How are sandstorms formed? Why is it so destructive?

Sandstorm refers to the meteorological phenomenon that dust is suspended in the air, the air is turbid and the visibility is reduced. According to the national standard "Dust Weather Grade" (GB/T? 20480-20 17), sandstorm weather is divided into five grades according to the horizontal visibility on the ground: floating dust, sand blowing, sandstorm, strong sandstorm and special post sandstorm. Among them, sandstorm refers to the weather phenomenon that the wind blows away the dust on the ground, the air is turbid, and the horizontal visual field is less than 1 km. The formation of sandstorm weather generally requires three basic conditions: dust on the ground, strong wind and unstable air state. Among them, the ground dust is the material basis for the formation of dust weather. Strong wind is the dynamic condition for the formation of dusty weather. Unstable air conditions are more conducive to the increase of wind power, creating strong convective weather and drying more dust.

The frequent sandstorm weather in northern China in spring is due to the drought and lack of rain in the north, the widespread Gobi desert, sparse vegetation and serious surface exposure, which can not play a role in fixing sandstorms. In spring, the temperature rises rapidly, the air is unstable and the wind speed is high, which has the basic conditions for the formation of sandstorm weather. If there is dusty weather, the elderly, children and pregnant women are easily affected by the crowd; Traffic police, environmental workers, construction workers, herders and other people who often move in the wild are also people who need attention. People with respiratory diseases and cardiovascular diseases should avoid outdoor activities. When the wind at a certain speed is too dry and sweeps over the soft ground, the large particles of sand will roll under the impetus of the wind, and the rolling sand will vibrate into small dust particles.

These small particles usually only stay in the air layer about 0. 1 mm above the ground. Usually, dust as short as the ground is not affected by the wind. In other words, the general wind can't push the dust flying, so as mentioned at the beginning, there must be certain customs to cause the root cause of the dust storm. Because only large grains of sand can blow them away, or the dust on the ground can rise from the ground to a higher place. And the thrust of the wind direction is greater than or equal to the gravity that makes them sink. So they can run with the wind.

In this process, if the wind keeps blowing at a certain speed, more sand will shake, more dust will rise into the air, and the smallest dust particles will be picked up by the airflow, forming a certain scale and producing dust clouds. Dust clouds move with the airflow. Usually only when facing the forest, the wind that keeps flying over the ground will be blocked by the forest, so it has to stop.