Why is there a sandstorm in Beijing every March?

Speaking of the causes of sandstorms, there are many aspects. The driving force of sandstorm is wind. The material basis is dust. Wind and dust have complex and diverse temporal and spatial changes. There is strong enough wind and enough dust. But blowing a lot of dust also requires many conditions. A strong northwest wind prevails in the arid area of northwest China. Due to the uplift of the ancient Mediterranean, a large number of soft dust deposits were formed. Drought, little rain and sparse vegetation, especially in spring, drought, strong wind and sparse vegetation all occur at the same time, so there are natural conditions for sandstorms in spring, and human activities destroy the vegetation on the ground, making sandstorms worse and worse.

What are the fundamental methods to control sandstorms?

Windbreak is afforestation. In fact, I have the same view as upstairs. Sandstorms are mainly caused by soil erosion, and all kinds of trees can be stopped.

Dust weather in China in recent years

According to statistics, there were eight sandstorms in China in 1960s, three in 1970s 14 in 1980s14, and more than 20 in 1990s, and the scope of sandstorms became wider and wider with heavy losses. The situation of several major gale and sandstorm weather in China since the 1990s is introduced as follows:1993: From April to early May, gale weather appeared many times in the north. From April 19 to May 8, Gansu, Ningxia and Inner Mongolia were successively hit by strong winds and sandstorms. On May 5-6, eastern Xinjiang, Hexi in Gansu, most of Ningxia and western Inner Mongolia were hit by severe sandstorms, causing serious losses. 1994: From April 6, strong winds blew from Mongolia and western Inner Mongolia, and the dust in the northern desert Gobi was lifted by the wind and floated over the Hexi Corridor, and the loess lasted for several days. 1 995:165438+1On 7 October, more than 40 counties (cities) in Shandong were hit by heavy rain, with 35 people killed, 12 1 missing, 320 injured and direct economic losses/kloc-0. 1996: On May 29th and 30th, 1965, the worst sandstorm swept the west of Hexi Corridor. The black wind suddenly broke out, the world was closed, the dust filled, the trees collapsed, and people had difficulty breathing. The direct economic loss in Jiuquan area, which suffered the most, reached more than 200 million yuan. 1998: On April 5, the central and western Inner Mongolia, southwestern Ningxia and Hexi Corridor in Gansu were hit by strong sandstorms, which affected a wide range, including Beijing, Jinan, Nanjing and Hangzhou. On April 19, Tutanto Basin in northern and eastern Xinjiang was hit by a strong wind with an instantaneous wind force of 12, and some areas were accompanied by dust. The devastating typhoon caused a lot of property losses, with 6 people dead, 44 missing and 256 injured. 19 In the early morning of May 1, northern Xinjiang was suddenly hit by strong winds. The wind power in the tuyere areas such as Alashankou and Tacheng reaches 9 to 10, and the instantaneous wind speed reaches 32 meters per second. The winds in other areas generally reach 6 to 7. Strong winds blew down trees and cut off power lines in some areas. 1999: From April 3rd to 4th, there were continuous strong winds and sandstorms in Hohhot for two consecutive days. Sandstorms range from the west of Inner Mongolia Autonomous Region to the south of Tongliao City in the east, with instantaneous wind speed 16 meters per second. Maximum wind force in Dalat Banner of Yikezhao League 10. 2000: On March 22-23, there was a large-scale dusty weather in Inner Mongolia Autonomous Region, and some dust was carried over Beijing by strong winds, which aggravated the degree of sand blowing. On March 27th, the sandstorm hit Beijing again, and the instantaneous wind force in some areas reached 8-9. Seven workers who were working on the roof of a two-story building in Anxiangli Community were blown down by strong winds, and two of them died on the spot. Some billboards were blown down by strong winds, causing pedestrian injuries and vehicle damage. 2002: From March 18 to March/2 1 day, a sandstorm weather process with the largest scope, strongest intensity, the most serious impact and the longest duration since the 1990s, attacked China North1400,000 square kilometers and affected the population1300,000.

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.