Wind Shear

Wind shear is the difference in speed and/or direction between two points (either areas or layers) of air in the atmosphere. Wind shear may occur in either a vertical or horizontal orientation, depending on whether the two points are positioned at different altitudes or at different geographical locations. An example of the former situation is the case in which one layer of air in the atmosphere is traveling from the west at a speed of 31 mph (50 km/h) while a second layer above it is traveling in the same direction at a speed of 6.2 mph (10 k/mh). The friction that occurs at the boundary of these two air currents is a manifestation of wind shear.

An example of horizontal wind shear occurs in the jet stream where one section of air moves more rapidly than other sections on either side of it. In this case, the wind shear line lies at the same altitude as various currents in the jet stream, but at different horizontal distances from the jet stream’s center.

Wind shear is a crucial factor in the development of other atmospheric phenomena. For example, as the difference between adjacent wind currents increases, the wind shear also increases. At some point, the boundary between currents may break apart and forms eddies that can develop into clear air turbulence or, in more drastic circumstances, tornadoes and other violent storms.

Wind shear has been implicated in a number of disasters resulting in property damage and/or loss of human life. The phenomenon is known as a microburst, a strong localization down draft (down burst) that, when it reaches the ground, continues as an expanding outflow. For example, it is associated with the movement of two streams of air at high rates of speed in opposite directions. An airplane that attempts to fly through a microburst passes through the wind shear at the boundary of these two air streams. The plane feels, in rapid succession, an additional lift from headwinds and then a sudden loss of lift from tailwinds. In such a case, a pilot may not be able to maintain control of the aircraft in time to prevent a crash.

Due to a number of commercial aircraft accidents during the 1970s and 1980s, the U.S. Federal Aviation Agency (FAA) required all U.S. commercial airplanes to use onboard wind shear detection systems by the mid-1990s. Because of these detection devices onboard commercial aircraft along with Doppler radar instruments on the ground, the number of deaths and injuries went from 26 major aircraft accidents involving hundreds of deaths and injuries in the twenty years from 1964 to 1985 to one major accident caused by wind shear from 1995 to 2005.

See also Atmospheric circulation; Wind.

Wind shear

Wind shear is a phenomenon describing highly localized variability in wind speed and/or wind direction. Because wind shear can affect the angle of attack on an airfoil (e.g., the wing, or control surfaces of an airplane) wind shear can cause a loss of lift or control. Dangerous to aviation, wind shear is particularly hazardous when encountered during take-off or landing.

Wind shear is the difference in speed or direction between two layers of air in the atmosphere. Wind shear may occur in either a vertical or horizontal orientation. An example of the former situation is the case in which one layer of air in the atmosphere is traveling from the west at a speed of 31 mph (50 km per hour) while a second layer above it is traveling in the same direction at a speed of 6.2 mph (10 km per hour). The friction that occurs at the boundary of these two air currents is a manifestation of wind shear.

An example of horizontal wind shear occurs in the jet stream where one section of air moves more rapidly than other sections on either side of it. In this case, the wind shear line lies at the same altitude as various currents in the jet stream, but at different horizontal distances from the jet stream's center.

Wind shear is a crucial factor in the development of other atmospheric phenomena. For example, as the difference between adjacent wind currents increases, the wind shear also increases. At some point, the boundary between currents may break apart and form eddies that can develop into clear air turbulence or, in more drastic circumstances, tornadoes and other violent storms.

Wind shear has been implicated in a number of disasters resulting in property damage and/or loss of human life. The phenomenon is known as a microburst, a strong localization down draft (down burst) which, when it when reaches the ground, continues as an expanding outflow. For example, it is associated with the movement of two streams of air at high rates of speed in opposite directions. An airplane that attempts to fly through a microburst passes through the wind shear at the boundary of these two air streams. The plane feels, in rapid succession, an additional lift from headwinds and then a sudden loss of lift from tailwinds. In such a case, a pilot may not be able to maintain control of the aircraft in time to prevent a crash.

See also Aerodynamics; Bernoulli's principle; Meteorology; Weather radar; Weather satellite

Wind shear

Wind shear is the difference in speed or direction between two layers of air in the atmosphere. Wind shear may occur in either a vertical or horizontal orientation. An example of the former situation is the case in which one layer of air in the atmosphere is traveling from the west at a speed of 31 mph (50 kph) while a second layer above it is traveling in the same direction at a speed of 6.2 mph (10 kph). The friction that occurs at the boundary of these two air currents is a manifestation of wind shear.

An example of horizontal wind shear occurs in the jet stream where one section of air moves more rapidly than other sections on either side of it. In this case, the wind shear line lies at the same altitude as various currents
in the jet stream, but at different horizontal distances from the jet stream's center.

Wind shear is a crucial factor in the development of other atmospheric phenomena. For example, as the difference between adjacent wind currents increases, the wind shear also increases. At some point, the boundary between currents may break apart and for eddies that can develop into clear air turbulence or, in more drastic circumstances, tornadoes and other violent storms.

Wind shear has been implicated in a number of disasters resulting in property damage and/or loss of human life. The phenomenon is known as a microburst, a strong localization down draft (down burst) which, when it when reaches the ground, continues as an expanding outflow. For example, it is associated with the movement of two streams of air at high rates of speed in opposite directions. An airplane that attempts to fly through a microburst passes through the wind shear at the boundary of these two air streams. The plane feels, in rapid succession , an additional lift from headwinds and then a sudden loss of lift from tailwinds. In such a case, a pilot may not be able to maintain control of the aircraft in time to prevent a crash.

See also Atmospheric circulation; Wind.

wind shear The gradient of horizontal wind velocity with height, which varies according to the rate of change of temperature with altitude. Vertical wind shear can be a cause of cloud formation in the turbulent mixing taking place in a boundary layer of air moving at different speeds. The shear between the wind at different levels can be expressed as a vector, measuring the difference in speed and direction.