Lightning: Mother Nature's Striking Force

Lightning is one of our most common weather phenomena. At any given time, there are approximately 1,500 to 2,000 active thunderstorms around the world. Scientists estimate lightning strikes the Earth about 100 times per second. Lightning, usually associated with thunderstorms, has been observed on Venus, Jupiter, and Saturn.

Between 75 and 150 people are reported killed in the United States every year due to lightning. Actually, the majority of persons struck by lightning do not die. It's estimated that the mortality rate from lightning strikes ranges from 5 to 30 percent. And yes, lightning can and does strike twice in the same place.

Where does lightning come from? It is generated in thunderheads or cumulonimbus clouds. These clouds have a negative electrical charge at the base and a positive charge at the top. According to the National Center for Atmospheric Research, scientists are still not yet certain how the clouds get these charges. They do know these charges are carried by water droplets and ice crystals. The negative charge at the cloud's base cause a "shadow" of positive charges on the Earth below.

This distribution of electric charges makes the conditions needed to form an electrical circuit. Initially the air around the cloud acts as an insulator, but eventually the negative charge in the cloud is too great for the air to hold it back. When that happens and electrical impulse moves down from the cloud in steps of approximately 150 feet each. When the electrical impulse, called a "leader", nears the ground, streamers rise to meet it. When they meet the circuit is completed causing a bright streak of electricity.

All this movement happens very fast. The leader travels at speeds as fast as 200,000 miles per hour, pausing only 50 millionths of a second between stages. The return stroke moves at 60,000 miles per second; a single flicker to the eye.

Benjamin Franklin underestimated the force of lightning when he performed his kite experiment. The average stroke has a peak current of 30,000 amps. However, scientists have measured current as high as 300,000 amps from a single superbolt. Harnessing lightning's electrical power, however is not practical. Though very powerful while it lasts, the typical stroke only lasts for millionths of a second. An average stroke will release enough energy to operate an ordinary household light bulb continuously for several months.

Lightning is hot as well. At 54,000 degrees Fahrenheit, its temperature can reach six times hotter than the surface of the sun! These are truly amazing statistics considering that the main channel of a typical lightning bolt is about the width of your thumb.

One common term often heard in the Heartland is "heat lightning". This phenomenon is usually referred to as a special form of lightning seen during fair weather. In reality, heat lightning is simply the reflection of regular lightning off atmospheric dust from distant thunderstorms occurring below the horizon.