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1、.,1,sandstrom,.,2,What is sandstorm?,Sandstorm is a meteorological phenomenon commonly found in arid and semi-arid regions.It is resulted from convection currents created by intensive heating of the ground.These currents can create wind up to 120km/h and appear as a solid wall of dust as much as 1,5
2、25m high which blow over a long distance.,.,3,Sandstorm is a kind of climatic hazard.It occurs when strong wind raises and carries along clouds of sand or dust which is so dense that it obscure the sun and reduce visibility to less than 1 km.Sandstorm usually occurs in deserts or areas near to arid
3、and semi-arid regions.It was found in areas like Sahara Desert in North Africa,Central Australia,Southwest of USA,Central Asia and Northwest China.,.,4,Sandstorms have been more serious in recent years.They occur earlier in the season and are affecting a wider area.In 2006,they came a week earlier a
4、nd the affected area had extended beyond 3 million km2.The air quality of northern China has been seriously affected by sandstorm.By 19 April 2006,55 out of 113 monitored cities had seen fewer clean days than a year before.In times of sandstorms,people need to wear masks and traffic was seriously af
5、fected due to lower visibility.The airborne particles in sandstorm cause an increase of allergies,especially among children.Respiratory and eye sickness become more common.Medical expenses of families may increase.,What are the effects of sandstorms on human activities?,.,5,Conditions for the format
6、ion of sandstormsA specialist in meteorology pointed out that sandstorms were formed under three conditions:strong wind,rich source of sand and unstable air conditions.The three conditions can be a result of natural causes.However,for the second condition,the supply of sand is more of a result of desertification caused by human activities.,Why do sandstorms occur in North China?,.,6,Relationship with the atmosphereRelationship with reliefRelationship with vegetation,.,7,pictures,.,8,.,9,thanks,
