What Are Dust Devils And How Do They Form?
Many videos have gone viral across the internet, showing dust devils spinning up out of nowhere and causing havoc to nearby people and property. One such video was submitted to KWTX out of Nolanville, Texas, showing a quick spin-up dust devil in a neighborhood street and knocking over garbage bins. Another viral video that began circulating the internet a few years ago, shows a dust devil spinning up in the middle of a little league baseball game in Florida, “catching” the unsuspecting catcher by surprise. So what are dust devils, and why do they appear to form out of nowhere?
What Is Needed For Dust Devil Development?
For a dust devil to form, there are some specific conditions that the atmosphere and the surface must meet.
1) The surface of the earth must be flat, to allow free flow of the surface winds and the different pressures that cause them. This is why you typically see dust devils occurring in places like the deserts of the southwestern United States, open farm fields, sports complexes, or in our case, a neighborhood street.
2) There must be little to no surface wind. To many people this might seem counterintuitive since a dust devil is a literal whirlwind, but its true...too much wind prior to dust devil development can actually lower the chances of a dust devil forming. This is due to the increased wind speeds doing a handful of things, such as cooling the surface of the earth, as well as tearing apart any potential circulations. It is a similar effect to what happens with hurricanes: too much wind shear in the upper atmosphere can actually tear a hurricane apart!
3) It must be sunny and clear! Too much cloud cover can hinder surface heating, just like too much wind can hinder any circulation or rotation. For a dust devil to form, it must be a calm and clear day to allow for the sun to warm the surface. As you will read in a moment, this is likely the most important step in the dust devil cycle.
So to summarize, three things must occur: the surface must be flat, the wind must be calm, and the sky must be clear and sunny! If the above conditions are met, then there is a chance that the lifecycle of a dust devil can begin.
The Dust Devil Cycle
1) Surface Heating
The most important stage in the lifecycle of a dust devil is the first one: the sun heats the earth’s surface. Once warm enough, this step allows for a column of warm air to form and begin rising into the atmosphere.
2) Low Pressure Center Develops
Once the warm air begins rising, after a short while it will develop a small surface low pressure center. This will accelerate the motion of the rising warm air column, as well as cause the surface winds to begin rotating counter clockwise around the pressure center.
3) Surrounding Air Attempts To Rebalance The Air Pressure
Now that the surface low pressure center has developed, the surrounding atmosphere will react by attempting to rebalance the surface pressure. It will do so by rushing even more air into the low pressure circulation, which increases the rotation around the surface low pressure center even further, creating the full whirlwind effect.
4) Dust, Dirt, And Debris Is Picked Up
With whirlwind fully formed, it will now pick up any surrounding dust, dirt, or debris, creating the dust devil as we know it.
5) Surrounding Cool Air Ends The Dust Devil
The dust devil’s lifecycle comes to an end when the surrounding cooler air, cuts off the circulation.
Varying Shapes, Sizes, and Strengths
Just like their distant cousin, tornadoes, dust devils also come in a variety of shapes, sizes, and strengths. However, the most common dust devils are much weaker than the strength of a tornado, only doing enough damage to get some dirt in your eye if you are near one...but some of the largest and strongest dust devils can even reach EF-0 to EF-1 status on the Enhanced Fujita (EF) Scale, which is the scale used to rate tornado damage. The EF scale goes up to EF-5, so even the strongest dust devils are only comparable to some of the weakest tornadoes.
Other Names For Dust Devils
The most common name for these whirlwinds is of course, “Dust Devil” or “Dirt Devil” but other names vary from person to person and even country to country. In Australia, they are referred to as “Willy-Willy’s.” In Ireland, they are referred to as “Sí gaoithe" which is the Irish term for “Fairy Wind.”
Dust Devils On Other Planets
Did you know - Earth isn’t the only planet in our solar system to have dust devils! In fact, they have been observed traversing the surface of Mars. Martian dust devils can be much larger and can stretch miles into the Martian atmosphere, which is only a fraction of the distance that they usually reach into the Earth’s atmosphere.
Conclusion
So, now you know even more about these elusive whirlwinds that are dust devils! Next time you come home to see your trash cans halfway down the street on a clear, warm, and sunny day, check your security camera footage...it might have been a dust devil!
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