Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site prometheus.UUCP Path: utzoo!linus!decvax!genrad!panda!talcott!harvard!seismo!umcp-cs!prometheus!pmk 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. - - NOTE: MAIL PATH MAY DIFFER FROM HEADER - - +-------------------------------------------------------+--------+ | Paul M. Koloc, President: (301) 445-1075 | FUSION | | Prometheus II Ltd., College Park, MD 20740-0222 | this | | pmk@prometheus.UUCP; ..seismo!prometheus!pmk.UUCP | decade | +-------------------------------------------------------+--------+