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CHILDREN fly kites in complete safety. Benjamin Franklin flew one and could have killed himself. The children are having fun. Franklin was living dangerously. In 1752 he sent a silk kite into a thunderstorm and drew sparks from a key. The harmless sparks could have been a deadly thunderbolt. Instead, Franklin’s kite-flying led to a happy ending—his development of the lightning rod. But long afterward, lightning itself remained a mystery.
Steps toward understanding began a century ago, but complete understanding is still elusive. Lightning may occur within a cloud, from cloud to cloud, or from earth to cloud. But how are positive and negative electrical charges built up to initiate the discharge? Theory holds that it happens when raindrops and pellets of ice collide with a mist of water droplets and ice crystals in those spectacular thunderheads—clouds several miles high, in turmoil with updrafts and downdrafts, billowing upward like heads of gigantic cauliflowers.
Concerning these tumultuous activities, an article on “The Electrification of Thunderstorms” in Scientific American comments: “The basic microphysics behind them remains to this day a neglected and unsolved problem. The lack of a microphysical description of static electrification is the most serious gap in the understanding of thundercloud electricity.” The article does, however, offer a very interesting analogy: “The underlying physical mechanism may well be related to whatever causes the shoes to charge when one walks on a rug or a glass rod to charge when it is rubbed with a piece of wool.”
While lightning’s origin in thunderheads is still debated, it happens often enough. Reader’s Digest in its article commented: “Right now, as you read this, approximately 1800 electrical storms are in progress around the world. They are giving forth about 600 lightning flashes a second, of which 100 strike the earth. That’s roughly 8.5 million lightning bolts touching down every 24 hours.” Scientific American’s figure is in close agreement—8 million.
The actual lightning flash comes as a climax of the following events. A thundercloud generates negative charges along its bottom, which induces a positive charge on the earth’s surface beneath it. This positive charge follows along under the cloud, running up trees, hills, tall buildings, even people, reaching for the negative bottom of the cloud. When the cloud accumulates a 100-million-volt potential—it can be as much as 300 million volts—its energy spills out in what is called a stepped leader. Its course is irregular and forms many branches on its downward path.
The Show Begins
Carrying a few hundred amperes in a latticework of streamers too faint for humans to see, the leader comes close to the surface of the earth—within a hundred yards or less. Now the positive charge on earth is finally able to jump the gap, meets the stepped leader, and with a tremendous burst of light, it flashes up the pathway the leader has left and reaches the cloud. As it goes, it fills outside channels and wrong turns to form the blazing many-channeled pattern that we are familiar with—a lightning bolt that seems to come from cloud to earth, but actually goes from earth to cloud. Immediately after this initial flash, however, lightning and leader then travel repeatedly back and forth between cloud and ground. A typical lightning flash has three or four of such strokes, but Scientific American reported on one that had 26!
Lightning produces thunder, one of the loudest sounds in nature. But how can one bolt of lightning producing one blast of thunder, essentially instantaneous, generate the protracted sequence of sound that crashes and rolls, rips and rumbles, for several seconds afterward? That lightning causes a thunderous blast is no mystery. Air has electrical resistance, so it is heated by the passage of an electric current just as a wire is. Lightning heats the surrounding air up to 50,000 degrees Fahrenheit [30,000 degrees C.], causing it to expand rapidly as a massive shock wave with pressure from 10 to 100 atmospheres, which in turn soon becomes a sonic boom—thunder. Since sound travels so much slower than light, it is no mystery that the thunder is usually heard seconds after the lightning is seen.
“Little Thunders” Make Big Thunder
But why do the sounds of thunder vary so much in nature? Lightning travels in a ragged course, but many segments of varying length are relatively straight. Each one of these segments points in a different direction, is of a different length, produces its own individual sound, and radiates its sound out in waves roughly parallel to its own orientation. Hence, many individual “little thunders” of varying volumes and directions combine to make the total cracks, rumbles, and reverberations you hear in the one great, long peal of thunder. All the little thunders are sounded almost simultaneously, but the ones nearest the listener are heard first and crack the loudest, while others farther up the thunderbolt add their contributions later—how much later depends on how far away they are. Hence, “what is heard in a peal of thunder,” the Scientific American article entitled “Thunder” explains, “depends in large measure on the characteristics of the particular lightning flash that produced it.”
There are many different kinds of lightning flashes, producing different thunderings, some heard by humans, some not. For example, there are lightnings called streak, ribbon, forked, heat, sheet, intracloud, bolt from the blue, and superbolt. Run-of-the-mill lightning bolts discharge about one billion watts, but superbolts, recently discovered rare flashes of lightning, give from a hundred billion to possibly ten trillion!
Lightning does harm. “In the U.S. alone lightning annually causes about 150 deaths and $20-million worth of property damage and sets 10,000 forest fires, which destroy $30-million worth of marketable timber,” says Scientific American.
Superior Fertilizers, Global Batteries
But it also does good. Around the world, eight million lightning bolts daily rip apart the atmosphere, ionizing the air, creating nitrogen oxides, which are dissolved in rain and carried to earth as dilute nitric acid. There it dissolves into solution the minerals needed by plants. Also it makes nitrogen available for plants. Farmers add nitrogen fertilizers, tens of millions of tons of it annually—so much that it becomes deadly to soil organisms and in runoff kills animals and fish in lakes, streams, and rivers. But lightning’s gentle “thunderstorm rainwater” adds fixed nitrogen in the right amount, and in comparative tests it has resulted in crop yields 50 percent higher than those obtained with commercial fertilizers. “Lightning,” New Scientist says, “may account for as much as half the world’s supply of fixed nitrogen, according to two American chemists. This is nearly five times more than previously thought.”
Also, thunderstorms form the “batteries” for maintaining the global circuit. Concerning this, Scientific American says: “Between the negatively charged surface of the earth and the positively charged atmosphere is a steady potential difference of about 300,000 volts. . . . It is now generally believed this 300-kilo-volt ‘ionospheric potential’ is the result of charging by thunderstorms, which form the ‘batteries’ of the global circuit. Electric currents of about one ampere per storm flow upward from the positive tops of thunderclouds and return to the earth in the fair-weather regions of the atmosphere. . . . [Then] a one-ampere current has to flow from the earth’s surface to the cloud bottom. Rain currents, corona discharge and lightning all contribute to this charge transfer.”
What is the ultimate source of the grandeur of the thunderstorm? Jehovah God is the Creator of the spectacular sky-shows that flash and thunder in awesome flashings and booming thunders. The Bible speaks of these as accompaniments to his dealings with mankind, as embellishments of his heavenly throne, and as harbingers of his approaching judgments. “His lightning is to the extremities of the earth. After it a sound roars; he thunders with the sound of his superiority.”—Job 37:3, 4, 11-13; 40:9; Exodus 19:16; 20:18; Psalm 18:13, 14; 29:3-9; Revelation 11:19.
[Pictures on page 16, 17]
Lightning displays during “monsoon” season in Arizona
[Pictures on page 16, 17]
Below: Two yuccas are highlighted by lightning
On opposite page: A fire started by lightning
[Credit Line]
John Kamenchuk
[Picture Credit Line on page 15]
Tucson, Arizona; photo by Manley Studios