Where do sandstorms mainly originate?

Sandstorm is a disastrous weather phenomenon in which wind and sand interact. Its formation is inseparable from factors such as the global greenhouse effect, El Ni?o phenomenon, forest decline, vegetation destruction, species extinction, and climate abnormalities. relationship. Among them, over-exploitation of natural resources, excessive deforestation, and over-cultivation of land caused by population expansion are the main reasons for frequent sand and dust storms.

As a high-intensity sandstorm disaster, sandstorms do not occur in all windy places. Sandstorms are only likely to occur in areas with arid climate and sparse vegetation. In the northwest region of my country, the forest coverage rate is not high, and the poor northwest people still want to make a fortune by digging licorice, nostrils, and mining. These predatory and destructive behaviors have aggravated the sandstorm disaster in this region. Bare land can easily be blown up by strong winds to form sandstorms or even strong sandstorms.

After large-scale sandstorms occurred in late winter and spring, the dust raised by strong winds caused a large amount of dust in the air, which blocked the local sunshine and even reduced visibility to zero. Therefore, super strong sandstorms are also called black sandstorms. storm. Sandstorms can cause heavy losses to people's lives, property and agriculture. Sandstorms mainly originate in desertified areas, where the soil is soft, the ground is dry, and there is no vegetation on the surface. Once the air in a large area is very unstable and the ground wind speed is very high, it is easy to blow the surface dust into the air and form a dust weather.

After a sandstorm occurs, most of the larger dust particles settle to the ground after affecting the source area or nearby areas, while the smaller particles can be transported upward to an altitude of 1,000 to 3,000 meters, and then through The air flow in the westerly belt is carried eastward. During the transmission process, part of the dust travels farther due to diffusion or dilution; the lower the concentration, part of it reaches the ground due to sedimentation or rainfall (snow) during the transportation process. Dust from northwest China can move eastward to Japan, South Korea, and Hawaii 10,000 kilometers away, and can affect Taiwan, Hong Kong, and even the Philippines in the south. The area of ??influence is quite vast.

After sandstorms are transmitted to other areas thousands of kilometers away, local visibility and suspended particles in the atmosphere increase, affecting the air quality in that area. As for the time or scope of being affected by sandstorms, it depends on the scale and duration of the sandstorm at the source, and whether the meteorological conditions in the remote area are conducive to the transmission of sandstorms. According to observation records, visibility can be affected in as little as a few hours, and as long as a week, it can even cause mud rain.

Sandy weather is divided into three categories: floating dust, blowing sand, and sandstorms:

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

Blowing sand: The wind blows up the dust on the ground, making the air quite turbid, and the horizontal visibility is within 1-10 kilometers;

Sandstorm: The strong wind blows up the dust on the ground It is a weather phenomenon that makes 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 research, sand and dust in desert areas are the main source of suspended particles in the earth. The sand and dust in the Sahara Desert alone account for 25% of the suspended particles in the global atmosphere. Northwest my country is located in the desert area of ??Central Asia, ranking second among the four largest desert areas in the world (in order, Central Africa, Central Asia, North America and Australia). Therefore, the impact of dust in northwest China on the atmospheric environment of East Asia cannot be ignored. . The conditions for the occurrence of sandstorms are:

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

Meteorological conditions: strong and persistent surface winds, vertically unstable meteorological conditions and no rainfall or snowfall.

The total area of ??major deserts in northwest China is nearly 600,000 square kilometers. The main source areas are located in northwest China, North China and Mongolia, north of 35 degrees north latitude and west of 125 degrees east longitude, including Xinjiang, Gansu, Hetao, Inner Mongolia, Mongolia and other regions. The annual rainfall in this area is less than 400mm, and the seasonal distribution is quite uneven. It is the main source of sandstorms in East Asia.

Sandstorms may induce allergic diseases, epidemics and infectious diseases. According to his explanation, under normal circumstances, the human nose, lungs and other organs have a certain filtering effect on dust, but the excessive and dense fine dust caused by severe weather phenomena such as sandstorms is very likely to cause respiratory allergic diseases. of people relapse. Even healthy people may develop various symptoms such as coughing and asthma if they inhale dust for a long time, leading to an epidemic. In addition, strong winds span thousands of kilometers and blow germs along the way to downwind areas, which may include some infectious germs.

Sand dust is the most harmful to the human respiratory system and should not be taken lightly. Especially the elderly, infants and children with poor resistance, and people with respiratory allergic diseases should stay indoors with closed doors and windows and stay away from dust sources as much as possible. Once you find any obvious discomfort, you must go to the hospital immediately. Find out the cause.

When you must be active outdoors, it is best to use a wet towel or gauze to protect your eyes and mouth. However, you need to be reminded that this simple protection does not work against viruses. Construction workers and cleaning workers should temporarily stop outdoor operations until the sandstorm recedes. He also advised people to drink more water, eat more light food and not buy open-air street food.

The concept, regulations and standards of sand and dust storms

1. The concept of sand and dust weather:

Sand and dust weather is divided into four types: floating dust, blowing sand, sand dust storms and strong sand and dust storms kind.

Floating dust: Dust and fine sand float evenly in the air, making the horizontal visibility less than 10 kilometers;

Blowing sand: The wind blows up the dust and sand on the ground, making the air quite dense. Turbidity, a weather phenomenon with horizontal visibility within 1 km to 10 km;

Sandstorm: A weather phenomenon in which strong winds blow up a large amount of dust and sand from the ground, making the air very turbid, with horizontal visibility less than 1 km;

Strong sandstorm: A weather phenomenon in which strong winds blow up dust and sand on the ground, making the air very turbid and the horizontal visibility less than 500 meters.

2. Classification of sand and dust weather processes

Sand and dust weather processes are divided into four categories: floating dust weather processes, blowing sand weather processes, sand and dust storm weather processes and strong sand and dust storm weather processes.

Floating dust weather process: During the same weather process, 5 or more national basic (accurate) stations in my country's weather forecast area experienced floating dust weather at the same observation time;

Sandstorm weather process: During the same weather process, 5 or more countries' basic (accurate) stations in my country's weather forecast area experienced sandstorm weather at the same observation time;

Sandstorms Weather process: During the same weather process, sandstorms occurred at the same observation time at three or more countries' basic (accurate) stations in my country's weather forecast area;

Strong sandstorm weather process: During the same weather process, strong sandstorms occurred at the same observation time at three or more national basic (accurate) stations in my country's weather forecast area.

3. Sand and dust weather forecast warning issuance standards:

1. Decision-making service

When sand and dust weather processes are expected to occur in the next 24 hours, in Sand and dust weather forecasts are published in internal bulletins, special reports and decision-making service materials.

2. Public forecast

National standards:

It is expected that sand and dust weather processes will occur in the next 24 hours, and the impact range will be large or affect In the Beijing-Tianjin area, a sandstorm warning was issued to the public. ;

When a sandstorm or strong sandstorm is expected to occur in the next 24 hours and will cause serious impacts, a sandstorm warning will be issued to the public.

Provincial standards:

Determined by the provincial (autonomous and municipal) meteorological bureaus with reference to national standards.

Notes:

1. Provincial sand and dust weather forecast and warning issuance standards shall be reported to the China Meteorological Administration for filing.

2. Sand and dust weather forecasts and warnings should include the area, period, intensity, possible impacts and countermeasures of sand and dust weather.

3. Before issuing sand and dust weather forecast warnings to the public, the Central Meteorological Observatory should promptly notify the relevant provincial meteorological observatories through effective means. Before issuing sand and dust weather forecast warnings to the public, provincial meteorological observatories should promptly and effectively notify the central Reports from the Meteorological Observatory and related meteorological stations.

Causes and physical mechanisms of sand and dust storms

Causes of sand and dust storms

Weather conditions that are conducive to strong winds or strong winds, favorable distribution of sand and dust sources and favorable Unstable air conditions are the main cause of the formation of sandstorms or severe sandstorms. Strong wind is the driving force for sandstorms, and sand and dust sources are the material basis of sandstorms. Unstable thermal conditions are conducive to the increase in wind power and the development of strong convection, thereby entraining more sand and dust and carrying it higher.

In addition, early drought and lack of rain, warm weather, and rising temperatures are the special weather and climate background for the formation of sandstorms; the development of convective cells in front of the ground cold front into clouds or squall lines is conducive to sandstorms The development and strengthening of small and medium-scale systems; the terrain conditions that are conducive to increased wind speed, that is, the narrow tube effect, are one of the favorable conditions for the formation of sandstorms.

The physical mechanism of the formation of sand and dust storms

Under the conditions of extremely favorable large-scale environment, high-altitude dry and cold jet stream, strong vertical wind speed, wind shear and thermally unstable stratification, frontal areas are caused The formation and development of nearby medium- and small-scale systems intensifies the pressure and temperature gradients before and after the frontal zone, forming a huge pressure-temperature gradient before and after the frontal zone. Under the simultaneous action of momentum downward transmission and gradient deviation wind, the near-surface wind speed rises sharply, kicking up surface sand and dust, forming sandstorms or strong sandstorms.

The main hazards of sandstorms

⑴ Strong winds: Strong winds carrying fine sand and dust destroy buildings and public facilities, causing death.

⑵ Sand burial: Farmland, channels, cottages, railways, pastures, etc. are buried by a large amount of sand due to wind and sand flow, 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 to varying degrees, and the depth of wind erosion can reach 1 to 10 cm. It is estimated that my country's annual loss of fine soil matter caused by sandstorms is as high as 106 to 107 tons, most of which have particle sizes below 10 microns, causing serious damage to the land productivity of farmland and pastures in the source areas.

⑷ Atmospheric pollution: In the source areas and affected areas of sandstorms, respirable particulate matter (TSP) in the atmosphere increases, and air pollution intensifies. Taking the "5.5" extremely severe sandstorm in 1993 as an example, the TSP concentration of outdoor air in Jinchang City, Gansu Province reached 1016 mg/m3 and indoors was 80 mg/m3, exceeding the national standard by 40 times. From March to April 2000, the Beijing area was affected by sandstorms. The air pollution index reached level 4 or above for 10 days, which also affected many cities in eastern my country. From March 24 to 30, the daily pollution index in 18 cities, including Nanjing and Hangzhou, exceeded level 4.