Moments after Samaras places pressure sensors and the team drives away (left top), rain starts falling and the tornado cuts like a scythe across a cornfield. Suddenly the tornado strikes the cameras: Cornstalks, rocks, sticks, leaves, and dirt fill the air. As it pushes past the probe, the tornado rolls a piece of farm equipment, snaps trees, and scours a field to bare soil. Each image, like this stick (above left), contains two superimposed pictures recorded milliseconds apart (above right)—a characteristic of video photography that enabled Samaras to estimate the velocities of objects picked up by the tornado. He matched the position of the stick to a spot where he stood while placing the probe (below) and then used measurements of his body to figure the stick's size and distance traveled. Knowing that the two pictures were taken 16.6 milliseconds apart, he calculated a speed of 71 mph. That's remarkably fast, given the stick's location just inches off the ground. Similarly, he found that a maple leaf (not shown) a few feet off the ground was traveling at 125 mph. Combining many such estimates will make it possible to create detailed pictures of wind speeds—and grasp what is happening inside tornadoes where they meet the ground.
—Karen E. Lange
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 (right), hefted the 80-pound probe, and shifted it 40 feet to the north. Samaras guessed right: The eye passed just 10 feet 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 to 206 mph. 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. 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.