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Spectacular bolts of jagged lightning streak across the sky as the astounding electrical power of a thunderstorm is unleashed. In the blink of an eye, a lightning bolt can discharge billions of watts of power; however, the power lasts for such a short period of time that no way has been found to harness this tremendous energy for man’s use, and it is unlikely a way will ever be found.
Except for its size and power, lightning is no different fro the spark you can create by shuffling your feet on the carpet and touching metal. Both are electrical charges caused by friction (the rubbing of one object against another).
Everything in the world is made up of atoms that contain tiny particles of electricity of two kinds—protons (positive charges) and electrons (negative charges). Opposite charges attract each other, while charges of the same type repel each other. If you have ever played with magnets, you have seen this action demonstrated. The positive end of one magnet will attract the negative end of another, but if you try to put both negative or both positive ends together, one magnet pushes the other one away.
Under ordinary circumstances, there are an equal number of protons and electrons within an atom, which team up to cancel each other’s power, causing the atom to behave as if it had no electrical charge at all. However, when you shuffle your feet, friction increases the number of electrons on your body by transferring them from the carpet to your shoes to your body. When this happens, your body builds up a negative charge of electricity. Since opposite charges attract, the electrons in your body try to find a path to rejoin the protons still in the carpet. Electrical currents flow from negative (–) to positive (+), so when you reach out to the metal doorknob, which is a good conductor of electricity, some of the electrons jump over, creating a spark. They then flow through the metal and drift back to the waiting protons in the carpet, causing a balance once more.
Friction within a cloud occurs as the whirling air currents cause the water droplets, ice crystals, and dust particles to rub together or break apart. As a rule, positive protons build up in the top of a cloud while negative electrons build up at the bottom. When the storm cloud passes over the ground, the negative electrons at the bottom repel the electrons on the ground, pushing them out of the way or beneath the surface. This causes a positive charge to build up on the ground beneath the cloud.
Attraction between these opposite charges builds as the electrons and protons try to get together, but air, which is a poor conductor of electricity, acts as an insulator to keep them apart. As the positive charge on the ground moves along under the cloud, it is drawn up trees, buildings, towers and any other tall objects in its path.
In a short time, the negative charge in the cloud increases enough to send out a short “leader” stroke toward the ground. As it shoots down about eight feet below the cloud, the electrons collide with the atoms in the air, breaking them apart. When air atoms are broken apart (ionized), they become better conductors of electricity. As more electrons follow this ionized path through the air, they break more atoms, moving farther downward. At the same time, the positive ground charge is being attracted and concentrated by the downward-flowing electrons. The attraction may even be strong enough to cause the ground charge to send up a leader of its own. When the two meet, the ionized air extends from cloud to ground, and the electrical circuit is complete. Although the eyes see only one lightning bolt, there actually is a return stroke from the ground to the cloud that is more powerful than the downward stroke. The downward stroke takes about five-thousandths of a second, but the return stroke only one-fiftieth of that time. Several other minor strokes also may follow the path between cloud and ground, but they happen so quickly they appear to be a part of the one lightning bolt. Only a fraction of a second passes between the time the first leader stroke heads toward the ground and when the final minor stroke occurs.
In addition to these cloud-to-ground bolts, lightning also can jump fro one cloud to another or travel within the same cloud from bottom to top.
Depending upon the location of the observer, lightning takes on different appearances and has been given different names. The most common type, known as streak, zigzag, or forked lightning appears when you are close enough to see the bolt and its branching parts as the lightning leaps from cloud to ground. When lightning is too far away for the individual bolts to be seen or the thunder heard, it is called heat lightning. This type usually is seen on the distant horizon. Sheet lightning occurs within one cloud or between clouds in the upper atmosphere, and the sound of the thunder can be heard.
Occasionally a lightning bolt leaves behind a line of bright beads or spots when it fades. These spots actually are the ends of the branch strokes. They look brighter and seem to last longer because of the way they are seen. As would be expected, this is known as bead lightning.
An extremely rare type of lightning that seldom is observed is known as ball lightning. It appears as a ball of fire as small as a walnut or as large as a big balloon. It moves quite slowly for lightning, lasting three to five seconds. People have reported seeing this type of lightning come down chimneys, pass in through windows, and even roll around inside a room on the floor or in the yard before disappearing with a loud bang.
Although you may not have seen all of the different views of lightning, it is a natural force you are familiar with. It has been estimated there are as many as 2,000 thunderstorms in progress somewhere on earth at any one time. Since these storms are capable of producing a total of 100 to 150 lightning bolts per second, 8 million to 12 million of these electrical discharges probably occur each day. Studies have shown that thunderstorms with hail produce twice as much lightning as storms without hail, probably because of the extra friction.
Lightning can travel at speeds up to 93,000 miles per second and may heat the air through which it passes to temperatures between 15,000 and 60,000 degrees Fahrenheit in a millionth of a second. This extreme heat causes the air to expand suddenly and violently, producing the sound called thunder. Since light and sound travel at different speeds, you can use the sound of thunder to tell the distance in miles between you and the flash. Lightning can be seen instantly, but the sound of thunder takes five seconds to travel one mile. When you see the flash, count the seconds until you hear the thunder. Divide the number of seconds by five to determine the distance in miles. If you don’t have a watch, count the seconds as one thousand one, one thousand two, one thousand three, etc.
Thunder cannot hurt you, but the tremendous force of lightning is not something to be taken lightly. If statistics from past years hold true, lightning probably will kill 500 people this year and injure three times that many. Ninety percent of these people will be outdoor recreationists or outdoor workers. Lightning also could start more than 9,000 fires next year and destroy thousands of acres of wildlife habitat, killing untold numbers of animals. During a study conducted in the national forests in Montana and Idaho, researchers discovered that lightning started 1,488 fires in one ten-day period.
According to the Federal Aviation Administration, it is not unusual for airplanes in flight to be struck by lightning. In fact, there may be as many as a thousand such strikes each year. One plane circling Chicago awaiting clearance to land was struck five times in twenty minutes. Little harm is done unless the lightning hits the controls or ignites the fuel. The strike usually causes only pitting and scorching of the plane’s outer metal skin, and passengers may not be aware the plane has been hit.
Lightning can strike almost anywhere and, regardless of the old saying to the contrary, may strike more than once in the same spot. As we learned earlier, lightning is drawn to the highest point on the land beneath it, explaining why trees, tall buildings, and communication towers attract lightning. The Empire State Building is hit thirty to fifty times each year, and one 1,000-foot telephone tower in Illinois has been hit more than a hundred times in one year.
A piece of bare, flat ground might attract only one lightning bolt in a hundred years, but a man standing on this same flat piece of ground becomes a high point and most likely would attract lightning during a thunderstorm.
Since your outdoor interests could cause you to be exposed to the dangers of a storm, here are some safety tips:
- Never seek shelter under a tree during a thunderstorm as it can be a double threat. Trees, especially solitary ones, attract lightning, and the current radiating from a struck tree can flash out at anything under or near it. Heat produced by the electrical current flowing through the wood also can turn the sap to steam so quickly that the tree explodes, often injuring anyone nearby.
- If you are out fishing or boating, head for shore as quickly as possible and get away from the water. Water has a flat surface, so any type of boat on the surface becomes a lightning target. Sailboats with their tall masts are especially dangerous.
- Get out of the water if you are swimming. If lightning strikes the water nearby, the electrical current can travel to you through the water. Even if it only stuns you, you could drown.
- Avoid beaches, fields, golf courses, and other such open areas. If you get caught out in the open, lie down on the ground so you will not attract lightning. Getting wet or dirty is better than being struck.
- Never hold a metal object such as a gun, golf club, or tennis racquet. Such metal objects are good conductors of electricity and could attract lightning to you.
- Don’t stand near wire fences or other wires. Electrical current can travel along barbed wire or other metal fences for long distances from the spot where lightning struck.
- Don’t ride a bicycle, horse, or open-type vehicle.
- When camping, don’t stay in a tent pitched near a tall tree.
- Stay away from exposed hilltops.
If you are indoors during an electrical storm, the center of a room is considered the safest spot. Avoid touching metal surfaces such as furnaces, washing machines, dishwashers, bathtubs, and sinks. Taking a bath or washing something in a sink can be very dangerous. Do not use electrical appliances, and turn off radios and televisions. Lightning has damaged or destroyed many expensive television sets. Electrical wires and water pipes can serve as good pathways for lightning. Telephone lines are equipped with lightning arresters, but it is still wise to postpone your calls until after the storm ha passed.
At this point, you are probably thinking that lightning is all bad and serves no useful purpose. Actually it has a useful side that few people know about. Each year lightning manufactures about 100 million tons of valuable nitrogen fertilizer out of thin air. Air contains about four parts of nitrogen gas to one part oxygen. As the tremendous energy of each lightning flash is released, some of this nitrogen and oxygen is combined to form nitrous oxide that mixes with rain and falls to the ground, where it can be soaked up by plant roots.
Lightning also converts oxygen from its usual form into a special active form known as ozone. Ozone layers high in the air help protect the earth from some of the sun’s ultraviolet rays.
Unlike the ancient Greeks and Romans, modern man no longer believes lightning bolts are weapons of the gods Jupiter and Zeus, thrown down to punish wrongdoers. He also understands that lightning is not an evil force with supernatural powers, but instead, an astounding natural force that must be given great respect. Although man may never learn to control lightning, through scientific study he is learning how to reduce its danger and destruction.
1983 Lightning. Young Naturalist. The Louise Lindsey Merrick Texas Environment Series, No. 6, pp. 138-142. Texas A&M University Press, College Station.