Lightning

[Magnus Danielson]

From: Rory McDonald <RMcDonald at wireone.com>
Subject: Lightning
Date: Wed, 2 Aug 2000 19:40:02 -0700 

> I just saw an interesting piece on Lightning striking humans on CNBC and
> made me wonder-is Lightning AC or DC? I know that the voltages can be huge.
> Some woman on the show got hit 3 times in her lift and lived to tell the
> tale-yikes!

I've seen some replies to this... so this is my take.

The terms AC and DC really relate to two forms of "steady-state" current where
AC alternates polarity and DC does not alternate polarity (actually, it does
not change at all).

My point is that one can argue that the usage of these terms is really not
very interesting since a lightning that strikes is a impulse event. This
impulse even may be followed by a ringing which may be caused by the physics
of whatever got hit. With or without ringing, the current has an impulse
characteristics and can not be said to be in any form of steady state.

The actual ligthning core is a gigantic stream of current which nature as put
in one direction. So this part you could claim has a DC component, even after
averaging out all ligthenings of a year or so (yeat again due to mother
nature). The DC component that our statistical analysis showed is not very
stable though...

One must realize that the direction of the current is of interest when you do
ligthning arresters etc. You can really speak of anode and catode and what
happends to the material.

There are very enligthning (sorry!) books on this subject, I just happend to
have and actually have read one of them!

Cheers,
Magnus - my new office will have an ESD carpet I discovered.