On May 8, Prof. Vladimir Rakov of the University of Florida, speaking at a CPS educational luncheon on Capitol Hill, discussed the science behind one of the most commonly viewed plasmas on earth - lightning.

In a talk entitled "What You Don't Know About Lightning," Rakov began his presentation by reviewing the spatial distribution of lightning around the world, illustrating that while parts of Florida receive the most lightning flashes in the U.S., central Africa appears to be the global hot spot.

We typically think of lightning as descending from the sky toward the earth, but lightning can also extend upward from a tall, grounded building or monument, like the Eiffel Tower. Rakov explained that the direction of the branches off the main lightning channel reveals the direction of the lightning.

We also hear of planes being "struck" by lightning. In fact, a plane can trigger lightning. Rakov showed an impressive slide of a plane just after take-off, initiating columns of plasma that extended both upward and downward. Rakov noted that if the plane had not been there, the lightning would not have occurred.

Lightning can be triggered intentionally as well, most often using a simple rocket with a trailing wire connected to ground. Rakov introduced the audience to the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, where researchers trigger lightning to investigate its effects and to determine ways of protecting people, objects and buildings.

For example, researchers at the Center investigated the effects of lightning on underground power cables. They buried three cables (each with varying degrees of insulation or protection) to see what effect lightning strikes would have on them. They discovered that even the cable with the most protection (an insulating jacket and PVC pipe) was severely damaged.

Rakov spoke also about fulgurites, which occur when lightning strikes the ground, melting the sand and soil, and creating glassy structures that sometimes snake and branch through the ground. The world's longest excavated fulgurite (about 5 m) was made by triggered lightning at Camp Blanding in 1996. The talk included video footage of triggered lightning strikes, accompanied by thunderous audio.

Following the presentation, a number of attendees had questions. One congresional staffer wondered whether rubber tires really do make a car the safest place to be during a lightning storm. Another asked about the potential for extracting energy from lightning.

A two-page write-up about lightning, recently completed by Rakov and CPS, was available at the luncheon, along with other topics in the "About Plasmas" series