17th April 2006
Dust Storms
Source: Excerpt from The Book " Weather "
Distribution:
Most frequent in arid areas or temperate zones after drought.Height:
From the surface up to around 10,000 feet.Cause: Lifting of dry topsoil by an active cold front. Associated Weather:
Strong winds.Hazard Warning: Restricted visibility; destruction of crops and farmland. Strong winds are always capable of lifting topsoil and scattering it over large areas, but occasionally, certain conditions combine to produce huge walls of moving dust that carry thousands of tons of soil and debris to another location.
Such events tend to occur after an extended drought has left the ground dry and dusty. If a vigorous cold front then moves across such an area, the ascending air at the face of the cold front may lift the topsoil, forming a huge moving wall of dust. This wall will be carried along by the front, with more soil feeding into the system as it advances.
A cloud of raised dust is generally considered to be a dust storm if visibility is reduced to about half a mile (1 km). It is considered severe if visibility decreases to a quarter of a mile (0.5 km) or less.
Dust can be lifted up as high as 10,000 feet (3000 m), and travel several thousand miles, remaining airborne for days. Dust storms generated by vigorous fronts over southeastern Australia have carried soil right across the Tasman Sea to New Zealand, producing dust-colored "red snow" on the New Zealand Alps. A similar phenomenon occurs in North America, when dust storms from the Plains produce dust-colored snow and rain along the Atlantic coast.
Dust storms may be preceded by dust devils that have detached themselves from the main front, but these are unlikely to cause much damage. Large dust storms frequently leave behind an enormous amount of fine dust that infiltrates every corner in a house, even making its way between book pages. By far the most serious damage caused by dust storms is the removal of valuable topsoil from farmland and other areas.
Acknowledgement due: John W. Zillman, William J. Burroughs,
Bob Crowder, Ted Robertson, Eleanor Vallier-Talbot and Richard Whitaker.
