On Wednesday, 1 August 2012 22:42:30 UTC+1, Metman2012 wrote:
A friend of mine experienced a very strong dust devil (or something

similar). It was on Wednesday 25th of July at about 2.0pm. It happened

in a field near the A 27 near to The Longman at what used to be

Longman's Nurseries about three miles outside Eastbourne.

The sky was clear blue. Two big plastic tubs were taken right across the

field and rubbish swirled around high in the sky. One green canvas tent

was taken down and the contents of another, which had its end flaps open

were tossed and turned around with two sleeping mats whisked out of the

tent and up into the sky over the field and out of sight. Two heavier

sleeping bags were taken up too but dropped back down again about 25

yards away. They weren't able to recover the mats as they went far away

across the road at the bottom of the field. A play tent was blown up

into the sky and fell about 200 yards down the lane.

Has anyone any idea what might have caused it; the field was of grass,

and it seems strange that such a thing could form over grass. There is a

photograph of paper rubbish which has been blown quite high gently

drifting down. Unfortunately the photos are only of the results not the

devil itself - it was strong enough to deter my friend from rushing to

get her camera.

I think they are a reaction to temperature inversions breaking down in very still layers of atmosphere. In northern Canada and Russia where the snow lies thick under pine trees yet the spring is well along, the air above the canopy can be very warm and yet under the trees very cold.

Similarly in lower latitudes the air on the surface can be warm and higher up of fairly varied temperature.

Then something disturbs the layers and the air erupts. Then they are contained by the surrounding air whose pressure/temperatures are constant. The result is that the air must rise since it is blocked from the sides and from below.

Once risen, there is now a change in the pressure that adjacent air has to fill.

There was a thread on here about 2 or 3 months ago discussing how a larger more powerful vortex behaves. And how it could be replicated in a bottle. Which of course it can't, due to the need for the surrounding air in the real thing to act as a container for the vortex.