No. 9: What Causes Lightning?

More than three centuries after Benjamin Franklin’s kite experiment, the cause of lightning is still a bit mysterious.

Scientists believe that static electricity is the root cause of lightning flashes.  In a storm, water and ice particles in a cloud collide, which causes a negative electric charge to form. To neutralize this imbalance, the extra electrons are transferred to something nearby that has a positive electric charge, such as another cloud, the ground, or a church steeple. The electrostatic transfer takes place in the spectacular flash that you see, and it can contain 100 million to 1 billion volts of electricity.

In the weeks after Eyjafjallajokull blew its top in April, jolts erupted out of the ash. Volcanic eruptions, as well as sandstorms and snowstorms, can create the same imbalances in electric charge that occur during thunderstorms.

Lightning comes in different forms, as the Palm Beach Daily News notes: “[c]loud-to-ground lightning, ground-to-cloud lightning, cloud-to-cloud lightning, bead lightning, ribbon lightning, staccato lightning, forked lightning, sheet lightning and heat lightning. …”

One form, though, may be only in our minds: Ball lightning looks like a grapefruit-sized ball that hovers or rolls on the ground before it disappears. Austrian researchers think that incidences might be an illusion caused by a real lightning strike’s magnetic field, which creates a phosphene image in our brain. (Think of those cartoons when a character sees stars after a conk on the head.)

We don’t have everything figured out about lightning, but one thing is for sure: You don’t want to get struck by it, as about 270 Americans were this year. The best policy in a thunderstorm is to head for shelter — or, as the the slogan for this year’s 10th anniversary Lightning Safety Awareness Campaign states, “When Thunder Roars, Go Indoors.” The campaign, sponsored by NOAA and the National Weather Service, also recommends waiting at least 30 minutes after that last thunder clap before heading out again.

If you find yourself outside in a lightning storm, you should avoid elevated places; open areas; tall, isolated objects; and bodies of water. And your elementary school teacher probably told you this, but don’t hide under a tree.

What’s the lightning capital of the U.S.? Florida, especially in summer. As for the world, that honor belongs to Kifuka in the Democratic Republic of the Congo, where 160 bolts hit every year.

–Katherine Leahey

Katherine Leahey manages the help pages for Yahoo! Finance and Yahoo Groups. Before coming to Yahoo, she worked in marketing and public relations.