by Nayab Naseer

Created on: March 15, 2009

WHAT ARE DUST DEVILS?

A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from half a meter wide and a few meters tall to over 10 meters wide and over 1000 meters tall. They resemble a funnel type chimney through which hot air moves both upward and downward.

Dust Devils are common around the world and known by different names in different locations. People in the southwestern United States refer to them as "dancing devil" or a "sun devil". In Death Valley, California, it takes the name "sand auger" or a "dust whirl". People in the Australian outback call them "willy-willy", whereas people in most parts of Arabia and the Middle East refer to them as "djin" or devils.

WHERE DO THEY FORM?

Dust devils form in flat areas with strong surface heating, usually at the interface between different surface types. Flat conditions provide constant hot air that acts as the "fuel" for these dust devils. They can form on any type of surface, be it dust or asphalt. However, only the presence of dust makes this phenomenon visible to the human eye.

Dust devils form most frequently in desert areas where the sun beats down on the poorly conducting sand surface. It can however, also form even on irrigated fields, dirt roads, and even parking lots where nearby large buildings cause irregular air currents. The presence of hot cinders in recently burned areas is an ideal condition for dust devils to form.

The conditions for the formation of Dust Devils ripen when the skies are clear and there is little or no wind. The surface needs to absorb significant amounts of solar energy to heat the air near the surface and create conditions ideal for the formation of dust devils.

The underlying factor for sustainability of a dust devil is the extreme difference in temperature between the near-surface air and the atmosphere. Windy conditions will destabilize the spinning effect of a dust devil.

HOW THEY FORM?

When the sky is clear and the winds are light, the surface of the earth warms the air near the surface to temperatures well above the temperatures that prevail slightly above the ground. The density of air tends to decrease when temperatures increase and the less dense tend to rise.

When surface heating intensify in a localized pocket, and air there would suddenly become considerably warmer and try to rise, when it immediately encounters the relatively cooler air above. This cool and stable air tries to resist the warm air, just like the surface tension of water. However,

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