gary@mic.UUCP (02/24/88)
Is it correct that lightning travels from the ground up instead of the sky down to the ground? I vaguely remember that this is the case but do not remember where I read about it. Gary Lewin killer!mic!gary
crown@dukempd.UUCP (Rick Crownover) (02/29/88)
In article <64600001@mic>, gary@mic.UUCP writes: > > Is it correct that lightning travels from the ground up instead of the > sky down to the ground? I vaguely remember that this is the case but > do not remember where I read about it. > Lightning can strike upwards in one sense: in the mountains, it is possible to see lightning originating in an air mass below the ground it strikesThere is a description of this phenom in Goethe's "Faust" in the Walpurgis scene. I doubt that lightning strikes from ground to sky for two reasons, 1) the slow motion films I've seen always show it going the other way, and 2) the ground is conductive and would have trouble building up a large local charge. But, I'm with you, does anyone know? Aloha, Rick -- Rick Crownover 1-919-684-8279 Duke University Dept. of Physics crown@dukempd.uucp Durham, N.C. 27706 mcnc!duke!dukempd!crown
g-rh@cca.CCA.COM (Richard Harter) (02/29/88)
In article <512@dukempd.UUCP> crown@dukempd.UUCP (Rick Crownover) writes: >In article <64600001@mic>, gary@mic.UUCP writes: >> >> Is it correct that lightning travels from the ground up instead of the >> sky down to the ground? I vaguely remember that this is the case but >> do not remember where I read about it. >> > Lightning can strike upwards in one sense: in the mountains, it is >possible to see lightning originating in an air mass below the ground it strikesThere is a description of this phenom in Goethe's "Faust" in the Walpurgis >scene. I doubt that lightning strikes from ground to sky for two reasons, 1) >the slow motion films I've seen always show it going the other way, and 2) the >ground is conductive and would have trouble building up a large local charge. >But, I'm with you, does anyone know? This may be unfair, but I took the liberty of looking up lightning in the Enc. Brit. I quote: "A faint luminous process in regular disinct steps, typically of 50-metre length, at time intervals of 50 microseconds, descends in a downward branching pattern toward the ground. Carrying currents on the order of hundreds of amperes, this stepped leader or initial stroke propogates at a typical velocity of 1.5E5 metres per second, or about one two- thousandth the speed of light... As the branching process nears the ground, approximately five coulombs of charge have been induced on the channel, inducing an opposite charge on the ground and increasing the electric field between the lead and the point to be struck. An upward discharge occurs from the ground, church steeple, house, or other object to meet the stepped leader about 50 metres above the surface. At this moment of junction the cloud is short circuited to the ground and a highly luminous return stroke of high current occurs." In conclusion, the original question is not well posed, because it assumes that there is a single direction of lightning stroke, whereas in fact there are two processes involved, one downwards and one upwards. However the highly luminous return stroke, which we see, is upwards. Ref Enc. Brit., 15th edition, vol 10 of the macropedia, pp 965-970. -- In the fields of Hell where the grass grows high Are the graves of dreams allowed to die. Richard Harter, SMDS Inc.
drich@bgsuvax.UUCP (Daniel Rich) (03/01/88)
From article <64600001@mic>, by gary@mic.UUCP: > > Is it correct that lightning travels from the ground up instead of the > sky down to the ground? I vaguely remember that this is the case but > do not remember where I read about it. > > Gary Lewin killer!mic!gary If I remember my physics correctly, the lightning strike that we see is from the ground upwards. Since the clouds are usually positively charged (the air strips electrons from them), the ground tends to take a negative charge near them. Electricity travels from negative to postive, therefore lightning travels upwards. I believe that someone said that the films they had seen show it traveling the other direction. Think about this for a second.... electricity travels at approximately the speed of light (actually, in air it is a little slower). At this speed, how could you ever determine a direction from film? - Dan Rich UUCP: ...!cbatt!osu-cis!bgsuvax!drich CSNET: drich@andy.bgsu.edu drich%andy.bgsu.edu@relay.cs.net SNAIL: 325 1/2 S. Church or Department of Computer Science Bowling Green, OH 43402 Bowling Green, OH 43403 (419) 354-7152 (419) 372-6002 - Sometimes a majority simply means that all the fools are on the same side -
bob@nih-csl.UUCP (Bob Dew) (03/02/88)
Several years ago, I attended a graduate seminar in electrical engineering devoted to the subject of lightning. Two types of lightning, positive and negative (or down & up), were identified that occur in common electrical thunder storms. The type of atomoshpere-to-ground lightning that strikes depends upon whether the atmosphere is positively or negatively charged with respect to the target. Both positive and negative lightning can be observed in a typical thunder storm, but positive lightning is observed about 100 times more frequently.
todd@uop.edu (Dr. Nethack) (03/03/88)
In article <512@dukempd.UUCP>, crown@dukempd.UUCP (Rick Crownover) writes: > In article <64600001@mic>, gary@mic.UUCP writes: > > > > Is it correct that lightning travels from the ground up instead of the > > sky down to the ground? As I recall, there is a ground to cloud stroke, and the cloud to ground follows. I don't have my library at work or I could tell you. See Martin Ulam's "Lightning"
jk3k+@andrew.cmu.edu (Joe Keane) (03/05/88)
In article <64600001@mic>, gary@mic.UUCP writes: > Is it correct that lightning travels from the ground up instead of the > sky down to the ground? I vaguely remember that this is the case but > do not remember where I read about it. In fact it's both. A slow, weak `leader' makes its way from the clouds to the ground. This sets up a number of return strokes, from the ground up, at intervals of about a tenth of a second. This is why you see quick flashes. In article <1620@bgsuvax.UUCP>, drich@bgsuvax.UUCP (Daniel Rich) writes: > Electricity travels from negative to > postive, therefore lightning travels upwards. Huh? > I believe that someone said that the films they had seen show it > traveling the other direction. Think about this for a second.... > electricity travels at approximately the speed of light (actually, in > air it is a little slower). At this speed, how could you ever > determine a direction from film? There's a device (can't remember its name) to photograph this on a rotating piece of film. Also, electricity may travel near the speed of light, but lightning doesn't. Gigavolts! --Joe
mergx@sp7040.UUCP (Bob Parker) (03/09/88)
In article <25074@cca.CCA.COM>, g-rh@cca.CCA.COM (Richard Harter) writes: > This may be unfair, but I took the liberty of looking up lightning in the > Enc. Brit. I quote: Unfair, perhaps. Unheard of, to be sure. How dare you actually look something up instead of just remembering it (with appropriate caveats) from some class you had years ago :-) What a novel idea! I commend your originality. Bob Parker (UNiSYS Salt Lake City) If you kiss your honey ..!utah-cs!utah-gr!uplherc!sp7040!mergx when your nose is runny -- you may think it's funny but it' snot.
wooding@daisy.UUCP (Mike Wooding) (03/16/88)
In article <1160@uop.edu>, todd@uop.edu (Dr. Nethack) writes: . In article <512@dukempd.UUCP>, crown@dukempd.UUCP (Rick Crownover) writes: . > In article <64600001@mic>, gary@mic.UUCP writes: . > > . > > Is it correct that lightning travels from the ground up instead of the . > > sky down to the ground? . . As I recall, there is a ground to cloud stroke, and the cloud to ground . follows. . . I don't have my library at work or I could tell you. . . See Martin Ulam's "Lightning" I seem to recall reading that what we perceive as a stroke, is really multiple surges of current, back and forth between ground and cloud. The first surge opens a path (kind of), and subsequent surges follow, until some sort of charge equilibrium is reached. My guess is that it might be a large RC circuit, which is pulsed and then oscillates. m wooding