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Wind shear is a difference in wind speed or direction between two points in the atmosphere. Depending whether the two points are at different altitudes or at geographically different locations, shear can be either vertical or horizontal.
Wind shear can affect aircraft airspeed during take off and landing in disastrous ways. An explanation in regard to vertical wind shear can be seen here: (wind gradient). It is also a key factor governing the severity of thunderstorms. An additional hazard is turbulence often associated with wind shear. Wind shear also generally inhibits tropical cyclone development.
Weather situations when shear is observed are:
- Weather fronts. Significant shear is observed, when the temperature difference across the front is 5 °C or more, and the front moves at 15 kt or faster. Because fronts are three-dimensional phenomena, frontal shear can be observed at any altitude between surface and tropopause.
- Obstacles to flow. When wind above a mountain blows from the direction of the mountain, vertical shear is observed on the lee side.
- Inversions. When on a clear and calm night, a radiation inversion is formed near the ground, the friction does not affect wind above the inversion top. Change in wind can be 90 degrees in direction and 40 kt in speed. Even a nocturnal low level jet can sometimes be observed. Density difference causes additional problems to aviation.
See also
- Air safety. Between 1964 and 1985, wind shear directly caused or contributed to 26 major civil transport aircraft accidents in the U.S. that led to 620 deaths and 200 injuries. Of these accidents, 15 occurred during take-off, 3 during flight, and 8 during landing. Since 1995, the number of major civil aircraft accidents caused by wind shear has dropped to approximately 1 each 10 years due to onboard detection, and Doppler radar on the ground.
External links
Cizalladura del viento | Rincihan angin | ウィンド・シア | Tuulishear | 风切变
"Wind shear"