Why, that looks like 13th and Coronodo Road. And you know what coronado means. Crowned. Crowned with what? Palm trees. Apparently.
But Chip, how do dust devils form?
*strikes a professorial pose*
Well you see, it occurs the sun heats portions of the ground more intensely than other spots. When sufficient heat builds up a bubble of hot air forms and lifts off the ground. The area vacated by the hot air bubble creates a low pressure area that is filled by surrounding air. If the ground is intensely hot then that hot spot produces a series of bubbles in a continuous stream. That stream of hot air bubbles creates an eddy pattern of cooler air filling the space continuously until the areas are more or less equal. The swirling motion of air moving in can cause the updraft to move off its spot. The dust particles lifted with it appear as a small short-lived tornado.
Hang glider pilots are well aware of this phenominon. They rely upon it for lift.
In the Golden area of Colorado on Lookout Mountain immediately adjacent to the white stone M for Colorado School of Mines, a fold in the mountain occurs, a crease, that funnels such thermals by prevailing winds of the Golden area in summer. The winds push the thermals that develop in the Golden valley against the mountain and the crease in the mountain channels them into a continuous stream. Like people lining up for a concert. This is a launching point for hang glider pilots who take two or three running steps down the mountain and straight into the stream of thermal bubbles and are lifted up immediately.
Spectators gathered at the launching spot see the runners disappear down the hill then see them lifted up several yards beyond. And they look exactly like the flying monkeys in the Wizard of Oz. Except different. Their little legs are dangling and still running and they're are just the cutest little things. And spectacular at the same time. They rise up, up, up, straight up, for over a thousand feet. The thermals are that steady and strong.
Skip the first 30 seconds.
7 comments:
The low pressure isn't from the hot air lifting but from the hot air being less dense than cold air, so the pressure necessary to hold it up from gravity is less at the ground under the hot air than at adjacent ground under cold air. The pressure difference causes the colder air to move sideways at the ground from its higher pressure to the hot air's lower pressure, and that lifts the hot air.
Know what I don't like about either of these ways of saying it?
Neither of them explain the power it has.
The colder air is hardly cold. It's Arizona after all. So it's a matter of hot air surrounding a patch of very hot air that is very not dense. Nearly vacant. Or else the dust devil wouldn't have the force to shake a tree so violently and to lift up dust and papers and crap like a tornado.
The explanation sounds benign compared to what we see happening. It's a tornado!
And less hot hair pushing up very hot air just doesn't cut it. And neither do thermals lifting creating space for cooler air to fill explain it either to my satisfaction.
One time we went out flying to keep up flight hours. There was no other purpose.
It was a hot summer day at Centennial airport, a small place on the outside southern edge of town at the time. This is high altitude, obviously, but there are airports much higher. We used the entire runway to lift off the ground in a Cessna 172 and it rose incredibly slowly.
I asked Myre, why is this taking so long?
He goes, the summer heat and the altitude and the low air pressure make the air too thin to get lift.
If the plane were to stall in mid flight, we'd need a lot of speed and a lot of room for correction.
Oh man, I'm looking outside at the most gore jus lavender on purple sunrise. Wait wait wait I gotta watch this. It only lasts a few minutes. The lavender is taking over the purple. Then it all changes to blue.
It spins because the cold air runs down a pressure gradient and speeds up, and any spin momentum is conserved, the forces being radial. Like an ice skater pulling in her arms.
They break up by kinking, or not getting organized if there's a wind shear.
Hot air airplane performance is hugely affected, first by the wings working with less massive air (being less dense) and second by the propeller, itself a wing, working with less massive air. So, on a 2000' runway, in the summer I'm a hundred feet over the wires taking off and in the winter 500' over the wires.
There are always wires at the ends of runways.
We didn't have these tornados before we started putting in traffic circles.
Tornados are nature's revenge for traffic circles? I wouldn't be surprised. Those traffic circles are so affected --"Look, we're sophisticated Europeans now." Hate 'em.
Traffic circles are pushed by the insurance lobby. The prevent injury T-bone accidents. They make sense in some intersections.
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