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From: pmk@prometheus.UUCP (Paul M Koloc)
Newsgroups: net.physics
Subject: Re: Re: lightening bursts
Message-ID: <159@prometheus.UUCP>
Date: Mon, 5-Aug-85 21:48:24 EDT
Article-I.D.: promethe.159
Posted: Mon Aug  5 21:48:24 1985
Date-Received: Wed, 7-Aug-85 04:17:17 EDT
References: <3305@decwrl.UUCP> <251@unccvax.UUCP> <454@utastro.UUCP>
Organization: Prometheus II Ltd., College Park, MD
Lines: 45

> > with this ultra-high-speed photography and other techniques, it has been 
> > shown that the cloud-to-ground burst is definitely 'ground - to -cloud'
> > and that ionization 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 ionization 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.  
> -- 
> Ethan Vishniac

Charge is lowered from the cloud toward the ground by the step leader process.
As it does the electrons spray off from the leading tip radially outward, 
generating a "comet like" discharge observable only with fast image 
intensifiers.  The electrons decelerate enough after expanding a few tens
of meters from the step leader channel to attach to O2 molecules where 
they are essentially stored in a "charge cylinder" for the remainder of the 
high speed lightning process.  The direction of the steps may be determined 
by ionization tracks due to cosmic rays so they are random.  Sometimes the 
step process "forks".  Now when the cloud to ground electron transfers reach 
several tens of meters from the ground, the potential is high enough to 
generate a "bright" anode streamer or return stroke.   The discharge largely 
consists of discharging the "charge cylinder".  That means as the channel 
reaches a "forked branch" the discharge then tracks through the fork as 
well as continues toward the cloud.  That's why lightning seems to have 
branches that just "end in the air" and never reach ground (except as noted 
above).

The upward flying radial discharge of the charge cylinder to the return 
stroke tip generates energetic electrons which can "trap" components of 
the earth's field in the channel.  That's why lightning in Florida is quite 
different than the stuff in New York.  Lightning in Florida can  do all kinds 
of loop the loops and follow wild paths.  In New York the component of the 
earth's field has much greater declination so lightning there may be more 
stablized and follow somewhat shorter (straighter sectioned zig-zag paths) 
to ground. 

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