Where does the sand in sandstorms come from?
Sandstorm refers to a weather phenomenon in which strong winds blow up dust and sand on the ground, making the air very turbid and the horizontal visibility is less than 1km. [2] Sandstorm is a weather phenomenon in wind erosion desertification. Its formation is affected by both natural factors and human activity factors. Natural factors include high winds, reduced precipitation and its sand sources. Human activity factors refer to the increase in the frequency of sandstorms caused by human damage to vegetation during the process of economic development. [3]
Sandstorms mainly occur in winter and spring. This is because semi-arid and arid areas have very little precipitation in winter and spring. The ground surface is extremely dry and loose, and its ability to resist wind erosion is very weak. When strong winds blow, There will be a lot of sand.
CausesEdit
Strong winds, strong thermal instability and sand sources, as dynamic factors and material basis respectively, are the three important conditions for the formation of sandstorms. [1]
Natural conditions
Sandstorms on the Gobi Desert
Sandstorms on the Gobi Desert
Conducive to producing strong or strong winds Weather conditions, favorable sand and dust source distribution and favorable unstable air conditions are the main reasons for the formation of sandstorms or strong sandstorms. Strong wind is the driving force for sandstorms, and sand and dust sources are the material basis of sandstorms. Unstable thermal conditions are conducive to the increase in wind power and the development of strong convection, thereby entraining more sand and dust and carrying it higher.
In addition, drought and lack of rain in the early stage, warm weather, and rising temperatures are the special weather background for the formation of sandstorms; the development of convective cells in front of the ground cold front into clouds or squall lines is conducive to the development of sandstorms And strengthened small and medium-scale systems; the terrain conditions that are conducive to increased wind speed, that is, the narrow tube effect, are one of the favorable conditions for the formation of sandstorms.
The main component of soil and yellow sand is silicate. When there is drought and little rain and the temperature warms, the silicic acid on the surface of the silicate loses water.
H2SiO4=Si2O3+H2O (gas )
In this way, the surfaces of silicate soil micelles and sand particles will be negatively charged, and they will repel each other. They will become aerosols and cannot condense together, thus forming blowing sand or sandstorms. Dust storms are essentially negatively charged silicate aerosols.
In short, the formation of sandstorms requires these three conditions:
First, the sand and dust material on the ground. It is the material basis for the formation of sandstorms.
The second is strong wind. This is the power basis for the formation of sandstorms and the power guarantee for sandstorms to be transported over long distances.
The third is unstable air state. This is an important local thermal condition. The fact that sandstorms mostly occur in the afternoon and evening illustrates the importance of local thermal conditions.
Physical factors
Giant sandstorms
Giant sandstorms (2 photos)
Under extremely favorable large-scale environment, high-altitude dry cold jets and Strong vertical wind speed, wind shear and thermally unstable stratification conditions cause the formation and development of small- and medium-scale systems near the frontal area, which intensifies the pressure and temperature gradients before and after the frontal area, forming a huge pressure-temperature gradient before and after the frontal area. Under the simultaneous action of momentum downward transmission and gradient deviation wind, the near-surface wind speed rises sharply, kicking up surface sand and dust, forming sandstorms or strong sandstorms.
Environmental factors
With the efforts of experts from the Institute of Cold and Arid Regions Environment and Engineering of the Chinese Academy of Sciences, a sandstorm study was specially set up to explore the initiation and transmission mechanisms of sand and dust materials. The wind tunnel simulation experiment was successfully completed.
Through experiments, experts have discovered 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 air flow, wind speed, and related conditions of wind force during soil wind erosion are the most important factors. In addition, soil moisture content is also one of the important reasons affecting soil wind erosion.
This experiment also proved that plant measures are one of the effective methods to prevent sandstorms. Experts believe that plants usually affect wind erosion in three ways: dispersing a certain amount of wind momentum on the ground and reducing the transfer between airflow and dust; and preventing the movement of soil, dust, etc.
Human factors
The occurrence of sandstorms is not only the product of specific natural environmental conditions, but also has a corresponding relationship with human activities. Man-made overgrazing, deforestation of forest vegetation, industrial and mining transportation construction, and especially man-made excessive reclamation destroy ground vegetation, disturb the ground structure, and form large areas of desertified land, which directly accelerate the formation and development of sandstorms.
Meteorological factors
The formation of sandstorms is based on the special atmospheric circulation in East Asia and is closely related to the winter monsoon. Its occurrence is mainly driven by the Siberian-Mongolian high pressure in the winter half. It is related to the passage of the cold front below and is a cold front type sandstorm.