[meteorite-list] Fireball questions

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Jun 17 12:33:05 2004
Message-ID: <20040617163109.69518.qmail_at_web51710.mail.yahoo.com>

Hello Vincent and George,

I did a Google search on "Fireball Altitude Bolide
Sonic Boom", and guess what I found high on the list
of results? I found that one of the many posts made
to the List on this subject was by me, back in July
2001. It appears that I was trying to make the point
that you don't have to have an explosive fragmentation
event in order for a bolide to generate a sonic boom -
here's a portion of that post where I quote the
referenced article:

Richardson, J.E. (2001, June). The Gold Basin
Meteorite Strewn Field, Meteor Trails, Journal of the
American Meteor Society (No. 12) [article]:

"Meteoroid Disintegration and The Strewn Field"
"Most meteorite dropping fireballs will become visible
at an altitude of about 70-90 km, which is below the
normal band for most meteors of about 100-120 km, due
to their very slow speeds (about 11-17 km/sec). As the
meteoroid penetrates the atmosphere to more and more
dense layers of the atmosphere, it will steadily lose
kinetic energy and decelerate, while losing mass to
the ablation process at the same time. The estimates
on the amount of mass lost vary widely, depending upon
the initial assumptions made, especially with regard
to meteoroid density and structural strength. It is
also not uncommon for fireballs to exhibit several
flares in brightness over their paths, as smaller
portions break off from the primary meteoroid due to
the large differential stresses across the length of
the body as it falls.
"At about 15-20 km in altitude, most meteorite
dropping fireballs will stop emitting visible light,
as the body is decelerated down to about 2-4 km/sec.
During the remainder of the meteorite’s flight, the
object will fall as a “dark body,” continue to
decelerate until it loses all of its initial cosmic
velocity (the retardation point), and then silently
and invisibly drops to the ground at the meteorite’s
terminal velocity. During the final deceleration phase
of the fall to the retardation point, sonic booms may
be emitted which will reach the ground a few minutes
after the meteorite has landed.
"More dramatically, some fireballs will end their
visible track in a brilliant terminal flare, as the
meteoroid catastrophically disintegrates into many
smaller bodies. If this event occurs late enough in
the meteoroid’s flight, the resulting collection of
bodies will rapidly decelerate until ablation stops,
and then fall to the ground as a “meteorite shower.”
The area on the ground where this collection of
meteorites from the same parent body are found is
called a strewn field."

(By the way, can't speak for the CalTech Seismo
Network but the June 3rd Washington Bolide event was
recorded on a number of Univ. of Wash. seismographs.)

Bob V.

-----------------------

[meteorite-list] Fireball questions
GeoZay at aol.com GeoZay at aol.com
Thu Jun 17 10:29:23 EDT 2004

  
>> If a fireball explode and create a sonic(shock)
wave observed in seismic stations; if the same
fireball create thump rumble or thump deflagrations;
can we suppose find a meteorite on the ground?<<

I once pursued in California a very loud sonic
producing fireball with Caltech who monitored the
various seismic stations. I was told that these kind
of sounds were somehow filtered out so they wouldn't
show up on the seismographs.

>>At wich altitude a normal bolide can explode, or
produce a audible sonic boom?<<

To produce a sonic boom, the meteoroid would have to
be at least 30 miles above the earth.
George Zay
Received on Thu 17 Jun 2004 12:31:09 PM PDT