What is wind shear?

Wind shear is an atmospheric phenomenon, the change of wind vector (wind direction, wind speed) in the horizontal and/or vertical distance in the air.

Wind shear can be divided into horizontal shear of horizontal wind, vertical shear of horizontal wind and vertical wind shear according to the wind direction.

The existence of vertical wind shear will cause damage to bridges, high-rise buildings, aviation flights, etc. Wind shear occurring at low altitudes is an important risk factor during the takeoff and landing phases of aircraft, and is known as the "invisible killer".

There are two main types of causes of wind shear. One is caused by changes in atmospheric movement itself; the other is caused by geographical and environmental factors. Sometimes it's a combination of the two.

Weather factors

The weather background that produces wind shear. There are three main types of weather backgrounds that can produce low-level wind shear that has a certain impact.

Wind shear

a. Strong convective weather. Usually refers to weather such as thunderstorms and cumulonimbus clouds. Strong wind shear can occur within a certain spatial range under the influence of such weather conditions. This is especially true in the strong downdraft areas in thunderstorm clouds and the gust front areas at the leading edge of cumulonimbus clouds. Especially strong downdrafts are called micro-downdrafts, which are the most harmful to flight. It is a comprehensive wind shear area characterized by vertical wind.

b. Frontal weather. Whether it is a cold front, a warm front or an imprisoning front, low-altitude wind shear can occur. However, their intensity and regional scope vary. The wind shear in this kind of weather is mostly dominated by horizontal and vertical shear of horizontal wind (except for frontal thunderstorm weather). Generally speaking, it is not as harmful as wind shear in strong convective weather.

c. Radiation inversion-type low-altitude jet weather. On clear nights in autumn and winter, a low-altitude inversion layer is formed due to strong ground radiation cooling. Momentum accumulates above this inversion layer, and the wind speed is high to form a jet stream. However, the wind speed below the inversion layer is small, and the wind near the ground is often The wind is calm, so inversion wind shear occurs. The intensity of this type of wind shear is usually smaller, but it is easily overlooked and can be dangerous if not handled properly once encountered.

Geographical and environmental factors

Wind shear caused by geographical and environmental factors. The geographical and environmental factors here mainly refer to mountainous terrain, water-land interface, tall buildings, patches of woods and other natural and man-made factors. These factors can also cause wind shear phenomena. The wind shear condition is related to the prevailing wind conditions (direction and size) at that time, as well as the size and complexity of the mountain terrain, the windward and leeward position, the size of the water surface and the distance between the airport and the water surface, the size and shape of the building, etc. . Generally, mountains have large height differences, large water areas, and tall buildings, which are not only prone to wind shear, but also have high intensity.