Re: [TCML] Re: Re: Spark models, revisited

["Udo Lenz" <udo_lenz@xxxxxxxxxxxxxx>]

Bert Hickman wrote:

> The 0.1*c figure is the experimentally-measured wave velocity for a
> disturbance through an established leader, such as the return stroke in
> lightning or the return current surge when a TC leader connects to a solid
> ground. The leader tip propagation velocity for a growing leader is
> considerably slower - by a factor of 10 - 100 depending on tip E-field and
> divergence of the background E-field.

I see, so this is for ground arcs. Recently Steve Ward posted a measurement
of the discharge time for ground arcs:
http://www.pupman.com/listarchives/2012/Sep/msg00133.html

Assuming for a rough estimate, that his top load had a capacitance of 20pF,
a discharge time of 200ns would require a total spark resistance of about
10k.
That is in marked contrast to my (model dependent) estimate of a resistance
of 1k/cm for my 70cm arc. Now his arcs are probably much bigger than mine,
but I believe the main difference is, that ground arcs can carry much more
current than "into the air" arcs. Together with the dispersive nature of
R-C transmission line models, which makes high frequency components
travel faster than low frequency ones, a speed of 0.1*c seems plausible also
for R-C models.

Udo

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