Two conditions for sandstorms
Sources of sand and dust and their paths
Sources and paths of sand and dust
From 1999 to the spring of 2002, 53 earthquakes occurred in my country ( 9 times in 1999, 14 times in 2000, 18 times in 2001, and 12 times in 2002) sand and dust weather, 33 of which originated from the Gobi region in central and southern Mongolia. In other words, the sand and dust that ravages our country every year is about Sixty percent are 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.
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.
Hazards of Sandstorms
Sandstorms are highly disastrous weather that occurs in northwest my country and northern North China, which can cause house collapse, traffic and power supply obstruction or interruption, fires, and casualties of humans and animals. 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, 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.
The formation of sandstorms
There are three elements in the formation of sandstorms: strong winds, sand sources and unstable air.
Strong winds
Strong enough and long-lasting winds are the driving force for the formation of sandstorms.
For example, according to observations, when a strong sandstorm forms, if the wind speed reaches 30 meters per second (level 11 wind), then coarse sand (0.5~1.0 mm in diameter) will fly dozens of centimeters off the ground, and fine sand (0.125~0.25 mm in diameter) will fly Flying 2 meters high, powdery sand (diameter 0.05~0.005 mm) can reach a height of 1.5 kilometers, and clay particles (diameter less than 0.005 mm) can fly to a very high altitude.
Source of Sand
Our country is one of the countries with more deserts in the world. The northwest, North China and Northeast regions are places where deserts and sandy areas are concentrated in our country. The area of deserts and sandy areas here is as large as Covering more than 700,000 square kilometers, there are various types of sand dunes in the desert, which are divided into mobile sand dunes, semi-fixed sand dunes and fixed sand dunes according to their degree of stability. When a sandstorm occurs, the amount of dust raised by mobile sand dunes is the largest, semi-fixed sand dunes are smaller, and fixed sand dunes are the smallest.
Except for deserts and sandy lands, most of northern my country belongs to mid-latitude arid and semi-arid areas. The ground is mostly sparse grassland and dry farmland, with sparse vegetation and man-made destruction. When the ground warms up and thaws in spring, The ground surface is exposed, and when strong winds arise, sand and dust spread, forming sand and dust weather locally and in areas where strong winds pass.
Unstable air
Let us first look at an example in life. When you poke the stove, the fire is burning brightly. If you poke it gently, the ashes will often fly all over the house. When the fire is extinguished, dust will generally not rise even if you exert greater force. This involves the issue of air stability. After the fire goes out, the temperature of the air above and below the stove is not much different, so the air is stable. When the fire is burning vigorously, the air near the stove is hot, and the air farther away from the stove is cooler. The hot air is lighter than the cold air and rises easily, so the air above the stove is unstable. In this way, the stirred ashes can easily rise with the hot air and then fly all over the house.
In nature, the same principle applies to sandstorms. If the air temperature at the lower level is lower and more stable, the sand and dust blown by the wind will not be carried very high; if the air at the lower level is If the temperature is high, it will be unstable and easy to move upward. When the wind blows, the sand and dust will be carried very high, forming a sandstorm. In fact, sandstorms in our country are generally strongest in the afternoon or afternoon to evening, because this is the time of day when the air is the most unstable.
In addition to the above three factors, factors such as human production activities are also important to the formation of sandstorms. Such as man-made destruction of vegetation, industrial and mining transportation construction, large-scale construction and other damage to the surface surface provide fine sand and dust for the occurrence and development of sandstorms.
my country's satellite meteorologists systematically analyzed the six characteristics of sand and dust storms
According to the China National Satellite Meteorological Center, at the academic annual meeting held recently by the China National Satellite Meteorological Center, the National Satellite Meteorological Center Dong Chaohua, chief engineer and researcher of the center, researchers Fang Zongyi, Zheng Xinjiang, Lu Naimeng and Shao Yaping, a professor at the University of New South Wales in Australia, 17 people participated in the research on the Chinese sand and dust storm topic. Six major characteristics, numerical model forecasts and quantitative sand and dust studies were exchanged, providing a scientific basis for controlling sand and dust storms.
1. Time: Sandstorms in China mainly occur from March to April. Taking 2002 as an example, there were 12 sand and dust processes across the country, including 4 severe sand and dust storms, all of which occurred in March and April. The National Satellite Meteorological Center monitored and analyzed all the above processes.
2. Region: The main areas where sandstorms occur are between 110 degrees and 117 degrees east longitude and the vast area north of 38 degrees north latitude, that is, bounded by Cangzhou, Hebei Province, going north to Tianjin, Beijing, and Inner Mongolia, and going west longitude. Shijiazhuang, Yinchuan, Lanzhou, Qinghai Qilian, and north to the border of Inner Mongolia.
3. Source: The main source of sandstorms in China is Mongolia and even the desert areas of Central Asia. This type of sandstorm is intense and its impact is significantly greater than that of sandstorms in the domestic source areas; the source areas in my country are the Gansu Hexi Corridor and Inner Mongolia. South, northern Hebei and other desert areas.
4. Paths: There are four main paths of sandstorms that have affected Beijing in recent years, especially last spring: one is the path from Mongolia-Inner Mongolia-Beijing turning to the northeast. The second is the path from which the Hexi Corridor moves eastward to Beijing. The third one affects Beijing from Zhurihe area in Inner Mongolia via Zhangjiakou area in Hebei Province. The fourth one affects the Beijing area from the northern Shanxi Plateau to the east.
5. Relevant factors: Through preliminary analysis of the main dust processes and related climatic factors in the Huahua area since 1998, especially in 2002, namely ground vegetation, snow cover in February, 0-10 cm soil moisture, and temperature According to the analysis, it is believed that sand and dust weather are closely related to the activity of cold air in spring. When the path of cold air in spring is to the west or south, such as April 1999, there were few sand and dust weather in North China, and the main process occurred in the northwest; conversely, when the main force of cold air was When moving eastward or northward, such as April 2000 or March 2002, the main process occurred in North China.
6. The impact of sandstorms: Strong sandstorms not only affect the northwest, north, central and east China, but also the situation where high-altitude jet streams are encountered at an altitude of 7-8 kilometers, and the cold air vortex develops strongly in the northeast. Under the conditions, strong sand and dust can be transported northeastward, affecting the northeast, far east, and even further north. This is caused by global atmospheric circulation.
China’s Sandstorm Weather Numerical Forecasting Experiment analyzed sand flux, dust flux, etc. and concluded that when the diameter of sand and dust particles is less than 22 microns, it is consistent with ground observation data and has a good effect on forecasting sandstorms in China. ; Ground vegetation data and soil types are more sensitive to sandstorm forecasting.
Experts pointed out that the potential sources of sand and dust weather in China span a large distribution span, the natural conditions are harsh, and ground measurement stations are scarce. There is currently a lack of observations on the occurrence, development, transmission and intensity changes of sand and dust weather. data. Therefore, satellite remote sensing is an extremely important means no matter from the perspective of time scale or spatial scale monitoring. In the 2001-2002 monitoring, the accuracy rate of identifying sand and dust weather was 88%, and the accuracy rate of identifying sand and dust storms was more than 95%.
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.
Distribution of the world’s four major sandstorm-prone areas
Currently, a quarter of the global land area is endangered by desertification. There are four major sandstorm-prone areas in the world. They are: North America, Australia, Central Asia, and the Middle East including Central Africa and West Asia.