically excited sounds among a sample population, particularly when the VLF electric field excites surface acoustic waves in surrounding objects. This fact, together with variable propagation effects and local conditions, can account for the sporadic distribution of reports of anomalous sounds from fireballs and auroras.

Abstract-Anomalous sounds from large meteor fireballs, anomalous because they are audible simultaneously with the sighting, have been a matter for debate for over two centuries. Only a minority of observers perceive them. Ten years ago a viable physical explanation was developed (Keay, I 980a) which accounts for the phenomenon in terms of ELF/VLF radiation from the fireball plasma being transduced into acoustic waves whenever appropriate objects happen to be in the vicinity of an observer. This explanation has now been verified observationally and supported by other evidence including the study of meteor fireball light curves reported here.

The chances of witnessing a very large meteor fireball and hearing sounds coincident with its passage are calculated from two independent sets of observational data and from the known rate of incidence upon the Earth of meteoroids large enough to produce the phenomenon.

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