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(meteorobs) Fireball elevation vs. probability of a sonic boom
***********
If a very bright fireball, usually greater than magnitude -8, penetrates
to
the stratosphere, below an altitude of about 50 km (30 miles), and
explodes
as a bolide, there is a chance that sonic booms may be heard on the
ground
below. This is more likely if the bolide occurs at an altitude angle of
about 45 degrees or so for the observer, and is less likely if the
bolide
occurs overhead (although still possible) or near the horizon. Because
sound travels quite slowly, at only about 20 km per minute, it will
generally be 1.5 to 4 minutes after the visual explosion before any
sonic
boom can be heard. Observers who witness such spectacular events are
encouraged to listen for a full 5 minutes after the fireball for
potential
sonic booms.
**********
I've taken this from AMS Fireball FAQ. One thing bothers me. Why is it
more
likely to hear the sonic boom when a fireball occurs at 45 degrees then
overhead.
The sound travels in concentric waves, and the intesity diminishes with
the
square of the range, so judging from this, the most likely spot to hear
a sonic
boom is right below the fireball, so the fireball should appear
overhead. It is
obviously not this way. What is the explanation for this?
I can't say much from my experience, because the sample of fireballs is
too
small. When a -11 sporadic fireball occured overhead on March 28, 1996,
I heard a sonic boom about 4 minutes later. On the other hand, when a
-15 mag fireball occured at an angle of 70 degrees on June 2, 1999, I
heard nothing (I guess it was of cometary origin).
Has anyone ever done an experiment at 'listening' to fireballs, perhaps
with
a sound intensifier so that sounds from fainter fireballs might be
recorded?
Clear skies!
Jure A.
" Fireballs are just meteors with attitude."
-NJmeteors
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