Why do cyclones form sandstorms?

Typhoon is a strong tropical cyclone with warm heart structure that occurs on the surface of tropical ocean, and it will bring disastrous weather.

Its forming conditions mainly include

1. Suitable sea surface temperature. When the sea surface temperature is 26 ~ 28 degrees Celsius, it is suitable for the development of typhoon warm core structure. This is the primary condition for the formation of typhoons. This temperature provides enough energy for the typhoon.

2. Initial disturbance.

3. Some kind of geostrophic migration. The geostrophic bias makes the disturbance develop into cyclone rotation, which is a necessary condition for the formation of typhoon. On the equator, the geostrophic deflection force is zero, and the disturbance cannot develop into rotation, so there is no typhoon.

4. The vertical shear of the wind becomes smaller. In the vertical direction, the wind speed should be equal. When there is a big difference between the upper and lower wind speeds, the heat in the lower layer will be blown away by the upper wind as soon as it gathers, which is not conducive to the formation of warm heart and the accumulation of typhoon energy.

Typhoon has brought abundant rain to vast areas and become a rainfall system closely related to human life and production. However, typhoons always bring all kinds of injuries. Because of its sudden and destructive power, it is one of the most serious natural disasters in the world.

The destructive power of typhoons is mainly caused by strong winds, heavy rains and storm surges.

1. Strong typhoon is a huge energy pool, and its wind speed is above 17m/s, even above 60m/s ... According to the measurement, when the wind reaches 12, the wind pressure per square meter on the plane perpendicular to the wind direction can reach 230kg.

2. Rainstorm typhoon is a strong precipitation system. When the typhoon lands, the rainstorm center can drop 100-300mm a day, or even reach 500-800mm. The floods caused by typhoons and rainstorms are the most dangerous disasters. Typhoon rainstorm is strong, flood occurs frequently, spreads widely, and is fierce and destructive.

3. Storm surge. The so-called storm surge means that when the typhoon moves to the land, due to the typhoon's strong wind force and low air pressure, the sea water accumulates strongly in the direction of the coast, the tide level rises sharply, and water waves come to the coast. The storm surge of a strong typhoon can raise the coastal water level by 5-6 meters. Storm surge meets astronomical high tide level, resulting in high-frequency tide level, which leads to tidal overflow, seawall burst, washed away houses and various building facilities, flooded towns and farmland, and caused a large number of casualties and property losses. Storm surge will also cause coastal erosion and land salinization caused by seawater intrusion.

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;

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.