An example of an atmospheric vortex phenomenon is the funnel cloud [1]. The term is used to designate a rotating funnel-shaped cloud of condensed water droplets that extends from the base of a much bigger cloud but does not reach the surface. Funnel clouds are usually visible as cone-shaped or needle-like protuberances from the main cloud base (usually a cumulonimbus or a towering cumulus cloud). Like tornadoes, they frequently, but not exclusively, form in association with severe thunderstorms. It is likely that a number of UFO reports that mention solid-looking, cigar-shaped objects, moving in and out of the clouds ("as if to hide themselves from detection"), can be explained by funnel clouds.

When a funnel cloud touches the ground, the term tornado is used. But not all tornadoes have a visible condensation funnel. Some may appear only as a debris swirl, with no obvious funnel extending below the rotating cloud base. Some meteorologists compare tornadoes to huge pulse generators because of the electric activity that is generated inside tornado funnels. These electrical charges are held responsible for a variety of luminous phenomena that have been reported in association with tornadoes. This can be a white or bluish glow radiating from inside the funnel, or a band of white or blue light rotating around the top. In some instances fireballs, streaks of lightning or bluish sparks (Saint Elmo's fire [2]) have been seen to emerge from the base of tornado funnels. During the night, such side effects can trick anyone into reporting a UFO.

Besides funnel clouds and tornadoes, there are rotating columns of air that are not associated with thunderstorms but which occur in fair weather: they are called landspouts (when they occur over land) and waterspouts (when they form over large bodies of water). Their appearance most often is that of a translucent tube that takes on a dark colour when collecting dust over land, or a bright white colour when drawing up water from a water surface. The UFO literature contains several well-documented reports in which witnesses have described circular UFOs that appeared to be sucking up water from lakes or seas. We believe that most of these incidents can be explained in terms of waterspouts.

Smaller, harmless versions of tornadoes and spouts are designated as wind devils. Contrary to their larger counterparts, they have no parent cloud and form from the surface upward. Depending upon the nature of entrained matter that makes them visible, they are called dust devils, water devils, steam devils, snow devils, fire devils, etc. Dust devils are the more common ones. They are spinning columns of wind that move across bare strips of land such as a parking lot or a playground, taking up dust. Dust devils look like miniature tornadoes and occur mostly on warm, sunny days in clear dry air. They are a common occurrence in desert landscapes and have been photographed and videotaped on numerous occasions.

Dust devils and landspouts can draw sharply defined circular and spiral-shaped patterns in crops. In a few isolated incidents, ufologists have attributed such traces to unworldly visitors.

[1] Wikipedia defines a vortex as "a spinning, often turbulent, flow (or any spiral motion) with closed streamlines".

[2] Saint Elmo's fire is the term to indicate a steady electrical discharge in the shape of a small blue or purple flame-like glow emanating from pointed structures during thunderstorms.