A whirlwind is a phenomenon in which a vortex of

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

(a vertically oriented rotating column of air) forms due to instabilities and

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between ...

created by heating and flow ( current) gradients. Whirlwinds can vary in size and last from a couple minutes to a couple hours.

Types

Whirlwinds are subdivided into two types, the great (or major) whirlwinds, and the lesser (or minor) whirlwinds. The first category includes

tornado A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the ...

es, waterspouts, and landspouts. The range of atmospheric vortices constitute a continuum and are difficult to categorize definitively. Some lesser whirlwinds may sometimes form in a similar manner to greater whirlwinds with related increase in intensity. These intermediate types include the gustnado and the fire whirl. Other lesser whirlwinds include dust devils, as well as steam devils, snow devils, debris devils, leaf devils or hay devils, water devils, and shear eddies such as the mountainado and eddy whirlwinds.

Formation

A major whirlwind (such as a

) is formed from supercell

thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...

s (the most powerful type of thunderstorm) or other powerful storms. When the storms start to spin, they react with other high altitude winds, causing a funnel to spin. A

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles, suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

forms over the funnel, making it visible. A minor whirlwind is created when local winds start to spin on the ground. This causes a funnel to form. The funnel moves over the ground, pushed by the winds that first formed it. The funnel picks up materials such as

dust Dust is made of particle size, fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian processes, aeolian process), Types of volcan ...

snow Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water througho ...

as it moves over the ground, thus becoming visible.

Duration

Major whirlwinds last longer because they are formed from very powerful winds, and it is hard, though not impossible, to interrupt them. Minor whirlwinds are not as long-lived; the winds that form them do not last long, and when a minor whirlwind encounters an obstruction (a

building A building or edifice is an enclosed Structure#Load-bearing, structure with a roof, walls and window, windows, usually standing permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, a ...

, a

house A house is a single-unit residential building. It may range in complexity from a rudimentary hut to a complex structure of wood, masonry, concrete or other material, outfitted with plumbing, electrical, and heating, ventilation, and air c ...

, a

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

, etc.), its rotation is interrupted, as is the windflow into it, causing it to dissipate.

Associated weather

Supercell thunderstorms, other powerful storms, and strong winds are seen with major whirlwinds. Wind storms are commonly seen with minor whirlwinds. Also, small, semi-powerful “wind blasts” may be seen before some minor whirlwinds, which can come from a wind storm. These wind blasts can start to rotate and form minor whirlwinds. Winds from other small storms (such as rain storms and local

s) can cause minor whirlwinds to form. Like major whirlwinds, these minor whirlwinds can also be dangerous at times.

Similar phenomena

Eddies and vortices may form in any

fluid In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...

. In water, a

whirlpool A whirlpool is a body of rotating water produced by opposing currents or a current running into an obstacle. Small whirlpools form when a bath or a sink is draining. More powerful ones formed in seas or oceans may be called maelstroms ( ). ''Vo ...

is a similar phenomenon.

External links

Fire whirlwind video September 11, 2012 Alice Springs Australia.

Severe Storm Definitions & Whirlwind Classification
( TORRO)
Whirlwinds
( TORRO)
A 'hay devil' from National Geographic

A longer version of the above but poorer quality

References

{{Cyclones Severe weather and convection Vortices Meteorological phenomena