How are sandstorms formed?

There are three elements in the formation of sandstorms:.

strong breeze

Persistent strong winds are the dynamic conditions for the formation of sandstorms. For example, it is observed that when a strong sandstorm is formed, if the wind speed reaches 30m per second (11wind), coarse sand (0.5 ~ 1.0mm in diameter) will fly out of the ground for several tens of centimeters, while fine sand (0. 125 ~ 0.25mm in diameter).

Shayuan

China is one of the countries with the most deserts in the world. Northwest China, North China and Northeast China are places where deserts and sandstorms are concentrated. The desert and sandy land here covers an area of over 700,000 square kilometers. Various sand dunes in the desert can be divided into mobile sand dunes, semi-fixed sand dunes and fixed sand dunes according to their stability. When sandstorms occur, the amount of dust raised by moving dunes is the largest, the semi-fixed dunes are smaller, and the fixed dunes are the smallest.

Except desert and sandy land, most of northern China belongs to mid-latitude arid and semi-arid areas, and the ground is mostly sparse grassland and arid cultivated land, with sparse vegetation and serious man-made damage. In spring, the ground warms up and thaws, the ground is bare, the wind blows wildly, and the dust is diffuse, forming dusty weather in some areas and areas where the wind passes.

Unstable air

Let's look at an example in life first. When you fiddle with the stove, the fire burns brightly. With a slight poke, ash will often fly all over the house. When the fire goes out, you usually don't spend much effort to raise dust, which involves the problem of air stability. After the fire is extinguished, there is little difference in air temperature between the top and bottom of the stove, so the air is stable. When the fire burns violently, the air near the fire is hot, and the air far away from the fire is cold. Hot air is lighter than cold air and tends to rise, so the air above the fire is unstable. In this way, the stirred furnace ash can easily rise with the hot air and then float all over the room.

In nature, so do sandstorms. If the lower air temperature is low and stable, the dust blown by the wind will not be lifted very high; If the lower air temperature is high, it will be unstable and easy to move upward. After the wind blows, the dust will be blown high, forming a sandstorm. In fact, sandstorms in China are usually strongest in the afternoon or from afternoon to evening, because this is the most unstable time of the day.

In addition to the above three factors, human production activities and other factors are also very important to the formation of sandstorms. Such as man-made destruction of vegetation, industrial and mining traffic construction, large-scale construction and other damage to the surface, provide fine dust for the occurrence and development of sandstorms.

China satellite meteorological expert system analyzes six characteristics of sandstorm.

According to the China National Satellite Meteorological Center, at the recent academic annual meeting of the China National Satellite Meteorological Center, Dong Chaohua, chief engineer and researcher of the National Satellite Meteorological Center, Fang, Zheng Xinjiang, Lu Naimeng, Professor Shao Yaping of the University of New South Wales, etc. 17 people participated in the study of the China sandstorm project, and predicted its occurrence time, region, source, path, related factors, six characteristics of impact and numerical model.

1. Time: Sandstorms in China mainly occur from March to April. Taking 2002 as an example, there were sandstorms 12 times in China, including 4 strong sandstorms, all of which occurred in March and April. All the above processes were monitored and analyzed by the National Satellite Meteorological Center.

2. Geography: Sandstorms mainly occur in east longitude 1 10-north latitude17 degrees, that is, the vast area north of 38 degrees north latitude, that is, taking Cangzhou, Hebei as the boundary, reaching Tianjin and Beijing to Inner Mongolia in the north, passing Shijiazhuang, Yinchuan, Lanzhou and Qilian in Qinghai in the west, and reaching north.

Source: The main source of sandstorms in China is Mongolia and even the desert areas in Central Asia. This kind of sandstorm is strong, and its influence is obviously greater than that of sandstorm in China. The source of China is the Hexi Corridor in Gansu, southern Inner Mongolia, northern Hebei and other desert areas.

Four. Path: In recent years, especially last spring, there are four main paths of sandstorms affecting Beijing: one is the path of Mongolia-Inner Mongolia-Beijing turning to the northeast. The second is the route from Hexi Corridor to Beijing. Third, it influences Beijing from Zhu Rihe in Inner Mongolia via Zhangjiakou in Hebei. The fourth is to influence Beijing from the northern plateau of Shanxi to the east.

5. Related factors: Based on the preliminary analysis of the main sand-dust processes in Huahua area since 1998, especially since 2002, and related climatic factors, namely, ground vegetation, snow in February, 0- 10 cm soil humidity and temperature, it is considered that sand-dust weather is closely related to cold air activities in spring. When the cold air path is west or south in spring, for example, in April of 1999, North China. On the contrary, when the main cold air moves eastward and northward, such as April 2000 and March 2002, the main process takes place in North China.

6. Impact of sandstorm: Strong sandstorm not only affects northwest, north, central and east China, but also can be transported to northeast China, affecting northeast, far east and even north China, which is caused by global atmospheric circulation.

The forecast analysis of dust flux and dust flux in the numerical forecast experiment of sandstorm weather in China shows that when the diameter of dust particles is less than 22 microns, it is in good agreement with the ground observation data, and the forecast effect of sandstorm in China is very good. Ground vegetation data and soil types are very sensitive to sandstorm forecast.

Experts pointed out that the potential sources of dust weather in China are widely distributed, with harsh natural conditions and few ground stations. At present, the observation data about the occurrence, development, spread and intensity change of sandstorm weather are very scarce. Therefore, satellite remote sensing is an extremely important means for monitoring both in time scale and space scale. In the monitoring from 200/kloc-0 to 2002, the accuracy of identifying sandstorm weather reached 88%, and the accuracy of identifying sandstorm reached over 95%.