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From Research in Review Magazine, Florida State University, Spring 2006:

Accentuating the Positive

Nature spins up lightning in assorted "flavors." By far, most of the flashes we see are from harmless cloud-to-cloud zaps, often-brilliant nighttime displays over water during warm-weather months, far and away Florida's best roadside attraction.

The most common type of lightning to strike any object on the ground is negative lightning—upwards of 95 percent of all strikes, in fact. This form originates from the relatively low-hanging, negatively charged underbellies of cumulonimbus clouds. These bolts deposit a negative charge on whatever they hit.

But the granddaddy of all bolts from the blue is positive lightning, the deadliest, most destructive form of all. These awesome arcs originate from the positively charged tops of cumulonimbus clouds, and often travel long distances (reportedly up to 100 miles) to connect—with astonishing force—with a negatively charged object on Earth. Scientists have estimated that an average bolt of positive lightning can generate up to 300,000 amperes—enough power to keep a 100-watt light bulb burning for nearly a century.

Positive lightning is thus blamed for most of the deaths and injuries to humans and farm animals nationwide. Then there's its super-hot (50,000 degrees F) "touch," which lingers up to twice as long as a negative bolt (into the hundreds of milliseconds) thereby making positive lightning a prime fire-starting menace for forests and buildings.

But it's the mighty wallop that positive bolts reserve for electric grids that give power companies fits. Nothing makes smoking wreckage out of transformers, transmission lines and power poles more effectively than positive lightning, which can arrive with all the stealth and pop of a cruise missile.

During the next phase of lightning forecast research that FSU meteorologists began in 2001 with Florida Power and Light, a focus will be on predicting the likelihood of positive strikes for a given area, said Henry Fuelberg , who directs the project. The study will be the master's thesis for Scott Rudlosky, another member of Fuelberg's "lightning team."

"If all that power companies had to worry about was negative lightning, they could prepare much more easily for approaching thunderstorms," he said. "It's that positive stuff they have to worry about the most, by far."—F.S.


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