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FRA1PS > ASTRO 19.02.13 18:19l 99 Lines 3983 Bytes #999 (0) @ WW
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From: FRA1PS@FRA1PR.FMPACA.FRA.EU.WW
To : ASTRO@WW
Feb 15, 2013 Fireball Event Summary
What follows are **initial** information gleaned for multiple instrumental
sources recording various aspects of the Feb 15, 2013 airburst over
Chelaybinsk, Russia (55.2N, 61.4E)
1. Time: The time of the main flare/airburst was 03:20:26 UT on Feb 15, 2013;
the fireball began ablation about 30 secs before this time.
2. Based on the long duration of the event and videos, it is clear this was a
very shallow entry (certainly less than 20 degrees, maybe more shallow).
3. It is **not** related to 2012 DA14
4. Energy: This is perhaps the hardest value to pin down so early in this
investigation. From multiple sensors using multiple technologies a best
initial estimate of the total energy of the event is about 300 kilotons of TNT
equivalent = ~10^15 J). This could easily be in error by a factor of two. I am
confident, however that it is in excess of 100 kTons, making it the largest
recorded event since the 1908 Tunguska explosion.
5. Speed: The fireball entered the atmosphere at 18 km/s
6. Damage: The airblast clearly caused window breakage and light structural
damage in downtown Chelaybinsk. The exact overpressure at which window failure
occurs tends to be probabilistic and varies by construction design (ANSI
S2.20, 1983). Normally some damage begins to occur around 500 Pa of
overpressure, widespread window damage is expected to occur up to around
ten-20 times this value. As the fireball had a shallow trajectory, the
cylindrical blast wave would have propagated directly to the ground and would
be expected to be intense. This could be further compounded by any
fragmentation, quasi-spherical blasts. My impression is that the key here is
that the terminal part of the fireball (probably between 15-20 km altitude)
occurred almost directly over Chelaybinsk; this was perhaps the single
greatest contributor to the blast damage (short range to the main part of the
terminal detonation).
7. Comparators: The Sikhote-Alin fall (Feb 12, 1947) in the former Soviet
Union was the equivalent of about 10 kilotons TNT, BUT as an iron impactor
much of this energy was deposited at the ground rather than at altitude. The
Oct 8, 2009 Indonesia event is the most recent similar event at about 50
kTons, but over the ocean (paper attached for quick reference).
8. Size: The pre-impacting asteroid was about 15 meters in diameter and had a
mass of ~7000 tonnes.
I fully expect revision of some of the numbers above, particularly the
estimate of the yield which could **easily** change by a factor of two upon
more complete analysis and will likely change as the day progresses
/end
--------------------
The earlier estimate of 300 kT for the Feb 15, 2013 airburst was based on
Infrasound period measurements at the four closest stations. Five additional
stations have now been found which show the signal clearly, including one as
far away as Alaska (range of 6500 km). Based on the infrasound period at all
stations and using the yield relation for multi-station fireball detections
found in
Ens T. a., Brown P., Edwards W. N., and Silber E. 2012. Infrasound production
by bolides: A global statistical study. /Journal of Atmospheric and
Solar-Terrestrial Physics/ 80: 208–229.
a mean period of 32.5 second for the event is found. This corresponds to a
nominal yield of 470 kT TNT equivalent. This represents a best estimate for
the yield of this event from infrasound records. As before there remains a
potential uncertainty of order a factor of two in this value.
--------------------
Dr. Peter Brown
Director - Centre for Planetary Science and Exploration
Canada Research Chair in Meteor Astronomy
Professor
Department of Physics and Astronomy
University of Western Ontario
London, Ontario
N6A 3K7
CANADA
73 De gerard
fra1pr.fmpaca.fra.eu.ww
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Message Written At 09:27 Local Time.
19 Feb 13
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