How are sandstorms formed? What's the harm? How to prevent and treat it?

Sand duststorm is a general term for both sandstorm and duststorm. It refers to strong wind blowing a large amount of sand and dust material from the ground into the air, making the air particularly turbid and horizontal. Severe wind and sand weather phenomenon with visibility less than 1km. A sandstorm refers to a sandstorm caused by strong winds blowing a large amount of sand into the near-surface layer; a dust storm is a storm caused by strong winds carrying a large amount of dust and other fine-grained materials into high altitudes.

Causes of sandstorms

Weather conditions that are conducive to strong winds or strong winds, favorable sand and dust source distribution and favorable air instability 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, early drought and lack of rain, warm weather, and rising temperatures are the special weather and climate 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 sandstorms The development and strengthening of 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 hazards of sandstorms

⑴ Strong winds: Strong winds carrying fine sand and dust destroy buildings and public facilities, causing death.

⑵ Sand burial: Farmland, channels, cottages, railways, pastures, etc. are buried by a large amount of sand due to wind and sand flow, especially posing a serious threat to transportation.

⑶ Soil wind erosion: The dust source and affected area of ??each sandstorm will be harmed by wind erosion to varying degrees, and the depth of wind erosion can reach 1 to 10 cm. It is estimated that my country's annual loss of fine soil matter caused by sandstorms is as high as 106 to 107 tons, most of which have particle sizes below 10 microns, causing serious damage to the land productivity of farmland and pastures in the source areas.

⑷ Atmospheric pollution: In the source areas and affected areas of sandstorms, respirable particulate matter (TSP) in the atmosphere increases, and air pollution intensifies. Taking the "5.5" extremely severe sandstorm in 1993 as an example, the TSP concentration of outdoor air in Jinchang City, Gansu Province reached 1016 mg/m3 and indoors was 80 mg/m3, exceeding the national standard by 40 times. From March to April 2000, the Beijing area was affected by sandstorms. The air pollution index reached level 4 or above for 10 days, which also affected many cities in eastern my country. From March 24 to 30, the daily pollution index in 18 cities, including Nanjing and Hangzhou, exceeded level 4.

The dangers of sandstorms

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Sandstorms are highly disastrous weather that occurs in northwest my country and northern China, and can cause damage to houses. Collapse, traffic and power supply obstruction or interruption, fire, human and animal casualties, etc., pollute the natural environment, destroy crop growth, and cause serious losses and great harm to the national economic construction and the safety of people's lives and property. The main hazards of sandstorms are in the following aspects:

1. Deterioration of the ecological environment

When sandstorms occur, sand, stones and floating dust wrapped in strong winds spread everywhere. The air in any area passing through is turbid and irritating. The number of eye, respiratory and other diseases has increased. For example, during the severe sandstorm that occurred in Jinchang City on May 5, 1993, the measured dust content in the outdoor air was 1016 mm/cubic centimeter, and the indoor dust content was 80 mm/cubic centimeter, exceeding the national dust content in living areas. 40 times the standard.

2. Impact on production and life

Sandstorm weather carries a large amount of sand and dust that blocks the sun and light. The weather is gloomy, resulting in reduced solar radiation and poor visibility for several hours to more than ten hours. It is easy to make people feel depressed and reduce the efficiency of work and study. In mild cases, a large number of livestock can be infected with respiratory and gastrointestinal diseases. In severe cases, it can lead to the death of a large number of "spring fatigue" livestock and scrape away fertile farmland, seeds and seedlings. Sandstorms will also intensify wind erosion and desertification of surface soil, covering plant leaves with thick dust, affecting normal photosynthesis and causing crop yield reductions.

3. Loss of life and property

On May 5, 1993, a severe sandstorm occurred in Jinchang, Weiwu, Minqin, Baiyin and other cities in Gansu Province, affecting 2.5355 million farmland mu, 42,800 trees were lost, causing direct economic losses of 236 million yuan, 50 deaths, and 153 serious injuries. On April 12, 2000, severe sandstorms occurred in Yongchang, Jinchang, Weiwu, Minqin and other cities. According to incomplete statistics, only Jinchang and Weiwu suffered direct economic losses of 15.34 million yuan.

4. Traffic safety (traffic accidents such as airplanes and cars)

Sandstorms often affect traffic safety, causing planes to be unable to take off or land normally, causing damage to the glass of cars and trains, and causing parking problems. Luck or derailment.

Causes of sandstorms

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Sandstorms are caused by soil wind erosion

According to Xinhua News Agency Lanzhou News in the Chinese Academy of Sciences Thanks to the efforts of experts from the District's Arid Area Environment and Engineering Research Institute, a sandstorm wind tunnel simulation experiment specially set up to explore the initiation and transmission mechanism of sand and dust materials was successfully completed recently.

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.

In addition, through experiments, researchers have drawn a conclusion: the occurrence of sandstorms is not only a 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.

The culprit of sandstorms: atmospheric circulation

The brief scene of sandstorms in Beijing in the spring is nothing more than the 300,000-square-kilometer-long Loess Plateau in northern China that has evolved over the past two to three million years. It is a weather process that must be experienced every year. The difference is that the wind in the latter is stronger and lasts longer (can last for several days). The source of sand and dust is not a crossroad 50 meters away, but hundreds of kilometers away in the desert and Gobi.

It’s like God is playing an incredible game: He picks up the sand and dust on the surface of the deserts and Gobi in northwest China and Central Asia and throws it toward the southeast, allowing the dust to gradually accumulate where it falls. A piece of high ground. This game started about 2.4 million years ago, and God still enjoys it (in 2002, "Nature" magazine published the latest research results of Chinese scholars, pushing the start time to 22 million years ago).

In fact, the wind is God’s hand that casts the sand.

After the Indian plate moved northward and collided with the Eurasian plate, the crust of the Indian continent was inserted under the crust of the Asian continent and held up the latter. As a result, the shallow sea in the Himalayas disappeared, the Himalayas began to form and gradually rose higher, and the Tibetan Plateau was also uplifted by the compression of the Indian plate. This process lasted for more than 60 million years, and by about 2.4 million years ago, the Qinghai-Tibet Plateau was more than 2,000 meters high.

The huge changes in surface morphology directly changed the pattern of atmospheric circulation. Before that, mainland China was bounded by the Pacific Ocean to the east, Siberia to the north and the Himalayas to the south were occupied by shallow seas respectively. The Mediterranean Sea to the west also stretched far into central Asia at that time, so most of the flat mainland China could get enough water. Moistened by ocean warm and humid air currents, the climate is warm and humid. Most of northwest China and the interior of Central Asia are subtropical areas, and there are no large-scale deserts and Gobis.

However, the east-west Himalayas blocked the northward movement of warm and humid air masses from the Indian Ocean. Over time, China's northwest region became increasingly dry, gradually forming large areas of desert and Gobi. This is the origin of the dust that accumulated on the Loess Plateau. The huge Tibetan Plateau stands right in the westerly wind belt of the Northern Hemisphere, and its height has continued to grow over the past 2.4 million years. The width of the Qinghai-Tibet Plateau accounts for about one-third of the westerly belt, dividing the near-surface layer of the westerly belt into north and south branches. The southern branch flows eastward along the southern side of the Himalayas, and the northern branch flows eastward from the northeastern edge of the Tibetan Plateau. This high-altitude airflow exists at an altitude of 3,500-7,000 meters all year round and becomes the main driving force for transporting sand and dust. At the same time, due to the uplift of the Tibetan Plateau, the East Asian monsoon has also been strengthened. The winter wind blowing from the northwest to the southeast, together with the westerly jet stream, has created a Loess Plateau in northern China.

In the deserts and Gobis of northwest China and the interior of Central Asia, due to drastic changes in temperature, rocks here can break apart and disintegrate faster than elsewhere, turning into debris. Geologists measure the diameter of They are divided into: gravel (larger than 2 mm), sand (2-0.05 mm), silt sand (0.05-0.005 mm), clay (less than 0.005 mm). Clay and silt particles can be carried to an altitude of more than 3,500 meters into the westerly belt, and are carried southeastward by the westerly jet stream before gradually falling down to the middle and lower reaches of the Yellow River.

For two to three million years, the process of transporting sand and soil from northwest to southeast has never stopped in this area of ??Asia. The area where large amounts of sand and soil fell happens to be the area where the Loess Plateau is located, including the Wutai Mountains, Taihang Mountains, etc. There are loess accumulations on the tops of many mountains in North China. Of course, the scouring effect of several large rivers in northern China, including the Yellow River, and countless valleys on the surface is exactly opposite to the accumulation of loess. Otherwise, the Loess Plateau would not be what it is now, with a thickness of no more than 409.93 meters. The North China Plain to the east of the Taihang Mountains is also a sedimentation area of ??sand, but it is a continuously sinking area and has developed many rivers. Therefore, the falling sand is either washed away by the rivers or is brought by the rivers. Buried.

There are hundreds of records about "rain soil", "rain loess", "rain yellow sand" and "rain haze" in ancient Chinese books. The earliest record of "rain soil" can be traced back to BC 1150: The sky is filled with yellow mist, and sand and soil fall from the sky like rain. What is recorded here is actually a sandstorm.

The locations of rain soil are mainly on the Loess Plateau and its vicinity.

The ancients regarded such things as strange catastrophic phenomena, and believed that this was a sign of "reception from heaven and man". It is recorded in the natural history compiled by Zhang Hua of the Jin Dynasty: "During the time of Xia Jie, the Changye Palace was located in a deep valley. Men and women lived together, and they did not come out for ten days to listen to politics. The sky was full of wind and sand, and the empty valley was filled overnight."

Between 1966 and 1999, there were as many as 60 sandstorms that lasted for more than two days in our country. Academician Liu Dongsheng of the Chinese Academy of Sciences believes that the Loess Plateau should be said to be a laboratory for sandstorms. This laboratory has accumulated records of sandstorms over the past millions of years. The wind and sand from the deserts and Gobi in northwestern China spread all over the sky, leaving a thin layer of loess on the Loess Plateau every year.

Sandstorm management and preventive measures

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1. Strengthen environmental protection and raise environmental protection to the level of the legal system.

2. Restore vegetation and strengthen the biological protection system to prevent sandstorms. Protect and restore forest and grass vegetation in accordance with the law, prevent further expansion of land desertification, and reduce the sources of sand and dust as much as possible.

3. Formulate disaster prevention, disaster resistance, and disaster relief plans based on local conditions in different regions, actively promote various disaster reduction technologies, and build a number of demonstration projects to gradually promote them on a point-by-point basis to further improve the regional comprehensive defense system.

4. People’s long-term predatory development of natural resources has caused serious damage to the natural ecological environment, and the deterioration of the environment has provided a rich source of sand and dust materials for sandstorms.

5. Control population growth, reduce the pressure of human factors on land, and protect the environment.

6. Strengthen popular science propaganda on the relationship between the occurrence and harm of sandstorms and human activities, so that people will realize that once the environment they live in is destroyed, it will be difficult to recover. This will not only aggravate natural disasters such as sandstorms, but also cause A vicious circle, so people must consciously protect their living environment.