<p>Photo: A huge cloud formation</p>

A rare, mother ship cloud formation hovers over Childress, Texas. Tornado-chasers there covered seven hours and 150 miles (241 kilometers) tracking the supercell thunderstorm that produced this cloud formation. Supercell thunderstorms are known to spawn tornadoes with winds exceeding 200 mph (322 kph).

Photograph by Carsten Peter

By Karen E. Lange

Republished from the pages of National Geographic magazine

Last June 11 Tim Samaras and two colleagues did the near impossible—they chased down a tornado and placed a probe with video cameras directly in its path. Beginning at precisely 2:23 p.m. the team caught images that have—in a breakthrough—made it possible to calculate wind speeds close to the ground, where tornadoes rip through human lives.

Even after his team found the tornado and drove along a dirt road in Iowa to a place they were fairly certain lay in its path. Samaras remained unsure of where exactly he should leave the probe. He stood watching the tornado boil toward him, then, at the last second, he jogged over, hefted the 80-pound (36-kilogram) probe, and shifted it 40 feet (12 meters) to the north. Samaras guessed right: The eye passed just 10 feet (3 meters) from the probe, giving the cameras the closest ever view of the fierce winds turning just off the ground around a tornado's center.

Wind speeds within tornadoes are so difficult to measure directly that scientists must rate tornadoes by the damage they cause. The one Samaras caught plucked up a steel bridge and threw it down in a twisted heap, severe damage that earned it an F3 rating, with estimated maximum wind speeds of 158 miles (254 kilometers) to 206 miles (331 kilometers) an hour. Scientists can measure wind speeds with mobile Doppler radar, but only from a safe distance. Samaras's cameras looked into a part of the tornado long hidden from scientists using Doppler: the bottom 30 feet (9 meters). Winds at this level flatten houses and hurl cars. Understanding these winds—the tornado's strongest and most erratic—may enable engineers to design better tornado-resistant structures.


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