Naked Science Forum
Life Sciences => The Environment => Topic started by: Kryptid on 19/08/2004 04:34:57
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I didn't see any meteorology-oriented forums on the board, so I figured that this should go in the General Science Forum.
My first question deals with dust devils developing into tornadoes. In the "Natonial Audubon Society Field Guide to North American Weather", on page 521, I came upon this statement:
Cumulus congestus clouds are sometimes seen above dust devils; on rare occasions the dust devil's rotating updraft merges with that of a growing cumulus congestus cloud to create a hybrid non-supercell tornado.
I find the prospect of dust devils developing into tornadoes to be very interesting, but I have been unable to find any other sources of information regarding this phenomenon. Could anyone here provide links to webpages that might discuss this?
My second question is about waterspouts: are waterspouts ever rated on the Fujita-Pearson scale of tornado intensity? When I refer to waterspouts in this sense, I am talking only about waterspouts that form over water and stay over water. I'm not talking about tornadoes that may happen to pass over water, or to waterspouts that pass onto land. I realize that tornadoes are almost always measured on the Fujita-Pearson scale based on the amount of damage that they cause to their surroundings, so such a similar approach to measuring waterspout intensity would not work.
Waterspouts could potentially be rated on the scale by measuring their windspeeds, which brings me to my third question: what is the fastest windspeed ever recorded in a waterspout?
Any replies would be appreciated.
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Good questions! Here's what little I can come up with.
First, a waterspout is exactly the same as a tornado except that it happens to be over water. The Fujita-Pearson scale is based on wind speed ranges and thus could be used to rate a waterspout. However, it is almost impossible to get accurate wind speed measurements in a tornado, and especially in a waterspout. Weather radar does not have the resolution to show more than an overall rotation.
Here is the scale along with the damage:
F0 is 72 MPH. & Light
F1 is 73-112 MPH & Moderate
F2 113-157 MPH & Considerable
F3 is 158-206 MPH & Severe
F4 is 207-260 MPH & Devastating
F5 is 260-319 MPH & Unbelievable
F6 is 319-379 MPH & Out of this World!
As for a dust devil developing into a tornado, I'm not so sure. I suppose it depends on your definition of a tornado. I've only heard of tornados being associated with storms.
I have no idea about the fastest wind speed measured in a waterspout.
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John - The Eternal Pessimist.
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what's a dust devil?
Am I dead? Am I alive? I'm both!
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.stupid-boy.com%2Fsmilies%2Fkao%2Fotn%2Fcat.gif&hash=e4b91a72c020cc1c5d28487fff5428f1)
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A dust devil is a natural whirlwind similar to a tornado but much smaller and weaker. They are formed from updrafts caused by heated ground, and operate independently of clouds. They are also called sand devils, sand augers, or just whirlwinds. They usually aren't dangerous, though some of the large ones can have winds around 60 miles per hour.
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...and they are the damndest things to see! I used to see them in Illinois, usually whirling around in a corner of a farmer's plowed field. The "black dirt" of Illinois soaked up a lot of heat from the sun and could really spawn these things. They were supposed to be dangerous, and be avoided, but once I had to go chase one. I drove down the road, a lot like in "Twister", then got out of my car and ran into it. It was pretty gusty, and spewing dirt all over the place. In the center it was dead calm, and especially hot, much hotter then on the outside. I don't think I'd do it again, however.
I saw tornados too, or their precursors, funnel clouds. They aren't at all like a dust devil, and I was inspired to drive at right angles to the approaching storm and avoid it. I felt no interest in approaching.
I think if a dust devil were sucked into a tornado, it would be a coincidence, and not much of an event to the tornado.