e dust whirls, or dust devils; sand whirls, or sand pillars; and fire, smoke, and even snow whirls, or spouts. In contrast to the pendant form of the tornado funnel, a dust or sand devil develops from the ground upward, usually under hot, clear-sky conditions. The whirl shape is normally that of a cylindrical column or an inverted cone. The axis of rotation is usually vertical, but it may be inclined. The direction of rotation may be either clockwise or counterclockwise. Vortices with a horizontal axis of rotation are sometimes called rolls, or rotors. Dust and sand whirls are not nearly as violent as tornadoes, although jackrabbits have been lifted by the more intense vortices. The whirls measure in diameter from several centimeters to a few hundred meters, and visible heights from a few meters to at least 1,500 meters. This is probably not the upper limit, for sailplane pilots have used their spirally ascending currents to soar to above 4,570 meters. Like tornadoes and waterspouts, dust and sand devils often appear in groups or series. Eleven of them were simultaneously sighted in Ethiopia, and in the Mojave Desert in eastern California a series of smaller whirls followed in the wake of a larger primary vortex. Such secondary spouts are sometimes referred to in India as "dancing devils." Fire whirlwinds are a problem to the forest rangers that must cope with them. A historical example of a great fire vortex, produced by war, is that which formed over Hamburg following a massive aerial bombing during the night of July 27-28, 1943. The fire fueled a storm of counterclockwise rotation 1.6 to three kilometers in diameter and nearly five kilometers high, with winds estimated to be more than 160 kilometers per hour in some sections....
