Packing the fastest winds on Earth, F5 tornadoes are truly terrifying apparitions. But even smaller tornadoes can wreak unbelievable destruction. Incredibly, some people spend significant amounts of money and time trying to get closer to them.
On May 30, 1998, storm chasers Martin Lisius and Keith Brown were following a supercell across the rolling hills of South Dakota when they came over a ridge and saw a rapidly moving tornado to the west. With lightning crashing around them, the two men stopped and captured several still pictures and some movies of the twister, which was now nearly a mile wide at its base. As the vortex entered an area of trees, they saw bright flashes of light as power lines and transformers arced and exploded. They didn’t realize it at the time, but they were witnessing the destruction of the town of Spencer.
At the end of the day the chasers convened at a restaurant in Sioux Falls, exuberant after their successful hunt. As they compared notes on the day’s events, a television in the restaurant broadcast a bulletin about the storm. The group grew silent as the news unfolded: the tornado had killed six people, injured more than one-third of the town’s 320 residents, and destroyed most of its 190 buildings.
The United States has the dubious distinction of being the tornado capital of the world, averaging more than 800 of the killer storms each year. In 1992 a record 1,293 tornadoes formed in America. Although tornadoes have been recorded in every state in the Union, most occur in the Tornado Alley states of Oklahoma, Texas, Nebraska, and Kansas, as well as in many southern states. Unlike hurricanes, which satellites can spot in their formative stages over a period of days, tornadoes form too quickly to study over a long period. This makes tornadoes an extremely dangerous short-term threat.
The gentlest type of whirlwind is the dust devil, caused by the Sun heating up the ground at different rates. Air rising faster in one area than in another nearby causes a weak low-pressure system to form. The air in adjacent areas flows into it, creating a spinning parcel of air that picks up dust, dirt, or leaves in its path.
Also unlike hurricanes, which may last for a week or more, most tornadoes last only a few minutes, and their paths average a mere 4 miles in length. They generally move along the ground at 20 to 50 miles per hour, but a few have been clocked doing more than 70. They’re a lot smaller than hurricanes, too, usually only 400 to 500 feet wide, although some monster storms grow to a girth of more than a mile. Tornadoes almost always turn in a counterclockwise direction in the Northern Hemisphere and clockwise in the Southern Hemisphere. A very few twisters somehow overcome the Coriolis force and rotate in the opposite direction of the norm.
Tornadoes may be smaller than hurricanes, but what they lack in size they make up for in intensity. While a Category 5 hurricane, the strongest on Earth, has winds of more than 155 miles per hour, the winds of some tornadoes exceed speeds of 300 miles per hour. Add to that the fact that these awe-inspiring funnels can descend from the clouds at a moment’s notice, and you have one very dangerous weather phenomenon on your hands.
In 1949, Edward M. Brooks of St. Louis University was examining the data from weather stations situated near the paths of tornadoes when he discovered a link between twisters and mesocyclones, the large rotating air masses found in supercells. In 1953 the first mesocyclone was actually seen on radar at Urbana, Illinois. It appeared as a hook shape, since the radar beam was reflecting off rain that was being drawn into a rotating cylinder of air within the storm. These classic “hook echoes” are still looked for on modern radar screens as evidence of possible tornado formation.
The man who really put tornadoes on the map was Dr. Tetsuya “Ted” Fujita, who developed a scale of tornado intensity measurement that’s still in use today. Fujita became interested in weather in his native Japan and came to the United States in 1953 to further his research in mesoscale meteorology.
Soon Fujita became interested in the damage caused by tornadoes and began collecting aerial photos of twister debris, hoping to find patterns that would help him understand the internal structure of tornadoes. In one image he noted “cycloidal marks,” or smaller swirls of damage within the larger path of a tornado that had torn through a cornfield. Fujita deduced that they had come from minitornadoes spinning around the vortex of the main twister. Later observations proved him right.
After years of studying piles of debris and other damage left behind by twisters, in 1971 Fujita (now known as “Mr. Tornado”) developed his famous Fujita Scale, or F-scale. The Fujita Scale was based on the damage a tornado would do to “strong frame houses,” and although the scientific community took him to task because there was no direct verification of his conclusions, his scale has proved remarkably accurate.
After an Eastern Airlines crash in 1975, Fujita examined the flight records of other planes in the area and discovered that some had experienced updrafts while others fought severe downdrafts. His research led him to postulate the existence of microbursts, violent but compact columns of air rushing toward the ground that could cause planes to crash on landing or takeoff.
Ted Fujita died on November 19, 1998, at the age of seventy-eight, leaving one of the most remarkable legacies in meteorology. He was not always right in every assumption and theory, but unlike many scientists, he never feared being wrong. “Even if I am wrong 50 percent of the time,” he once said, “that would still be a tremendous contribution to meteorology.” And so it was.
THE FUJITA SCALE |
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F# |
DAMAGE |
WIND SPEED |
F0 |
Light |
Up to 72 mph |
F1 |
Moderate |
73 to 112 mph |
F2 |
Considerable |
113 to 157 mph |
F3 |
Severe |
158 to 206 mph |
F4 |
Devastating |
207 to 260 mph |
F5 |
Incredible |
Above 261 mph |