What causes a dust devil?

Question

On a perfectly sunny day I saw a dust devil pick up a metal barn and turn it over - are they like tornados? Does the wind turn counter-clockwise and create a vacuum? How do they form?

Answer 1

Dust devils do Not form like tornados do, tornadoes form from supercell storms, and Dust devils form from the sun heated ground. But they are like a tornado in the way they spin and the way they can lift objects into the air.

Dust devils form most frequently in desert areas where the sun beats down on the poorly conducting sand surface but they can form anywhere the sun is shining bright and hot. They also occur in non-vegetated areas such as parking lots, especially if there are nearby large buildings to help cause irregular air currents. The hot desert or parking lot surface heats a thin layer of air just above--setting the stage for the dance of the sun devils. They can also form over a lake or field.

Even though the hot near-surface air wants to rise up through the cooler, and therefore heavier, air above, quiet air tends to retain a degree of stability--a resistance to new air motion. One can visualize that resistance as something like the surface tension on water--it is strong but it does have a breaking point.

As the stability limit is approached, almost any sort of irregularity can cause the limit to be exceeded so that a bubble of hot surface air bursts upward kind like a hot air balloon which pulls more hot air upward from the hot sun beaten ground. A place on the ground that is hotter than elsewhere will cause the limit to be surpassed there first. Or an irregularity caused by a minor gust of wind, the nearby motion of a car, and even the passage of a rabbit can initiate a dust devil.

The sudden uprush of hot air causes air to speed horizontally inward to the bottom of the newly-forming funnel. One of the rules of the physics of moving air is that its vorticity is preserved. The requirement that vorticity be preserved leads to a large speed-up in the circular motion of air spiraling inward to the bottom of the new funnel.

And so a dust devil is formed; it is an almost self-sustaining whirlwind that maintains a funnel-like chimney through which hot air moves both upward and circularly.

A dust devil may last less than a minute up to several hours. Air speeds up to 70 to 80 mph have been measured in vigorous dust devils. This enables them to pick up dust, leaves or, sometimes, rather large objects. Dust devils sometimes tend to form in groups; a large dust devil is sometimes seen to have little, shorter-lived devils traveling along behind it.

So to put in simple terms it forms when the sun heats up the surface very hot. Usually the air right above the surface is a tad bit "cooler" So if a bubble of the calm hot air below the "cooler" air starts to rise through the “cooler” air above (Hot air rises and cold air sinks) it will cause a chain reaction pulling in more sun heated surface hot air which gets stretched upwards and gets tighter and tighter (like a ballerina that pulls her arms in to spin faster) until it reaches a peak and it starts to die if the flow of hot air gets disrupted by a building, object, normal winds, or if the hot surface air runs out.

Answer 2

What Is A Dust Devil

Answer 3

What Causes Dust

Answer 4

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The same processes the create a tornado creates a dust devil. It's hot air rising, as the air rises it pulls in air from around it to fill the void. Now is could be warm air on the surface or it could be a lot of warm air high above you. As the air is pulled to the center it's stats to swirl, and bingo a dust devil is born. When the air rises enough that it find equilibrium then the dust devil dies. You will often see tiny dust devils in a corner where two buildings meet like an inside corner of a L, and if the inside of the L is facing the sun it will heat up. As the sun heats the building the energy is transfered to the air and as the air heats up rises and a little dust devil forms. Now lastly warm air rises because just like water and most other materials when you heat something up is density is reduced. And it become lighter as it is lighter is floats on top of the colder air. Just like the little air bubbles the rises out of your soda. ~D

Answer 5

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RE:
What causes a dust devil?
On a perfectly sunny day I saw a dust devil pick up a metal barn and turn it over - are they like tornados? Does the wind turn counter-clockwise and create a vacuum? How do they form?

Answer 6

For your real answer, they are form when wind from 2 different directions converage. WIth the convergance in the bill and a little lifting action to bring the vortex(middle of the spinning area) to run paralle with the ground causing the dust devil. they are somewhat like a week tornado, just formed in mild weather not sever thunder storms

Answer 7

If a tar(black substance obtainede from coal) road is laid over a mud road, you can somtimes see small dust devils along the line of separation of the tar road and the mud road during bright sunshine.This is due to the differential heating of the tar road and the mud road.Similarly big dust devils are formed due to the diffential heating of the land surfaces of different types lying side by side on a sunny day.

Answer 8

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Answer 9

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Answer 10

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