Word: shears
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Dates: during 1960-1969
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...ripped apart by an invisible tempest. CAT is most often met just above or just below the 30,000-35,000-ft. jet stream - and modern aircraft like best the levels near the great, racing jet stream. It has been agreed that CAT is caused by wind shear -the "friction" between adjacent air masses moving at different speeds. Last week Joseph J. George, chief meteorologist for Eastern Airlines, told how this knowledge might be put to work to predict CAT's claws so that airliners can be warned to skirt the peril...
After studying the meteorological records of bad CAT occurrences, George and his research team concluded that not one, but two different sorts of wind shear must be present to cause dangerous clear air turbulence. One is horizontal shear, caused by friction between air masses moving side by side at different speeds. The other is vertical shear, caused by the friction between two air masses, the one above the other, moving at different speeds...
...forecast severe CAT, George studies weather data in search of above-and-below air layers that are being dragged violently past each other by the jet stream. He draws on a map the area where this vertical shearing is sufficiently intense. Then he scans the data a second time to see if any air masses on the same level are moving rapidly past each other. If this is the case, he marks another area on his map (see diagram). If the areas overlap, the overlap has the two necessary kinds of violent shear. It is therefore apt to be full...
Snaking Around Earth. Dr. Harry Wexler, chief of research for the U.S. Weather Bureau, explains that CAT is generally caused by wind shear, the conflict of air masses moving at different speeds or in different directions. When such masses meet, a belt of swirls and waves appears in the boundary between them. A slow airplane can fly through moderate CAT with hardly any unpleasantness, but for a fast-flying jet the sensation is like driving a car over a cobblestone pavement with some of the stones missing...