[PD] pd thunder

Andy Farnell padawan12 at obiwannabe.co.uk
Wed Feb 6 17:30:19 CET 2008

Yes. That's part of it.

According to Ribner and Roys first paper the vacuum collapse model
is refuted - well, they don't use that exact word - more like
they suggest it is replaced... 

"As recently as the late 1800's, four theories of thunder were in competition:
The vacuum collapse theory, the explosive electrolysis theory (recombination 
of electrolyzed water), the steam  expansion theory, and the Ohmic heating 
theory (resistive heating and consequent expansion due to heavy current
discharge). The last, proposed by M. Hirn in 1888, is now accepted, being
supported by a large body of consistent experimental data and theory."

However I disagree, since it is one necessary flip side of the favoured 
primary cause - collapse happens after the expansion (in a remarkably 
short time frame) Therefore the vacuum collapse theory must be incorporated
into a complete model, being responsible for the negative impulse of the N-wave.

"One prevailing theory proposed that thunder was produced when lightning,
passing through the air, caused a vacuum to form. When this vacuum collapsed,
the air rapidly rushing back in produced a thunderous explosion."


As I see, the unipolar vacuum collapse theory only makes sense, if there 
is a chemical reaction that removes CO2, H2O, O2 or N2 from the atmosphere,
(and one assumes no matter is transformed to energy) - well NO2 and O3
are produced, but that doesn't account for the volume.

Vacuum collapse theory ?? (< 1800)
Steam theory of R.V. Reynolds (1903)
Electrolysis theory R.S. Mershon (1870)
Ohmic heating theory M. Hirn in 1888

In a 1888 article in Scientific American, M. Hirn advanced the theory that

"thunder is due simply to the fact that the air traversed by an electrical 
spark, that is, a flash of lightning, is suddenly raised to a very high 
temperature, and has its volume, moreover, considerably increased. The 
column of gas thus suddenly heated and expanded is sometimes several miles
long, and as the duration of the flash is not even a millionth of a second,
it follows that the noise burst forth at once from the whole column, though 
for a observer in any one place it commences where the lightning is at the
least distance....the beginning of the thunderclap gives us the minimum 
distance of the lightning, and the length of the thunder clap gives us the 
length of the column."

So, in summary, there is no single cause and all these theories
are sensibly incorporated into the process.

Least likely is perhaps Mershon - but in a plasma we know the gasses 
are monatomic and there is still a lot of stuff to be discovered in
plasma physics, so he may have been on to something after all.

Reynolds clearly contributes something sensible, because water vapour 
has the highest thermal expansive coefficient.

And the vacuum collapse theory _must_ be incorporated if the Ohmic
expansion theory holds.


On Wed, 6 Feb 2008 16:00:58 +0100
plessas at mur.at (Peter Plessas) wrote:

> * Andy Farnell <padawan12 at obiwannabe.co.uk> [2008-02-05 23:33]:
> > 
> > 
> > You're spot on there. I will develop the stereo image as I work on
> > the environment model.
> > 
> > But interestingly enough, lightning _is_ an explosion, one hell of
> > a big explosion. The plasma is as hot as the Sun for an instant and
> > that's why the air expands, the energy in a lightning bold makes most
> > bombs seem like little fireworks. The difference is, and this is
> > unusual, it radiates in a cylinder not a sphere, and sound comes
> > from a simultanoeus extent (because the bolt moves at the speed of
> > electricity which is closer to the speed of light than the speed of
> > sound)
> Isn't the noise happening when the light/plasma channel is collapsing
> after the lightning happened?
> regards, Peter
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