Where does the sand from the sandstorm come from?

Sandstorm refers to the weather phenomenon that strong winds blow up dust on the ground, making the air very turbid and the horizontal visibility less than 1km. [2] Sandstorm is a weather phenomenon in wind erosion and desertification, and its formation is influenced by both natural factors and human activities. Natural factors include strong wind, decreased precipitation and its sand source. Human activity factor refers to the increase of sandstorm frequency after vegetation destruction in the process of economic development. [3]

Sandstorm weather mainly occurs in winter and spring, because there is little precipitation in winter and spring in semi-arid and arid areas, the ground is extremely dry and loose, and the wind erosion resistance is very weak. When there is a strong wind, there will be a lot of sand.

Formation reason editing

Strong wind, strong thermal instability and sand source are the dynamic factors and material basis of sandstorm formation respectively. [ 1]

natural conditions

Sandstorm in Gobi Desert

Sandstorm in Gobi Desert

The weather situation favorable to strong winds or strong winds, favorable distribution of dust sources and favorable air instability conditions are the main reasons for the formation of sandstorms or strong sandstorms. Strong wind is the driving force of sandstorm, and the source of sandstorm is the material basis of sandstorm. Unstable thermal conditions are conducive to the increase of wind power and the development of strong convection, thus carrying more dust and winding it higher.

In addition, drought and lack of rain in the early stage, warming weather and rising temperature are the special weather background for the formation of sandstorms; The convective cells before the ground cold front develop into clouds or squall lines, which is a small and medium-sized system conducive to the development and strengthening of sandstorms. The topographic condition conducive to the increase of wind speed, that is, the narrow tube effect, is one of the favorable conditions for the formation of sandstorms.

The main component of soil and yellow sand is silicate. When there is less rain and the temperature gets warmer, the silicic acid on the silicate surface loses water.

H2SiO4=Si2O3+H2O (gas)

In this way, the surface of silicate soil micelles and sand particles will be negatively charged and repel each other, becoming aerosols that cannot be aggregated together, thus forming sand blowing, that is, sandstorms. Sandstorms are essentially silicate aerosols with negative charges.

In short, the formation of sandstorms requires these three conditions:

One is the dust on the ground. It is the material basis for the formation of sandstorms.

The second is the strong wind. This is the dynamic basis for the formation of sandstorms and the dynamic guarantee for the long-distance transportation of sandstorms.

Third, the air state is unstable. This is an important local thermal condition. Sandstorms often occur in the afternoon and evening, which shows the importance of local thermal conditions.

Physical factors

Giant sandstorm

Giant sandstorm (2 photos)

Under the favorable conditions of large-scale environment, high-altitude dry and cold jet, strong vertical wind speed, wind direction shear and thermal instability stratification, the generation and development of small and medium-scale systems near the front area intensified the pressure and temperature gradient before and after the front area, forming a huge pressure and temperature gradient before and after the front area. Under the joint action of momentum downward transfer and gradient deviation wind, the wind speed in the near-surface layer rises sharply, causing dust on the surface and forming sandstorm or strong sandstorm weather.

environmental factor

With the efforts of experts from the Institute of Environment and Engineering in Cold and Arid Regions, Chinese Academy of Sciences, the wind tunnel simulation experiment of sandstorm was successfully completed to explore the starting and transport mechanism of sandstorm materials.

Experts found through experiments that soil wind erosion is the primary link in the occurrence and development of sandstorms. Wind is the most direct driving force of soil, among which the nature of airflow, the magnitude of wind speed and the related conditions of wind action in soil wind erosion are the most important factors. In addition, soil water content is also one of the important reasons that affect soil wind erosion.

This experiment also proves that plant measures are one of the effective methods to prevent and control sandstorms. Experts believe that plants usually affect wind erosion in three forms: dispersing certain wind momentum on the ground to reduce the transmission between airflow and dust; Stop the movement of soil, dust, etc.

human factor

The occurrence of sandstorm is not only the product of specific natural environmental conditions, but also has a corresponding relationship with human activities. Man-made overgrazing, deforestation, industrial and mining traffic construction, especially man-made overgrazing, destroyed the ground vegetation, disturbed the ground structure, formed a large area of sandy land, and directly accelerated the formation and development of sandstorms.

Meteorological factors

The formation of sandstorm is based on the special atmospheric circulation in East Asia, which is closely related to the winter monsoon. Its occurrence is mainly related to the cold front transit driven by Siberian-Mongolian high in winter, which belongs to cold front sandstorm.