Scientific view of 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.

Concept, regulations and standards of sandstorm weather

First, the concept of dusty 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 turbid and the horizontal visibility less than 500 meters.

Second, the classification of dust weather process

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.

Three, sand and dust weather forecast and early warning standards:

1, decision service

When there is expected to be a sandstorm weather process in the next 24 hours, the sandstorm weather forecast will be released in internal bulletins, special reports and decision-making service materials.

2. Public forecast

National standards:

It is expected that there will be a sandstorm weather process in the next 24 hours, and when it has a great impact or affects Beijing and Tianjin, a sandstorm warning will be issued to the public. ;

It is expected that there will be a sandstorm or strong sandstorm weather process in the next 24 hours, which will cause serious impact and issue a sandstorm warning to the public.

Provincial standards:

Determined by the meteorological bureaus of provinces (autonomous regions and municipalities) with reference to national standards.

Description:

1, the provincial sandstorm weather forecast and early warning release standard was reported to China Meteorological Bureau for the record.

2. The forecast and early warning of sandstorm weather shall include the area, time, intensity, possible impacts and countermeasures of sandstorm weather.

3. The Central Meteorological Observatory shall promptly and effectively notify the relevant provincial meteorological stations before releasing the forecast and warning of dust weather to the society, and the provincial meteorological stations shall promptly and effectively notify the Central Meteorological Observatory and the relevant meteorological stations before releasing the forecast and warning of dust weather to the society.

Causes 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

(1) Strong wind: Strong wind accompanied by fine dust damages buildings and public facilities, causing death.

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.

Strong winds have two other hazards: 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.

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, casualties, etc., pollute the natural environment, destroy crop growth, and cause serious losses and great harm to national economic construction and people's lives and property safety. 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.

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 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.

The role of sandstorm in 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.

Dust storm prevention measures

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.