By Neal Lineback and Mandy Lineback Gritzner, Geography in the News^TM

Lightning can be both beautiful and deadly.

Knowing where lightning occurs across the Earth is important for many economic and safety-related reasons. Every year lightning strikes kill approximately 2,000 people and many farm and wild animals worldwide. In the United States, lightning is the second-highest storm-related killer, killing about two dozen people annually. Only flash floods kill more.

Lightning causes billions of dollars in property damage to buildings, communication systems, power lines and electrical systems each year. It is a frequent cause of wildfires and house fires and costs airlines billions of dollars in delays, cancellations and alternative routes to bypass storms.

Lightning is caused by an imbalance between positive and negative charges. When rain, ice or snow particles collide with one another during a storm, large electrical fields build up in the clouds. When these electrical fields become large enough, a giant “spark” occurs between them to reduce the charge separation. In essence, nature passes current between the two charges to diminish the imbalance between them.

The lightning spark can take place between clouds, between the cloud and air, or between the cloud and the ground. Only 30 percent of all strikes are cloud to ground. Trees, cell phone towers, steeples or the ground itself have positive charges and, therefore, are often struck by lightning. Lightning bolts are hot—their temperature can reach 50,000 degrees F (27,769 degrees C), which is hotter than the surface of the sun.

With the advent of widespread satellites that can detect lightning even in the most remote locations, we learned that lightning occurs 44 times a second on average. Nearly 1.4 billion flashes of lightning occur every year.

Lightning is distributed unevenly around the globe. Much more lightning—about 70 percent—occurs in the tropics. These equatorial regions are warmer than the poles and atmospheric convection is more prevalent (the vertical movement of air caused by heating at the land surface). Thunderstorms and lightning are widespread across the tropics almost daily. Lightning almost never strikes at the north or south poles.

Furthermore, more lightning occurs over land than over the ocean. Daily sunshine heats up the land surface faster than the ocean. The heated land surface heats the air above it, leading to stronger atmospheric convection, thunderstorms and lightning.

In the United States, Central Florida receives more lightning than any other area. In fact, an area between Tampa and Orlando is known as “Lightning Alley.” Lightning Alley sees approximately 50 strikes per square mile (about 20 per sq. km) each year.

Everyone should be aware of the danger of lightning. If caught in the open during a lightning storm, crouch down immediately, keeping both feet on the ground. Avoid water and metal objects such as fences, wires, power tools and railroad tracks. Stay away from tents, golf carts, trees, hilltops and open spaces. Find shelter in a building or car, never under a tree. If you are in a boat on a lake, river or the ocean, seek shelter on land at the first sign of thunder or lightning, if possible.

Lightning is one of the most sinister threats to outdoor enthusiasts. A little common sense can help mitigate the threat of a lightning strike.

And that is Geography in the News.

Co-authors are Neal Lineback, Appalachian State University Professor Emeritus of Geography, and Geographer Mandy Lineback Gritzner. University News Director Jane Nicholson serves as technical editor.

Sources: GITN 1037, “Lightning Strikes,” Maps.com, April 6, 2010; http://environment.nationalgeographic.com/environment/natural-disasters/lightning-profile.html; and http://geology.com/articles/lightning-map.shtml

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