Editing Tornado (section)

== Characteristics ==

=== Size and shape ===
[[File:A Texas twister in Wichita County April 1964.jpg|thumb|[[1964 Wichita Falls tornado|This F5 rated tornado]] in [[Wichita Falls, Texas]] in April 1964, has a "rope" structure. This usually occurs when a tornado first forms or when a tornado ropes out and dissipates.]]
[[File:Greensburg tornado on the highway.jpg|thumb|286x286px|[[2007 Greensburg tornado|This nocturnal wedge EF5 tornado]] near [[Greensburg, Kansas]] in May 2007, has a "wedge" structure, these can reach widths of 1 mile or even 2 miles in rare occasions.]]
Most tornadoes take on the appearance of a narrow [[funnel]], a few hundred meters (yards) across, with a small cloud of debris near the ground. Tornadoes may be obscured completely by rain or dust. These tornadoes are especially dangerous, as even experienced meteorologists might not see them.<ref name="Handy Weather Answer Book"/>

Small, relatively weak landspouts may be visible only as a small swirl of dust on the ground. Although the condensation funnel may not extend all the way to the ground, if associated surface winds are greater than {{convert|40|mph|km/h|abbr=on|order=flip}}, the circulation is considered a tornado.<ref name="Advanced Spotter Guide"/> A tornado with a nearly cylindrical profile and relatively low height is sometimes referred to as a "stovepipe" tornado. Large tornadoes which appear wider than their cloud-to-ground height can look like large [[wedges]] stuck into the ground, and so are known as "wedge tornadoes" or "wedges".<ref name="wedge tornado"/> The "stovepipe" classification is also used for this type of tornado if it otherwise fits that profile. 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. Many, but not all major tornadoes are wedges.<ref name="wedge tornado">{{cite web|url=http://www.spc.noaa.gov/faq/tornado/binger.htm|title=Wedge Tornado|first=Roger|last=Edwards|author-link=Roger Edwards (meteorologist)|work=[[National Weather Service]]|publisher=National Oceanic and Atmospheric Administration|date=2008-07-18|access-date=2007-02-28|archive-date=2021-05-11|archive-url=https://web.archive.org/web/20210511042056/https://www.spc.noaa.gov/faq/tornado/binger.htm|url-status=live}}</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". When they rope out, the length of their funnel increases, which forces the winds within the funnel to weaken due to [[conservation of angular momentum]].<ref name="thebible">{{cite journal|pages=57–58|journal=Bible of Weather Forecasting|volume=1|issue=4|title=27.0.0 General Laws Influencing the Creation of Bands of Strong Bands|last=Singer|first=Oscar|date=May–July 1985 }}</ref> Multiple-vortex tornadoes can appear as a family of swirls circling a common center, or they 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|work=[[National Weather Service]]|publisher=National Oceanic and Atmospheric Administration|date=2008-07-18|title=Rope Tornado|access-date=2007-02-28|first=Roger|last=Edwards|author-link=Roger Edwards (meteorologist)|archive-date=2007-07-11|archive-url=https://web.archive.org/web/20070711024223/http://www.spc.noaa.gov/faq/tornado/el_reno.htm|url-status=live}}</ref>

In the United States, tornadoes are around {{convert|500|ft|m}} across on average.<ref name="Handy Weather Answer Book"/> However, there is a wide range of tornado sizes. Weak tornadoes, or strong yet dissipating tornadoes, can be exceedingly narrow, sometimes only a few feet or couple meters across. One tornado was reported to have a damage path only {{convert|7|ft|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&nbsp;km) wide or more. A [[2004 Hallam tornado|tornado that affected Hallam, Nebraska]] on May 22, 2004, was up to {{convert|2.5|mi|km}} wide at the ground, and [[2013 El Reno tornado|a tornado in El Reno, Oklahoma]] on May 31, 2013, was approximately {{convert|2.6|mi|km}} wide, the widest on record.<ref name="widest tornado" /><ref>{{cite web|title=May 31–June 1, 2013 Tornado and Flash Flood Event: The May 31, 2013 El Reno, OK Tornado|url=http://www.srh.noaa.gov/oun/?n=events-20130531-elreno|date=July 28, 2014|access-date=December 25, 2014|work=National Weather Service Weather Forecast Office|publisher=National Oceanic and Atmospheric Administration|location=Norman, Oklahoma|archive-date=July 25, 2015|archive-url=https://web.archive.org/web/20150725013446/http://www.srh.noaa.gov/oun/?n=events-20130531-elreno|url-status=live}}</ref>

=== Track length ===
In the United States, the average tornado travels on the ground for {{convert|5|mi|km}}. However, tornadoes are capable of both much shorter and much longer damage paths: one tornado was reported to have a damage path only {{convert|7|ft|m}} long, while the record-holding tornado for path length—the [[Tri-State Tornado]], which affected parts of [[Missouri]], [[Illinois]], and [[Indiana]] on March 18, 1925—was on the ground continuously for {{convert|219|mi|km}}.<ref name="Handy Weather Answer Book" /> Many tornadoes which appear to have path lengths of {{convert|100|mi|km}} or longer are composed of 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|first=Thomas P.|last=Grazulis|title=Significant Tornadoes 1680–1991|date=July 1993|publisher=The Tornado Project of Environmental Films|location=St. Johnsbury, VT|isbn=1-879362-03-1}}</ref> A 2007 reanalysis of the path suggests that the tornado may have begun {{convert|15|mi|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|archive-url=https://web.archive.org/web/20070614014358/http://apollo.lsc.vsc.edu/ams/AMS%20VP/Storm%20Conference/NESC%20Presentations/32ndNESC_Presentation/Banquet/Doswell.ppt|url-status=dead|archive-date=2007-06-14|title=The Tri-State Tornado of 18 March 1925 |publisher=Reanalysis Project|access-date=2007-04-07|first=Charles A. III|last=Doswell |format=Powerpoint Presentation}}</ref>

===Appearance===
[[File:Waurika Oklahoma Tornado Back and Front.jpg|thumb|right|Photographs of the [[Waurika, Oklahoma]] tornado of May 30, 1976, taken at nearly the same time by two photographers. In the top picture, the tornado is lit by the sunlight focused from behind the [[camera]], thus the funnel appears bluish. In the lower image, where the camera is facing the opposite direction, the sun is behind the tornado, giving it a dark appearance.<ref name="PD tornado images">{{cite web|url=http://www.spc.noaa.gov/faq/tornado/torscans.htm|title=Public Domain Tornado Images|work=[[National Weather Service]]|access-date=2009-11-17|year=2009|first=Roger|last=Edwards|author-link=Roger Edwards (meteorologist)|publisher=National Oceanic and Atmospheric Administration|archive-date=2006-09-30|archive-url=https://web.archive.org/web/20060930133841/http://www.spc.noaa.gov/faq/tornado/torscans.htm|url-status=live}}</ref>]]Tornadoes can have a wide range of colors, depending on the environment in which they form. Those that form in dry environments can be nearly invisible, marked only by swirling debris at the base of the funnel. Condensation funnels that pick up little or no debris can be gray to white. While traveling over a body of water (as a waterspout), tornadoes can turn white or even blue. Slow-moving funnels, which ingest a considerable amount of debris and dirt, are usually darker, taking on the color of debris. Tornadoes in the [[Great Plains]] can turn red because of the reddish tint of the soil, and tornadoes in mountainous areas can travel over snow-covered ground, turning white.<ref name="Handy Weather Answer Book" />

Lighting conditions are a major factor in the appearance of a tornado. A tornado which is "[[Backlighting (lighting design)|back-lit]]" (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="TT">{{cite web|first=Tim|last=Marshall |url=http://www.tornadoproject.com/cellar/tttttttt.htm |title=The Tornado Project's Terrific, Timeless and Sometimes Trivial Truths about Those Terrifying Twirling Twisters! |access-date=2008-11-09 |publisher=The Tornado Project |date=2008-11-09 |url-status=dead |archive-url=https://web.archive.org/web/20081016163615/http://www.tornadoproject.com/cellar/tttttttt.htm |archive-date=2008-10-16 }}</ref><ref name="target tornado">{{cite video|people=Linda Mercer Lloyd|date=1996|title=Target: Tornado|medium=Videotape|publisher=The Weather Channel}}</ref>

Dust kicked up by the winds of the parent thunderstorm, heavy rain and hail, and the darkness of night are all factors that can reduce the visibility of tornadoes. Tornadoes occurring in these conditions are especially dangerous, since only [[weather radar]] observations, or possibly the sound of an approaching tornado, serve as any warning to those in the storm's path. Most significant tornadoes form under the storm's ''updraft base'', which is rain-free,<ref>{{cite web|url=http://www.srh.noaa.gov/oun/stormspotting/basics.php |work=[[National Weather Service]]|publisher=National Oceanic and Atmospheric Administration|title=The Basics of Storm Spotting|date=2009-01-15|access-date=2009-11-17 |archive-url = https://web.archive.org/web/20031011045434/http://www.srh.noaa.gov/oun/stormspotting/basics.php |archive-date = 2003-10-11}}</ref> making them visible.<ref>{{cite journal | last1 =Peterson | first1 = Franklynn | last2 =Kwsselman | first2 = Judi R | title =Tornado factory – giant simulator probes killer twisters | journal = Popular Science | volume =213 | issue =1 | pages = 76–78 | date = July 1978| url = {{GBUrl|YwEAAAAAMBAJ|p=76}}}}</ref> Also, most tornadoes occur in the late afternoon, when the bright sun can penetrate even the thickest clouds.<ref name="significant tornadoes"/>

There is mounting evidence, including [[Doppler on Wheels]] mobile radar images and eyewitness accounts, that most tornadoes have a clear, calm center with extremely low pressure, akin to the [[eye (cyclone)|eye]] of [[tropical cyclone]]s. 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=https://www.sciencenews.org/archive/oklahoma-tornado-sets-wind-record?mode=magazine&context=1921|title=Oklahoma Tornado Sets Wind Record|access-date=2006-10-20|first=R.|last=Monastersky|date=1999-05-15|work=Science News|pages=308–09|archive-date=2015-04-02|archive-url=https://web.archive.org/web/20150402141112/https://www.sciencenews.org/archive/oklahoma-tornado-sets-wind-record?mode=magazine&context=1921|url-status=live}}</ref><ref name="inside eyewitness">{{cite journal |last=Justice |first=Alonzo A. |year=1930 |title=Seeing the Inside of a Tornado |journal=Monthly Weather Review |volume=58 |issue=5 |pages=205–06 |bibcode=1930MWRv...58..205J |doi=10.1175/1520-0493(1930)58<205:STIOAT>2.0.CO;2 |doi-access=free}}</ref><ref>{{cite book|first=Roy S.|last=Hall|isbn=0-7377-1473-5|title=Tornadoes|year=2003|publisher=Greenhaven Press|pages=59–65|chapter=Inside a Texas Tornado}}</ref>

===Rotation===
Tornadoes normally rotate [[cyclone|cyclonically]] (when viewed from above, this is counterclockwise in the [[northern hemisphere]] and clockwise in the [[southern hemisphere|southern]]). While large-scale storms always rotate cyclonically due to the [[Coriolis effect]], thunderstorms and tornadoes are so small that the direct influence of the Coriolis effect is negligible, as indicated by their large [[Rossby number]]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|first=Robert|last=Davies-Jones|author-link=Robert Davies-Jones|title=Streamwise Vorticity: The Origin of Updraft Rotation in Supercell Storms|journal=J. Atmos. Sci.|volume=41|issue=20|pages=2991–3006|doi=10.1175/1520-0469(1984)041<2991:SVTOOU>2.0.CO;2|bibcode = 1984JAtS...41.2991D|year=1984 |doi-access=free}}</ref><ref name="Rotation and Propagation of Simulated Supercells">{{cite journal|first1=Richard|last1=Rotunno|author2-link=Joseph B. Klemp|first2=Joseph|last2=Klemp|title=On the Rotation and Propagation of Simulated Supercell Thunderstorms|volume=42|issue=3|pages=271–92|journal=J. Atmos. Sci.|doi=10.1175/1520-0469(1985)042<0271:OTRAPO>2.0.CO;2|bibcode=1985JAtS...42..271R|year=1985|url=https://zenodo.org/record/1234689|doi-access=free|access-date=2019-08-01|archive-date=2019-08-01|archive-url=https://web.archive.org/web/20190801200317/https://zenodo.org/record/1234689|url-status=live}}</ref> Low-level [[mesocyclone]]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|first1=Louis J.|last1=Wicker|first2=Robert B.|last2=Wilhelmson|title=Simulation and Analysis of Tornado Development and Decay within a Three-Dimensional Supercell Thunderstorm|pages=2675–703|journal=J. Atmos. Sci.|volume=52|issue=15|doi=10.1175/1520-0469(1995)052<2675:SAAOTD>2.0.CO;2|bibcode = 1995JAtS...52.2675W|year=1995|doi-access=free}}</ref>

Approximately 1&nbsp;percent of tornadoes rotate in an anticyclonic direction in the northern hemisphere. Typically, systems as weak as landspouts and gustnadoes can rotate anticyclonically, and usually only those which form on the anticyclonic shear side of the descending [[rear flank downdraft]] (RFD) 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=anticyclonic tornado in El Reno, OK |publisher=The Weather Channel |date=2006-04-26 |access-date=2006-12-30 |first=Greg|last=Forbes |url-status=dead |archive-url=https://web.archive.org/web/20071011194725/http://www.weather.com/blog/weather/8_9262.html |archive-date=2007-10-11 }}</ref> On rare occasions, [[anticyclonic tornado]]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 1998-05-04|access-date=2006-10-20|first=John|last=Monteverdi|date=2003-01-25|archive-date=2013-06-13|archive-url=https://web.archive.org/web/20130613194202/http://tornado.sfsu.edu/geosciences/StormChasing/cases/Sunnyvale/Sunnyvale.html|url-status=dead}}</ref>

=== Sound and seismology ===
[[File:Tornado infrasound sources.png|thumb|upright=1.2|An illustration of generation of infrasound in tornadoes by the [[Earth System Research Laboratories]]'s Infrasound Program]]
Tornadoes emit widely on the [[acoustics]] [[Audio frequency|spectrum]] and the sounds are caused by multiple mechanisms. Various sounds of tornadoes have been reported, mostly related to familiar sounds for the witness and generally some variation of a whooshing roar. Popularly reported sounds include a freight train, rushing rapids or waterfall, a nearby jet engine, or combinations of these. Many tornadoes are not audible from much distance; the nature of and the propagation distance of the audible sound depends on atmospheric conditions and topography.<ref name="SPC FAQ" />

The winds of the tornado vortex and of constituent turbulent [[eddy (fluid dynamics)|eddies]], 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 bees 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|first=Abdul|last=Abdullah|title=The "Musical" Sound Emitted by a Tornado"|journal=Mon. Wea. Rev.|volume=94|issue=4|pages=213–20|date=April 1966|doi=10.1175/1520-0493(1966)094<0213:TMSEBA>2.3.CO;2|bibcode=1966MWRv...94..213A|url=http://docs.lib.noaa.gov/rescue/mwr/094/mwr-094-04-0213.pdf|url-status=dead|archive-url=https://web.archive.org/web/20170921230829/https://docs.lib.noaa.gov/rescue/mwr/094/mwr-094-04-0213.pdf|archive-date=2017-09-21|citeseerx=10.1.1.395.3099}}</ref>

Since many tornadoes are audible only when very near, sound is not to be thought of as a reliable warning signal for a tornado. Tornadoes are also not the only source of such sounds in severe thunderstorms; any strong, damaging wind, a severe hail volley, or continuous thunder in a thunderstorm may produce a roaring sound.<ref name="sound obs">{{cite journal|first=David K.|last=Hoadley |title=Tornado Sound Experiences |journal=[[Storm Track]] |volume=6 |issue=3 |pages=5–9 |date=1983-03-31 |url=http://www.stormtrack.org/archive/0636.htm |url-status=dead |archive-url=https://web.archive.org/web/20120619210634/http://www.stormtrack.org/archive/0636.htm |archive-date=2012-06-19 }}</ref>

Tornadoes also produce identifiable inaudible [[infrasonic]] signatures.<ref name="tornado infrasonics">{{cite journal|first=A. J.|last=Bedard|title=Low-Frequency Atmospheric Acoustic Energy Associated with Vortices Produced by Thunderstorms|journal=Mon. Wea. Rev.|volume=133|issue=1|pages=241–63|date=January 2005|doi=10.1175/MWR-2851.1|bibcode = 2005MWRv..133..241B |s2cid=1004978|doi-access=free}}</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 [[seismic]] signature, and research continues on isolating it and understanding the process.<ref name="tornado seismic signal">{{cite journal|first1=Frank|last1=Tatom |first2=Kevin R.|last2=Knupp |first3=Stanley J.|last3=Vitto  |name-list-style=amp |title=Tornado Detection Based on Seismic Signal|journal=J. Appl. Meteorol.|volume=34|issue=2|pages=572–82|doi=10.1175/1520-0450(1995)034<0572:TDBOSS>2.0.CO;2|bibcode = 1995JApMe..34..572T|year=1995 |doi-access=free}}</ref>

===Electromagnetic, lightning, and other effects===
Tornadoes emit on the [[electromagnetic spectrum]], with [[sferics]] and [[E-field]] effects detected.<ref name="field programs history"/><ref>{{cite journal|first1=John R.|last1=Leeman|first2=E. D.|last2=Schmitter|title=Electric signals generated by tornados|journal=Atmos. Res.|volume=92|issue=2|pages=277–79|date=April 2009|doi=10.1016/j.atmosres.2008.10.029|bibcode=2009AtmRe..92..277L}}</ref><ref name="in situ history">{{cite conference|first=Timothy M.|last=Samaras|author-link=Tim Samaras|title=A Historical Perspective of In-Situ Observations within Tornado Cores|book-title=Preprints of the 22nd Conf. Severe Local Storms|publisher=American Meteorological Society|date=October 2004|location=Hyannis, MA|url=http://ams.confex.com/ams/11aram22sls/techprogram/paper_81153.htm|access-date=2007-05-23|archive-date=2011-01-15|archive-url=https://web.archive.org/web/20110115081005/http://ams.confex.com/ams/11aram22sls/techprogram/paper_81153.htm|url-status=live}}</ref> There are observed correlations between tornadoes and patterns of lightning. Tornadic storms do not produce more lightning than other storms and some tornadic cells never produce lightning at all. More often than not, overall cloud-to-ground (CG) lightning activity decreases as a tornado touches the surface and returns to the baseline level when the tornado dissipates. In many cases, intense tornadoes and thunderstorms exhibit an increased and anomalous dominance of positive polarity CG discharges.<ref name="CG tor">{{cite journal|first1=Antony H.|last1=Perez |first2=Louis J.|last2=Wicker |first3=Richard E.|last3=Orville  |name-list-style=amp |title=Characteristics of Cloud-to-Ground Lightning Associated with Violent Tornadoes|journal=Weather Forecast|volume=12|issue=3|pages=428–37|doi=10.1175/1520-0434(1997)012<0428:COCTGL>2.0.CO;2|bibcode = 1997WtFor..12..428P|year=1997 |doi-access=free}}</ref>

[[Luminosity]] has been reported in the past and is probably due to misidentification of external light sources such as lightning, city lights, and [[power flash]]es from broken lines, as internal sources are now uncommonly reported and are not known to ever have been recorded. In addition to winds, tornadoes also exhibit changes in atmospheric variables such as [[temperature]], [[moisture]], and [[atmospheric pressure]]. For example, on June 24, 2003, near [[Manchester, South Dakota]], a probe measured a {{convert|100|mbar|hPa inHg|adj=on|lk=on}} pressure decrease. The pressure dropped gradually as the vortex approached then dropped extremely rapidly to {{convert|850|mbar|hPa inHg|abbr=on|lk=on}} 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|first1=Julian J.|last1=Lee|first2=Timothy P.|last2=Samaras|first3=Carl R.|last3=Young|title=Pressure Measurements at the ground in an F-4 tornado|book-title=Preprints of the 22nd Conf. Severe Local Storms|publisher=American Meteorological Society|date=2004-10-07|location=Hyannis, Massachusetts|url=http://ams.confex.com/ams/11aram22sls/techprogram/paper_81700.htm|access-date=2007-07-06|archive-date=2011-06-09|archive-url=https://web.archive.org/web/20110609164901/http://ams.confex.com/ams/11aram22sls/techprogram/paper_81700.htm|url-status=live}}</ref>