Re: TC & Lightning

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson" <paul-at-abelian.demon.co.uk> 

Let me try to connect this discussion with Tesla coils, to
illustrate a point or two...

Ed wrote:

 > To the extent that the lightning stroke discharges the cloud in
 > the region from which it originated there will also be a strong
 > transient field change of the order of those same hundreds of
 > volts per meter

I thoroughly approve of this kite flying, rocket firing, balloon
lofting dangerous fun!!  (ok I admit, I like rock climbing and rally
driving and playing with high voltages, so I'm not very normal.)

Lightning discharges seem to be a pretty complicated thing,  not
least their interaction with the environment.  Let me give some
examples picked up with a VLF receiver (basically: radio waves
at audio frequencies received by hooking a rod antenna to a
sensitive hi-Z audio amp).

All mp3 recordings:-
Triggered emissions following a 50 mile distant discharge:
  http://www.abelian.demon.co.uk/vlf/lta.100303b1.mp3
  http://www.abelian.demon.co.uk/vlf/lta.100303b2.mp3

Multiple whistlers (long, dispersed echoes of a lightning
discharge) from a discharge (the loud snap) a few hundred miles away:
  http://www.abelian.demon.co.uk/vlf/wh.070303a.mp3
  http://www.abelian.demon.co.uk/vlf/wh.3010b.mp3
  http://www.abelian.demon.co.uk/vlf/wh.3110a.mp3

Just to ensure that this actually relates somewhere to TCs, these
whistler echoes demonstrate EM waves travelling rather slowly,
zig-zagging or spiralling through space up in the magnetosphere.
The high dispersion spreads the 'click' of the discharge out into
a descending whistle.  Different frequencies follow different
effective paths (just as the effective velocity varies with freq in
a solenoid).   Their strength is maintained by 'ducting' through the
graded refractive index of a space full of mag fields and charged
particles - so this is a natural guided wave phenomena. [+]

Nearby discharges have some funny effects locally too. For several
seconds after the discharge you can receive all sorts of crackles
and hisses as the neighborhood fields and charge distributions sort
themselves out.
  http://www.abelian.demon.co.uk/vlf/sf010303a.mp3

That one was so strong (just a few miles away) that the receiver
shut down for a second or two.  Listen for the funny hollow hiss
that lasts a few seconds after.  I'm working on a robust rx that I
can leave running throughout a storm.

Lightning sounds like a crack or snap from a few hundred miles
distances, but close up, as in lta.100303b2.mp3 above, you can tell
that it takes perhaps a whole second for the cloud to discharge.

Gary wrote:
 > A good lightning bolt sounds like a stick of dynamite, "BOOM."

I can't wait to try it...

[+]  Imagine trying to do this process in reverse: Start with a
TC made to have a suitable pattern of dispersion.  Send in a
CW burst having a swept frequency (a chirp) carefully chosen so
that the entire chirp (and therefore all the burst energy) is
concentrated by the dispersion into a single pulse at the far
end of the coil.
--
Paul Nicholson
http://www.abelian.demon.co.uk/vlf/
--