Causes and hazards of sand and dust weather
Hello, sandstorm is a general term for both sandstorm and dust storm. It refers to a severe sandstorm weather where strong wind blows a large amount of sand and dust material from the ground into the air, making the air particularly turbid and the horizontal visibility is less than 1km. Phenomenon. A sandstorm refers to a sandstorm caused by strong winds blowing large amounts of sand into the near-surface layer; a dust storm is a storm caused by strong winds carrying large amounts of dust and other fine-grained materials into high altitudes.
Causes of sandstorms
Weather conditions that are conducive to strong winds or strong winds, favorable sand and dust source distribution and favorable air instability conditions are the main reasons for the formation of sandstorms or strong 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.