Two conditions of sandstorm

Sources and paths of dust

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.

What is a sandstorm?

Sandstorm is a general term for sandstorm and sandstorm, which refers to a serious sandstorm weather phenomenon in which strong winds blow a large amount of dust substances on the ground into the air, making the air particularly turbid and the horizontal visibility is 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.

Hazards 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. It pollutes the natural environment, destroys the growth of crops and causes 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.

Formation of sandstorm

Sandstorm has three elements: strong wind, sand source and unstable air.

strong breeze

Persistent strong winds are the dynamic conditions for the formation of sandstorms. For example, it is observed that when a strong sandstorm is formed, if the wind speed reaches 30m per second (11wind), coarse sand (0.5 ~ 1.0mm in diameter) will fly out of the ground for several tens of centimeters, while fine sand (0. 125 ~ 0.25mm in diameter).

Shayuan

China is one of the countries with the most deserts in the world. Northwest China, North China and Northeast China are places where deserts and sandstorms are concentrated. The desert and sandy land here covers an area of over 700,000 square kilometers. Various sand dunes in the desert can be divided into mobile sand dunes, semi-fixed sand dunes and fixed sand dunes according to their stability. When sandstorms occur, the amount of dust raised by moving dunes is the largest, the semi-fixed dunes are smaller, and the fixed dunes are the smallest.

Except desert and sandy land, most of northern China belongs to mid-latitude arid and semi-arid areas, and the ground is mostly sparse grassland and arid cultivated land, with sparse vegetation and serious man-made damage. In spring, the ground warms up and thaws, the ground is bare, the wind blows wildly, and the dust is diffuse, forming dusty weather in some areas and areas where the wind passes.

Unstable air

Let's look at an example in life first. When you fiddle with the stove, the fire burns brightly. With a slight poke, ash will often fly all over the house. When the fire goes out, you usually don't spend much effort to raise dust, which involves the problem of air stability. After the fire is extinguished, there is little difference in air temperature between the top and bottom of the stove, so the air is stable. When the fire burns violently, the air near the fire is hot, and the air far away from the fire is cold. Hot air is lighter than cold air and tends to rise, so the air above the fire is unstable. In this way, the stirred furnace ash can easily rise with the hot air and then float all over the room.

In nature, so do sandstorms. If the lower air temperature is low and stable, the dust blown by the wind will not be lifted very high; If the lower air temperature is high, it will be unstable and easy to move upward. After the wind blows, the dust will be blown high, forming a sandstorm. In fact, sandstorms in China are usually strongest in the afternoon or from afternoon to evening, because this is the most unstable time of the day.

In addition to the above three factors, human production activities and other factors are also very important to the formation of sandstorms. Such as man-made destruction of vegetation, industrial and mining traffic construction, large-scale construction and other damage to the surface, provide fine dust for the occurrence and development of sandstorms.

China satellite meteorological expert system analyzes six characteristics of sandstorm.

According to the China National Satellite Meteorological Center, at the recent academic annual meeting of the China National Satellite Meteorological Center, Dong Chaohua, chief engineer and researcher of the National Satellite Meteorological Center, Fang, Zheng Xinjiang, Lu Naimeng, Professor Shao Yaping of the University of New South Wales, etc. 17 people participated in the study of the China sandstorm project, and predicted its occurrence time, region, source, path, related factors, six characteristics of impact and numerical model.

1. Time: Sandstorms in China mainly occur from March to April. Taking 2002 as an example, there were sandstorms 12 times in China, including 4 strong sandstorms, all of which occurred in March and April. All the above processes were monitored and analyzed by the National Satellite Meteorological Center.

2. Geography: Sandstorms mainly occur in east longitude 1 10-north latitude17 degrees, that is, the vast area north of 38 degrees north latitude, that is, taking Cangzhou, Hebei as the boundary, reaching Tianjin and Beijing to Inner Mongolia in the north, passing Shijiazhuang, Yinchuan, Lanzhou and Qilian in Qinghai in the west, and reaching north.

Source: The main source of sandstorms in China is Mongolia and even the desert areas in Central Asia. This kind of sandstorm is strong, and its influence is obviously greater than that of sandstorm in China. The source of China is the Hexi Corridor in Gansu, southern Inner Mongolia, northern Hebei and other desert areas.

Four. Path: In recent years, especially last spring, there are four main paths of sandstorms affecting Beijing: one is the path of Mongolia-Inner Mongolia-Beijing turning to the northeast. The second is the route from Hexi Corridor to Beijing. Third, it influences Beijing from Zhu Rihe in Inner Mongolia via Zhangjiakou in Hebei. The fourth is to influence Beijing from the northern plateau of Shanxi to the east.

5. Related factors: Based on the preliminary analysis of the main sand-dust processes in Huahua area since 1998, especially since 2002, and related climatic factors, namely, ground vegetation, snow in February, 0- 10 cm soil humidity and temperature, it is considered that sand-dust weather is closely related to cold air activities in spring. When the cold air path is west or south in spring, for example, in April of 1999, North China. On the contrary, when the main cold air moves eastward and northward, such as April 2000 and March 2002, the main process takes place in North China.

6. Impact of sandstorm: Strong sandstorm not only affects northwest, north, central and east China, but also can be transported to northeast China, affecting northeast, far east and even north China, which is caused by global atmospheric circulation.

The forecast analysis of dust flux and dust flux in the numerical forecast experiment of sandstorm weather in China shows that when the diameter of dust particles is less than 22 microns, it is in good agreement with the ground observation data, and the forecast effect of sandstorm in China is very good. Ground vegetation data and soil types are very sensitive to sandstorm forecast.

Experts pointed out that the potential sources of dust weather in China are widely distributed, with harsh natural conditions and few ground stations. At present, the observation data about the occurrence, development, spread and intensity change of sandstorm weather are very scarce. Therefore, satellite remote sensing is an extremely important means for monitoring both in time scale and space scale. In the monitoring from 200/kloc-0 to 2002, the accuracy of identifying sandstorm weather reached 88%, and the accuracy of identifying sandstorm reached over 95%.

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 of 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.

Control and preventive measures of sandstorm

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

2. Restore vegetation, strengthen biological protection system and prevent sandstorms. Protect and restore forest and grass vegetation according to law, prevent further expansion of land desertification, and minimize dust sources.

3. According to the local conditions in different regions, formulate disaster prevention, disaster prevention and relief plans, actively promote various disaster reduction technologies, and build model projects, gradually promote them from point to area, and further improve the regional comprehensive defense system.

4. The long-term predatory exploitation of natural resources has caused serious damage to the natural ecological environment, and the deterioration of the environment has provided a rich source of dust for sandstorms.

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

6. Strengthen the popular science propaganda on the relationship between the occurrence and harm of sandstorms and human activities, and make people realize that once the living environment is destroyed, it will be difficult to recover, which will not only aggravate natural disasters such as sandstorms, but also form a vicious circle, and people should consciously protect their living environment.

Four lines of defense to stop sandstorms

First, establish an ecological barrier mainly based on afforestation in the surrounding areas of Beijing and Tianjin in the north of Beijing;

The second is to build an ecological restoration and protection belt with returning farmland to forests as the core in the central and western parts of Hunshandake, Inner Mongolia;

Thirdly, the Ordos ecological barrier centered on the Yellow River irrigation area and Mu Us sandy land should be built in Hetao and Huangsha areas.

Fourth, establish a long-term cooperation plan framework with Mongolia to prevent and control sandstorms as soon as possible and set up a protective barrier for Mongolia.

Distribution of four sandstorm-prone areas in the world

At present, a quarter of the global land area is threatened by desertification, and there are four sandstorm-prone areas in the world, namely North America, Australia, Central Asia and the Middle East, including Central Africa and West Asia.