Dust Whirl or Sand Whirl (Dust Devil)
(Section 3.2.2.2.3)Definition: Dust whirl or sand whirl (dust devil): An ensemble of particles of dust or sand, sometimes accompanied by small litter, raised from the ground in the form of a whirling column of varying height with a small diameter and an approximately vertical axis.
Dust whirls or sand whirls occur when the air near the ground is very unstable as, for instance, when the soil is strongly heated by the Sun (insolation). The rotation may be in either direction around the centre. Heights are generally less than 30 m, but heights of up to 1 km have been reported.
Gustnadoes are a very specific dustwhirl. They are generally a weak, short-lived, shallow dust whirl that may occasionally be observed along the edge of a gust front (arcus) of a cumuliform cloud. This feature is in the form of a whirling column of dust that visually resembles the debris cloud of a tornado but without any condensation funnel. A gustnado is not formed in the same manner as a dust devil (that is, by strong heating of the ground), or is this whirling vertically oriented column (vortex) a true tornado. Gustnadoes are rarely strong enough to cause much damage.