Sunday, May 3, 2015

Dust Devils

We are finally getting some warmer air in the great lakes region.  It has been a while since we have gotten some summerlike temperatures.  One of the things that happens when we get the warmer weather at this time of year, we get dust devils.  The American Meterological Society defines a dust devil thusly,  Dust devils are best developed on a hot, calm afternoon with clear skies, in a dry region when intense surface heating causes a very steep lapse rate of temperature in the lowest 100 m of the atmosphere. 

In English, the air just above the ground heats up fast and rises and begins rotating.  At spots where the low air heats up and rises fastest, it creates a hole through the cold air, and more hot air fills in.    They are especially visible in the late spring because the farm fields have just been plowed up creating a dark surface that heats the surface air quickly.  Then the loose dirt is easily picked up by the swirling winds, making the vortex visible.  Add a little wind and these things move across the fields like a mini tornado. 

They are usually quite harmless, but there have been some circumstances where they have caused some damage and created some havoc.  This dust devil at the Rose Bowl this last year caused some real problems and 4 people got hurt.

I was actually stuck by one while driving one time and it moved my car over a lane and sucked my hat off my head and out the window.  Wish I had that one on video.  I did catch a couple small dust devils Saturday May 2nd out in some farm fields. 

Here is a simple graphic to help visually show what is happening with a dust devil.  They don't usually last very long and often only go up about 100 feet.  Some can get rather big though with multiple vorticies.  The wind speeds can be up to 60mph which is enough to do damage when in an area with loose objects.  Often, as in my video, the only thing disturbed was the dirt and some corn leaves left over from the last harvest. 

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