The geography of dust storms
Dust storms have a great many environmental implications in the world's dry lands where they are particularly common. Four main classes of dust event are identified and defined: dust storms, dust haze, blowing dust and dust devils. The geography of dust storms is analysed in each of eight major world regions: Africa, the Middle East, South-west Asia, Europe and the USSR, China, Australia, North America and Latin America. Terrestrially observed meteorological data and data from remote sensing platforms are employed to identify the major source areas in each region, their seasonality, diurnal patterns of activity and trajectories of long-range transport. Among the important controls on the frequency distribution of dust storm activity are the meteorological conditions that generate dust-raising winds, and a number of meteorological systems commonly cause dust storms in all global regions. These include low pressure fronts with intense baroclinal gradients, pressure gradient winds between moving or stationary air masses, katabatic winds and convectional cells. The nature of the surface upon which deflation occurs is also important; typical dust-producing geomorpholological units include alluvial spreads, lacustrine deposits, desert depressions, loess deposits and reactivated fossil dunes. Dust storm activity is prone to considerable variation. The seasonal characteristics are explicable with reference to the meteorological systems generating dust, the state of ground cover, particularly vegetation, and the effects of seasonal rainfall. Substantial variations also occur from year to year, and land use and climatic variations can substantially affect their occurrence.