In a Learjet streaking at 45,000 feet over Mississippi, "Mr. Tornado" is stalking his quarry. As the plane slips above the towering thunderheads, he instructs his pilot to "fly close to that top but not too close—it might suck us in." Then, while still and movie cameras record the historic moment, "a crater surrounded by a horseshoe-shaped wall of clouds suddenly appeared...We flew over the tornado cloud at 3:09 p.m., about 50 miles northeast of Jackson."

The tornado chaser is T. (for Tetsuya) Theodore Fujita, 56, professor of meteorology at the University of Chicago. Later, aerial and ground surveys verified that the thunderstorm Fujita photographed on Feb. 23 spawned three twisters, including one that cut a 10-mile swath of devastation beneath his flight path. "It was the first time we have ever seen the top of a tornado cloud," says Fujita, still perking with excitement.

Ted Fujita ranks among a handful of experts on nature's most violent and least understood storm. He has advanced a theory that tornadoes are produced when a thundercloud "overbuilds." If the top collapses, it creates fearsome downward air currents that set off tornadoes. To test his ideas, Fujita has built a machine that can produce tiny laboratory twisters.

The knowledge he is gaining may save lives, Fujita says. "Many survivors report they had only a minute's warning to get to shelter. We want to increase the warning time." The professor acknowledges that his research dominates his life. "I love tornadoes," he says. "They have become a passion." While his flights are financed by NASA and the National Oceanic and Atmospheric Administration (at a cost of as much as $5,000 a day), Fujita claims that, if necessary, he would clean out his own bank account to continue his studies.

"It's like looking for the Loch Ness monster," says Fujita, who is fond of animal analogies and mixes them at random. "You may be touching a tiger. It's a calculated risk." His close friend Allen Pearson, chief tornado forecaster for the National Weather Service, worries that Fujita may one day wander too close to a killer storm. "Ted will be the last of the kamikaze if he does," Pearson jokes.

Born in Japan, the son of a teacher, Fujita chose meteorology as his specialty. On the basis of a paper he wrote on thunderstorms, he was invited to Chicago in 1953 as a researcher. He now shares a greenery-filled, two-story home near the university with his second wife, Sumiko (Susie).

"He could be a meteorological millionaire if he wished, acting as a consultant at $1,000 a day," says Pearson. Fujita shows little concern for getting rich. His science class of 200 undergraduates is one of the largest at the university. "When students are involved in excitement," says the professor, who keeps his class up-to-date on his tornado hunts, "they learn more." He is also helping redesign nuclear reactors to withstand tornado damage.

Fujita has passed on his scientific interest to his only child, Kazuya, 24, who is working on his Ph.D. at Northwestern University. But unlike his father, Kazuya Fujita has no yen to play tag with tornadoes. He's studying earthquakes.