Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!lll-crg!dual!qantel!hplabs!sri-unix!ABOULANGER@BBNG.ARPA 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 BoulangerCharge 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 -------