[geeks] Whee! Lightning strikes, AGAIN!

[gsm at mendelson.com]

On Mon, Jul 27, 2009 at 10:17:16PM +0000, wa2egp at att.net wrote:
>
>Enlighten me.

Zap!!!!!   :-)


http://en.wikipedia.org/wiki/Lightning

"When a stepped leader approaches the ground, the presence of opposite
charges on the ground enhances the strength of the electric field. The
electric field is strongest on ground-connected objects whose tops are
closest to the base of the thundercloud, such as trees and tall
buildings. If the electric field is strong enough, a conductive
discharge (called a positive streamer) can develop from these points.
This was first theorized by Heinz Kasemir. As the field increases, the
positive streamer may evolve into a hotter, higher current leader which
eventually connects to the descending stepped leader from the cloud. It
is also possible for many streamers to develop from many different
objects simultaneously, with only one connecting with the leader and
forming the main discharge path. Photographs have been taken on which
non-connected streamers are clearly visible.[21] When the down and up
leaders meet, the flow of electric current greatly increases."

"Once a channel of ionized air is established between the cloud and
ground this becomes a path of least resistance and allows for a much
greater current to propagate from the Earth back up the leader into the
cloud. This is the return stroke and it is the most luminous and
noticeable part of the lightning discharge."

What it does not say, is that if you disipate the charges from the ground
side, there are no up leaders, and therefore no connections. 

A Franklin designed lightening rod (grounded point source) focuses the
ground charges and creates up leaders, forcing connections to them. 

With no up leaders, you either get a discharge after a negative leader
reaches the ground, or more likely, an up leader from a different source
forms and reaches a down leader. Remember we are talking about cloud
sized objects in the sky and relatively small ones on the ground.

Geoff.

-- 
Geoffrey S. Mendelson, Jerusalem, Israel gsm at mendelson.com  N3OWJ/4X1GM