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Name: Rich
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Question:
Is there something like a clear air tornado? I witnessed something that resembled a tornado but the top dissipated into a clear sky. The funnel was a hazy gray color with some counter clock wise rotation and the funnel did not appear to reach the ground. Lateral movement was limited, if any. I saw this on the afternoon of August 22, 2007 slightly southwest of Caldwell, KA. There were only a few, scattered puffy white clouds in an otherwise clear sky. The air temperature was in the 90's and there was a moderate wind from the southwest. I could not associate any wind emanating from the area of the funnel.


Replies:
What you describe sounds like a dust devil. They typically occur on hot, clear days as air warmed by the sun-heated ground rises. They make nice swirling columns, but their wind strength is significantly less than a tornado's.

See, for instance,

http://www.gc.maricopa.edu/earthsci/imagearchive/dust_devils.htm (nice pictures and a little explanatory test);

http://www.gi.alaska.edu/ScienceForum/ASF2/227.html (brief, readable text description)

You can see for yourself if this is what you saw.

Richard Barrans
Department of Physics and Astronomy
University of Wyoming


Rich,

What you saw sounds like a dust devil. These begin from very large horizontal differences in temperature of the ground, for instance the difference in temperature between a grassed area and bare soil under strong sunlight conditions. They can usually only form during light wind conditions, so the dust devil may not move or move only slowly with light wind speeds. Dust devils usually dissipate soon after leaving the proximity of the horizontal temperature difference, but if there is a long horizontal distance over which those differences occur, the dust devil can last for a long time.

I saw a good example of large, long-lasting dust devils just north of the Columbia River in central Oregon in summer 1992. The difference in horizontal temperature came from the cool Columbia River and the very dry hot sand just north of the river. 100 foot tall dust devils formed and moved eastward along the river with the light westerly wind.

David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory


With only the qualitative observations such as lifetime, size, etc., you describe it is not possible to make a meteorological diagnosis, but there is a lower atmospheric disturbance called a "Dust Devil". They are not associated with damaging high winds nor with a long lifetime, but do behave the way you describe.

Vince Calder


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