Landspout

A landspout near North Platte, Nebraska on May 22, 2004. Note the characteristic smooth, tubular shape, similar to that of a waterspout.

A landspout is a term coined by meteorologist Howard B. Bluestein in 1985 for a kind of tornado not associated with the mesocyclone of a thunderstorm.[1] The Glossary of Meteorology defines a landspout as

"Colloquial expression describing tornadoes occurring with a parent cloud in its growth stage and with its vorticity originating in the boundary layer.
The parent cloud does not contain a preexisting mid-level mesocyclone. The landspout was so named because it looks like "a weak Florida Keys waterspout over land."[2]

Landspouts form during the growth stage of a cumulus congestus cloud by stretching boundary layer vorticity upward and into the cumulus congestus's updraft. They generally are smaller and weaker than supercellular tornadoes and do not contain a mesocyclone or pre-existing rotation in the cloud. Because of this, landspouts are rarely detected by Doppler weather radar.[3]

Landspouts share a strong resemblance and development process to that of waterspouts, usually taking the form of a translucent and highly laminar helical tube. Landspouts are considered tornadoes since a 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. Landspouts are most common in semi-arid climates characterized by high cloud bases and considerable low-level instability. These conditions tend to favor the High Plains of the United States from Spring through Summer.

A few landspouts can persist in excess of 15 minutes and have produced F3 damage;[4] however, most of them rarely produce damage given their abbreviated duration, typical slow forward motion, and compact wind field. The potential for damage is further minimized over sparsely populated regions such as the High Plains.

See also

References

  1. ↑ Bluestein, Howard B. (1985). "The formation of a "landspout" in a "broken-line" squall line in Oklahoma". Preprints, 14th Conf. on Severe Local Storms, Indianapolis, American Meteorological Society. pp. 267–270. Retrieved 27 March 2007.
  2. ↑ American Meteorological Society (2000). "Glossary of Meteorology, Second Edition". ametsoc.org. Retrieved 27 March 2007.
  3. ↑ Wakimoto; Wilson (1989). "Non-supercell Tornadoes". Monthly Weather Review. 117: 1113–1140. Bibcode:1989MWRv..117.1113W. doi:10.1175/1520-0493(1989)117<1113:NST>2.0.CO;2.
  4. ↑ Forbes; Wakimoto (1983). "A Concentrated Outbreak of Tornadoes, Downbursts and Microbursts, and Implications Regarding Vortex Classification". Monthly Weather Review. 111: 220–235. Bibcode:1983MWRv..111..220F. doi:10.1175/1520-0493(1983)111<0220:ACOOTD>2.0.CO;2.
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