About sandstorms

Sand duststorm is a general term for both sandstorm and duststorm. It refers to strong winds that blow up a large amount of sand and dust material from the ground and roll it into the air, making the air particularly turbid. Severe sandstorm weather phenomenon with horizontal visibility less than 100 meters. A sandstorm refers to a sandstorm caused by strong winds blowing large amounts of sand into the near-surface layer; a dust storm is a storm caused by strong winds carrying large amounts of dust and other fine-grained materials into high altitudes.

From a global perspective, sandstorms mostly occur in inland desert areas. The main source areas are the Sahara Desert in Africa. The Midwest and Australia of North America are also one of the sources of sandstorms. From 1933 to 1937, due to severe drought, the famous bowl-shaped dust storm occurred in the central and western parts of North America. The centers of Asian sandstorm activity are mainly in the Jordanian desert, Lower Mesopotamia between Baghdad and the northern coast of the Gulf, the southern coast of Iran near Abbas, and the plains of northern Afghanistan. Kazakhstan, Uzbekistan and Turkmenistan in Central Asia of the former Soviet Union are all areas affected by frequent sandstorms (≥15/year), but their centers are in the sandy plains between the Caspian Sea and the Aral Sea and the Amu Darya River area. Due to its unique geographical environment, northwest my country is also an area where sandstorms frequently occur. The main source areas are the Gurbantunggut Desert, Taklimakan Desert, Badain Jaran Desert, Tengger Desert, Ulan Buh Desert and Mu Us Desert. . From 1999 to the spring of 2002, 53 sand and dust weather events occurred in my country (9 in 1999, 14 in 2000, 18 in 2001, and 12 in 2002), 33 of which originated in central Mongolia. In the southern Gobi region, in other words, about 60% of the sand and dust that ravages our country every year comes from abroad. This is the research result announced to the media by Li Huang, deputy director of the China Meteorological Administration on July 2. He said that in the spring of 2002, 12 sand and dust weather processes occurred in northern my country. It has three characteristics: concentrated occurrence period, high intensity of occurrence, and wide range of influence. The sources of sand and dust weather affecting my country can be divided into two types: overseas and domestic. Analysis shows that: two-thirds of the sand and dust weather originates in the southern region of Mongolia, and is supplemented by sand and dust materials when passing through northern my country; the sand source within the country is only about one-third. The sand and dust weather that occurs in Central Asia (Kazakhstan) is unlikely to affect the eastern part of northwest my country and even North China. The Taklimakan Desert in southern Xinjiang is an area with high incidence of sand and dust weather in my country, but it generally does not affect the eastern part of Northwest China and North China. my country's sand and dust weather paths can be divided into northwest paths, westward paths and northerly paths: Northwest 1 path, sand and dust weather generally originates from the central and western Mongolian Plateau or the Alxa Plateau in western Inner Mongolia, mainly affecting northwest my country and North China; In the northwest 2 path, the sand and dust weather originates in southern Mongolia or central and western Inner Mongolia, mainly affecting the eastern part of Northwest China, northern North China, and most of Northeast China; in the west path, the sand and dust weather originates in the Gobi area in southwest or southern Mongolia. The desert area in western Inner Mongolia mainly affects northwest my country and northern China; in the northerly direction, sand and dust weather generally originates from the vast area south of Ulaanbaatar, Mongolia, mainly affecting the eastern northwest region, most of northern China, and southern northeastern China. There are four major sandstorm-prone areas in the world, namely: North America, Australia, Central Asia and the Middle East. Deserts in North America are mainly found in the western United States and northern Mexico. In the arid desert areas bordering the desert, sandstorms occur from time to time, and even the famous black storm in history broke out on the Great Plains. The main causes of dust storms in North America are improper land use and persistent drought. In the 1930s, a huge dust storm occurred in the Great Plains of the western United States, known as the Black Storm. In this dust storm, the most serious black storm in the United States on May 12, 1934, 300 million people were lost in the Great Plains. Tons of fertile soil. After the catastrophe, millions of hectares of farmland were abandoned, hundreds of thousands of people were displaced, and many towns became desolate and empty cities. Many people were forced to move to California, triggering the largest immigration wave in U.S. history. Australia is an arid country, with 75% of its land area belonging to arid and semi-arid areas. Australia's central and western coasts experience the most frequent dust storms, with an average of five times a year. Due to the dry climate in many places, coupled with farming and grazing, the soil surface lacks vegetation coverage, leading to the gradual desertification of the land. Once strong winds blow, sandstorms will occur. Desert areas in central Asia are also expanding. The five Central Asian countries are areas with relatively serious desertification, with a total area of ​​nearly 4 million square kilometers. Due to rapid population growth, excessive irrigation water, deforestation, overgrazing, grassland degradation, and serious desertification. The salt soil area in Central Asia is very vast, reaching 150,000 square kilometers, which causes a mixture of sand and salt storms. Sandstorms in the Middle East mainly occur in the southern edge of the Sahara Desert in Africa. From the early 1970s to the mid-1980s, due to successive years of drought and excessive grazing and reclamation, grasslands were degraded, fields were barren, desertified land spread, and sandstorms intensified, affecting people's lives. The environment has deteriorated dramatically. Frequent sandstorms also affect other areas. Some dust is carried across the Atlantic Ocean to the Amazon region of South America by wind, and other dust is blown to Europe.

Causes of sandstorm weather

Weather conditions that are conducive to strong winds or strong winds, favorable sand and dust source distribution and favorable air instability conditions are sandstorms or strong sandstorms on the Gobi Desert. The main reason for the formation of 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 and climate background for the formation of sand and dust storms; the development of convective cells in front of the ground cold front into clouds or squall lines is a medium- and small-scale system that is conducive to the development and intensification of sand and dust storms. ; The terrain conditions that are conducive to the increase of wind speed, that is, the narrow tube effect, are one of the favorable conditions for the formation of sandstorms. The main components of soil and yellow sand are silicates. When there is drought and little rain and the temperature warms, the silicic acid on the surface of the silicate loses water, H2SiO4=SiO3 -2 + H2O (gas) ↑ In this way, the surface of silicate soil micelles and sand grains They will be negatively charged, repelling each other, and become aerosols that cannot condense together, thus forming blowing sand, that is, a sandstorm. Dust storms are essentially negatively charged silicate aerosols.

The physical mechanism of the formation of sand and dust storms

Under the conditions of extremely favorable large-scale environment, high-altitude dry and cold jet stream, strong vertical wind speed, wind shear and thermally unstable stratification, frontal areas are caused The formation and development of nearby medium- and small-scale systems intensifies the pressure and temperature gradients before and after the frontal zone, forming a huge pressure-temperature gradient before and after the frontal zone. 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.

The main hazards of sandstorms

⑴ Strong winds: Strong winds carrying fine sand and dust destroy buildings and public facilities, causing casualties to humans and animals. 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 centimeters. 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 Air pollution: In the source areas and affected areas of sandstorms, respirable particulate matter (TSP) in the atmosphere increases Sandstorms

, 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 hazards of black wind

There are two main hazards of black wind, one is wind and the other is sand. There are two dangers of strong wind: one is wind damage, and the other is land erosion. Let’s talk about wind damage first. Strong winds damaged buildings, knocked down or uprooted trees and poles, and tore off farmers' plastic greenhouses and farmland mulch films, etc. In addition, April and May in the northwest region are the time when economic crops such as fruits, vegetables, sugar beets, and cotton emerge, grow cotyledons or true leaves, and fruit trees bloom. At this time, they are least resistant to wind and sand. At least, the leaves are covered with dust, which weakens photosynthesis, affects respiration, and reduces crop yield; at worst, the seedlings die and the flowers fall, let alone mature fruits. For example, the black wind on May 5, 1993 knocked down the stamens of 85,000 fruit trees in the northwest region, and broke or uprooted 109,400 shelterbelts and timber forests. In addition, strong winds knocked down power poles, causing water and power outages, affecting industrial and agricultural production. The power outage and water outage caused by the black wind on May 5, 1993 caused economic losses of 83 million yuan to Jinchuan Company in Jinchang City alone. When strong winds act on loose soil in arid areas, they will remove a layer of topsoil, which is called wind erosion. For example, the average wind erosion depth of the black wind on May 5, 1993 was ten centimeters (up to 50 centimeters), which means that an average of 60 to 70 cubic meters of fertile topsoil per acre was blown away by the wind. In fact, strong winds not only blow away the fine clay and organic matter in the soil, but also accumulate the sand they brought in the soil, greatly reducing the soil fertility. In addition, strong winds and sand particles can also wear away a layer of the surface of buildings and crops, which is called abrasion, which is also a disaster. The main harm caused by sand is sand burial. As mentioned before, in terrains such as narrow tubes, windward and ridges, due to high wind speeds, the main damage caused by wind and sand is wind erosion, while in terrains with low wind speeds such as leeward depressions, the main damage caused by wind and sand is sand burial. For example, where sand burial occurred during the black wind on May 5, 1993, the sand burial thickness averaged 20 centimeters, with the thickest point reaching 1.2 meters. And more importantly, the loss of human life. For example, in the black storm on May 5, 1993, 85 people were killed, 264 were injured, and 31 were missing. In addition, 120,000 large livestock died or were lost, 5.6 million acres of crops were damaged, more than 2,000 kilometers of water channels, the lifeline of sand-buried arid areas, were lost, and the Lanzhou-Xinjiang Railway was suspended for 31 hours. The total economic loss exceeded 540 million yuan.

Sandstorm is a disastrous weather phenomenon in which wind and sand interact. Its formation is inseparable from factors such as the global greenhouse effect, El Niño phenomenon, forest decline, vegetation destruction, species extinction, and climate anomalies. Among them, over-exploitation of natural resources, excessive deforestation, and over-cultivation of land caused by population expansion are the main reasons for frequent sand and dust storms.

Sandstorms cause soil wind erosion

According to Xinhua News Agency, Lanzhou, with the efforts of experts from the Institute of Cold and Arid Regions Environment and Engineering, Chinese Academy of Sciences, a project was launched to explore the origin of sand and dust materials. The sandstorm wind tunnel simulation experiment specially set up to study the transmission mechanism was successfully completed recently. Through experiments, experts found 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 ways 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

The culprit of sandstorms: Atmospheric circulation The brief scene of sandstorms in Beijing in the spring was nothing more than the 300,000-square-kilometer Loess Plateau in northern China. It is a weather process that has been experienced every year for ten thousand years. The difference is that the wind in the latter is stronger and the wind blows for a longer time (can last for several days). The source of the sand and dust is not the intersection 50 meters away, but It's the desert and Gobi hundreds of kilometers away. It was like God was playing an incredible game: He picked up the sand and dust on the surface of the deserts and Gobis in northwest China and Central Asia and threw it toward the southeast, allowing a high ground to gradually accumulate where the dust fell. 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 the hand of God 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. Huge changes in surface morphology directly change 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. Sandstorm However, the east-west Himalayas block the northward movement of warm and humid air masses from the Indian Ocean. Over time, the northwest of China has become 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 in northwest China and the interior of Central Asia, due to drastic changes in temperature, rocks here can break apart and disintegrate faster than elsewhere and become debris. Geologists divide them into gravels according to diameter. (greater than 2 mm), sand (2-0.05 mm), silt (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 happened to be the area where the Loess Plateau is located, even on the tops of many mountains in North China such as Wutai Mountain and Taihang Mountain. There is accumulation of loess. 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 1150 BC: Four days of yellow fog in the sky Blockade, sand and soil fell from the sky like rain. What is recorded here is actually a sandstorm. The locations of rain soil are mainly in and around the Loess Plateau. 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." 1966- In 1999, there were 60 sandstorms lasting 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.