Dust storm

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Image:Sandstorm big.jpg A dust storm (or sandstorm in some contexts) is a meteorological phenomenon common on the Great Plains of North America, the desert southwest of the United States before the summer monsoon, in Arabia, in the eastern Mediterranean and in Cyprus, the Gobi Desert of Mongolia, the Taklamakan Desert of northwest China, the Sahara Desert of northern Africa, the Thar Desert of India and other arid and semi-arid regions. Such a storm is usually the result of convection currents created by intense heating of the ground. The air over the sand becomes hot, and rises. This creates differences in air pressure and temperature, and the cooler winds begin to rush in. The wind is strong enough to move dunes, and it often interferes with travel, sometimes obliterating roads in flat, dry regions such as those of the western United States. For instance, on the 29th of November 1991 a convective dust storm formed over Interstate-5 in the San Joaquin Valley, California. The storm picked up dust in a suspension with winds at speeds of over 120km/h. Visibility was reduced to less than half a car's length, causing a pile-up accident involving 164 cars, killing 17 and injuring 151. The simoom or simoon (sîmūm, sîmūn) is the dust- and sand-laden desert wind of N Africa and Arabia that contributes largely to the atmospheric dust over Europe; evidence of the dust from simoon winds has also been found on the seafloor at considerable distances from shore. The haboob (həbūb) is a sandstorm prevalent in the region of Sudan around Khartoum. Sandstorms, the leading edges of which often appear as solid walls of dust as much as 5,000 ft (1,525 m) high, also occur, although less frequently, in the SW United States. One that occurred near Tucson, Arizona, on July 16 1971, was extensively documented by meteorologists. Similar duststorms from windborne particles are evident on the planet Mars and are thought to be seasonal. Severe dust storms can reduce visibility to zero, making travel impossible, and can blow away valuable topsoil, while depositing soil in places where it may not be wanted. Drought and wind contribute to the emergence of dust storms, as do poor farming and grazing practices. The dust picked up in such a storm can be carried thousands of kilometers: Sahara dust storms influence plankton growth in the western Atlantic Ocean and, according to some scientists, are an important source of scarce minerals for the plants of the Amazon rainforest. Dust storms can often be observed from satellite photos, the use of which is highly valuable in forecasting; of particular use are the NASA imaging devices MODIS and SeaWIFS.

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On other planets

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Dust storms are also known to occur on a massive scale on the planet Mars. Storms on Mars last longer, and cover larger areas, than on Earth; some of these storms cover the entire planet and last for hundreds of days.

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