The flash of fireballs (bright meteors) is sometimes followed by thunderclap-like noises. Witnesses have likened the noises to cannon detonations, explosions. rolling thunder, small arms or machine-gun fire, fireworks, and roaring trains. The ancients often assigned the production of such "thunderbolts" to the same storm and sky gods who produced the more common forms of thunder and lightning.
The delayed thunderclap sound is reasonably explained as the arrival of the shock wave produced when an incoming meteoroid strikes the atmosphere. Rolling thunder or train-like noises are produced by turbulent air behind the meteoroid and the reflections of sound waves off clouds and the ground. Machine-gun like noises occur when the meteoroid breaks up in the atmosphere and each fragment causes its own shock wave.
Many witnesses over the centuries have reported that fireballs are accompanied by a low thunder-like noise coincident in time with the meteor flash. These sounds cannot originate acoustically since sound waves cannot not travel fast enough to be heard at the same time as the meteor flashes.
The best explanation for many of these simultaneous meteor sounds is offered by Colin Keay. He suggests the sounds arise by electrophonic transduction. The wake of the fireball traps its magnetic field which creates very long radio waves which travel at the speed of light. The radio waves engender audio waves by interacting with ground-level objects such as trees or spectacles. This is still a controversial idea even though the sounds have now been recorded by several researchers. The same principle may explain reports of auroral sounds, animal unease prior to earthquakes, and sounds heard prior to a nearby lightning strike.
The usual electrophonic explanation fails for some short duration "pops" and staccato "clicks" which accompany certain meteors. Luigi Foschini and Martin Beech suggest such short duration pulses are generated by a strong electric field across the shock wave propagating in the plasma formed by the catastrophic disruption of the meteoroid in the atmosphere.
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Last modified by pib on May 12, 2009.