What Causes Lighting Bolts?

We all see the spectacular natural light shows that occur when a thunderstorm passes through, and stories abound of the power of lightning. Power grids fail, computers are ruined and data is lost, raging forest fires start and airplanes are brought to the ground or forced to land because of equipment failure. Even so, lightning bolts are still mysterious and not completely understood.

Research Into the Nature of Lightning

When Benjamin Franklin did his famous experiment with a kite and a key in 1752, he was exploring not just the nature of lightning, but the nature of electricity, one of the fundamental forces of the universe. Franklin acknowledges that he was not the first to try this. In his autobiography, he notes that a French researcher, Thomas-Francois Dalibard, had conducted this same experiment a few weeks before his own experiment. Another early researcher, George Richmann, lost his life when he attempted a similar experiment in Russia. The question of the nature of lightning stopped at that point and lay dormant for 164 years, until 1916, when the power industry tried to find ways to protect itself and its equipment from lightning. In doing research into insulators, Charles Steinmetz became the first human to create artificial lightning.

The Nature of Lightning

First and foremost, lightning is static electricity. When you walk across a carpet, barefoot, and get a small shock as you touch a metal doorknob, that's a small charge of static electricity. Lightning, however, produces a static charge in the range of 300 kiloampers--roughly 300,000 times the charge required to kill a person. Lightning bolts don't travel at the speed of light, but at the speed of electricity, about 60,000 miles per second, or one-third the speed of light, and a lightning flash lasts about 30 microseconds.

Atmospheric Theories About Its Cause

One popular theory states that ice crystals forming in clouds combine with the water vapor in clouds and become a kind of two-molecule slush called graupel. As this slush falls through the cloud, friction builds up a static charge in much the same way as your bare feet walking across the carpet. Eventually the charge is released as lightning. Another theory states that, as the atmosphere near a thundercloud moves over the surface of the planet (again, like your feet on the carpet) in the form of wind, it causes friction and builds up a positive charge in objects and surfaces on the ground. This charge dissipates quickly, but if it interacts with the negative charge in the cloud that results from the movement of ice crystals in the cloud, the result is lightning. A third theory was proposed by Alexsandr Gurevich in 1992, linking lightning to cosmic rays.

Terrestrial Theories about Lightning's Cause

The huge eruptions of super-volcanoes, like that of Mt. St. Helens in May 1980, throw huge plumes of ash into the air, changing the charge of the atmosphere, and lightning occurs. Pliny the Elder first recorded this phenomenon in 79 AD during the eruption of Mt. Vesuvius, which buried the Roman cities of Pompeii and Herculaneum. In 1994, a NASA scientist linked lightning to "terrestrial gamma ray flashes."

Considerations and Final Thoughts

Lightning is potentially deadly. Some activities, though, are unaffected by lightning and among them is sailing. The mast of the sailboat or larger power boats acts as a lightning rod, dissipating the charge to the water in much the same way. Swimming and other water sports on small boats, like fishing, are still as much of a no-no as hiding under a convenient tree. Pro golfer Lee Trevino was struck twice by lightning and has since gone on to the PGA Senior Tour. Even so, when your mother told you to come inside during a thunderstorm, it was good advice.

Resources

• Autobiography of Benjamin Franklin