The Behaviour of Sand Grains in the Air

Abstract

A POPULAR misconception exists regarding sand storms, due to a failure to distinguish sand from dust. When, in any arid country, after a spell of calm weather, a strong wind begins to blow from a new direction, the air becomes charged with a mist of small particles. Where the surface is alluvial, with little or no sand on it, such as in Iraq or the country round Khartoum, the dust rises in dense clouds to a height of several thousand feet and the sun is obscured for a long period. This is obviously a dust storm, though it is often wrongly designated by the possibly more thrilling and cleanly term ‘sand storm’. Owing to their feeble terminal velocity of fall the very small dust particles are raised and kept aloft by the upward currents of the wind’s internal movement, as described in Chapter I (3).