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Landspout is a term created by atmospheric scientist Howard B. Bluestein in 1985 for a

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 ...

not associated with a mesocyclone. The ''Glossary of Meteorology'' defines a landspout as: Landspouts are typically weaker than mesocyclone-associated tornadoes spawned within

supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone, a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms (su ...

thunderstorms, in which the strongest tornadoes form.

Characteristics

Landspouts are a type of tornado that forms during the growth stage of a cumulus congestus or occasionally a

cumulonimbus Cumulonimbus () is a dense, towering, vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water va ...

cloud when an

updraft In meteorology, an updraft (British English: ''up-draught'') is a small-scale air current, current of rising air, often within a cloud. Overview Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that mov ...

stretches

boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a Boundary (thermodynamic), bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces ...

vorticity upward into a vertical axis and tightens it into a strong

vortex In fluid dynamics, a vortex (: vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...

. The parent clouds are often predominantly liquid when producing landspouts. Landspouts can also occur due to interactions from outflow boundaries, as they can occasionally cause enhanced convergence and vorticity at the surface. These generally are smaller and weaker than supercell tornadoes and do not form from a mesocyclone or pre-existing rotation in the cloud. Because of this lower depth, smaller size, and weaker intensity, landspouts are rarely detected by

Doppler weather radar A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pu ...

. Landspouts share a strong resemblance and development process to that of waterspouts, usually taking the form of a translucent and highly laminar helical tube. "They are typically narrow, rope-like

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...

funnels that form while the thunderstorm cloud is still growing and there is no rotating updraft", according to the

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...

. Landspouts are considered tornadoes since a rapidly rotating column of air is in contact with both the surface and a cumuliform cloud. Not all landspouts are visible, and many are first sighted as debris swirling at the surface before eventually filling in with condensation and dust. Orography can influence landspout (and even mesocyclone tornado) formation. A notable example is the propensity for landspout occurrence in the Denver Convergence Vorticity Zone (DCVZ).

Life cycle

Forming in relation to mesocyclones and under updrafts, a landspout generally lasts for less than 15 minutes; however, they can persist substantially longer, and produce significant damage. Landspouts tend to progress through recognizable stages of formation, maturation, and dissipation, and usually decay when a

downdraft In meteorology, an updraft (British English: ''up-draught'') is a small-scale current of rising air, often within a cloud. Overview Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that move vertically ...

or significant

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

(outflow) occur nearby. They may form in lines or groups of multiple landspouts.

Damage

Landspouts are usually at EF0 level where the intensity of winds is low and weak. However, winds inside a landspout tornado can reach (EF1 wind speeds) .

References

External links

*
Advanced Spotters' Field Guide

Online Tornado FAQ
{{Cyclones Severe weather and convection Tornado Vortices fr:Tornade#Trombes terrestres

Characteristics

Life cycle

Damage

See also

References

External links