When do sandstorms occur, their distribution areas, causes, hazards, and prevention and control measures?
Sources and paths of sand and dust
From 1999 to the spring of 2002, 53 earthquakes occurred in my country (9 in 1999, 14 in 2000, and 18 in 2001) times, 12 times in 2002), 33 of which originated from the Gobi region in central and southern Mongolia. 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.
Strong sand and dust storms in my country in recent years
According to statistics, extremely large sandstorms occurred in our country 8 times in the 1960s, 13 times in the 1970s, and 14 times in the 1980s. It has happened more than 20 times since the 1990s, and its scope has become wider and wider, causing more and more losses. The relevant situation of several major strong winds and sandstorms that have occurred in my country since the 1990s is introduced as follows: 1993: From April to early May, strong winds occurred many times in the north. From April 19 to May 8, Gansu, Ningxia, and Inner Mongolia were successively hit by strong winds and sandstorms. Among them, from May 5 to 6, a huge sandstorm hit eastern Xinjiang, Hexi of Gansu, most of Ningxia, and western Inner Mongolia, causing serious losses. 1994: Starting on April 6, strong winds blew from Mongolia and western Inner Mongolia. Sand and dust from the Gobi desert in the northern part of the country rose with the wind and floated over the Hexi Corridor, filling the sky with loess for several days. 1995: On November 7, more than 40 counties (cities) in Shandong were hit by a storm. 35 people died, 121 people were missing, 320 people were injured, and direct economic losses were more than 1 billion yuan. 1996: From May 29th to 30th, the most serious severe sandstorm since 1965 hit the western part of the Hexi Corridor. Black winds suddenly rose, the sky and the earth closed, sand and dust filled the air, trees collapsed, people had difficulty breathing, and the most destructive The severe direct economic losses in Jiuquan area amounted to more than 200 million yuan. 1998: On April 5, the central and western parts of Inner Mongolia, the southwestern part of Ningxia, and the Hexi Corridor of Gansu were hit by strong sandstorms, which affected a wide range of areas, including Beijing, Jinan, Nanjing, Hangzhou and other places. On April 19, the Tushantuo Basin in northern and eastern Xinjiang was hit by strong winds with an instantaneous wind force of magnitude 12, accompanied by sand and dust in some areas. This severe typhoon caused a large amount of property damage, with 6 people dead, 44 missing, and 256 injured. In the early morning of May 19, northern Xinjiang was suddenly hit by strong winds. The wind force in Alashankou, Tacheng and other wind outlet areas reached level 9 to 10, and the instantaneous wind speed reached 32 meters per second. The wind force in other areas generally reached level 6 to 7. Strong winds knocked down trees and cut power lines in some areas. 1999: From April 3 to 4, sustained strong winds and sandstorms occurred in Hohhot for two consecutive days. The sandstorm ranged from the western part of the Inner Mongolia Autonomous Region to the southern part of Tongliao City in the east, with an instantaneous wind speed of 16 meters per second. The highest wind force in Dalat Banner of Yikezhao League reached level 10. 2000: From March 22 to 23, a large-scale sandstorm occurred in the Inner Mongolia Autonomous Region. Some of the sand was carried over Beijing by strong winds, aggravating the level of sand blowing. On March 27, a sandstorm hit Beijing again, with instantaneous winds reaching level 8 to 9 in some areas. Seven workers who were working on the roof of a two-story building in Anxiangli Community were blown off by strong winds, and two died on the spot. Some billboards were knocked down by strong winds, injuring pedestrians and damaging vehicles. 2002: From March 18 to 21, the sand and dust weather process with the largest scope, strongest intensity, most severe impact, and longest duration since the 1990s hit more than 1.4 million square kilometers of land in northern my country, affecting the population. Reaching 130 million.
What is a sandstorm?
Sandstorm 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 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.
Sand and dust weather concepts, regulations and standards
1. Sand and dust weather concepts:
Sand and dust weather is divided into floating dust, blowing sand, sand dust storms and strong sand and dust storms Four categories.
Floating dust: Dust and fine sand float evenly in the air, making the horizontal visibility less than 10 kilometers;
Blowing sand: The wind blows up the dust and sand on the ground, making the air thicker. Turbidity, a weather phenomenon with horizontal visibility within 1 km to 10 km;
Sandstorm: Strong winds blow up a large amount of dust and sand on the ground, making the air very turbid, and a weather phenomenon with horizontal visibility less than 1 km;
Strong sandstorm: A weather phenomenon in which strong winds blow up dust and sand on the ground, making the air very turbid and the horizontal visibility less than 500 meters.
2. Classification of sand and dust weather processes
Sand and dust weather processes are divided into four categories: floating dust weather processes, blowing sand weather processes, sand and dust storm weather processes and strong sand and dust storm weather processes.
Dust weather process: During the same weather process, 5 or more national basic (accurate) stations in my country’s weather forecast area experienced floating dust weather at the same observation time;
Sand-blowing weather process: During the same weather process, 5 or more national basic (accurate) stations in my country's weather forecast area experienced sand-blowing weather at the same observation time;
Sand storm Weather process: During the same weather process, sandstorms occurred at the same observation time at three or more countries' basic (accurate) stations in my country's weather forecast area;
Strong sandstorm weather process: During the same weather process, strong sandstorms occurred at the same observation time at three or more national basic (accurate) stations in my country's weather forecast area.
3. Sand and dust weather forecast warning issuance standards:
1. Decision-making service
When sand and dust weather processes are expected to occur in the next 24 hours, in Sand and dust weather forecasts are published in internal bulletins, special reports and decision-making service materials.
2. Public forecast
National standard:
It is expected that sand and dust weather processes will occur in the next 24 hours, and the impact range will be large or affect In the Beijing-Tianjin area, a sandstorm warning was issued to the public. ;
When a sandstorm or strong sandstorm is expected to occur in the next 24 hours and will cause serious impacts, a sandstorm warning will be issued to the public.
Provincial standards:
Determined by the provincial (autonomous and municipal) meteorological bureaus with reference to national standards.
Notes:
1. Provincial sand and dust weather forecast and warning issuance standards shall be reported to the China Meteorological Administration for filing.
2. Sand and dust weather forecasts and warnings should include the area, period, intensity, possible impacts and countermeasures of sand and dust weather.
3. Before issuing sand and dust weather forecast warnings to the public, the Central Meteorological Observatory should promptly and effectively notify the relevant provincial meteorological observatories. Before issuing sand and dust weather forecast warnings to the public, provincial meteorological observatories should promptly and effectively notify the central Reports from the Meteorological Observatory and related meteorological stations.
Causes and physical mechanisms of sand and dust storms
Causes of sand and dust storms
Weather conditions that are conducive to strong winds or strong winds, favorable sand and dust source distribution and favorable Unstable air conditions are the main reason for the formation of sandstorms or severe 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 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 physical mechanism of the formation of sand and dust storms
Under the conditions of extremely favorable large-scale environment, high-altitude dry 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 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 harm of black wind
The harm of black wind mainly has two words, 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.
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.
Hazards of sandstorms
Sandstorms are highly disastrous weather that occurs in northwest my country and northern parts of North China. They can cause house collapse, traffic and power supply obstruction or interruption, fires, and human storage. casualties, etc., polluting the natural environment, destroying crop growth, causing 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, the sand, stones and floating dust wrapped in strong winds spread everywhere, making the air in any area passing through turbid and choking. 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 dust that blocks the sun and light, and 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)
Sandstorm weather often affects traffic safety, causing planes to be unable to take off or land normally, causing damage to the glass of cars and train carriages, and causing parking problems. Luck or derailment.
Causes of sandstorms
Sandstorms cause soil wind erosion
According to Xinhua News Agency, Lanzhou News, with the efforts of experts from the Cold and Arid Regions Environment and Engineering Institute of the Chinese Academy of Sciences, , 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 grown 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 rain soil is mainly located 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
1. Strengthen environmental protection and elevate environmental protection to the level of the legal system.
2. Restore vegetation and strengthen the biological protection system to prevent sandstorms. We will protect and restore forest and grass vegetation in accordance with the law, prevent the 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.
Four lines of defense to prevent sandstorms
First, establish an ecological barrier focusing on afforestation in the areas surrounding Beijing and Tianjin in northern Beijing;
Second, In the central and western Hunshandake region of Inner Mongolia, an ecological restoration protection zone centered on returning farmland to forest has been established;
Third, an ecological restoration protection zone centered on the yellow irrigation belt and Mu Us sandy land has been established in the Hetao and Huangsha areas. Ordos ecological barrier in the center;
Fourth, establish a long-term cooperation plan framework for sandstorm prevention and control with Mongolia as soon as possible and set up a protective barrier to Mongolia.