Whirlwinds, dancing dervishes, willy-willy, whirly whirly; dust devils have many different names across the world.
A dust-devil is a strong, powerful, long-lived tumultuous cyclone. They are very rare however when they strike; although some can be harmless; some can strike with immense power and inflict severe harm to people and their property. They range from many sizes including over 10 meters wide to over 1000 meters tall; this is the largest type of dust devil that has been recorded. A small dust devil ranges from half a meter wide and a few meters tall, these types of dust devils would not cause much harm onto anybody or anything.
How Dust devils form
When hot air collides near the surface of the ground and rises rapidly upwards into a low pressure that lies above, a dust devil is formed. With the right conditions applied, the air then begins to rotate intently. As the air continues to rise with great speed it is pulled upwards causing the spinning effect of the two air pressures to become even more colossal and immense ; the spinning rotates at a much faster rate.
With the spinning motion rotating faster the dust devil causes more hot air to form which is made to flow horizontally at a hasty pace to the bottom of the newly forming whirlpool. As more hot air tears inwards to the emerging whirlpool it substitutes the air that is escalating upwards. This results in the spinning rotation becoming yet more powerful and vigorous, which starts to cause concern for destruction of people and their assets.
Dust devils are very similar to tornadoes by the shape that they form, as they begin to become in full flow. It outlines a funnel-chimney like shape as the hot air soars off the ground as well as in the centre of the whirlpool.
Although the hot air continually rises it meets the cooler air and as a result of this the air starts to cool down. This causes the air to lose its resilience and optimism to carry on its journey of demolition and eventually stops rising. As the cool air returns its balances the hot air that is placed on the outside wall of the dust devil. This acts as a way of calming down the dust devil to reduce its speed.
However this process is affected by the environmental conditions surrounding the dust devil. For example; the hotter the surface the longer the spinning effect is able to maintain itself, for a longer period of time. The surface friction that is caused by the spinning motion continues the forward momentum as well.
The dust devil tries to rebel against the cooler air in a bid to stop it was being as powerful. The cooler air is sucked in by the hotter air which causes the colder air to warm up. The repercussions of this result in the dust devil stopping in its tracks after a matter of seconds. This will occur when the dust devil is not upholding enough speed to retain itself and the temperatures start falling dramatically causing unbalance in the whirlpool, so that it cannot carry on any longer.
Conditions that increase chance of a Dust Devil
A flat terrain could cause a dust devil to strike. If the conditions are dusty or sandy this could prompt the development of the whirlpool formation allowing a dust devil to be created.
Clear sky with little cloud can also fire up a dust devil. This is because the surface is able to receive enough heat energy from the sun, to fuel the dust devil and create the right conditions for it to form.
Air pressure, with light or no wind and low temperatures can also play a part in instigating the formation of a dust devil. The difference in temperature and atmospheric pressure gives the perfect conditions for the dust devil spinning effect o take place; the windy conditions help it on its journey of destruction.
Dust devils are as the name imposes devils of obliteration. They are also not just restricted to our planet and on the 486th day of the Martian year in Mars a dust devil was recorded to have taken place in the 1970s.
Sources
http://en.wikipedia.org/wiki/Dust_devil#Formation
http://www.islandnet.com/~see/weather/almanac/arc2008/alm08jul.htm
