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Electrophonic sounds vs. "booms" (was Re: (meteorobs) Bolide booms)
>I was under the impression that the sound produced from a bolide was NOTHING
>to do with the meteor itself, but a massive flux of energy travelling at the
>speed of light which causes wire fences and other similar objects to
>resonate violently, causing the "boom" sound often confused with a sonic
>boom. I was told that sounds from the actual meteor were only heard several
>minutes after the observation and were often undetectable by the human ear.
>I learned this from a physics lecturer.
Yup, Matthew, your physics lecturer was (amazingly) well-informed. (Meteor
science seems to be the LAST THING many prof astronomers learn about.)
The simultaneous sounds sometimes reported with bright fireballs have been
called "electrophonic" sounds, and one of the most plausible explanations I've
heard involves the ionized column of air produced by the meteor's passage,
interacting with earth's magnetic field to produce a burst of radio waves, which
in turn cause metallic objects near ground-based observers to resonate. Again,
this is theory: another theory actually posits this is a psychological effect!
Anyway, these simultaneous sounds are generally reported as "swishing" or
"whistling" sounds, or in some cases (and the one I heard was best described
this way) as "like a light bulb quietly fizzling out". They're quite distinct
from the low, "distant" booming associated with NON-simultaneous sounds.
===============
Anyway, with all that said, what we were ORIGINALLY discussing on this thread
were the NON-simultaneous sounds that have been heard one to 60 minutes after a
visual fireball. Because of their delay, they are clearly propogating AS SOUND
from the distance of the actual meteoric event. My question then on these "sonic
booms" was: Are they in fact sonic booms, produced by entry of a hypervelocity
object in the ultrathin atmosphere at 30-80 km altitude? Or are they instead due
to the rapid expansion of that column of heated air around the meteor's path?
Anyone care to comment? I'm interested to hear myself!
Lew Gramer
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