- jet stream
1. strong, generally westerly winds concentrated in a relatively narrow and shallow stream in the upper troposphere of the earth.2. similar strong winds in the atmosphere of another planet: jet streams on Jupiter.3. the exhaust of a jet or rocket engine.[1945-50]
* * *Any of several long, narrow, high-speed air currents that flow eastward in a generally horizontal zone in the stratosphere or upper troposphere.Jet streams are characterized by wind motions that generate strong vertical shearing action, considered largely responsible for the clear-air turbulence experienced by aircraft. They also have an effect on weather patterns. Jet streams circle the Earth in meandering paths, shifting position as well as speed with the seasons. In the winter they are nearer the Equator and their speeds are higher than in the summer. There are often two, sometimes three, jet-stream systems in each hemisphere.
* * *a region of long, narrow, high-speed winds that typically flow northeastward, eastward, and southeastward in the middle and upper troposphere or lower stratosphere. Jet streams are characterized by wind motions that generate strong vertical shearing action, which is thought to be largely responsible for clear air turbulence. A brief treatment of jet streams follows. For full treatment, see climate: Jet streams (climate).First discovered by airmen during World War II, the jet streams have speeds of up to 90 metres per second (200 miles per hour) along hundreds of kilometres at their centres, but velocities fall off very sharply both laterally and vertically, so that the high speeds are limited to narrow bands at heights between 6 and 14 km (20,000 and 45,000 feet). The jet stream results from horizontal differences in temperature that exist over a considerable vertical distance through the troposphere. These temperature differences produce a horizontal pressure gradient that drives geostrophic and gradient winds. The greater the horizontal temperature difference, the stronger the jet stream.Jet streams encircle the Earth in meandering paths, shifting position as well as speed with the seasons. During the winter their positions are nearer the equator and their speeds higher than during the summer. There are often two, sometimes three jet-stream systems in each hemisphere. One is related to the Polar Front, lying in midlatitudes where the air-mass contrasts (the fronts) promote the formation of squalls, storms, and cyclones. The other distinct system, the Subtropical Jet Stream, lies above the subtropical high-pressure belt and is usually associated with fair weather. During summer a third system occurs over Southeast Asia, India, the Arabian Sea, and tropical Africa. This tropical jet stream affects the formation and duration of Indian and African summer monsoons.
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