The Miracle of Lightning - Lightning Facts

Almost 80 per cent of our atmosphere is nitrogen -an essential food for plants. About 22 million tons of this nutriment float over each square mile of earth. But in its aerial form nitrogen is insoluble, un­usable. Before plants can take life from it, it must undergo what our food undergoes in our digestive machinery: a series of chemical reactions. Lightning touches off the series.

This is how the extraordinary process occurs. Air particles are made white hot by lightning. They reach temperatures as high as 30,000°C. Under this intense heat, the nitrogen combines with the oxygen in the air to form nitrogen oxides that are soluble in water. The rain dissolves the oxides and carries them down to earth as dilute nitric acid. You can smell this acid-the pungent, tingly odor that hangs in the rainy air of a thunderstorm. Reaching the earth, the nitric acid reacts with minerals there to become nitrates on which plants can feed.

This is a wonder, indeed: lightning, which meteorologists estimate to be bombarding the earth at a rate of more than 100 times a second, transforms the upper air into fertilizer for earthbound plants.

August Lightning

The story of lightning is one that sings the great­ness of science. Every schoolboy knows that the story began with Benjamin Franklin and the kite, which led to his invention of the lightning con­ductor. This simple device, which has remained basically unchanged since Franklin's day, must be included in any list of great inventions.

Very little more was learnt about lightning until an August afternoon in 1920, when a bolt struck a gnarled 'snake tree' a foot away from an unoccupied shack owned by scientist Charles Steinmetz. The bolt bounced off the tree and broke a window; it splintered a work-table, then leapt across the room to shatter a mirror. Discovering the debris, Steinmetz had every fragment and splinter of the mirror collected and fitted together between two sheets of glass. It was the first time that the pattern struck off by a lightning charge had been studied.

Then scientists devised instruments to measure and record bolts. They hunted lightning, trapped it on film, learnt how to make it in the laboratory. They even developed a camera that takes a high­speed, slow-motion picture of a lightning bolt.
Scientists were urged to make these studies because of the growing dependence on electric power. Lightning plays havoc when it hits electric power-lines, and it hits them frequently. Lightning can run along the line directly into expensive machinery in the power station or transformer or, if it makes an arc to the ground before it travels that far, it can be followed into the earth by all the electricity in the line, until the line is drained or shut off.

The scientists eventually learnt how to control the power failures by discovering how lightning strokes are formed. To begin with, a thundercloud gets under way when warm, humid air rises from the earth in a steady up-draught, generally over a hill or mountain-top. The humidity condenses as the air cools on rising. We see the tiny water droplets as mist that gradually assumes the familiar shape of a cumulo-nimbus cloud. Sometimes looking like a huge cauliflower, or an enormous white anvil, the cumulo-nimbus is often topped by a 'cirrus umbrella'. It is composed of millions of minute ice crystals.

These formations can be enormous-up to 50,000 ft or more in height. They can contain as much as
300,000 tons of water. In them is a so-called 'chimney current'-a column of air rising at a full gale force of about 100 ft a second. The moisture in this column condenses rapidly, and the droplets are swept upwards to freeze into hailstones. The hailstones do not fall. They dance on the chimney current like table-tennis balls on a gushing fountain, rising steadily higher until, near the top of the cloud, the force of the current is exhausted. There the hail­stones shower out in all directions, carrying cold air with them as they descend. Frequently they are sucked back into the chimney current, to be dis­solved and reformed again and again.
In this turbulent motion something still unex­plained happens. There is a separation of electric charges. The smaller particles near the top of the cloud become charged positively, while the rain­drops in the lower portion are charged negatively.

Meanwhile, on the surface of the earth directly below the cloud, there is a corresponding build-up of a positive charge. As the cloud drifts, a positive charge on earth follows it like a shadow, climbing trees, church steeples, towers, poles. It races into houses, and climbs water-pipes, television aerials, lightning conductors-whatever can bring it closer to the cloud.

Enormous differences of electric potential develop between the top and bottom of the thundercloud, and between the bottom of the cloud and its image on the earth.

Suddenly a thin white arm reaches down for per­haps 50 ft from the base of the cloud-a 'leader'. It is a gaseous arc path, reacting to electricity like the gas in a neon tube. The leader hangs, hesitating a moment, thickening and brightening as the elec­trons in the cloud swarm into it. Then it reaches down again, perhaps as much as 300 ft.
The activity of the positive particles on the earth may have increased now to where 'streamers'-the opposite of leaders-can be noticed leaping up from the high points in the vicinity. Photographs have been made showing them snaking as high as 50 ft upwards. This phenomenon is familiarly called 'St Elmo's fire'. Now, in time, a streamer meets a leader and a path between the earth and the cloud has been opened.

Lightning Striking Tree II

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The great sky-splitting spear of light that we see is actually hurtling up, not down. It starts at the point of first contact between negative and positive charges and rips up to the cloud along the gas path that has been formed by the descending leader. The fact that the spear of light seems to travel down is an optical illusion that occurs when speeds become too great for the eye to follow.

There is often a great pulsing in the light, made by successive strokes along the same path. There may be as many as 40 pulses in a second, which is about how long the lightning's path stays open. The heat in the path rises so abruptly that the surround­ing air breaks the sound barrier in moving away. The result is thunder.

Lightning usually 'strikes' one of the higher points in any area--a tree, a house, a golfer on a fairway. Current flows through the object struck via the best conducting path that object offers. If your clothing is wet, the current will go through it. You may even survive such an experience, for moisture is a good conductor of electricity. But when lightning strikes a tree with dry bark, it travels inside the bark, in the sap. The sap is instantly super-heated to steam, and expands so abruptly that the tree explodes.

The work of the devil, it was called, and in the last cen­tury the civilized world shot off cannon to frighten it away. Now science has learnt at last that there is good in this most awesome force; and lightning is recognized as one of the great spasms in the continu­ing miracle of creation and existence.

Lightning is one of the most underrated severe weather hazards, yet it ranks as the second-leading weather killer in the United States. More deadly than hurricanes or tornadoes, lightning strikes in America each year kill an average of 73 people and injure 300 others, according to the National Weather Service.

Lightning often strikes as far as 10 miles away from any rainfall.
Many deaths from lightning occur ahead of the storm because people try to wait to the last minute before seeking shelter.

Lightning

Ralph Wetmore

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Use the 30-30 rule where visibilty is good and there is nothing obstructing your view of the thunderstorm. When you see lightning, count the time until you hear thunder. If that time is 30 seconds or less, the thunderstorm is within 6 miles of you and is dangerous. Seek shelter immediately.Wait at least 30 minutes after the last clap of thunder before leaving shelter. Don't be fooled by sunshine or blue sky!

Lightning Safety Tips for Inside the Home

1) Avoid contact with corded phones

2) Avoid contact with electrical equipment or cords. If you plan to unplug any electronic equipment, do so well before the storm arrives.

3) Avoid contact with plumbing. Do not wash your hands, do not take a shower, do not wash dishes, and do not do laundry.

4) Stay away from windows and doors, and stay off porches.

5) Do not lie on concrete floors and do not lean against concrete walls.