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Lightning

Lightning

by Vincent Mallette
Copyright © 1999 Inwit Publishing, Inc. and Georgia Tech

"Everything You Wanted To Know About Lightning...But Were Too Shocked To Ask" is a radio script which was broadcast in part on Aug. 17, 1991 on station WTJH-AM under the auspices of SciTrek, and with the collaboration of Carol Galbreath. It was written by Vincent Mallette, a Former Research Scientist in Physics and the Project Coordinator at the Center for Education in Science, Mathematics, and Computing for the Office of the Dean, the College of Sciences at The Georgia Institute of Technology. It is Copyright © 1991 The Center for Education in Science, Mathematics, and Computing, The Georgia Institute of Technology.

"Is nature a giant cat? If so, who strokes its back?" — Nikola Tesla as a child, upon seeing a lightning storm1

Usually a talk like this on lightning starts out with a discussion of frequently asked questions or misconceptions about the heavenly fireworks display. But there have been so many tragedies lately, in Georgia and the USA, due to lightning, that the very first thing I want to talk about is lightning safety rules.

Consider:

Just this week a fisherman on the Chattahoochee River was killed by lightning2

The previous week a spectator at the PGA championship was killed by lightning in Indiana; he was the second spectator killed in two months at a major golf tournament3

Earlier this month two Boy Scouts were killed when lightning struck their camp in Utah4

In late July, here in the Atlanta area, a woman was hurt by a lightning strike as she talked on the telephone during a storm5

Earlier in July, 17 soldiers were struck by lightning on maneuvers in New York state; one died and six were hospitalized6

The list goes on and on. Lightning is the leading cause of weather-related injuries in Georgia.7 Quoting the Gwinnett Daily News,8 tornadoes are more feared, but lightning is far more deadly. In the 15 years prior to 1990, only 5 Georgians died from tornadoes — but 35 were killed by lightning.9 Worldwide, about one person "is killed by lightning somewhere on Earth every day."10

I could read you a long list of lightning safety rules — the National Oceanic and Atmospheric Administration has an excellent list of 15, which I will be glad to mail to anyone who sends me a self-addressed, stamped envelope. [The NOAA list is at the end — this remark was for the radio talk.] But I'd rather just summarize; you'll remember it better when your life might be in danger:

First, stay away from trees. I would estimate that half of the people who are killed or seriously injured by lightning have been sheltering under, or near, trees during a thunderstorm. I know we'd all like to stay dry, but if you get soaked during a rainstorm, you'll have the rest of your life to dry out — if you don't get struck by lightning. The trouble with trees is...they conduct electricity, but not very well. The lightning often jumps out of the tree, seeking another path — you for instance.

So go out there in the open and get wet — but don't seek the high ground. Make yourself lower than your surroundings. Crouch down. But don't lie flat on the ground — the wet soil can conduct a fatal bolt to your body.

It is permissible, in a forest area, to seek shelter in a thick growth of small trees on low ground.

Lightning

Don't use the telephone, or plug-in electrical appliances like blow dryers, electric toothbrushes, or electric razors during a lightning storm. Cordless appliances are O. K. (except cordless telephones outdoors, with their antennas).

Don't swim. Get out of the water and off small boats.

Stay in your car. Close the moon roof, though! Hardtop cars, trucks, and vans offer excellent protection against lightning. But don't dash through an electrical storm to reach your car — that is exactly what the gentleman killed at the PGA match on August 8 was doing.

Since we brought up cars, what about airplanes? Many airplane crashes occur in lightning storms, frequently at take-off or landing, but lightning itself is very, very rarely the cause of these accidents. Wind shear and poor visibility are more usually the culprits. In the last 30 years, about the only airplane accident blamed on lightning that I could find was the crash of a Boeing 707 in 1963.11 Flying at 5000 feet over Maryland, the plane suffered a lightning strike to the fuel tank and exploded, killing all aboard. Lightning can certainly strike a plane in flight, but it usually does no more than punch a small hole or knock off a rivet head.

Returning to the matter of talking on the telephone during an electrical storm, I remember listening to a call-in show years ago that brought up that very question. An engineer called in to say that there was no danger about using a phone during a storm because, as he put it, the wire is so thin that it acts like a natural fuse, and melts before a harmful amount of electricity can be conducted to the caller. The trouble with that is, sure the wire melts, vaporizes even — but it establishes a plasma channel that can carry large amounts of current long enough to do serious damage. And we can find plenty of people who weren't saved by the "natural fusing action" that that engineer was relying on. So control your urge to call your friends at the height of the storm to tell them how beautiful the lightning is.

Now that we've got the serious stuff out of the way, let's just talk about lightning. People always want to know, does lightning strike from the cloud down, or from the earth up? "The bolt generally goes up from the ground, but looks like it goes downward."12 However, well over half of all flashes occur wholly within a cloud and don't involve the earth at all.13 World-wide, there are about 40,000 thunderstorms every day, accounting for about 100 lightning flashes every second.14

An individual bolt can pack several hundred million volts15 at 10,000 amperes, one trillion watts, briefly burning up more electrical power than is being used in the entire United States. Monsters of one billion volts and over 100,000 amperes are not unknown. The lightning process usually starts in a cloud with a weak, barely visible discharge called a leader groping its way toward the ground. When the leader encounters a discharge coming up from the ground, the two typically meet about 150 feet above the earth and the stage is set for the main act of lightning, the return stroke. The return stroke, traveling at almost half the speed of light, is able to reach 3 or 4 miles back up to the cloud and relieve it of its large excess of negative charge — about 100 quintillion electrons. But that's just the first act — the play is not over. The channel that was established by the first big bolt can be used again and again. The cloud is not fully drained and after a thirtieth of a second or so another bright zinger may occur. This usually happens 3 or 4 times during the half-second that we call "a lightning flash." On one occasion lightning used the same track 42 times. This accounts for the "flicker" of lightning that is often seen. If a strong wind is blowing, the paths of the individual bolts may be seen separated in the sky, giving the appearance of multiple flashes side-by-side, whereas there was actually only one plasma channel being used over and over. And speaking of the plasma channel, the bright core of the lightning, it may be as small as half an inch but has a temperature 3 times hotter than the sun. It is, of course, this sudden heating and expansion of the air that produces the sound of lightning: thunder. Thunder starts out as a supersonic shock wave but decays to an ordinary sound wave in a yard or two. Curiously, some ancient peoples thought that the thunder was the primary phenomenon and lightning was secondary. The Book of Job, for instance, speaks16 of the "lightning of the thunder," whereas we would say the thunder of the lightning. And the ancient Greeks imagined Zeus hurling thunderbolts, not lightning bolts.17

This is as good a place as any to discuss what people call "heat lightning." This is the distant flickering you see on the horizon, unaccompanied by thunder, during hot, sultry summer evenings. Because the thunder cannot be heard and individual bolts cannot be discerned, people believe that heat lightning is a different kind of animal from good old regular, kill-you-on-the-golf-course lightning. This is rarely the case. You are just too far away to hear the thunder, and the flashes are below the horizon and reflected off clouds or just above the horizon and diffused by cloud banks. Still, there are thought to be "quiet" lightning bolts, slow strokes lasting a leisurely one-tenth of a second, that produce no thunder because the air heating is not sudden enough.

And speaking of heat, there is evidence that global warming (from the much-discussed greenhouse effect and other factors) may cause a "dramatic" increase in lightning strikes.18 "Even a slight rise in air temperature at ground level leads to a furious increase in the frequency of lightning during thunderstorms," said Earle Williams, a meteorologist at M.I.T. "A rise in ground temperature of only about two degrees Fahrenheit corresponded to a 20-fold increase in lightning rate." Still, Dr. Williams was not willing to predict exactly how much increase in lightning we might see in the next 20 years.

Another frequently asked question concerns "bolts from the blue" — lightning flashes that supposedly come down from a clear blue sky. This is called by atmospheric specialists "clear air lightning." The phenomenon is rare in any case, but it is believed that although the sky directly above the bolt is blue, there is almost always a thunderstorm 10 or more kilometers away to establish the electric field. Still, especially where tall structures are involved, there are a very few cases where a bolt has occurred when the air is wholly clear and there is no obvious thunderstorm around. A related phenomenon is so-called dry lightning, lightning that occurs when there is no rain. This is much more common than clear air lightning and is thought to happen when conditions are so dry that rain evaporates before it hits the ground.19

There is a folk belief that lightning never strikes twice in the same spot. Nothing could be further from the truth, especially in the case of tall structures. The Empire State Building has been struck as many as twelve times in 20 minutes. Still, it is unusual for individual human beings to be struck repeatedly by lightning. The most amazing case is the park ranger, Roy Sullivan, who has been struck by lightning 7 times. He used to live in a mobile home surrounded by a dozen lightning rods, but he killed himself in 1983.

Which brings us to the subject of lightning rods. Just as you learned in grade school, the lightning rod was invented by Benjamin Franklin. But in the next 150 years the lightning rod, especially in the United States, acquired a very bad reputation. It was sold to farmers by traveling salesmen with the promise that their farm would never be struck by lightning again. The farmers put a lot of them on their barns, which were promptly struck by lightning and burned to the ground. The thing is this: an incorrectly installed lightning rod is worse than none at all.20 The rod must be driven deep into the ground and attached with a thick, smooth cable. It's not a project for do-it-yourselfers. Few people choose to protect private homes with lightning rods, but if you do, seek the services of a licensed electrician who specializes in this kind of work. But he probably won't recommend the lightning rod used on the Washington Monument — made of platinum.

We just mentioned Benjamin Franklin, and everyone always wants to hear about his famous experiment of flying a kite in a thunderstorm. He did it, all right, and lived, but a Russian scientist who tried to repeat the experiment not long after was killed on the spot.21 Franklin would probably have been killed himself if he hadn't flown the kite from a doorway that kept him dry. So don't even think of repeating this experiment. Remember, Franklin's kite wasn't even struck by lightning — the sparks that were seen coming off the brass key represented the mildest form of atmospheric electricity being gently released.

No lightning talk is complete without a few stories of the oddities of lightning. I'm not sure I believe the one about lightning setting fire to a building and then leaping to the fire alarm box to summon the fire engines, even if I did read it in National Geographic. But I believe the one about the two boys camping by a lake in Maine. Lightning struck between them, completely melting an ax blade. Though burned, the boys did recover. Not so lucky were the 835 sheep killed by a single bolt in Utah. They must have been very wet and clustered together.

Incidentally, six of the nine planets have lightning. In addition to Earth, lightning strikes have been recorded on Jupiter, Neptune, Saturn, Uranus, and Venus.22 Jupiter's lightning is 100 times more powerful than Earth's23; Jupiterian bolts can make static on Earth radios. It seems somehow appropriate that the ancient god who was depicted as hurling thunderbolts should pack the most powerful lightning of all.

Is there anything good to be said about lightning? Yes. Lightning manufactures about 100 million tons of natural nitrogen fertilizer every year by forcibly combining the nitrogen and oxygen of the air with the water of the rain, which carries the fixed nitrogen down to enrich the soil.

There is one matter that I almost hesitate to bring up, and that is ball lightning. The McGraw-Hill Encyclopedia of Science and Technology has not one word to say about ball lightning. Still, most atmospheric scientists today accept at least the existence of ball lightning. There is, however, no agreement on what it might be or even whether it is related to ordinary, garden-variety lightning. Typically, ball lightning appears toward the end of a thunderstorm, looks like a fuzzy ball, has various colors, rolls around aimlessly, and then either disappears silently or explodes.24 I've never seen it, but two good friends of mine have seen it close up, rolling inside a building, and they both agree that it was like nothing else on earth. It has even been suggested that ball lightning is the form taken by extraterrestrial aliens when they visit earth, but please do not ask me any questions about that!


Lightning Safety Rules Courtesy of the National Oceanic and Atmospheric Administration (NOAA), U. S. Department of Commerce

When lightning threatens...

1. Stay indoors and don't venture outside unless absolutely necessary.

2. Stay away from open doors and windows, fireplaces, radiators, stoves, metal pipes, sinks, and plug-in electrical appliances.

3. Don't use plug-in electrical equipment like hair driers, electric toothbrushes, or electric razors during the storm.

4. Don't use the telephone during the storm. Lightning may strike telephone lines outside.

5. Don't take laundry off the clothesline.

6. Don't work on fences, telephone or power lines, pipelines, or structural steel fabrication.

7. Don't use metal objects like fishing rods and golf clubs. Golfers wearing cleated shoes are particularly good lightning rods.

8. Don't handle flammable materials in open containers.

9. Stop tractor work, especially when the tractor is pulling metal equipment, and dismount. Tractors and other implements in metallic contact with the ground are often struck by lightning.

10. Get out of the water and off small boats.

11. Stay in your automobile if you are traveling. Automobiles offer excellent lightning protection.

12. Seek shelter in buildings. If no buildings are available, your best protection is a cave, ditch, canyon, or under head-high clumps of trees in open forest glades.

13. When there is no shelter, avoid the highest object in the area. If only isolated trees are nearby, your best protection is to crouch in the open, keeping twice as far away from isolated trees as the trees are high.

14. Avoid hilltops, open spaces, wire fences, metal clotheslines, exposed sheds, and any electrically conductive elevated objects.

15. When you feel the electrical charge — if your hair stands on end or your skin tingles — lightning may be about to strike you. Drop to the ground immediately. [Don't forget the Ziggy cartoon that goes with this article]

Further ref: "Thunder," by Arthur A. Few, Scientific American, July 1975, pp. 80-90. Much valuable info about lightning in this article

Further ref: "The Electrification of Thunderstorms," by Earle R. Williams, Scientific American, Nov. 1988, pp. 88-99. Has bibliography.

Further ref: "The Lightning Rod Fallacy," AJP, Sept 1985, p. 843 <> "Earth Week: A Diary of the Planet" — by Steve Newman, Atlanta Journal-Constitution, Nov. 19, 1994, p. E1


1 "The Work of the World" — by Curt Wohleber, in: Invention & Technology, Winter 1992, p. 46

2 Atlanta Journal-Constitution, Aug. 12, 1991

3 Atlanta Journal-Constitution, Aug. 9, 1991

4 Atlanta Journal-Constitution, Aug. 4, 1991

5 Gwinnett Daily News, July 25, 1991

6 Gwinnett Daily News, July 18, 1991

7 Gwinnett Daily News, July 18, 1991

8 July 18, 1991

9 Gwinnett Daily News, July 18, 1991

10 Atlanta Journal/Atlanta Constitution November 23, 1991

11 "Natural and Artificially Initiated Lightning" — by Martin A. Uman and E. Philip Krider, Science, October 27, 1989, p. 457

12 Gwinnett Daily News, July 18, 1991

13 Uman and Krider, p. 458

14 The Feynman Lectures on Physics, Vol. II — by Richard P. Feynman, Robert B. Leighton, and Matthew Sands (Reading, MA: Addison-Wesley Publishing Company, 1964), p. 9-4

15 Weather Elements: A Text in Elementary Meteorology, 5th Edition — by Thomas A. Blair and Robert C. Fite (Englewood Cliffs, NJ: Prentice-Hall, Inc., 1965). Of the half-dozen sources consulted, values between "in excess of" 10 million volts (Uman and Krider, p.459) and one billion volts are listed; typical is the 100 million volts given by Blair and Fite (p. 201). The recent Scientific American article, "The Electrification of Thunderstorms," gives "several hundred million volts" (Nov. 1988, p. 88, photo caption).

15 Job 28:26 and elsewhere

17 Not all ancient peoples believed in the primacy of thunder. For the pre-Columbian Zapotecs of southern Mexico, one of their great gods was in the lightning: he had the power to cause thunder. ("Formative Oaxaca and the Zapotec Cosmos" — by Kent V. Flannery and Joyce Marcus, American Scientist, July-August 1976, p. 376.)

18 The Atlanta Journal/The Atlanta Constitution, November 23, 1991

19 The Atlanta Constitution, August 10, 1994, p. A2

20 "On the evening of April 25 last [1891], during a violent thunder storm, the lightning struck the lightning rod until it came to a defective insulator [probably a conducting connector is meant], then entered the house, striking Mr. Roode about half an inch back of the ear and burning its way through the entire length of his body, then through a wool mattress, splitting a hard maple bedstead, afterward passing through various parts of the house until it reached the water pipe. Mr. Roode regained consciousness and is on the road to recovery. His body is now so heavily charged with electricity that he can impart to any one an electric shock equal to that received from a powerful battery." [The last sentence is completely erroneous and fanciful.] From the May 1891 Scientific American, quoted in Scientific American for May 1991, p. 14

21 The Russian, Georg-Wilhelm Richman, was killed in St. Petersburg in 1753. "Ball Lightning," by James R. Powell and David Finkelstein, American Scientist, May-June 1970, p. 262, p. 279, and the cover of the issue, front and back.

22 Atlanta Constitution, Sept. 27, 1991, p. A5.

23 Science, Sept. 27, 1991, p. 1492

24 "Ball Lightning," by James R. Powell and David Finkelstein, American Scientist, May-June 1970, pp. 262-280 and cover. The cover of this issue reproduces the famous 1884 woodcut of Professor Richman in St. Petersburg being killed by lightning in 1753. This article has a number of references at the end.


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