Sandstorm weather mainly occurs in late spring and early summer. This is because there is little precipitation in winter and spring in arid areas, the surface is unusually dry and loose, and the wind erosion resistance is very weak. When a strong wind blows, a lot of dust will be involved in the air, forming dust.
dust storm/devil
atrocious weather
Globally, sandstorms mostly occur in inland desert areas, mainly the Sahara desert in Africa, and the midwest of North America and Australia are also one of the sources of sandstorms. 1933- 1937 Due to severe drought, a famous bowl-shaped sandstorm occurred in the midwest of North America. Asian sandstorm activity centers are mainly located in the Jordanian desert, Lower Mesopotamia between Baghdad and the northern coast of the Gulf, the southern Iranian coast near Abbas and the northern Afghan plain. Kazakhstan, Uzbekistan and Turkmenistan in Central Asia of the former Soviet Union are all affected areas with frequent sandstorms (≥ 15/ year), but their centers are on the sandy plain between Caspian Sea and Aral Sea and Amu Darya River.
Due to its unique geographical environment, the northwest of China is also a region where sandstorms frequently occur. The main source areas are Gurbantunggut Desert, Taklimakan Desert, Badain Jaran Desert, Tengger Desert, Wulanbuhe Desert and Mu Us Desert.
From 1999 to the spring of 2002, there were 53 sandstorms in China (1999, 2000 14, 2006 18 and 2002 12). This is the research result released by Li Huang, deputy director of China Meteorological Bureau, to the media on July 2nd. He said that in the spring of 2002, there were 12 sandstorms in northern China. It has three characteristics: concentrated occurrence period, strong occurrence intensity and wide influence range. The sources of dust weather affecting China can be divided into two types: overseas and domestic. The analysis shows that two-thirds of the dusty weather originated in southern Mongolia and was supplemented by dusty materials when passing through northern China. The sand source in China is only about one third. The dusty weather in Central Asia (Kazakhstan) is unlikely to affect the eastern part of Northwest China or even North China. The Taklimakan Desert in southern Xinjiang is a high incidence area of sandstorm weather in China, but it generally does not affect the eastern part of northwest China and North China. The path of sandstorm weather in China can be divided into northwest path, west path and north path: northwest path 1. Sandstorm weather generally originates in the central and western plateau of Mongolia or Alashan Plateau in western Inner Mongolia, and mainly affects northwest and north China. Northwest Route 2. Dust weather originated 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; To the west, dusty weather originated in Gobi area in southwest or south Mongolia and desert area in western Inner Mongolia, mainly affecting northwest and north China. In the northerly route, dusty weather generally originates in the vast area south of Ulaanbaatar, Mongolia, and mainly affects the eastern part of northwest China, most of north China and southeast China.
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Second, the windy and dusty weather in China in recent years.
According to statistics, there were eight sandstorms in China in 1960s, three in 1970s 14 in 1980s14, and more than 20 in 1990s, and the scope of sandstorms became wider and wider with heavy losses. The situation of several major gale and sandstorm weather in China since the 1990s is introduced as follows:1993: From April to early May, gale weather appeared many times in the north. From April 19 to May 8, Gansu, Ningxia and Inner Mongolia were successively hit by strong winds and sandstorms. On May 5-6, eastern Xinjiang, Hexi in Gansu, most of Ningxia and western Inner Mongolia were hit by severe sandstorms, causing serious losses. 1994: From April 6, strong winds blew from Mongolia and western Inner Mongolia, and the dust in the northern desert Gobi was lifted by the wind and floated over the Hexi Corridor, and the loess lasted for several days. 1 995:165438+1On 7 October, more than 40 counties (cities) in Shandong were hit by heavy rain, with 35 people killed, 12 1 missing, 320 injured and direct economic losses/kloc-0. 1996: On May 29th and 30th, 1965, the worst sandstorm swept the west of Hexi Corridor. The black wind suddenly broke out, the world was closed, the dust filled, the trees collapsed, and people had difficulty breathing. The direct economic loss in Jiuquan area, which suffered the most, reached more than 200 million yuan. 1998: On April 5, the central and western Inner Mongolia, southwestern Ningxia and Hexi Corridor in Gansu were hit by strong sandstorms, which affected a wide range, including Beijing, Jinan, Nanjing and Hangzhou. On April 19, Tutanto Basin in northern and eastern Xinjiang was hit by a strong wind with an instantaneous wind force of 12, and some areas were accompanied by dust. The devastating typhoon caused a lot of property losses, with 6 people dead, 44 missing and 256 injured. 19 In the early morning of May 1, northern Xinjiang was suddenly hit by strong winds. The wind power in the tuyere areas such as Alashankou and Tacheng reaches 9 to 10, and the instantaneous wind speed reaches 32 meters per second. The winds in other areas generally reach 6 to 7. Strong winds blew down trees and cut off power lines in some areas. 1999: From April 3rd to 4th, there were continuous strong winds and sandstorms in Hohhot for two consecutive days. Sandstorms range from the west of Inner Mongolia Autonomous Region to the south of Tongliao City in the east, with instantaneous wind speed 16 meters per second. Maximum wind force in Dalat Banner of Yikezhao League 10. 2000: On March 22-23, there was a large-scale dusty weather in Inner Mongolia Autonomous Region, and some dust was carried over Beijing by strong winds, which aggravated the degree of sand blowing. On March 27th, the sandstorm hit Beijing again, and the instantaneous wind force in some areas reached 8-9. Seven workers who were working on the roof of a two-story building in Anxiangli Community were blown down by strong winds, and two of them died on the spot. Some billboards were blown down by strong winds, causing pedestrian injuries and vehicle damage. 2002: From March 18 to March/2 1 day, a sandstorm weather process with the largest scope, strongest intensity, the most serious impact and the longest duration since the 1990s, attacked China North1400,000 square kilometers and affected the population1300,000.
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3. What is a sandstorm?
Sandstorm is a general term for sandstorm and sandstorm, which means that strong winds blow a lot of dust on the ground into the air, making the air particularly turbid and horizontally visible.
dust storm/devil
Strong sandstorm weather phenomenon with temperature less than 1km. Among them, sandstorm refers to a sand-laden storm formed by strong winds blowing a large number of sand near the ground; Sandstorm is a storm formed by strong winds, which brings a lot of dust and other particles into the sky.
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Four. Concept, regulations and standards of sandstorm weather
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(A) the concept of dust weather:
Dust weather is divided into four categories: floating dust, sand blowing, sandstorm and strong sandstorm.
Floating dust: a weather phenomenon in which dust and fine sand float evenly in the air, making the horizontal visibility less than 10 km;
Sand blowing: a weather phenomenon in which the wind blows up dust on the ground, making the air quite turbid and the horizontal visibility is within the range of 1 km to1km;
Sandstorm: a weather phenomenon in which strong winds blow up a lot of dust on the ground, making the air very turbid and the horizontal visibility is less than 1 km;
Strong sandstorm: a weather phenomenon in which strong winds blow up dust on the ground, making the air fuzzy and turbid, and the horizontal visibility is less than 500 meters.
Satellite photos of sandstorms in Australia
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(2) Classification of dust weather processes
Sandstorm weather process can be divided into four categories: floating dust weather process, sand blowing weather process, sandstorm weather process and strong sandstorm weather process.
Floating dust weather process: in the same weather process and at the same observation time, floating dust weather occurred in five or more countries in China's weather forecast area;
Sand blowing weather process: in the same weather process and the same observation time, sand blowing weather occurs in five or more countries in China's weather forecast area;
Sandstorm weather process: in the same weather process, sandstorms occurred in three or more countries in China's weather forecast area at the same observation time;
Strong sandstorm weather process: In the same weather process, more than three countries in China's weather forecast area basically (quasi) stand at the same observation time and have strong sandstorms.
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(
Verb (abbreviation of verb) The cause and physical mechanism of sandstorm weather.
Causes of sandstorm weather
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 and climate 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.
Physical mechanism of sandstorm formation
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.
Main failure modes of sandstorm
⑴ Strong wind: Strong wind accompanied by dust damages buildings and public facilities, causing human and animal casualties.
⑵ Sand burial: Farmland, channels, cottages, railways, grasslands, etc. are buried by a large number of quicksand in the form of quicksand, 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 in different degrees, and the depth of wind erosion can reach 1 ~ 10 cm. It is estimated that the annual loss of soil fine matter caused by sandstorms in China is as high as 106 ~ 107 tons, most of which are below 10 micron, which seriously damages the land productivity of farmland and grassland in the source area.
⑷ Air pollution: In the source area and influence area of sandstorm, the inhalable particulate matter (TSP) in the atmosphere increases, and air pollution intensifies. Taking 1993 "5.5" sandstorm as an example, the outdoor air TSP concentration in Jinchang, Gansu Province reached 10 16 mg/m3, and the indoor air TSP concentration was 80 mg/m3, exceeding the standard by 40 times. From March to April, 2000, Beijing was affected by sandstorms, and the number of days when the air pollution index reached Grade 4 or above was 10, which also affected many cities in eastern China. From March 24th to 30th, the daily pollution index of Nanjing, Hangzhou and other cities 18 exceeded Grade IV.
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 hazards of strong winds: one is wind damage, and the other is scraping the ground.
Let's talk about the typhoon first. Strong winds destroy buildings, blow down or pull up tree stems, tear up farmers' plastic greenhouses and farmland plastic films, and so on. In addition, April and May in northwest China are the time when cash crops such as melons, fruits, vegetables, beets and cotton emerge, cotyledons or true leaves grow, and fruit trees bloom, at this time, they are least resistant to sandstorms. Light leaves are covered with dust, which weakens photosynthesis, affects respiration and reduces crop yield; In the worst case, the seedlings will die, not to mention the mature results. For example,1May 5, 1993, black wind in northwest China knocked out 85,000 stamens of fruit trees, and shelter forests and timber forests were broken or uprooted 109400. In addition, the strong wind blew down the telephone poles, causing water and electricity cuts and affecting industrial and agricultural production. 1On May 5, 993, the black wind caused power failure and water cut, and Jinchang Jinchuan Company alone caused economic losses of 83 million yuan.
When strong wind acts on loose soil in arid areas, it will scrape off a layer of topsoil, which is called wind erosion. For example,1May 5, 1993, the average wind erosion depth of black wind 10 cm (up to 50 cm), that is, an average of 60 to 70 cubic meters of fertile topsoil per mu 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 pile up the sand in the soil, which greatly reduces the fertility of the soil. In addition, the strong wind with sand will wear off a layer of buildings and crops, which is called abrasion and also a disaster.
The harm of sand is mainly sand burial. As mentioned above, in narrow pipelines, windward and uplifted terrain, due to high wind speed, the wind-blown sand hazard is mainly wind erosion, while in leeward depressions and other terrain with low wind speed, the wind-blown sand hazard is mainly sand burial. Such as1where sand burial occurred in the black wind on May 5, 993, the average thickness of sand burial was 20 cm, and the thickest part reached1.2 m.
More importantly, the loss of human life. For example,1May 5, 993, 85 people were killed, 264 people were injured and 3 1 person was missing. In addition, the death loss of large livestock was 1.2 million, the crops were affected by 5.6 million mu, the total length of the lifeline canal buried by sand in arid areas was more than 2,000 kilometers, and the Lanzhou-Xinjiang railway was stopped for 3 1 hour. The total economic loss exceeded 540 million yuan.
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Sixth, the harm of sandstorm weather
Sandstorm weather is a disastrous weather in northwest China and northern North China, which can cause houses to collapse, traffic power supply to be blocked or interrupted, fires, human and animal casualties and so on. Pollution of the natural environment and destruction of crop growth.
dust storm/devil
It has caused serious losses and great harm to the national economic construction and the safety of people's lives and property. The hazards of sandstorms mainly include the following aspects:
1, ecological environment deterioration
When sandstorms occur, dust and floating dust carried by strong winds are everywhere, and the number of people passing through areas with air turbidity, choking nose and eyes, respiratory tract and other diseases increases. For example,1A serious sandstorm occurred in Jinchang on May 5, 993. The dust content in outdoor air is 10 16 mm/cm3, and the dust content in indoor air is 80 mm/cm3, which is 40 times higher than the national standard for dust content in living quarters.
2. Production and life are affected.
A lot of dust carried by sandstorm weather blocked the sun, and the weather was gloomy, which led to the decrease of solar radiation. A few hours to ten hours of poor visibility can easily make people feel depressed and reduce the efficiency of work and study. In light cases, a large number of livestock can be infected with respiratory and gastrointestinal diseases, and in severe cases, a large number of "spring-deficient" livestock will die, and fertile soil, seeds and seedlings in farmland will be scraped away. Sandstorm will also aggravate the wind erosion and desertification of the surface soil, cover thick dust on the leaves of plants, affect normal photosynthesis and cause crop yield reduction.
3. Loss of life and property
1On May 5, 1993, severe sandstorms occurred in Jinchang, Wei Wu, Minqin, Baiyin and other cities in Gansu Province, affecting 2,535,500 mu of farmland, losing 42,800 trees, resulting in a direct economic loss of 236 million yuan, 50 people died and 0/53 people were seriously injured. On April 12, 2000, strong sandstorms occurred in Yongchang, Jinchang, Wei Wu and Minqin. According to incomplete statistics, the direct economic losses of Jinchang and Wei Wu alone amounted to15.34 million yuan.
4, traffic safety (plane, car and other traffic accidents)
Sandstorm weather often affects traffic safety, causing planes to fail to take off or land normally, and making cars and train carriages rupture, stop or derail.
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Seven, the cause of sandstorm.
Sandstorms originate from soil wind erosion.
According to Xinhua News Agency, Lanzhou Electric Power Co., Ltd., with the efforts of experts from the Institute of Environment and Engineering in Cold and Arid Regions, Chinese Academy of Sciences, recently successfully completed a sandstorm wind tunnel simulation experiment specially designed to explore the mechanism of sandstorm initiation and propagation.
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.
In addition, through experiments, the researchers concluded that 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, 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.
The culprit of sandstorm: atmospheric circulation
The brief scene of spring sandstorm in Beijing is just a weather process that has been experienced every year for two or three million years on the Loess Plateau, which stretches for about 300,000 square kilometers in the north of China. The difference is that the wind in the latter is stronger and the wind lasts longer (it can last for several days). The source of sandstorm is not the crossroads 50 meters away, but the desert and Gobi hundreds of kilometers away.
It's like God is playing an incredible game: he grabs the dust on the surface of deserts and Gobi in northwest China and Central Asia and throws it to the southeast, leaving a highland where the dust falls. This game started about 2.4 million years ago, and God is still enjoying it (in 2002, Nature published the latest research results of China scholars, pushing the start time to 22 million years ago).
In fact, the wind is God's hand that throws sand.
After the Indian plate moved northward and collided with the Eurasian plate, the Indian continental crust was inserted under the Asian continental crust to prop up the latter. As a result, the shallow sea of the Himalayas disappeared, the Himalayas began to form and gradually lifted, and the Qinghai-Tibet Plateau was also squeezed and lifted by the Indian plate. After this process lasted more than 60 million years, by about 2.4 million years ago, the height of the Qinghai-Tibet Plateau had exceeded 2,000 meters.
The great change of surface morphology directly changed the pattern of atmospheric circulation. Before that, the Pacific Ocean was in the east of Chinese mainland, Siberia in the north and Himalaya in the south were occupied by shallow seas respectively, and the Mediterranean Sea in the west also extended to far places in Central Asia at that time, so most flat Chinese mainland could get enough moist air from the ocean, and the climate was warm and humid. Northwest China and Central Asia are mostly subtropical areas, and there are no large areas of deserts and Gobi.
However, the east-west Himalayan mountains stopped the warm and humid air mass in the Indian Ocean from moving northward. With the passage of time, the northwest of China has become more and more arid, gradually forming a large area of desert and Gobi. This is the birthplace of dust accumulated on the Loess Plateau. The huge Qinghai-Tibet Plateau just stands in the westerly belt of the northern hemisphere, and its height has been increasing for 2.4 million years. The width of the Qinghai-Tibet Plateau accounts for about one third of the westerly belt, which divides the surface of the westerly belt into two branches. The south branch flows eastward along the south side of the Himalayas, and the north branch flows eastward from the northeast edge of the Qinghai-Tibet Plateau. This kind of high-altitude airflow exists at an altitude of 3500-7000 meters all the year round and becomes the main driving force for carrying dust. At the same time, due to the uplift of the Qinghai-Tibet Plateau, the East Asian monsoon has also been strengthened. The winter wind blowing from northwest to southeast, together with westerly jet, formed the Loess Plateau in the north of China.
In the desert and Gobi in the northwest of China and the inland of Central Asia, the rocks here disintegrate into pieces faster than other places because of the drastic change of temperature. Geologists divide it into gravel (more than 2 mm), sand (2-0.05 mm), silt (0.05-0.005 mm) and clay (less than 0.005 mm) according to its diameter. Clay and sediment particles can be carried to an altitude of more than 3,500m, enter the westerly belt, be transported to the southeast by westerly jet, and gradually fall until the middle and lower reaches of the Yellow River.
For two or three million years, the process of transporting sand from northwest to southeast in this part of Asia has never stopped. A lot of sand falls in the area where the Loess Plateau is located, and even many mountains in North China, such as Wutai Mountain and Taihang Mountain, have loess accumulation at the top. Of course, the scouring effect of several large rivers and countless valleys in northern China, including the Yellow River, is just the opposite of the accumulation of loess. Otherwise, the loess plateau will not be like this, and the thickness will not exceed 409.93 meters. The North China Plain east of Taihang Mountain is also a subsidence area of sand, but it is a subsidence area, and at the same time many rivers have developed, so the falling sand is either washed away by the rivers or buried by the sediment brought by the rivers.
There are hundreds of records about rain soil, rain loess, rain yellow sand and rain haze in China ancient books. The earliest record of "rainy soil" can be traced back to 1 150 BC: the sky is yellow and foggy, and sand falls from the sky like rain. What is recorded here is actually a sandstorm.
The location of rainy soil is mainly in the Loess Plateau and its vicinity. The ancients regarded this kind of thing as a strange catastrophe phenomenon and thought it was a sign of "harmony between man and nature" It is recorded in the Natural History compiled by Zhang Hua in the Jin Dynasty: "When Xia Jie was in the deep valley, the night palace was mixed with men and women, and he did not go out to listen to politics for ten days. It was a windy day and filled the empty valley overnight. "
During the period of 1966- 1999, there were 60 sandstorms lasting more than two days in China. Academician Liu Dongsheng of the Chinese Academy of Sciences thinks that the Loess Plateau should be regarded as a laboratory for sandstorms, which has accumulated records of sandstorms for millions of years. Sandstorms from the northwest desert and Gobi are scattered all over the sky, leaving a thin layer of loess on the Loess Plateau every year.
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Eight, the role of sandstorms in the ecosystem.
Although there are many hazards of sandstorm, the whole process of sandstorm is also an indispensable part of natural ecosystem. For example, a large amount of iron contained in the red sandstorm in Australia has been proved to be an important nutrient source for plankton in the Antarctic Sea. Phytoplankton can consume a large amount of carbon dioxide to mitigate the harm of greenhouse effect, so the impact of sandstorm is not all negative. Perhaps on another level, sandstorms may also be a symptom of the earth's response to environmental changes, just as we cough when we have a cold to remove waste from the trachea. Many climatologists gathered in Australia to study the nutrients provided by sandstorms in tasman sea and many other impacts. They found that the red seasonal sediments from Australian sandstorms can also be found in New Zealand, which enriched the land of New Zealand. Therefore, nutrient loss caused by dust storms in Australia will lead to nutrient harvesting in New Zealand. For example, the fertile soil sediments in Hawaii can also prove that many nutrients also come from distant Eurasia. Just because the two places are separated from Wan Li, it is impossible for ordinary winds to blow inland dust so far. So it is the sandstorm that brings tiny dust containing nutrients to an altitude of 3000 meters, crosses the ocean, and then spreads them, which will generally disperse them. In addition to Hawaii, scientists also found that the rain forest in the Amazon basin, the largest green lung on earth, also benefited from sandstorms, and an important source of its nutrients was dust in the air. The secret that sandstorms can make the rocks lush is that the dust aerosol contains iron ions and other ingredients that help plants grow. In addition, because sandstorms are mostly born in dry and high saline-alkali land, some soil particles carried by sandstorms often contain some alkaline substances, so they can often slow down acid rain or soil acidification in the settlement area near sandstorms. Mr. Wang Zifa of lasg once said, "Sandstorms really reduce the acidity of acid rain. The neutralization of sand dust and its soil particles increased the PH value of precipitation in northern China, Korea and Japan by 0.8-2.5, 0.5-0.8 and 0.2-0.5 respectively. If there is no dust, the harm of acid rain in many parts of the north is much more serious. " Therefore, although sandstorm is very harmful, it is also a necessary process in the natural ecology of the earth, because sandstorm has appeared since the beginning of human history. Only by actively looking for the mechanism of abnormal frequency of sandstorms can we really solve the harm of abnormal climate change to the environment.