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From: ethan@utastro.UUCP (Ethan Vishniac)
Newsgroups: net.physics
Subject: Re: lightening bursts
Message-ID: <454@utastro.UUCP>
Date: Wed, 31-Jul-85 10:43:16 EDT
Article-I.D.: utastro.454
Posted: Wed Jul 31 10:43:16 1985
Date-Received: Sun, 4-Aug-85 06:48:07 EDT
References: <3305@decwrl.UUCP> <251@unccvax.UUCP>
Organization: U. Texas, Astronomy, Austin, TX
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> One thing the guest did mention was that they found lightning
> paths were one 'helluva' lot longer than was originally postulated. Also,
> with this ultrahighspeed photography and other techniques, it has been 
> shown that the cloud-to-ground burst is definitely 'ground - to -cloud'
> and that ionisation occurs first (several hundreds of milliseconds).
> This thing (called a 'stepped leader') precedes the actual event in 
> almost every case.
> 
> David Anthony

I saw a seminar on this a year ago.  Evidently the ionisation path forms
from the clouds to the ground in a series of short "steps".  The path
is like a biased random walk toward the ground.  Then, as you say,
the most energetic event occurs, a massive ground-to-cloud surge of
current.  I believe this surge starts once the ionisation path is some
tens of meters from the ground.
-- 

"Don't argue with a fool.      Ethan Vishniac
 Borrow his money."            {charm,ut-sally,ut-ngp,noao}!utastro!ethan
                               Department of Astronomy
                               University of Texas