You can't see it coming. Clear-air turbulence, which evidently jolted an Air Canada flight Thursday over the Pacific Ocean, strikes out of the blue, with no visible signs in the sky ahead. An aircraft's radar can't spot it coming, either. When it hit the Air Canada flight, people were slammed against the ceiling, and more than two dozen were taken to hospitals after an emergency landing in Honolulu. Clear-air turbulence happens most often in or near the high-altitude rivers of air called jet streams, per the AP. The culprit is wind shear, which happens when two huge air masses close to each other are moving at different speeds. If the difference in speed is big enough, the atmosphere can't handle the strain, and it breaks into turbulent patterns like eddies in water. Another source is masses of air that bob up and down in the atmosphere, somewhat like waves in the ocean.
They can arise spontaneously or form as air flowing over mountains is forced up, starting the up-and-down cycle. Weather forecasters can't be much help in warning pilots about where they'll encounter clear-air turbulence, says Thomas Guinn, a meteorology professor at the Embry-Riddle Aeronautical University in Daytona Beach, Florida. "It's probably one of the most challenging forecast problems we have right now for aviation meteorology," he said. Paul Williams of the University of Reading in England said some tests suggest that specialized radar-like devices could make the atmospheric disruptions visible to pilots. But the devices are expensive and heavy, so they are not widely used. Once pilots hit turbulence, they can try to fly out of it, possibly by changing altitude, said Clint Balog, also of Embry-Riddle.
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