Lightning Tamers

Plunging directly into the massive dark thunderheads high above northeastern Colorado, the World War II-vintage B-26 released its payload: a swarm of tiny, aluminum-coated strands of fiber glass. The strange--and dangerous--flight was part of science's latest attempt to tame one of nature's most spectacular and damaging phenomena: lightning storms.

Lightning strikes somewhere on the earth roughly 100 times every second. It is a greater killer, on the average, than hurricanes or tornadoes, causing hundreds of deaths each year in the U.S. alone, and sets off the majority of forest fires. The ancients believed that lightning bolts were hurled from heaven by wrathful gods. Modern scientists know that thunderheads, like all clouds, contain a hodgepodge of ions (atoms or molecules with either a surplus or deficiency of electrons). But for reasons that are still not fully understood, the ions in storm clouds begin to separate according to their charge, with the negative ions settling to the bottom of the cloud and the positive ions moving to the top. The negatively charged cloud bottoms, in turn, repel negative ions in the earth below, leaving the ground with a positive charge. When the electrical potential, or voltage, between cloud and earth becomes great enough, a stream of ionized particles will suddenly burst down from the cloud to equalize that potential, becoming visible as a flash of lightning.

The purpose of last week's B-26 mission, part of a six-week test being conducted by the National Oceanic and Atmospheric Administration (NOAA), was to prevent the buildup of electrical potential during a storm, and thus to prevent the occurrence of damaging lightning. Like iron filings near a bar magnet, the 4-in.-long, hair-thin fibers, when released in a thunderhead, align themselves with the lines of force in the electrical field of the cloud. What is more, negative and positive charges build up at opposite ends of the fibers, creating miniature electrical fields and ionizing the air around them. The ionization increases the conductivity of air within the thunderhead and allows electrons to flow from the bottom of the cloud to the top, sharply reducing the electrical potential and thus preventing lightning. In one seeding run by the B26, for instance, a charge of 300,000 volts per meter in a thunderhead was completely neutralized in only ten minutes.

The NOAA experimenters know that they are playing with fire. Two weeks ago, an unanticipated lightning bolt burned an inch-wide hole in the wing of their plane. But Project Director Heinz Kasemir and his fellow scientists think that the risks are worth taking. Lightning suppression could be used to help prevent fatalities and forest fires, and might even benefit the space program. NASA could eventually employ suppression techniques at storm-prone Cape Kennedy, where lightning bolts have occasionally hit giant Saturn rockets on their pads and once, during a launch, knocked out the electrical system of Apollo 12, threatening the mission with disaster.

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