Russian meteor

[Chew]

The Nuclear Weapons Archive has a Repository of software of nuclear weapons effects but the good program (we.zip) is DOS based and I don't feel like fighting 64 bit Windows to make it work.

You can try running it in DOSBox.

That is exactly what I was referring to when I said I don't feel like fighting.

[Daggerstab]

Well, I managed to run it with DOSBox on my Linux machine. As in my experience DOSBox results are quite consistent across multiple platforms, it should work on Windows, too. No fiddling required - in my case, it involved only unzipping the archive to a directory, calling dosbox with that directory as an argument (it mounted it as C:) and running we.exe in the DOSBox window that had opened.

The Nuclear Weapons Archive page with the software is here:
http://nuclearweaponarchive.org/Library/Nukesims.html

And speaking of simulations, there's always the Earth impact calculator:
http://www.purdue.edu/impactearth

[ka9q]

I just played with that Purdue calculator, it's just what we're looking for.

The closest results I got were with: diameter, 18 m; density 3000 kg/m³; velocity 30 km/s; angle 20 deg; target sedimentary rock; observer distance 30 km. This yielded total energy 985 kt; average time between comparable impacts 109 yr; object begins breakup at 63.1 km; explodes at 33.6 km; residual velocity 24.1 km/s; airburst energy 350 kt; no crater; airblast arrives 2.27 min later; peak overpressure 194 Pa.

Some of these are in the ballpark but there are a few things I don't understand. Only about a third of the energy is released in the airburst. The fragments still have substantial velocity and the model doesn't say what happens to them. They certainly can't hit the ground with that energy as they're all going much faster than Mach 1 in even denser air, and being smaller they have lower ballistic coefficients. I think they should continue to generate a strong shock wave that will dissipate most of their energy.

The peak overpressure seems low; the tables I see say that small windows break at 0.1 psi; 10% of windows break at 0.3 psi; windows shattered, limited minor structure damage at 0.5 psi. This last one seems roughly comparable to what happened in Chelyabinsk, but 0.5 psi is about 3500 Pa, much more than the modeled 194 Pa. Maybe I was too far away at 30 km, but when I use anything smaller I get much less than the observed 2.4 minute delay.

I bet the maintainers of this model will recalibrate it with this event. After all, nothing like this has ever happened before in modern history.

[smartcooky]

....average time between comparable impacts 109 yr

Interesting!!

Tunguska Event......1908
Chelyabinsk Event..2013

Difference: 105 yrs

Looks about right to me, although I am willing to bet that the Berwyn Mountain incident in 1974 (a.k.a. the "Welsh Roswell") was something similar to Chelyabinsk; a bright trail across the sky seen from Ireland in the west to Cornwall in the south and to the Midlands in the east, a loud explosion and what people in Llandrillo, Wales reported as a shaking "like an earthquake".   

[Daggerstab]

The peak overpressure seems low; the tables I see say that small windows break at 0.1 psi; 10% of windows break at 0.3 psi; windows shattered, limited minor structure damage at 0.5 psi. This last one seems roughly comparable to what happened in Chelyabinsk, but 0.5 psi is about 3500 Pa, much more than the modeled 194 Pa. Maybe I was too far away at 30 km, but when I use anything smaller I get much less than the observed 2.4 minute delay.

I bet the maintainers of this model will recalibrate it with this event. After all, nothing like this has ever happened before in modern history.

That calculator is mostly edutainment. If you click on the "Documentation" link in the upper bar, you'll get a PDF with an article explaining the different models and the assumptions and simplifications they used.

I'm not even sure how the sound delay is calculated in the case of an airburst - the source parameter is "distance to impact site", not "to airburst", so this may be a possible source of the discrepancy. I skimmed the article, but couldn't find anything for sure.

Anyway, is it clear whether the broken glass was due to the "sonic boom" travelling shockwave, or the shockwave caused by the meteoroid disintegration event/explosion?

[ka9q]

I think it has to be the sonic boom.

While there are parallels between large bolides and nuclear weapons, especially in the total amount of energy released, there are some important differences.

A nuclear weapon releases all its energy in an instant (< 1 μs) and in a very small volume (~1 m³). It can do this in the air, on the surface or under ground or water. An asteroid's energy is entirely in its motion, and unless there's something to slow it down it cannot release that energy. In particular it cannot simply "detonate" in midair as a nuclear bomb can.

What it can do is to release that energy continuously as it decelerates in the air. If it breaks apart, its total surface area and energy release rate will suddenly increase, but it still won't "detonate". Unless perhaps it suddenly breaks apart into so many tiny pieces that decelerate so rapidly due to drag that all their remaining kinetic energies are released quickly enough to be considered an "explosion". But for a shallow trajectory like the Chelyabinks bolide, this didn't seem to happen. It seemed to release its energy more or less continuously over several seconds and quite a few km.

If there's still a lot of kinetic energy left when the object(s) hits the ground, then it/they will "detonate" and release all that energy in a very small volume and period of time. The effect will be much like the surface detonation of a nuclear weapon, with an incendiary thermal pulse, a blast wave and a crater, though no radiation of course.