The characteristics of sandstorms

　　According to modern meteorology, dusty and sandy weather can be roughly putsintosthree ascending categories.

　　Floating dust: It happens with or without little wind. The dust is either carried to the present location by high-altitude air currents or is suspended evenly in the air after a sand storm. The visibility when floating dust occurs is less than 10 kilometres. The sun appears white and any distant scenery is yellow brown.

　　The next level is floating sand, which is blownsintosthe air by strong wind. The air is rather indistinct and visibility is between 1-10 kilometres.

　　The highest level is of course the sandstorm. The powerful wind takes ground sand and dustsintosthe air, lowering visibility to less than one kilometre. The sky appears dusty brown or even reddish brown.

　　Distribution Characteristics of Severe Sandstorms in Different Areas: (desert-map)

　　Northwest China is a regionswheressevere sandstorms occur frequently and bring about serious damage. Two routes allow cold high pressure systems to initiate severe sandstorms.

　　The Western Route: Affected by anticyclones from Siberia and the Inner Mongolia Autonomous Region of China, the sandstorms on this route move rapidly, intensify quickly, have a wide influence and bring severe disasters. The route passes through:

　　1.The Tarim Basin and Tulu-Bishan-Toksun Basin, through Gansu Province to northern Shaanxi. The center of cold high pressure after the front is in the Xinjiang Uygur Autonomous Region or west of Inner Mongolia.

　　2. The Kalpin, Hotan, Minfeng and Geermu route in Xinjiang. Severe sandstorms last for long periods in this area.

　　3. The route through Dunhuang and Minqin and moves eastward. The Northern Route: Cold air goes southward from Lake Baikal through central Mongolia to northern Shaanxi Province, which influences the Inner Mongolia, Ordos and Alxa plateaus, Bayinmaodao and Yulin.

　　Distribution Characteristics of Strong Sandstorms in Time

　　Severe sandstorms started to occur frequently after the 13th century, and increased rapidly after the 18th century. The number of severe sandstorms grew rapidly after the founding of the People's Republic of China. There were five in the 1950s, eight in the 1960s, 13 in the 1970s, 14 in the 1980s and 20 in the 1990s. The frequency is rising. Severe and widespread sandstorms mainly occur in the period from March to May, especially in April.

　　The Damages They Caused

　　Severe sandstorms are major disasters in arid and semi-arid areas. They occur suddenly and affect large areas causing great losses to the national economy and the people. One example was an especially severe sandstorm on the Western Route, affected by cold air from Siberia. It moved quickly southward from May 4 to 6, 1993, affecting a total area of 1.1 million sq km, from northern Xinjiang to the Hexi area of Gansu, western Inner Mongolia and most of the Ningxia Hui Autonomous Region. The wind speed reached 37.9 m/s (greater than a Force 12 wind). The average wind speed was 21m/s (equal to a Force 8 wind), and the visibility was less than 50 m. The sandstorm caused great losses. In Xinjiang, Gansu, Inner Mongolia and Ningxia, 85 persons died and 264 were injured, 4,412 houses were destroyed, and 120,000 animals died or went missing. About 373,333 million hectares of crops were destroyed, over 2,000 km of ditches were buried, and transportation and telecommunications facilities were severed in some areas. The direct economic losses hit 550 million yuan, which further damaged the ecological environment and economic development. Another example is the sandstorm which raged from April 16 to 18, 1998. Blowing from west to east, it even reached the lower reaches of the Yangtze River. This was almost unprecedented in history. A severe sandstorm meeting rain over Beijing formed "muddy rain" there. In the city of Nanjing, Jiangsu Province, the suspended solids in the air were eight times the normal index. Floating dust afflicted the Inner Mongolia Autonomous Region, Beijing, Jinan of Shandong Province and Nanjing.

　　Benefits they bring:

　　As a natural phenomenon, what sandstorms bring are not all damages for that it is not an isolated phenomenon. If we were to eliminate sandstorms or the deserts ( it is impossible actually), we also eliminated a kind of natural zoology. All the creatures in the deserts will be killed out.

　　First, sandstorms can reduce acid rains. There are abundant alkalescency positive hydroniums such as calcium, which can neutralize acid rains. That explains why there are fewer acid rains in northern China than in the south.

　　Second, the sandy weather created the Loess Plateau, the largest plateau of its kind in the world. Therefore, people in this area living in cave-houses also rank the highest. The cave-houses in which it is warm in winter and cool in summer are very comfortable to live in.

　　Third, the sand grains help form clouds and rains and release the tension of drought. The sand grains’surface is not round, which make it easy for the water vapor to coagulate on them and form rain drops.

　　Fourth, the sand grains bring much mineral that will benefit the plants in the coming years and those blown to the ocean will benefit the oceanic creatures, too. There in the sand grains contain plenty iron and phosphorus which are badly needed by the oceanic creatures.

　　Fifth, the sandy and dusty clouds help cool the world. They can reflect sunshine and form an effect called“Umbrella Effect”, which protects the earth from being too hot.