| Revision as of 21:50, 24 February 2008 view sourceA. Parrot (talk | contribs)Extended confirmed users, Pending changes reviewers, Rollbackers32,734 edits →Supercell relationship← Previous edit | Revision as of 16:06, 25 February 2008 view source 217.33.71.100 (talk) ←Replaced page with 'GAMING !!!!!!!!'Next edit → | ||
| Line 1: | Line 1: | ||
| GAMING !!!!!!!! | |||
| {{Otheruses1|the weather phenomenon}} | |||
| ]. The tornado itself is the thin tube reaching from the cloud to the ground. The lower part of this tornado is surrounded by a ] dust cloud, kicked up by the tornado's strong winds at the surface]] | |||
| A '''tornado''' is a violently rotating column of air which is in contact with both a ] or, in rare cases, a ] base and the surface of the earth. Tornadoes come in many sizes but are typically in the form of a visible ] ], whose narrow end touches the earth and is often encircled by a cloud of ]. | |||
| Most tornadoes have wind speeds of 110 ](177 ]) or less, are approximately 250 ] (75 ]) across, and travel a few ]s (several ]) before dissipating. Some attain wind speeds of more than 300 mph (480 km/h), stretch more than a mile (1.6 km) across, and stay on the ground for dozens of miles (more than 100 km).<ref name="fastest wind"> | |||
| {{cite web| url = http://cswr.org/dow/DOW.htm| title = Doppler On Wheels| accessdate = 2006-12-29| publisher =| year = 2006}}</ref><ref name="widest tornado">{{cite web| url = http://www.crh.noaa.gov/oax/archive/hallam/hallam.php| title = Hallam Nebraska Tornado | accessdate = 2006-09-08| publisher = Omaha/Valley, NE Weather Forecast Office | date = ]}}</ref><ref name="SPC FAQ"> {{cite web| url = http://www.spc.noaa.gov/faq/tornado| title = The Online Tornado FAQ| accessdate = 2006-09-08| last = Edwards| first = Roger| date = ]| publisher = ]}}</ref> | |||
| Although tornadoes have been observed on every continent except ], most occur in the ].<ref name="Science News 1">{{cite web| url = http://www.sciencenews.org/articles/20020511/bob9.asp| title = Tornado Alley, USA| accessdate = 2006-09-20| last = Perkins| first = Sid| date = ]| work = ]| pages = 296–298}}</ref> They also commonly occur in southern ], south-central and eastern ], east-central ], ], northwestern and southeast ], ], western and southeastern ], and ].<ref name="EB tornado climatology"/> | |||
| <div style="clear:both;"></div> | |||
| {{Weather nav}} | |||
| == Definitions == | |||
| ].]] | |||
| ; Tornado | |||
| : A '''tornado''' is defined by the ''Glossary of Meteorology'' as "a violently rotating column of air, in contact with the ground, either pendant from a ] or underneath a cumuliform cloud, and often (but not always) visible as a ]..."<ref name="Glossary of Meteorology">{{cite web| url = http://amsglossary.allenpress.com/glossary/browse?s=t&p=34| title = Glossary of Meteorology, Second Edition| accessdate = 2006-11-17| publisher = American Meteorological Society| year = 2000| publisher = }}</ref> In practice, for a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base. Scientists have not yet created a complete definition of the word; for example, there is disagreement as to whether separate touchdowns of the same funnel constitute separate tornadoes.<ref name="SPC FAQ"/> | |||
| ; Condensation funnel | |||
| : A tornado is not necessarily visible; however, the intense low pressure caused by the high wind speeds (see ]) and rapid rotation (due to ] balance) usually causes ] in the air to condense into a visible '''condensation funnel'''.<ref name="Science News 1"/> The tornado is the ] of ], not the condensation ]. | |||
| : A ''']''' is a visible condensation funnel with no associated strong winds at the surface. Not all funnel clouds evolve into a tornado. However, many tornadoes are preceded by a funnel cloud. Most tornadoes produce strong winds at the surface while the visible funnel is still above the ground, so it is difficult to discern the difference between a funnel cloud and a tornado from a distance.<ref name="SPC FAQ"/> | |||
| ; Tornado family | |||
| : Occasionally, a single storm will produce more than one tornado, either simultaneously or in succession. Multiple tornadoes produced by the same storm are referred to as a ''']'''. <ref>{{cite web| url = http://www.srh.noaa.gov/oun/severewx/glossary4.php#t| title = A Comprehensive Glossary of Weather Terms for Storm Spotters| accessdate = 2007-02-27| last = Branick| first = Michael| year = 2006| publisher = NOAA}}</ref> | |||
| ; Tornado outbreak | |||
| : Occasionally, several tornadoes are spawned from the same large-scale storm system. If there is no break in activity, this is considered a ''']''', although there are various definitions. A period of several successive days with tornado outbreaks in the same general area (spawned by multiple weather systems) is a '']'', occasionally called an ''extended tornado outbreak''.<ref name="Glossary of Meteorology"/><ref name="significant tornadoes"/><ref>{{cite web| url = http://ams.confex.com/ams/pdfpapers/81933.pdf| title = Tornado Outbreak Day Sequences: Historic Events and Climatology (1875–2003)| accessdate = 2007-03-20| author = Russell S. Schneider| coauthors = Harold E. Brooks, and Joseph T. Schaefer| year = 2004| format = PDF}}</ref> | |||
| == Etymology == | |||
| The word "tornado" is an altered form of the ] word ''tronada'', which means "thunderstorm". This in turn was taken from the ] ''tonare'', meaning "to ]". It most likely reached its present form through a combination of the Spanish ''tronada'' and ''tornar'' ("to turn"); however, this may be a ].<ref name="etymology 1">{{cite web| url = http://www.etymonline.com/index.php?term=tornado| title = Online Etymology Dictionary| accessdate = 2006-09-20| last = Harper| first = Douglas| year = 2001| month = November}}</ref><ref name="etymology 2">{{cite book | title = Merriam Webster's Collegiate Dictionary | url = http://www.m-w.com | edition = 10th Edition| year = 1993 | publisher = Merriam-Webster, Incorporated | location = Springfield, MA | isbn = 0-87779-709-9 }}</ref> Tornadoes are also commonly referred to as ''twisters''.<ref name="TT"/> | |||
| == Types == | |||
| ] outside of ] on ], ].]] | |||
| === True tornadoes === | |||
| ; Multiple vortex tornado | |||
| : A ] is a type of tornado in which two or more columns of spinning air rotate around a common center. Multivortex structure can occur in almost any circulation, but is very often observed in intense tornadoes. | |||
| ; Satellite tornado | |||
| : A ] is a term for a weaker tornado which forms very near a large, strong tornado contained within the same mesocyclone. The satellite tornado may appear to "]" the larger tornado (hence the name), giving the appearance of one, large multi-vortex tornado. However, a satellite tornado is a distinct funnel, and is much smaller than the main funnel.<ref name="SPC FAQ"/> | |||
| ].]] | |||
| ; Waterspout | |||
| : A ] is officially defined by the US ] simply as a tornado over water. However, researchers typically distinguish "fair weather" waterspouts from tornadic waterspouts. | |||
| :* Fair weather waterspouts are less severe but far more common, and are similar in dynamics to ] and ]s.<ref name="USA Today 1"/> They form at the bases of ] cloud towers in tropical and semitropical waters.<ref name="USA Today 1"/> They have relatively weak winds, smooth ] walls, and typically travel very slowly, if at all.<ref name="USA Today 1">{{cite web| url = http://www.usatoday.com/community/chat/0504tornb.htm | title = Tornado Chase 2000| accessdate = 2007-05-19| last = Zittel| first = Dave| date = ] ] | publisher = ]}}</ref> They occur most commonly in the ].<ref name="USA Today 2">{{cite web| url = http://www.usatoday.com/weather/wspouts.htm | title = Waterspouts are tornadoes over water| accessdate = 2007-05-19| last = Golden| first = Joseph| publisher = ]}}</ref> | |||
| :* Tornadic waterspouts are more literally "tornadoes over water". They can form over water like ] tornadoes, or be a land tornado which crosses onto water. Since they form from ]s and can be far more intense, faster, and longer-lived than fair weather waterspouts, they are considered far more dangerous. | |||
| ] on ], ].]] | |||
| ; Landspout | |||
| : '']'' is an unofficial term for a tornado not associated with a ]. The name stems from their characterization as essentially a "fair weather waterspout on land". Waterspouts and landspouts share many defining characteristics, including relative weakness, short lifespan, and a small, smooth condensation funnel which often does not reach the ground. Landspouts also create a distinctively ] cloud of dust when they make contact with the ground, due to their differing mechanics from true mesoform tornadoes. Though usually weaker than classic tornadoes, they still produce strong winds and may cause serious damage.<ref name="SPC FAQ"/><ref name="Advanced Spotter Guide"> {{cite web| url = http://www.weather.gov/os/brochures/adv_spotters.pdf| title = Advanced Spotters' Field Guide| accessdate = 2006-09-20| author = Doswell, Moller, Anderson et al.| year = 2005| format = PDF| publisher = }}</ref> | |||
| === Tornado-like circulations === | |||
| ;Gustnado | |||
| :A '']'' (gust front tornado) is a small, vertical swirl associated with a ] or ]. Because they are technically not associated with the cloud base, there is some debate as to whether or not gustnadoes are actually tornadoes. They are formed when fast moving cold, dry outflow air from a ] is blown through a mass of stationary, warm, moist air near the outflow boundary, resulting in a "rolling" effect (often exemplified through a ]). If low level wind shear is strong enough, the rotation can be turned horizontally (or diagonally) and make contact with the ground. The result is a gustnado.<ref name="SPC FAQ"/><ref name="gustnado AMS"> {{cite web| url = http://amsglossary.allenpress.com/glossary/search?id=gustnado1 | title = Gustnado| accessdate = 2006-09-20| publisher = ] | work = Glossary of Meteorology}}</ref> They usually cause small areas of heavier rotational wind damage among areas of straight-line wind damage. It is also worth noting that since they are absent of any Coriolis influence from a mesocyclone, they seem to be alternately ] and ] without preference. | |||
| ].]] | |||
| ;Dust devil | |||
| :A '']'' resembles a tornado in that it is a vertical swirling column of air. However, they form under clear skies and are rarely as strong as even the weakest tornadoes. They form when a strong convective updraft is formed near the ground on a hot day. If there is enough low level ], the column of hot, rising air can develop a small cyclonic motion that can be seen near the ground. They are not considered tornadoes because they form during fair weather and are not associated with any actual cloud. However, they can, on occasion, result in major damage, especially in ] areas.<ref name="Handy Weather Answer Book"> {{cite book | last = Lyons | first = Walter A | title = The Handy Weather Answer Book | edition = 2nd Edition | year = 1997 | publisher = Visible Ink press | location = ] | isbn = 0-7876-1034-8 | pages = pgs. 175–200 | chapter = Tornadoes }}</ref><ref name="dust devil injury">{{cite web| url = http://www.srh.noaa.gov/ssd/techmemo/sr207.htm| title = Severe Weather Climatology for New Mexico | accessdate = 2006-09-29| author = Charles H. Jones| coauthors = Charlie A. Liles| year = 1999}}</ref> | |||
| ;Winter Waterspout | |||
| :A ], also known as a snow devil, an icespout, an ice devil or a snowspout, is an extremely rare meteorological phenomenon in which a vortex resembling that of a waterspout forms under the base of a snow squall. | |||
| ;Fire whirl | |||
| :Tornado-like circulations occasionally occur near large, intense ]s and are called '']s''. They are not considered tornadoes except in the rare case where they connect to a ] or other cumuliform cloud above. Fire whirls usually are not as strong as tornadoes associated with thunderstorms. However, they can produce significant damage.<ref name="significant tornadoes"/> | |||
| ;Cold air vortex | |||
| :A '']'' or ''shear funnel'' is a tiny, harmless funnel cloud which occasionally forms underneath or on the sides of normal cumuliform clouds, rarely causing any winds at ground-level.<ref name="cold air funnel">{{cite web| url = http://www.crh.noaa.gov/fsd/science/faqsummer.php| title = FAQ's of Summer Weather | accessdate = 2007-02-28| last = Schumacher| first = Phil| year = 2005| publisher = National Weather Service, Sioux Falls, South Dakota}}</ref> Their genesis and mechanics are poorly understood, as they are quite rare, short lived, and hard to spot (due to their non-rotational nature and small size). | |||
| <div style="clear:both;"></div> | |||
| == Characteristics == | |||
| ] | |||
| ] | |||
| === Shape === | |||
| Most tornadoes take on the appearance of a narrow ], a few hundred yards (a few hundred meters) across, with a small ] of ] near the ground. However, tornadoes can appear in many shapes and sizes. | |||
| Small, relatively weak ]s may only be visible as a small swirl of dust on the ground. While the condensation funnel may not extend all the way to the ground, if associated surface winds are greater than 40 mph (64 km/h), the circulation is considered a tornado.<ref name="Advanced Spotter Guide"/> Large single-vortex tornadoes can look like large ] stuck into the ground, and so are known as ''wedge tornadoes'' or ''wedges''. A wedge can be so wide that it appears to be a block of dark clouds, wider than the distance from the cloud base to the ground. Even experienced storm observers may not be able to tell the difference between a low-hanging cloud and a wedge tornado from a distance.<ref name="wedge tornado">{{cite web| url = http://www.spc.noaa.gov/faq/tornado/binger.htm| title = Wedge Tornado | publisher = National Weather Service Storm Prediction Center | accessdate = 2007-02-28| last = Edwards| first = Roger}}</ref> | |||
| Tornadoes in the dissipating stage can resemble narrow tubes or ropes, and often curl or twist into complex shapes. These tornadoes are said to be ''roping out'', or becoming a ''rope tornado''. Multiple-vortex tornadoes can appear as a family of swirls circling a common center, or may be completely obscured by condensation, dust, and debris, appearing to be a single funnel.<ref name="rope tornado">{{cite web| url = http://www.spc.noaa.gov/faq/tornado/el_reno.htm| publisher = National Weather Service Storm Prediction Center | title = Rope Tornado | accessdate = 2007-02-28| last = Edwards| first = Roger}}</ref> | |||
| In addition to these appearances, tornadoes may be obscured completely by rain or dust. These tornadoes are especially dangerous, as even experienced meteorologists might not spot them.<ref name="Handy Weather Answer Book"/> | |||
| === Size === | |||
| In the ], on average tornadoes are around 500 feet (150 m) across, and stay on the ground for 5 miles (8 km).<ref name="Handy Weather Answer Book"/> Yet, there is an extremely wide range of tornado sizes, even for typical tornadoes. Weak tornadoes, or strong but dissipating tornadoes, can be exceedingly narrow, sometimes only a few feet across. A tornado was once reported to have a damage path only 7 feet (2 m) long.<ref name="Handy Weather Answer Book"/> On the other end of the spectrum, wedge tornadoes can have a damage path a mile (1.6 km) wide or more. A ] on ], ] was at one point 2.5 miles (4 km) wide at the ground.<ref name="widest tornado">"." ''''. November 2, 2005.</ref> | |||
| In terms of path length, the ], which affected parts of ], ], and ] on ], ], was officially on the ground continuously for 219 miles (352 km). Many tornadoes which appear to have path lengths of {{convert|100|mi|km}} or longer are actually a family of tornadoes which have formed in quick succession; however, there is no substantial evidence that this occurred in the case of the Tri-State Tornado.<ref name="significant tornadoes">{{cite book | last = Grazulis | first = Thomas P | title = Significant Tornadoes 1680–1991 | year = July | month = 1993 | publisher = The Tornado Project of Environmental Films | location = St. Johnsbury, VT | isbn = 1-879362-03-1 }}</ref> In fact, modern reanalysis of the path suggests that the tornado began 15 miles (24 km) further west than previously thought.<ref>{{cite web| url = http://apollo.lsc.vsc.edu/ams/AMS%20VP/Storm%20Conference/NESC%20Presentations/32ndNESC_Presentation/Banquet/Doswell.ppt| title = The Tri-State Tornado of 18 March 1925 Reanalysis Project| accessdate = 2007-04-07| last = Doswell| first = Dr. Charles A, III| format = Powerpoint Presentation}}</ref> | |||
| === Appearance === | |||
| Tornadoes can have a wide range of colors, depending on the environment in which they form. Those which form in a dry environment can be nearly invisible, marked only by swirling debris at the base of the funnel. Condensation funnels which pick up little or no debris can be gray to white. While travelling over a body of water as a waterspout, they can turn very white or even blue. Funnels which move slowly, ingesting a lot of debris and dirt, are usually darker, taking on the color of debris. Tornadoes in the ] can turn red because of the reddish tint of the soil, and tornadoes in mountainous areas can travel over snow-covered ground, turning brilliantly white.<ref name="Handy Weather Answer Book"/> | |||
| <div style="clear: both"></div> | |||
| ] tornado of ], ], taken at nearly the same time by two photographers. In the top picture, the tornado is ''front-lit'', with the sun behind the east-facing ], so the funnel appears nearly white. In the lower image, where the camera is facing the opposite direction, the tornado is ''back-lit'', with the sun behind the clouds.<ref name="PD tornado images">{{cite web| url = http://www.spc.noaa.gov/faq/tornado/torscans.htm | title = Public Domain Tornado Images| accessdate = 2006-10-20| last = Edwards| first = Roger| publisher = ]}}</ref>]] | |||
| Lighting conditions are a major factor in the appearance of a tornado. A tornado which is "]" (viewed with the sun behind it) appears very dark. The same tornado, viewed with the sun at the observer's back, may appear gray or brilliant white. Tornadoes which occur near the time of sunset can be many different colors, appearing in hues of yellow, orange, and pink.<ref name="target tornado">{{cite video | people = Lloyd, Linda Mercer | year = 1996 | title = Target: Tornado | medium = Videotape | location = ] | publisher = ]}}</ref><ref name="TT">{{cite web| url = http://www.tornadoproject.com/cellar/tttttttt.htm| title = The Tornado Project's Terrific, Timeless and Sometimes Trivial Truths about Those Terrifying Twirling Twisters!| accessdate = 2007-03-21| publisher = The Tornado Project| year = 1999}}</ref> | |||
| Dust kicked up by the winds of the parent thunderstorm, heavy rain and hail, and the darkness of night are all factors which can reduce the visibility of tornadoes. Tornadoes occurring in these conditions are especially dangerous, since only ] observations, or possibly the sound of an approaching tornado, serve as any warning to those in the storm's path. Fortunately most significant tornadoes form under the storm's ''rain-free base'', or the area under the thunderstorm's updraft, where there is little or no rain. In addition, most tornadoes occur in the late afternoon, when the bright sun can penetrate even the thickest clouds.<ref name="significant tornadoes"/> Also, night-time tornadoes are often illuminated by frequent lightning. | |||
| There is mounting evidence, including ] mobile radar images and eyewitness accounts, that most tornadoes have a clear, calm center with extremely low pressure, akin to the ] of ]s. This area would be clear (possibly full of dust), have relatively light winds, and be very dark, since the light would be blocked by swirling debris on the outside of the tornado. Lightning is said to be the source of illumination for those who claim to have seen the interior of a tornado.<ref name="Science News 2">{{cite web| url = http://www.sciencenews.org/pages/sn_arc99/5_15_99/fob1.htm| title = Oklahoma Tornado Sets Wind Record| accessdate = 2006-10-20| author = R. Monastersky| date = ]| work = Science News| pages = 308–309}}</ref><ref name="inside eyewitness">{{cite web| url = http://docs.lib.noaa.gov/rescue/mwr/058/mwr-058-05-0205.pdf| title = Seeing the Inside of a Tornado| accessdate = 2006-10-20| last = Justice| first = Alonzo A| year = 1930| month = May| format = PDF| work = ]| publisher = ]| pages = 205–206}}</ref><ref>{{cite book | last = Hall | first = Roy S. | title = Tornadoes | year = 2003 | publisher = Greenhaven Press | location = Farmington Hills, MI | isbn = 0-7377-1473-5 | pages = 59–65 | chapter = Inside a Texas Tornado}}</ref> | |||
| === Rotation === | |||
| Tornadoes normally rotate ] in direction (counterclockwise in the ], clockwise in the ]). While large-scale storms always rotate cyclonically due to the ], thunderstorms and tornadoes are so small that the direct influence of Coriolis effect is inconsequential, as indicated by their large ]s. Supercells and tornadoes rotate cyclonically in numerical simulations even when the Coriolis effect is neglected.<ref name="Origin of Updraft Rotation in Supercells">{{cite journal| last = Davies-Jones| first = Robert| authorlink = Robert Davies-Jones| title = Streamwise Vorticity: The Origin of Updraft Rotation in Supercell Storms| journal = ]| volume = 41| issue = 20| pages = 2991–3006| publisher = ]| date = October 1984| url = http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469(1984)041%3C2991%3ASVTOOU%3E2.0.CO%3B2| accessdate = 2007-04-13}}</ref><ref name="Rotation and Propagation of Simulated Supercells">{{cite journal| last = Rotunno| first = Richard| authorlink = Richard Totunno| coauthors = Joseph Klemp| title = On the Rotation and Propagation of Simulated Supercell Thunderstorms| journal = ]| volume = 42| issue = 3| pages = 271–292| publisher = ]| date = February 1985| url = http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469(1985)042%3C0271%3AOTRAPO%3E2.0.CO%3B2| accessdate = 2007-04-13}}</ref> | |||
| Low-level ]s and tornadoes owe their rotation to complex processes within the supercell and ambient environment.<ref name="Tornado Development and Decay within a Supercell">{{cite journal| last = Wicker| first = Louis J.| authorlink = Louis J. Wicker| coauthors = Robert B. Wilhelmson| title = Simulation and Analysis of Tornado Development and Decay within a Three-Dimensional Supercell Thunderstorm| journal = ]| volume = 52| issue = 15| pages = 2675–2703| publisher = ]| date = August 1995| url = http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469(1995)052%3C2675%3ASAAOTD%3E2.0.CO%3B2| accessdate = 2007-04-13}}</ref> | |||
| Approximately 1% of tornadoes rotate in an anticyclonic direction. Typically, only landspouts and gustnados rotate anticyclonically, and usually only those which form on the anticyclonic shear side of the descending ] in a cyclonic supercell.<ref name="Recent Example of an anticyclonic tornado in El Reno, OK">{{cite web| url = http://www.weather.com/blog/weather/8_9262.html| title = weather.com - Blog: The Weather Channel on weather news, hurricanes, tornadoes & meteorology| accessdate = 2006-12-30| last = Forbes| first = Greg}}</ref> However, on rare occasions, ]es form in association with the mesoanticyclone of an anticyclonic supercell, in the same manner as the typical cyclonic tornado, or as a companion tornado—either as a satellite tornado or associated with anticyclonic eddies within a supercell.<ref name="Sunnyvale Tornado">{{cite web| url = http://tornado.sfsu.edu/geosciences/StormChasing/Cases/Sunnyvale/Sunnyvale.html| title = Sunnyvale and Los Altos, CA Tornadoes May 4, 1998| accessdate = 2006-10-20| last = Monteverdi| first = John| date = ]}}</ref> | |||
| === Sound and seismology === | |||
| Tornadoes emit widely on the ] ] and the sounds are cased by multiple mechanisms. Various sounds of tornadoes have been reported throughout time, mostly related to familiar sounds for the witness and generally some variation of a whooshing roar. Popularly reported sounds include a freight ], rushing rapids or ], a ] from close proximity, or combinations of these. Many tornadoes are not audible from much distance; the nature and propagation distance of the audible sound depends on atmospheric conditions and topography. | |||
| The winds of the tornado vortex and of constituent ] ], as well as airflow interaction with the surface and debris, contribute to the sounds. Funnel clouds also produce sounds. Funnel clouds and small tornadoes are reported as whistling, whining, humming, or the buzzing of innumerable ]s or electricity, or more or less harmonic, whereas many tornadoes are reported as a continuous, deep rumbling, or an irregular sound of “noise”.<ref name="tornado music">{{cite journal |last=Abdullah |first=Abdul |authorlink=Abdul Jabber Adbullah |title=The "Musical" Sound Emitted by a Tornado" |journal=] |volume=94 |issue=4 |pages=213–220 |publisher=] |date=April 1966 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0493%281966%29094%3C0213%3ATMSEBA%3E2.3.CO%3B2 }}</ref> | |||
| Since many tornadoes are audible only in very close proximity, sound is not reliable warning of a tornado. And, any strong, damaging wind, even a severe hail volley or continuous thunder in a thunderstorm may produce a roaring sound.<ref name="sound obs">{{cite journal |last=Hoadley |first=David |authorlink=David K. Hoadley |title=Tornado Sound Experiences |journal=] |volume=6 |issue=3 |pages=5-9 |date=March 1983 |url=http://www.stormtrack.org/archive/0636.htm }}</ref> | |||
| ]'s .]] | |||
| Tornadoes also produce identifiable inaudible ] signatures.<ref name="tornado infrasonics">{{cite journal |last=Bedard |first=A. J. |authorlink=Alfred J. Bedard, Jr. |title=Low-Frequency Atmospheric Acoustic Energy Associated with Vortices Produced by Thunderstorms |journal=] |volume=133 |issue=1 |pages=241–263 |publisher=] |date=January 2005 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2FMWR-2851.1 }}</ref> | |||
| Unlike audible signatures, tornadic signatures have been isolated; due to the long distance propagation of low-frequency sound, efforts are ongoing to develop tornado prediction and detection devices with additional value in understanding tornado morphology, dynamics, and creation.<ref name="field programs history"/> Tornadoes also produce a detectable ] signature, and research continues on isolating it and understanding the process.<ref name="tornado seismic signal">{{cite journal |last=Tatom |first=Frank |authorlink=Frank B. Tatom |coauthors=Kevin R. Knupp, and Stanley J. Vitto |title=Tornado Detection Based on Seismic Signal |journal=] |volume=34 |issue=2 |pages=572–582 |publisher=] |date=February 1995 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0450(1995)034%3C0572%3ATDBOSS%3E2.0.CO%3B2 }}</ref> | |||
| === Electromagnetic, lightning, and other effects === | |||
| Tornadoes emit on the ], for example, with ] and ] effects detected.<ref name="field programs history"/><ref name="in situ history">{{cite conference |first=Tim M. |last=Samaras |authorlink=Timothy M. Samaras |title=A Historical Perspective of In-Situ Observations within Tornado Cores |booktitle=Preprints of the 22nd Conference on Severe Local Storms |publisher=] |date=October 2004 |location=Hyannis, MA |url=http://ams.confex.com/ams/11aram22sls/techprogram/paper_81153.htm }}</ref> The effects vary, mostly with little observed consistency. | |||
| Correlations with patterns of ] activity have also been observed, but little in way of consistent correlations have been advanced. Tornadic storms do not contain more lightning than other storms, and some tornadic cells never contain lightning. More often that not, overall cloud-to-ground (CG) lightning activity decreases as a tornado reaches the surface and returns to the baseline level when the tornado lifts. In many cases, very intense tornadoes and thunderstorms exhibit an increased and anomalous dominance in positive polarity CG discharges.<ref name="CG tor">{{cite journal |last=Perez |first=Antony H. |coauthors=Louis J. Wicker, and Richard E. Orville |title=Characteristics of Cloud-to-Ground Lightning Associated with Violent Tornadoes |journal=] |volume=12 |issue =3 |pages=428-437 |date=September 1997 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0434(1997)012%3C0428%3ACOCTGL%3E2.0.CO%3B2 }}</ref> ] and lightning have little to nothing to do directly with what drives tornadoes (tornadoes are basically a ] phenomenon), though there are likely connections with the storm and environment affecting both phenomena. | |||
| ] has been reported in the past, and is probably due to misidentification of external light sources such as lightning, city lights, and power flashes from broken lines, as internal sources are now uncommonly reported and are not known to ever been recorded. | |||
| In addition to winds, tornadoes also exhibit changes in atmospheric variables such as ], ], and ]. For example, on ], ] near ], a probe measured a 100 ] (]) (2.95 ]) pressure deficit. The pressure dropped gradually as the vortex approached then dropped extremely rapidly to 850 ] (]) (25.10 ]) in the core of the violent tornado before rising rapidly as the vortex moved away, resulting in a V-shape pressure trace. Temperature tends to decrease and moisture content to increase in the immediate vicinity of a tornado.<ref name="Manchester">{{cite conference |first=Julian J. |last=Lee |coauthors=Timothy P. Samaras, Carl R. Young |title=Pressure Measurements at the ground in an F-4 tornado |booktitle=Preprints of the 22nd Conference on Severe Local Storms |publisher=] |date=October 2004 |location=Hyannis, Massachusetts |url=http://ams.confex.com/ams/11aram22sls/techprogram/paper_81700.htm }}</ref> | |||
| == Life cycle == | |||
| ], was one of the best-observed violent tornadoes in history.]] | |||
| {{Further|]}} | |||
| === Supercell relationship === | |||
| {{seealso|Supercell}} | |||
| Tornadoes often develop from a class of thunderstorms known as '']s''. Supercells contain ]s, an area of organized rotation a few miles up in the atmosphere, usually 1–6 miles (2–10 km) across. Most intense tornadoes ('''EF3''' to '''EF5''' on the ]) develop from supercells. In addition to tornadoes, very heavy rain, frequent lightning, strong wind gusts, and hail are common in such storms. | |||
| Most tornadoes from supercells follow a recognizable life cycle.<ref name="Advanced Spotter Guide"/> That begins when increasing rainfall drags with it an area of quickly descending air known as the ] (RFD). This downdraft accelerates as it approaches the ground, and drags the supercell's rotating mesocyclone towards the ground with it. | |||
| === Formation === | |||
| As the mesocyclone approaches the ground, a visible condensation funnel appears to descend from the base of the storm, often from a rotating ]. As the funnel descends, the RFD also reaches the ground, creating a gust front that can cause damage a good distance from the tornado. Usually, the funnel cloud becomes a tornado within minutes of the RFD reaching the ground. | |||
| === Maturity === | |||
| Initially, the tornado has a good source of warm, moist inflow to power it, so it grows until it reaches the ''mature stage''. This can last anywhere from a few minutes to more than an hour, and during that time a tornado often causes the most damage, and in rare cases can be more than one mile (1.6 km) across. Meanwhile, the RFD, now an area of cool surface winds, begins to wrap around the tornado, cutting off the inflow of warm air which feeds the tornado. | |||
| === Demise === | |||
| As the RFD completely wraps around and chokes off the tornado's air supply, the vortex begins to weaken, and become thin and rope-like. This is the ''dissipating stage''; often lasting no more than a few minutes, after which the tornado fizzles. During this stage the shape of the tornado becomes highly influenced by the winds of the parent storm, and can be blown into fantastic patterns.<ref name="PD tornado images"/><ref name="target tornado"/><ref name="significant tornadoes"/> | |||
| As the tornado enters the dissipating stage, its associated mesocyclone often weakens as well, as the rear flank downdraft cuts off the inflow powering it. In particularly intense supercells tornadoes can develop ]. As the first mesocyclone and associated tornado dissipate, the storm's inflow may be concentrated into a new area closer to the center of the storm. If a new mesocyclone develops, the cycle may start again, producing one or more new tornadoes. Occasionally, the old (''occluded'') mesocyclone and the new mesocyclone produce a tornado at the same time. | |||
| Though this is a widely-accepted theory for how most tornadoes form, live, and die, it does not explain the formation of smaller tornadoes, such as landspouts, long-lived tornadoes, or tornadoes with multiple vortices. These each have different mechanisms which influence their development—however, most tornadoes follow a pattern similar to this one.<ref name ="tornadogenesis"> {{cite web| url = http://ams.allenpress.com/amsonline/?request=get-document&doi=10.1175%2F1520-0469(2003)060%3C0795:TRFTTO%3E2.0.CO%3B2| title = Tornadogenesis Resulting from the Transport of Circulation by a Downdraft: Idealized Numerical Simulations| accessdate = 2006-09-13| author = Markowski, Straka, and Rasmussen| date = ]| work = ]: Vol. 60, No. 6| pages = 28}}</ref> | |||
| <div style="clear: both"></div> | |||
| == Intensity and damage == | |||
| ]''' damage. Here, the roof has been substantially damaged, and the ] blown outwards, but the walls and supporting structures are still intact.]] | |||
| {{main|Tornado intensity and damage}} | |||
| The ] and the ] rate tornadoes by damage caused. The Enhanced Fujita Scale was an upgrade to the older Fujita scale, with engineered (by ]) wind estimates and better damage descriptions, but was designed so that a tornado rated on the Fujita scale would receive the same numerical rating. An '''EF0''' tornado will likely damage trees but not substantial structures, whereas an '''EF5''' tornado can rip buildings off their foundations leaving them bare and even deform large ]s. The similar ] ranges from a '''T0''' for extremely weak tornadoes to '''T11''' for the most powerful known tornadoes. ] ] data, ], and ground swirl patterns (cycloidal marks) may also be analyzed to determine intensity and award a rating. | |||
| Tornadoes vary in intensity regardless of shape, size, and location, though strong tornadoes are typically larger than weak tornadoes. The association with track length and duration also varies, although longer track tornadoes tend to be stronger.<ref name ="width/length intensity relationship"> {{cite web| url = http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0434%282004%29019%3C0310%3AOTROTP%3E2.0.CO%3B2| title = On the Relationship of Tornado Path Length and Width to Intensity| accessdate = 2007-04-06| author = Brooks, Harold E.| date = ]| work = ]: Vol. 19, No. 2| pages = 310–319}}</ref> In the case of violent tornadoes, only a small portion of the path is of violent intensity, most of the higher intensity from ].<ref name="significant tornadoes"/> | |||
| In the United States, 80% of tornadoes are '''EF0''' and '''EF1''' ('''T0''' through '''T3''') tornadoes. The rate of occurrence drops off quickly with increasing strength—less than 1% are violent tornadoes, stronger than '''EF4''', '''T8'''.<ref name="Basic Spotter Guide">{{cite web| url = http://www.nws.noaa.gov/om/brochures/basicspot.pdf| title = Basic Spotters’ Field Guide| accessdate = 2006-11-01| author = Edwards, Moller, Purpura et al| year = 2005| format = PDF| publisher = , }}</ref> | |||
| Outside the United States, areas in south-central Asia, and perhaps portions of southeastern South America and southern Africa, violent tornadoes are extremely rare. This is apparently mostly due to the lesser number of tornadoes overall, as research shows that tornado intensity distributions are fairly similar worldwide. A few significant tornadoes occur annually in Europe, Asia, southern Africa, and southeastern South America, respectively.<ref name ="intensity distribution"> {{cite web| url = http://www.essl.org/people/dotzek/pdf/ecss02p.pdf| format = PDF | title = Statistical modeling of tornado intensity distributions| accessdate = 2007-04-06| author = Dotzek, Nikolai, Jürgen Grieser, Harold E. Brooks| date = ]| work = ]: Vol. 67–68| pages = 163–187}}</ref> | |||
| <div style="clear: both"></div> | |||
| == Climatology == | |||
| {{main|Tornado climatology}} | |||
| ] | |||
| ].]] | |||
| The United States has the most tornadoes of any country, about four times more than estimated in all of Europe, not including waterspouts.<ref name="European tornado climatology">{{cite journal | author = Dr. Nikolai Dotzek | year = 2003 | month = March | title = An updated estimate of tornado occurrence in Europe | journal = Atmospheric Research | url = http://www.essl.org/people/dotzek/pdf/ecss02s.pdf | format = PDF | accessdate = 2007-03-11 }}</ref> | |||
| This is mostly due to the unique geography of the continent. ] is a relatively large continent that extends from the ] south into ] areas, and has no major east-west mountain range to block air flow between these two areas. In the ], where most tornadoes of the world occur, the ] block moisture and atmospheric flow, allowing drier air at mid-levels of the ], and causing ] downstream to the east of the mountains. The desert Southwest also feeds drier air and the ], while the ] fuels abundant low-level moisture. This unique topography allows for many collisions of warm and cold air, the conditions that breed strong, long-lived storms many times a year. A large portion of these tornadoes form in an area of the ] known as ].<ref name="Science News 1"/> This area extends into Canada, particularly ] and the ]. Strong tornadoes also occasionally occur in northern ]. | |||
| The United States averages about 1,200 tornadoes per year. The ] has the highest average number of recorded tornadoes per area of any country (more than 20, or 0.0013 per sq mi (0.00048 per km²), annually), followed by the ] (around 33, or 0.00035 per sq mi (0.00013 per km²), per year), but most are small and cause minor damage. In absolute number of events, ignoring area, the UK experiences more tornadoes than any other European country, excluding waterspouts.<ref name="European tornado climatology"/> | |||
| ] and surrounding areas of eastern ] suffer from tornadoes of equal severity to those in the US, and occurring more frequently than anywhere else in the world, but such events are under-reported due to the scarcity of media coverage in third-world countries. Tornados kill about 179 people per year in Bangladesh, many more than in the US. This is due to high population density, poor quality of construction, lack of tornado safety knowledge, and other factors.<ref name="Bangladesh tornado">{{cite web| url = http://www.colorado.edu/hazards/qr/qr169/qr169.pdf| title = The April 2004 Tornado in North-Central Bangladesh: A Case for Introducing Tornado Forecasting and Warning Systems| accessdate = 2006-08-17| author = Paul, Bhuiyan| year = 2004}}</ref> | |||
| Other areas of the world that have frequent tornadoes include ], parts of ], ], and southern ], as well as portions of ], ] and ], and far eastern ].<ref name="EB tornado climatology">{{cite web| url = http://www.britannica.com/eb/article-218357/tornado| title = Tornado: Global occurrence| accessdate = 2007-03-21| author = Encyclopædia Britannica| authorlink = Encyclopædia Britannica}}</ref> | |||
| Tornadoes are most common in spring and least common in winter.<ref name="significant tornadoes"/> Since autumn and spring are transitional periods (warm to cool and vice versa) there are more chances of cooler air meeting with warmer air, resulting in thunderstorms. Tornadoes can also be caused by ]ing ]s, which tend to occur in the late summer and autumn. But favorable conditions can occur at any time of the year. | |||
| Tornado occurrence is highly dependent on the time of day, because of ].<ref name="tornado time of day">{{cite web| url = http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0493(1978)106%3C1172%3AAATC%3E2.0.CO%3B2| title = An Augmented Tornado Climatology| accessdate = 2006-09-13| author = Kelly, Schaefer, McNulty, et al.| date = ]| format = PDF| work = ]| pages = 12}}</ref> Worldwide, most tornadoes occur in the late afternoon, between 3 and 7 pm local time, with a peak near 5 pm.<ref>{{cite web| url = http://www.britannica.com/eb/article-218362/tornado| title = Tornado: Diurnal patterns| accessdate = 2007-02-27| year = 2007| work = Encyclopædia Britannica Online| pages = pg. 6}}</ref><ref>{{cite journal | last = Holzer | first = A. M. | year = 2000 | title = Tornado Climatology of Austria | journal = Atmospheric Research | issue = 56 | pages = 203–211 | url = http://tordach.org/at/Tornado_climatology_of_Austria.html | accessdate = 2007-02-27 }}</ref><ref> {{cite journal | last = Dotzek | first = Nikolai | date = ] | title = Tornadoes in Germany| journal = Atmospheric Research | url = http://essl.org/people/dotzek/pdf/etss_1p.pdf | format = PDF | accessdate = 2007-02-27}}</ref><ref>{{cite web| url = http://www.weathersa.co.za/References/Tornado.jsp | title = South African Tornadoes| accessdate = 2007-05-21| year = 2003| publisher = ]}}</ref><ref>{{cite web| url = http://bangladeshtornadoes.org/climo/btorcli0.htm | title = Bangladesh Tornado Climatology| accessdate = 2007-02-27| last = Finch | first = Jonathan D. | coauthors = Dewan, Ashraf M}}</ref> | |||
| However, destructive tornadoes can occur at any time of day. The ] of 1936, one of the deadliest tornadoes in history, occurred at 8:30 am local time.<ref name="significant tornadoes"/> | |||
| === Associations to climate and climate change === | |||
| Associations to various ] and environmental trends exist. For example, an increase in the ] of source region (e.g. Gulf of Mexico and ]) increases moisture content, potentially fueling an increase in severe weather and tornado activity, particularly in the cool season.<ref name=”Edwards GoM”>{{cite conference |first=Roger |last=Edwards |coauthors=Steven J. Weiss |title=Comparisons between Gulf of Mexico Sea Surface Temperature Anomalies and Southern U.S. Severe Thunderstorm Frequency in the Cool Season |booktitle=18th Conference on Severe Local Storms |pages= |publisher=] |date=Feb 1996 |location=San Francisco, CA |url=http://www.spc.noaa.gov/publications/edwards/sstsvr.htm }}</ref> | |||
| Although insufficient support exists to make conclusions, evidence does suggest that the ] is weakly correlated with some changes in tornado activity; which vary by season and region as well as whether the ] phase is that of ] or ].<ref name="AGU ENSO tor">{{cite conference |first=Ashton Robinson |last=Cook |coauthors=Joseph T. Schaefer |title=The Relation of El Nino Southern Oscillation (ENSO) to Winter Tornado Outbreaks |booktitle=19th Conference on Probability and Statistics |publisher=] |date=] |location=New Orleans, LA |url=http://ams.confex.com/ams/88Annual/techprogram/paper_134378.htm }}</ref> | |||
| Climatic shifts affect tornadoes via ]s in shifting the jet stream and the larger weather patterns. The climate-tornado link is confounded by the forces affecting larger patterns and by the local, nuanced nature of tornadoes. Although it is reasonable that the ] phenomenon of ] may affect tornado activity, any such effect is not yet identifiable due to the complexity, local nature of the storms, and database quality issues. Any effect would vary by region.<ref name=”IPCC4-WGI”>{{cite book |last=Solomon |first=Susan |coauthors=et al |authorlink=Susan Solomon |title=Climate Change 2007 - The Physical Science Basis |series=Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=] for the ] |date=2007 |location=Cambridge, UK and New York, USA |url=http://ipcc-wg1.ucar.edu/wg1/wg1-report.html |isbn=9780521880091 }}</ref> | |||
| == Prediction == | |||
| ] maps issued by the ] during the heart of the ]. The top map indicates the risk of general ] (including large ], damaging winds, and tornadoes), while the bottom map specifically shows the percent risk of a tornado forming within 25 miles (40 km) of any point within the enclosed area. The hashed area on the bottom map indicates a 10% or greater risk of an ] or stronger tornado forming within 25 miles (40 km) of a point.]] | |||
| ] is handled regionally by many national and international agencies. For the most part, they are also in charge of the prediction of conditions conducive to tornado development. | |||
| ===Australia=== | |||
| Severe thunderstorm warnings are provided to Australia by the ]. The country is in the middle of an upgrade to ] ] systems, with their first benchmark of installing six new radars reached in July 2006.<ref>{{cite web| url = http://www.bom.gov.au/weather/nsw/sevwx/warning_service.shtml | title = Severe Thunderstorm Warning Service in NSW and the ACT| accessdate = 2006-10-25| publisher = Australian Government Bureau of Meteorology| year = 2006}}</ref> | |||
| ===Europe=== | |||
| The ] founded a project in 2002 called the European Severe Storms virtual Laboratory, or ESSL, which is meant to fully document tornado occurrence across the continent. The ESTOFEX (European Storm Forecast Experiment) arm of the project also issues one day forecasts for severe weather likelihood.<ref>{{cite web| url = http://essl.org/ESWD| title = European Severe Weather Database | accessdate = 2006-10-25| publisher = European Severe Storms Laboratory}}</ref> In Germany, Austria, and Switzerland, an organization known as ] collects information regarding tornadoes, waterspouts, and downbursts from Germany, Austria, and Switzerland. A secondary goal is collect all severe weather information. This project is meant to fully document severe weather activity in these three countries.<ref>{{cite web| url = http://www.tordach.org/| title = TorDACH Homepage| accessdate = 2006-10-25| publisher = TorDACH}}</ref> | |||
| ====United Kingdom==== | |||
| In the United Kingdom, the ] makes experimental predictions. The ] provides official forecasts for the UK. | |||
| ===United States=== | |||
| In the United States, generalized severe weather predictions are issued by the ], based in ]. For the next one, two, and three days, respectively, they will issue categorical and probabilistic forecasts of severe weather, including tornadoes. There is also a more general forecast issued for the four to eight day period. Just prior to the expected onset of an organized severe weather threat, SPC issues severe thunderstorm and tornado watches, in collaboration with local ] offices. ] are issued by local National Weather Service offices when a severe thunderstorm or tornado is occurring or imminent. | |||
| ===Other areas=== | |||
| In Japan, predictions and study of tornadoes in Japan are handled by the ]. In Canada, weather forecasts and warnings, including tornadoes, are produced by the ], a division of ]. | |||
| == Detection == | |||
| ] ] image indicating the likely presence of a ] over ]. Green colors indicate areas where the precipitation is moving towards the radar dish, while red areas are moving away. In this case the radar is in the bottom right corner of the image. Strong ]s show up as adjacent areas of bright green and bright red, and usually indicate an imminent or occurring tornado. When these bright colors are one against the other on a radar display when in association with rotation, it is called a ].]] | |||
| Rigorous attempts to warn of tornadoes began in the United States in the mid-20th century. Before the 1950s, the only method of detecting a tornado was by someone seeing it on the ground. Often, news of a tornado would reach a local weather office after the storm. | |||
| However, with the advent of ], areas near a local office could get advance warning of severe weather. The first public ]s were issued in 1950 and the first ]es and ] in 1952. In 1953 it was confirmed that ]es are associated with tornadoes. By recognizing these radar signatures, meteorologists could detect thunderstorms likely producing tornadoes from dozens of miles away.<ref name="hook echoes">{{cite journal |last=Markowski |first=Paul M. |authorlink=Paul M. Markowski |title=Hook Echoes and Rear-Flank Downdrafts: A Review |journal=] |volume=130 |issue=4 |pages=852-876 |date=April 2002 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0493(2002)130%3C0852:HEARFD%3E2.0.CO%3B2 }}</ref> | |||
| === Storm spotting === | |||
| In the mid 1970s, the US National Weather Service (NWS) increased its efforts to train ]s to spot key features of storms which indicate severe hail, damaging winds, and tornadoes, as well as damage itself and ]ing. The program was called ], and the spotters were local ], ], ]s, ]s, ]s, ] (now ]) spotters, ]s, and ordinary citizens. When severe weather is anticipated, local weather service offices request that these spotters look out for severe weather, and report any tornadoes immediately, so that the office can issue a timely warning. | |||
| Usually spotters are trained by the NWS on behalf of their respective organizations, and report to them. The organizations activate public warning systems such as ] and the ], and forward the report to the NWS.<ref name="spotter history">{{cite journal |last=Doswell |first=Charles A. III |authorlink=Charles A. Doswell, III |coauthors=Alan R. Moller and Harold E. Brooks |title=Storm Spotting and Public Awareness since the First Tornado Forecasts of 1948 |journal=] |volume=14 |issue=4 |pages=544-557 |date=August 1999 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0434%281999%29014%3C0544%3ASSAPAS%3E2.0.CO%3B2 }}</ref> | |||
| There are more than 230,000 trained Skywarn weather spotters across the United States.<ref name="NWS SKYWARN">{{cite web |url=http://www.weather.gov/skywarn/ |publisher=National Weather Service |title=What is SKYWARN? |accessdate=2007-02-27 }}</ref> | |||
| In ], a similar network of volunteer weather watchers, called ], helps spot severe weather, with more than 1,000 volunteers.<ref name="environment Canada detection">{{cite web |url=http://www.mb.ec.gc.ca/air/summersevere/ae00s10.en.html |title=Tornado Detection at Environment Canada |accessdate=2007-03-16 |publisher=] |date=2004-06-02 }}</ref> | |||
| In Europe, several nations are organizing spotter networks under the auspices of Skywarn Europe<ref> Retrieved on ]</ref> | |||
| and the ] (TORRO) has maintained a network of spotters in the ] since the 1970s. | |||
| Storm spotters are needed because radar systems such as ] do not detect a tornado; only indications of one. Radar may give a warning before there is any visual evidence of a tornado or imminent tornado, but ] from an observer can either verify the threat or determine that a tornado is not imminent. The spotter's ability to see what radar cannot is especially important as distance from the radar site increases, because the radar beam becomes progressively higher in altitude further away from the radar, chiefly due to curvature of Earth, and the beam also spreads out. Therefore, when far from a radar, only high in the storm is observed and the important areas are not sampled, and data resolution also suffers. Also, some meteorological situations leading to tornadogenesis are not readily detectable by radar and on occasion tornado development may occur more quickly than radar can complete a scan and send the batch of data. | |||
| ==== Visual evidence ==== | |||
| ] with ] clear slot evident to its left rear.]] | |||
| Storm spotters are trained to discern whether a storm seen from a distance is a ]. They typically look to its rear, the main region of ] and ]. Under the updraft is a rain-free base, and the next step of ] is the formation of a rotating ]. The vast majority of intense tornadoes occur with a wall cloud on the backside of a supercell.<ref name="Basic Spotter Guide">{{cite web |url=http://www.nws.noaa.gov/om/brochures/basicspot.pdf |title=Basic Spotters’ Field Guide |accessdate=2006-11-01 |author=Edwards, Moller, Purpura, et al |year=2005 |publisher=] }}</ref> | |||
| Evidence of a supercell comes from the storm's shape and structure, and ] features such as a hard and vigorous updraft tower, a persistent, large ], a hard anvil (especially when backsheared against strong upper level ]s), and a corkscrew look or ]. Under the storm and closer to where most tornadoes are found, evidence of a supercell and likelihood of a tornado includes inflow bands (particularly when curved) such as a "beaver tail", and other clues such as strength of inflow, warmth and moistness of inflow air, how outflow- or inflow-dominant a storm appears, and how far is the front flank precipitation core from the wall cloud. Tornadogenesis is most likely at the interface of the updraft and ], and requires a balance between the outflow and inflow.<ref name="Advanced Spotter Guide">{{cite web |url=http://www.weather.gov/os/brochures/adv_spotters.pdf |title=Advanced Spotters' Field Guide |accessdate=2006-09-20 |author=Doswell, Moller, Anderson, et al |year=2005 |publisher=] }}</ref> | |||
| Only wall clouds that rotate spawn tornadoes, and usually precede the tornado by five to thirty minutes. Rotating wall clouds are the visual manifestation of a ]. Barring a low-level boundary, tornadogenesis is highly unlikely unless a ] occurs, which is usually visibly evidenced by evaporation of ] adjacent to a corner of a wall cloud. A tornado often occurs as this happens or shortly after; first, a ] dips and in nearly all cases by the time it reaches halfway down, a surface swirl has already developed, signifying a tornado is on the ground before condensation connects the surface circulation to the storm. Tornadoes may also occur without wall clouds, under flanking lines, and on the leading edge. Spotters watch all areas of a storm, and the ] and surface.<ref name="NSSL tornadoes">{{cite web |title=Questions and Answers about Tornadoes |work=A Severe Weather Primer |publisher=] |date=2006-11-15 |url=http://www.nssl.noaa.gov/primer/tornado/tor_basics.html |accessdate=2007-07-05 }}</ref> | |||
| === Radar === | |||
| Today, most developed countries have a network of ]s, which remains the main method of detecting signatures likely associated with tornadoes. In the United States and a few other countries, ] ] stations are used. These devices measure the velocity and radial ] (towards or away from the radar) of the winds in a storm, and so can spot evidence of rotation in storms from more than a hundred miles (160 km) away. | |||
| Also, most populated areas on Earth are now visible from the ]s (GOES), which aid in the ] of tornadic storms.<ref name="environment Canada detection"/> | |||
| <div style="clear: both"></div> | |||
| == Extremes == | |||
| {{main|Tornado records}} | |||
| The most extreme tornado in recorded history was the ] which roared through parts of ], ], and ] on ], ]. It was likely an '''F5''', though tornadoes were not ranked on any scale in that era. It holds records for longest path length (219 miles, 352 km), longest duration (about 3.5 hours), and fastest forward speed for a significant tornado (73 mph, 117 km/h) anywhere on earth. In addition, it is the deadliest single tornado in United States history (695 dead).<ref name="significant tornadoes"/> It was also the second costliest tornado in history at the time, but has been surpassed by several others non-normalized. When costs are normalized for wealth and inflation, it still ranks third today.<ref name="tornado damage cost">{{cite web| url = http://www.nssl.noaa.gov/users/brooks/public_html/damage/tdam1.html | title = Normalized Damage from Major Tornadoes in the United States: 1890–1999| accessdate = 2007-02-28| last = Brooks| first = Harold E. | coauthors = Doswell, Charles A, III | year = 2000| month = September}}</ref> | |||
| The deadliest tornado in world history was the ] in ] on ], ], which killed approximately 1300 people.<ref name="Bangladesh tornado"/> | |||
| ] | |||
| The most extensive ] on record, in almost every category, was the ], which affected a large area of the central United States and extreme southern ] in Canada on ] and ] ]. Not only did this outbreak feature an incredible 148 tornadoes in only 18 hours, but an unprecedented number of them were violent; six were of '''F5''' intensity, and twenty-four '''F4'''. This outbreak had a staggering ''sixteen'' tornadoes on the ground at the same time at the peak of the outbreak. More than 300 people, possibly as many as 330, were killed by tornadoes during this outbreak.<ref name="super outbreak">{{cite web| url = http://www.ncdc.noaa.gov/oa/climate/extremes/1999/april/TornOut.pdf| title = Tornado Outbreak of April 3–4, 1974; Synoptic Analysis| accessdate = 2007-03-02| author = Hoxit, Lee R| coauthors = Chappell, Charles F| year = 1975| month = October| format = PDF| publisher = National Oceanic and Atmospheric Administration}}</ref> | |||
| While it is nearly impossible to directly measure the most violent tornado wind speeds (conventional ]s would be destroyed by the intense winds), some tornadoes have been scanned by ], which can provide a good estimate of the tornado's winds. The highest wind speed ever measured in a tornado, which is also the highest wind speed ever recorded on the planet, is 301 ± 20 mph (484 ± 32 km/h) in the '''F5''' ] tornado. Though the reading was taken about 100 feet (30 m) above the ground, this is a testament to the power of the strongest tornadoes.<ref name="fastest wind"/> | |||
| Storms which produce tornadoes can feature intense updrafts (sometimes exceeding 150 mph, 240 km/h). Debris from a tornado can be lofted into the parent storm and carried a very long distance. A tornado which affected ] in November, 1915 was an extreme case, where a "rain of debris" occurred 80 miles (130 km) from the town, a sack of flour was found 110 miles (177 km) away, and a cancelled check from the Great Bend bank was found in a field outside of ], 305 miles (491 km) to the northeast.<ref name="tornado project oddities">{{cite web| url = http://www.tornadoproject.com/oddities/oddities.htm| title = Tornado Oddities| accessdate = 2007-02-28| last = Grazulis| first = Thomas P. | year = 1999}}</ref> | |||
| <div style="clear: both"></div> | |||
| == Safety == | |||
| Though tornadoes can strike in an instant, there are precautions and preventative measures that people can take to increase the chances of surviving a tornado. Authorities such as the ] advise having a tornado plan. When a tornado warning is issued, going to a basement or an interior first-floor room of a sturdy building greatly increases chances of survival.<ref name="tornado safety">{{cite web| url = http://www.spc.noaa.gov/faq/tornado/safety.html| title = Tornado Safety| accessdate = 2007-02-28| last = Edwards| first = Roger | publisher = Storm Prediction Center}} | |||
| </ref> In tornado-prone areas, many buildings have ]s on the property. These underground refuges have saved thousands of lives.<ref>{{cite web| url = http://www.srh.noaa.gov/hun/preparedness/brochures/storm_shelter.pdf| title = Storm Shelters| accessdate = 2007-02-28| publisher = National Weather Service, Huntsville Alabama| year = 2002| month = August| format = PDF}}</ref> | |||
| Some countries have meteorological agencies which distribute tornado forecasts and increase levels of alert of a possible tornado (such as ]es and ] in the United States and Canada). ]s provide an alarm when a severe weather advisory is issued for the local area, though these are mainly available only in the United States. | |||
| Unless the tornado is far away and highly visible, meteorologists advise that drivers park their vehicles far to the side of the road (so as not to block emergency traffic), and find a sturdy shelter. If no sturdy shelter is nearby, getting low in a ditch is the next best option. Highway overpasses are extremely bad shelter during tornadoes (see next section).<ref name="highway overpasses"/> | |||
| == Myths and misconceptions == | |||
| ], ], ]. This tornado disproved several myths, including the idea that tornadoes cannot occur in areas like ].]] | |||
| {{main|Tornado myths}} | |||
| One of the most persistent myths associated with tornadoes is that opening windows will lessen the damage caused by the tornado. While there is a large drop in ] inside a strong tornado, it is unlikely that the pressure drop would be enough to cause the house to explode. Some research indicates that opening windows may actually increase the severity of the tornado's damage. Regardless of the validity of the explosion claim, time would be better spent seeking shelter before a tornado than opening windows. A violent tornado can destroy a house whether its windows are open or closed.<ref name="tornado myths">{{cite book | last = Grazulis | first = Thomas P | title = The Tornado: Nature's Ultimate Windstorm | year = 2001 | publisher = University of Oklahoma Press | location = Norman, OK | isbn = 0-8061-3258-2 | chapter = Tornado Myths }}</ref><ref name="tornado project myths">{{cite web| url = http://www.tornadoproject.com/myths/myths.htm| title = Myths and Misconceptions about Tornadoes| accessdate = 2007-02-28| publisher = The Tornado Project| year = 1999}}</ref> | |||
| Another commonly held belief is that highway overpasses provide adequate shelter from tornadoes. On the contrary, a highway overpass is a dangerous place during a tornado. In the ] of ], ], three highway overpasses were directly struck by tornadoes, and at all three locations there was a fatality, along with many life-threatening injuries. The small area under the overpasses created a kind of ], increasing the wind's speed, making the situation worse.<ref name="highway overpass danger">{{cite web| url = http://www.usatoday.com/weather/resources/basics/tornado-underpass.htm| title = Overpasses are tornado death traps| accessdate = 2007-02-28| last = Cappella| first = Chris | date = ]| publisher = ]}}</ref> By comparison, during the same tornado outbreak, more than 2000 homes were completely destroyed, with another 7000 damaged, and yet only a few dozen people died in their homes.<ref name="highway overpasses">{{cite web| url = http://www.srh.noaa.gov/oun/papers/overpass.html| title = Highway Overpasses as Tornado Shelters| accessdate = 2007-02-28| last = Miller| coauthors = Doswell, Brooks et al| year = 1999| month = October| publisher = National Weather Service, Norman, Oklahoma}}</ref> | |||
| An old belief is that the southwest corner of a basement provides the most protection during a tornado. The safest place is the side or corner of an underground room opposite the tornado's direction of approach (usually the northeast corner), or the central-most room on the lowest floor. Taking shelter under a sturdy table, in a basement, or under a staircase increases chances of survival even more.<ref name="tornado myths"/><ref name="tornado project myths"/> | |||
| Finally, there are areas which people believe to be protected from tornadoes, whether by a major river, a hill or mountain, or even protected by "]s". Tornadoes have been known to cross major rivers, climb mountains,<ref name="Tornadoes in mountains">{{cite web | |||
| |url = http://tornado.sfsu.edu/RockwellPassTornado/index.html | |||
| |title = Tornado, Rockwell Pass, Sequoia National Park, July 7, 2004 | |||
| |accessdate = | |||
| |accessdaymonth = | |||
| |accessmonthday = | |||
| |accessyear = | |||
| |author = | |||
| |last = | |||
| |first = | |||
| |authorlink = | |||
| |coauthors = John Monteverdi, SFSU; Roger Edwards, SPC; Greg Stumpf, NSSL; Daniel Gudgel, NWS San Joaquin Valley Weather Forecast Offce | |||
| |date = 2006-09-13 | |||
| |year = | |||
| |month = | |||
| |format = | |||
| |work = | |||
| |publisher = | |||
| |pages = | |||
| |language = English | |||
| |doi = | |||
| |archiveurl = | |||
| |archivedate = | |||
| |quote = | |||
| }}</ref> and affect valleys. As a general rule, no area is "safe" from tornadoes, though some areas are more susceptible than others.<ref name="tornado myths"/><ref name="tornado project myths"/><ref name="Handy Weather Answer Book"/> (See ]). | |||
| <div style="clear:both;"></div> | |||
| == Continuing research == | |||
| ] unit observing a tornado near ].]] | |||
| Meteorology is a relatively young science and the study of tornadoes even more so. Although studied for about 140 years and intensively for around 60 years, there are still aspects of tornadoes which remain a mystery.<ref name="VORTEX book">{{cite web| url = http://www.nssl.noaa.gov/noaastory/book.html| title = VORTEX: Unraveling the Secrets| accessdate = 2007-02-28| publisher = ]| year = 2006}}</ref> Scientists do have a fairly good idea of the development of thunderstorms and ]s, and the meteorological conditions conducive to their formation; however, the step from ] (or other respective formative processes) to ] and predicting tornadic vs. non-tornadic mesocyclones is not yet well understood and is the focus of much research. | |||
| Also under study are the low-level mesocyclone and the stretching of low-level ] which tightens into a tornado, namely, what are the processes and what is the relationship of the environment and the convective storm. Intense tornadoes have been observed forming simultaneously with a mesocyclone aloft (rather than succeeding mesocyclogenesis) and some intense tornadoes have occurred without a mid-level mesocyclone. In particular, the role of ]s, particularly the ], and the role of ] boundaries, are intense areas of study. | |||
| Reliably predicting tornado intensity and longevity remains a problem, as do details affecting characteristics of a tornado during its life cycle and tornadolysis. Other rich areas of research are tornadoes associated with ]s within linear thunderstorm structures and within tropical cyclones.<ref name="tornado forecasting">{{cite web |url=http://cimms.ou.edu/~erik/Tornadoes/Forecasting/Detailed/Detailed.htm |title=Tornado Forecasting |accessdate = 2007-03-27 |last=Rasmussen |first=Erik |authorlink=Erik N. Rasmussen |date=] |work=Severe Storms Research by Erik Rasmussen and Collaborators}}</ref> | |||
| Scientists still do not know the exact mechanisms by which most tornadoes form, and occasional tornadoes still strike without a tornado warning being issued, especially in under-developed countries. Analysis of observations including both stationary and mobile (surface and aerial) ] and ] (passive and active) instruments generates new ideas and refines existing notions. ] also provides new insights as observations and new discoveries are integrated into our physical understanding and then tested in ]s which validate new notions as well as produce entirely new theoretical findings, many of which are otherwise unattainable. Importantly, development of new observation technologies and installation of finer spatial and temporal resolution observation networks have aided increased understanding and better predictions. | |||
| Research programs, including field projects such as ], deployment of ] (the TOtable Tornado Observatory), ] (DOW), and dozens of other programs, hope to solve many questions that still plague meteorologists.<ref name="field programs history">{{cite journal | |||
| |last=Bluestein |first=Howard |authorlink=Howard B. Bluestein |title=A History of Severe-Storm-Intercept Field Programs |journal=] |volume=14 |issue=4 |pages=558–577 |publisher=] |date=August 1999 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&issn=1520-0434&volume=014&issue=04&page=0558 }}</ref> Universities, government agencies such as the ], private-sector meteorologists, and the ] are some of the organizations very active in research; with various sources of funding, both private and public, a chief entity being the ]. | |||
| == See also == | |||
| {{sisterlinks|tornado}} | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| ** ] | |||
| ** ] | |||
| ** ] | |||
| ** ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| {{WeatherPortal}} | |||
| <div style="clear:both;"></div> | |||
| == References == | |||
| <div class="references-small" style="column-count:2;-moz-column-count:2;"> | |||
| <references/> | |||
| </div> | |||
| == Further reading == | |||
| *{{cite book | |||
| |last=Grazulis | |||
| |first=Thomas P | |||
| |year=1997 | |||
| |month=January | |||
| |authorlink=Thomas P. Grazulis | |||
| |title=Significant Tornadoes Update, 1992–1995 | |||
| |publisher=Environmental Films | |||
| |location=St. Johnsbury, VT | |||
| |isbn=1-879362-04-X | |||
| }} | |||
| *{{cite book | |||
| |last=Bradford | |||
| |first=Marlene | |||
| |year=2001 | |||
| |title=Scanning the Skies: a History of Tornado Forecasting | |||
| |publisher=University of Oklahoma Press | |||
| |address=Norman, OK | |||
| |isbn=0-8061-3302-3 | |||
| }} | |||
| *{{cite book | |||
| |last=Bluestein | |||
| |first=Howard B | |||
| |year=1999 | |||
| |title=Tornado Alley: Monster Storms of the Great Plains | |||
| |publisher=Oxford University Press | |||
| |address=New York, NY | |||
| |isbn=0-19-510552-4 | |||
| }} | |||
| == External links == | |||
| ;General | |||
| * | |||
| * | |||
| * Free archive of more than 50,000 newspaper articles detailing tornadoes throughout history. | |||
| * Searchable database of tornadoes overlaid on a Google Map | |||
| * Fly tornado paths in your area using Google Maps and Google Earth | |||
| * | |||
| ;Research | |||
| * (]) | |||
| * | |||
| * | |||
| * (]) | |||
| ;Safety and Preparedness | |||
| * | |||
| * | |||
| * (The Tornado Project) | |||
| * (NOAA / SPC) | |||
| * (National Weather Service, Norman, Oklahoma) | |||
| * | |||
| * by ''Southern Spaces'', 19 February 2008. | |||
| {{Featured article}} | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| {{Link FA|af}} | |||
| {{Link FA|fr}} | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
Revision as of 16:06, 25 February 2008
GAMING !!!!!!!!