Where does the sandstorm mainly start?

Sandstorm is a disastrous weather phenomenon in which wind and sand interact. Its formation is closely related to global greenhouse effect, El Nino phenomenon, forest decline, vegetation destruction, species extinction, climate anomaly and other factors. Among them, excessive exploitation of natural resources, excessive deforestation and excessive land reclamation caused by population expansion are the main reasons for frequent sandstorms.

As a kind of high-intensity sandstorm disaster, sandstorm can't happen in all windy places, but only in those areas with dry climate and sparse vegetation. In the northwest of China, the forest coverage rate is not high, and the poor northwest people want to make a fortune by digging licorice, holding seaweed and mining. These predatory acts of destruction further aggravated the sandstorm disaster in this area. Exposed land is easily rolled up by strong winds, forming sandstorms or even strong sandstorms.

After a large-scale sandstorm occurred in late winter and early spring, the dust raised by strong winds caused a lot of dust in the air, which blocked the local sunshine and even made the visibility zero. Therefore, super sandstorms are also called black storms. Sandstorm will cause great losses to people's lives, property and agriculture. Sandstorms mainly originate in desertification areas, with soft soil, dry ground and no vegetation. Once the air is unstable in a large range and the surface wind speed is high, it is easy to blow up the surface dust and enter the air to form dusty weather.

After the occurrence of sandstorm, the larger dust particles are mostly behind the influence source or adjacent areas; That is, smaller particles can be transported upward to an altitude of 1000 to 3000m, and then transported eastward by the airflow in the westerlies. In the process of transportation, some dust is diffused or diluted, which makes the dust farther and farther along with the transportation distance; The lower the concentration, the ground will be reached under the action of settlement or rainfall (snow) during the transmission. Dust in the northwest of China can move eastward to Japan, South Korea and Hawaii, which is 10000 km away, and southward to Taiwan Province Province, Hongkong and even the Philippines, with a wide range of influence.

After the sandstorm spread to other areas thousands of kilometers away, the local visibility and suspended particles in the atmosphere increased, which affected the air quality there. As for the time or scope affected by sandstorm, it depends on the scale and duration of sandstorm in the source area and whether the meteorological conditions in remote areas are conducive to sandstorm transportation. According to the observation records, the visibility is affected for a few hours, and it is as long as a week, even causing mud rain.

Dust weather is divided into three categories: floating dust, sand blowing and sandstorm:

Floating dust: a weather phenomenon in which sand or soil particles suspended in the atmosphere make the horizontal visibility less than 10 km;

Sand blowing: the wind blows up the dust on the ground, making the air quite turbid, and the horizontal visibility is within 1- 10 km;

Sandstorm: a weather phenomenon in which strong winds blow up dust on the ground, making the air very turbid and the horizontal visibility is less than 1 km; When the horizontal visibility is less than 500 meters, it is a strong sandstorm.

According to the research, sand dust in desert area is the main source of suspended particulate matter on the earth, and sand dust in Sahara desert alone accounts for 25% of suspended particulate matter in the global atmosphere. Northwest China is located in the desert area of Central Asia, ranking second among the four desert areas in the world (Central Africa, Central Asia, North America and Australia in turn), so the impact of dust in the northwest on the atmospheric environment in East Asia can not be ignored. The conditions for the occurrence of sandstorms are:

Surface characteristics: soft and dry soil, no vegetation or vegetation growth, no snow.

Meteorological conditions: the ground wind is strong and continuous, and the meteorological conditions are vertically unstable, with no rainfall and snowfall.

The total area of desert in northwest China is nearly 600,000 square kilometers. The main source areas are located in northwest China, north China and Mongolia, including Xinjiang, Gansu, Hetao, Inner Mongolia and Mongolia, north of 35 degrees north latitude and west of 125 degrees east longitude. The annual rainfall in this area is below 400 mm, and the seasonal distribution is quite uneven, which is the main source of sandstorm weather in East Asia. Late winter and spring are the main seasons for sandstorms, with the highest frequency from March to May, accounting for more than 60% of the whole year, and the number of sandstorms varies from year to year.

Mongolia is the main foreign dust source that affects most parts of North China, especially Beijing. The external dust sources that affect the dust weather in northern China are mainly located in the desertification areas of Kazakhstan and Russia.

Mongolian vortex system is the main factor affecting the dust weather in eastern China. After the formation of the Mongolian vortex, the local dust is generally rolled up and gradually moved south. In the process of moving, the updraft at the tail of the vortex will drag the dust from the dust source along the way into the vortex and transport it downstream. Beijing is in the downwind zone, and the deep vortex system often brings dusty weather to Beijing.

There are two main moving paths that affect the dusty weather in Beijing: the North Road starts from the eastern and western regions of Mongolia and passes through Hunshandake Desert, Huade and Zhangjiakou in western Inner Mongolia to Beijing; West Road starts from Hami City, Gansu Province, reaches the border between China and Mongolia in Alashan League, Inner Mongolia, along Hexi Corridor, south foot of Helan Mountain, passes through Mu Us Desert and Wulanbuhe Desert, Hohhot City and Zhangjiakou, and finally reaches Beijing. Sandstorms that occur on the edge of Taklimakan Desert in Xinjiang will form long-distance transportation when encountering strong transit systems, which can affect Beijing area.

According to the frequency and intensity of sandstorms, the composition and distribution of aeolian materials, ecological conditions, soil moisture content, water and soil utilization mode and intensity, and combined with the regional environmental background, northern China is divided into four main sandstorm centers and source areas: 1, Hexi Corridor in Gansu Province and Alashan League in Inner Mongolia; 2. The area around Taklimakan Desert in southern Xinjiang; 3. The northern slope of Yinshan Mountain in Inner Mongolia and its adjacent Hunshandake sandy land; 4. Along the Great Wall in Mongolia, Shaanxi and Ningxia. The dust in the above-mentioned sandstorm-prone areas is often transported to North China and the middle and lower reaches of the Yangtze River with the westerly wind and northwest airflow, forming dusty weather.

The frequent occurrence of sandstorms is one of the signs of ecological environment deterioration. The area of desert, Gobi and desertified land in China has reached 654.38+6530 square kilometers, and it is developing at the rate of 2460 square kilometers per year. Land desertification is very different between the east and the west. Taking Helan Mountain as the boundary, the west is controlled by the arid climate in the northwest, and there is no rainfall. Land use is an oasis irrigated agricultural area. The main factors and manifestations of desertification are improper allocation of water resources, waste of downstream farmland due to lack of water or blind reclamation, firewood collection and overgrazing in the transitional zone between desert and oasis, or natural vegetation death and wind erosion in grassland due to depletion of surface water and decline of groundwater level. Affected by the East Asian monsoon, there is some precipitation in summer and autumn in the east. Desertification mainly occurs in the farming-pastoral ecotone. In the dry season of winter and spring, it is caused by excessive reclamation, serious overgrazing, grassland degradation and firewood harvesting. The main forms are soil desertification, gravel, shrub desertification and sand activation of agricultural land. At the beginning of the 20th century, the United States exploited the western land on a large scale, which led to the "black storm" that shocked the world in the 1930s. In 1960s, the land around Karakum Desert in Kazakhstan was reclaimed by the former Soviet Union, and there were also strong sandstorms. After the 1930s, the United States made great efforts to adjust the agricultural planting structure in the construction and transformation of the western region, and adopted a set of effective methods, such as crop intercropping, interplanting and crop stubble with different maturity and sowing dates, vigorously promoted the no-tillage method and reformed agricultural machinery. After the 1960s, the former Soviet Union attached great importance to building water conservancy projects in the construction and transformation of Central Asia, and vigorously built farmland shelterbelts, which achieved good results. It provides the world with two different technical models to prevent and control sandstorms-agricultural measures (USA) and forestry measures (former Soviet Union). We should learn from the successful experience of other sandstorm-prone areas in the world and formulate ecological restoration strategies and policies suitable for China's national conditions.

Sandstorm is the product of the interaction between weather process and ground process. However, at present, human's ability to control the weather is still very limited. The key to slow down the frequency and intensity of sandstorms lies in the ecological protection and construction of the ground. Adhere to the ecological protection and construction policy of "giving priority to prevention, giving priority to protection and paying equal attention to prevention and control"; Establish and improve the system of ecological protection laws and policies, stop all production activities that lead to the continuous deterioration of the ecological environment, and take certain ecological immigration measures for areas beyond the ecological carrying capacity.

Sandstorms may induce allergic diseases, epidemics and infectious diseases. According to him, under normal circumstances, people's nasal cavity, lungs and other organs have a certain filtering effect on dust, but sandstorms, a disastrous weather phenomenon, bring too much and too dense fine dust, which is very likely to make people with respiratory allergic diseases relapse. Even healthy people, if they inhale dust for a long time, will have uncomfortable symptoms such as cough and asthma, which will lead to the outbreak. In addition, strong winds span thousands of kilometers, blowing germs along the way to downwind areas, which may include some infectious germs.

Dust is the most harmful to human respiratory system, so people should not underestimate it. In particular, the elderly, infants and patients with respiratory allergic diseases with poor resistance should stay indoors, close doors and windows and try to stay away from dust sources. Once you find that you have obvious discomfort, you must go to the hospital immediately to find out the reason.

When you have to be outdoors, it is best to protect your eyes and mouth with wet towels and gauze towels, but it needs to be reminded that this simple protection does not work for the virus. Before the dust storm recedes, construction workers and cleaning personnel should temporarily stop outdoor work. He also suggested that people drink more water, eat more light food and don't buy street open-air food.

Concept, regulations and standards of sandstorm

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.