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Inside the Jet Stream
Jet Stream Glossary

angular momentum—An object's momentum when that object follows a path around a fixed point, such as an axis. See also momentum below.

convection cell—Convection is the movement of heat within a gas or liquid by the circulation of currents. With natural convection—the type responsible for atmospheric movement—the circulation is the result of gravity. Convection cell describes the cyclical pattern of movement of a gas or liquid such as the atmosphere, the ocean, or the Earth's mantle.

jet stream—High-speed winds usually found at high altitudes, just below the tropopause, between 25,000 and 45,000 ft. The term jet stream was coined by the first pilots who encountered this strong wind, to whom it seemed as though the air was being blown out of a gigantic nozzle, or jet.

low- and high-pressure systems—Depicted as either an "L" or an "H" on weather maps, these are weather systems in which air pressure is either low or high. Low-pressure systems are often associated with clouds and precipitation; high-pressure systems often bring clear skies.

momentum—The force or energy associated with an object in motion. Also known as linear momentum. If an object's linear momentum has no external force acting on it, then that object's momentum will not change.

polar front—The boundary between the colder air of the polar regions and the warmer air of the tropics. The wind generated at polar fronts helps to power polar-front jet streams.

tropopause—The zone in the atmosphere that divides the troposphere and the stratosphere. The altitude of the tropopause varies with latitude, being highest above the equator (about 12 miles) and lowest near the poles (less than five miles).

troposphere—The lowest layer of atmosphere.

stratosphere—The layer of atmosphere that extends from the tropopause to the mesosphere. (The mesosphere is, on average, 30 miles high.)

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