Dust Devil

Whirling with a metallic rushing or buzzing sound, whipping dust into twirling columns that can rise anywhere from a few feet to half a mile or more, dust devils are the mostly-harmless cousins of tornadoes. Known by many names across the world, from "sun devil" to "ghost's wind" and numerous others, dust devils are also the spawn of updrafts -- but, in this case, ground-level updrafts caused by the heat of the sun, especially in flat, dry country.

Dust devils have no known effect on weather patterns beyond a tiny, local scale, and usually have scant human effect other than the interest of their appearance. A few rare, large dust devils can cause minor property damage, and a tiny minority have been strong enough to kill people by collapsing small buildings on them. Even the largest dust devil doesn't have winds powerful enough to pick up a human being, and usually carries nothing more than dust.

How dust devils form

A dust devil is born when air along the ground level becomes intensely hot -- something that usually happens over dry flatland, desert, or even large parking lots in the summer. The necessary heat can only be provided by the sun's rays, so dust devils happen on sunny days, unlike the larger whirlwinds like tornadoes. This explains some of their alternative names, like "sun devil."

The simple presence of hot air isn't enough to make a dust devil form. A small pocket of cool air must also be present, and not far above the surface. Since hot air rises faster through cool air than warm air, the cool air of this air pocket sucks the hot air beneath it upwards very strongly, narrowing it into a spout as it rises. Because of its momentum and the narrowing effect, the hot air starts to spin rapidly -- the rapid spin and upward flow become a small but intense updraft -- and in a few moments, a dust devil has come into existence.

The life of a dust devil

Since hot, dry conditions are the prerequisite for a dust devil, there is always at least some dust presence for the devil to pick up. This makes it visible as it twirls lightly across the landscape. The dust devil's dust particles, scraping swiftly against each other thousands of times per second, generate static electricity, and the dust devil quickly develops a powerful electrical field and magnetic field, as well as generating a weak radio signal. The devil thus becomes more than a simple phenomenon of air and dust.

A small dust devil, with winds of about 45 miles per hour and a width of around a yard, can last for a few minutes and makes a sound similar to a hard jet of water from a hose playing over a sheet of corrugated metal. If the dust devil manages to grow, however, with just the right conditions, it can get up to half a mile high and may last for half an hour or more. These dust devils are large enough to cause some damage if they strike human-made structures, although it is rare for them to do so.

Dust devils can only exist when winds are still or very light. This may seem paradoxical, since the dust devil is a whirl of wind, but it is in fact a very fragile updraft because of its small size, and even a fairly light puff of breeze may be enough to disrupt the updraft and 'deflate' the dust devil.