Hello, Marco and the list,
Marco, don�t know, did Jarmo sent to you the final calculations we
have about the Feb. 12:th bolide, but here�s a link to a graphic of some
potential pieces (unfortunately in finnish, but I think you can get the idea).
The flight of one piece is marked as a red line, in following I�m just
speaking about this fragment.
http://www.nuuska.pp.fi/elmi.jpg
The detonating-altitude is counted as 35 km:s / 0 seconds, the last point
marked is in altitude 0.74 km:s / 396 seconds. We used the radar-data to
find some "hot spots", they can be real, or just from the ionisation of the
bolide. The effect of wind was quite interresting in this calculation, the
potential mass of the fragment was calculated as 50 grams chondrite.
We got a great help from Marco, Peter Jenniskens and Pavel Spurny, so my warmest thanks again to all of them.
Unfortunately we got some 7 cm:s snow just after the bolide, and the potential
strewn-field was mainly on ice, so it was quite hopeless to find anything, but
this was a very interresting case, and think we are next time much wiser...;-
Some translations;
- korkeus = altitude - aika = time - tuulen suunta = wind
The graphics may be correct or may be not. As I told, we used the "hot-spots"
from the radar-data, and if this data is incorrect, the whole graphics in incorrect.
Anyway, in this calculation it took 396 secs from 35 km:s to 0.74 km:s for a 50
gram fragment of ordinary chondrite. (If the radar-data is correct). So time in
minutes from 35 km:s to 0.74 km:s would be 6.6 minutes, and it may make sence,
if we check the calculations of Glanerbrug time, 2.5 minutes from 15 km:s.
take care,
pekka
Marco Langbroek wrote:
Steve wrote:
Does anyone have the actual rate of fall already calculated? Is the fall time a universal law of physics learned by all meteoritic students in "Strewnfields 101" class?
I have some indicative data for you from the Dutch Glanerbrug fall. This hit a house and shattered, and Peter Jenniskens was able to determine from the fragment size distribution that the velocity upon impact was of order 30-120 meter/s (see P. Jenniskens et al., Pub. Astr. Inst. Czech. no. 79 (1992), 1-18). If we take that as a typical value, it would take some 2.5 minutes to come down from 15 km altitude.
Casper ter Kuile made a model calculation of the free fall of Glanerbrug which does take in account atmospheric drag on the falling meteorite. For an object (assumed spherical) of about 1 kg falling in free fall from 25 km altitude, this indeed provides impact velocities of order 50-110 meter/s, and a fall duration of some 3 minutes. (see Radiant (J. Dutch Meteor Soc.) 12 (1990), 78-80).
So yes: the actual impact of a meteorite will occur a few minutes after the fireball in a typical case.
- Marco
---------- Marco Langbroek
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William Shakespeare The Tempest act I scene 2 ----------
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