What is windshear?

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

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

The existence of vertical wind shear will cause damage to bridges, high-rise buildings and aviation flight. Low-altitude wind shear is an important risk factor in the take-off and landing stages of aircraft, and it is called "invisible killer".

There are two main reasons for wind shear, one is caused by the change of atmospheric movement itself; The other is caused by geographical and environmental factors. Sometimes it is a combination of the two.

Weather factor

The weather background that produces wind shear. There are three main types of weather background that can produce low-level wind shear with certain influence.

wind shear

a.？ Strong convective weather. Usually refers to weather such as thunderstorms and cumulonimbus clouds. Under the influence of this weather condition, strong wind shear can be produced in a certain spatial range. Especially, this phenomenon is more serious in the strong downward flow area in thunderstorm clouds and the gust front area in the front of cumulonimbus clouds. Especially strong downward flow is called micro-downward flow, which is the most harmful to flight. It is a comprehensive wind shear area characterized by vertical wind.

B. Positive weather. Whether it is a cold front, a warm front or an occluded front, low-altitude wind shear can be produced. But its intensity and regional scope are different. The wind shear in this weather is mainly horizontal and vertical shear of horizontal wind (except frontal thunderstorm weather). Generally speaking, it is not as harmful as the wind shear in strong convective weather.

c.？ Low level jet weather with radiation inversion. On a clear night in autumn and winter, due to the intense ground radiation cooling, a low-altitude inversion layer appeared. There is momentum accumulation above the inversion layer, and the wind speed below the inversion layer is small, and it is often quiet near the ground, so there is inversion layer wind shear. This kind of wind shear strength is usually small, but it is easy to be ignored, and it can be dangerous if it is not handled properly.

Geographical and environmental factors

Wind shear caused by geographical and environmental factors. The geographical and environmental factors here mainly refer to natural and human factors such as mountain topography, land-water interface, high-rise buildings and forest patches. These factors can also lead to wind shear. Wind shear is related to prevailing wind conditions (direction and size) at that time, as well as the size and complexity of mountainous terrain, windward and leeward positions, water surface size, distance from airport to water surface, and size and shape of buildings. Generally, mountain areas have large height difference, large water area and tall buildings, which are not only prone to wind shear, but also have high strength.