Rotation of ‘Dust Devils”

Abstract

THE direction of rotation of ‘dust devils’ has been noted in Lower Egypt and Iraq during the past four years, and the reports received in this office indicate that in about 50 per cent of cases the direction of rotation is clockwise, and in the other 50 per cent anticlockwise. This seems a surprising result, because if a ‘dust devils’ is due to the raising of dust and sand by the vigorous upward movement of air over a limited area, the rising column should assume an anti-clockwise rotation. I had an opportunity recently of watching the formation of numerous small whirls over a hot sandy space. The whirls did not attain a height of more than 2 ft., and the objects raised were leaves and feathers (not sand); the eye of the observer, being at a height of about 4 ft. 6 in., was well above the rotating column. Thirty disturbances were observed in about twenty minutes, and in no case was the rotation other than anti-clockwise (that is, cyclonic).