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From: ABOULANGER@BBNG.ARPA
Newsgroups: net.physics
Subject: Re: Re: lightening bursts
Message-ID: <489@sri-arpa.ARPA>
Date: Mon, 12-Aug-85 10:58:42 EDT
Article-I.D.: sri-arpa.489
Posted: Mon Aug 12 10:58:42 1985
Date-Received: Sun, 18-Aug-85 21:42:41 EDT
Lines: 34

From:  Albert Boulanger 


  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 analogy that Martin Uman, a lightning researcher, gives is
that this charge cylinder is like a long forking sand bag; when
it reaches ground it unzips. The wave of sand falling out is
what causes what you see as lightning. There was a pulsed
nitrogen laser project in SciAm a few years back that worked on a
similar principle. I found the design simple, clever, and
elegant.

By the way, lightning seems to be a fractal curve. There have
been some papers about this. 

Albert Boulanger
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