Causes of sandstorms

In desert areas, sandstorms are most commonly caused by either thunderstorm outflows, or by strong pressure gradients（气压梯度）which cause an increase in wind speed over a wide area. In some cases, dust and sand may set a limit to a shallow depth by a low-lying temperature change. 【小题1】 Drought is another cause of sand storms. Poor farming practices make dust and sand free of protection from the wind. 【小题2】 A sandstorm can transport and carry large amounts of sand. Desert is the key source of sandstorms. Saharan sandstorms have increased abut 10 times during the half century since the 1950’s, causing topsoil loss in nearby countries. In Mauritania, there were just two sandstorms a year in the early 1960’s, but there are 80 a year today.【小题3】

Sand storms have also been shown to increase the spread of disease across the globe. Virus in the dust is blown into the atmosphere by the storms. Some diseases may not be urgent at the very beginning, but they can develop into deadly ones if left untreated. 【小题4】

Sandstorms cause soil loss from the dry lands, doing harm to agriculture. Sandstorms also reduce visibility, affecting airplanes and road transportation. 【小题5】

Dust can also have good effects. Central and South American rainforests get most of their mineral nutrients from the Sahara; iron-poor ocean regions get iron.