Tornado

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For other uses of Tornado, see Tornado (disambiguation).

Image:Tornado.jpg A tornado is a violently deceptive spinning column of air in contact with both a cumiliform cloud base and the surface of the earth. A tornado is typically shaped like a funnel with the narrow end on the ground. Tornadoes are known for being extremely destructive and are usually visible due to water vapor from low pressure condensation and debris from the ground. Tornadoes form in storms all over the world, and though they have been recorded in all fifty U.S. states, they form most famously in a broad area of the American Great Plains, Midwest, as well as South known colloquially as Tornado Alley. In pure number of incidences, the United States reports more tornadoes than any other country, however, the Netherlands is the most tornado-prone country relative to land area.

1 Terminology
2 Characteristics
3 Intensity
4 Frequency of occurrence
5 Social implications of tornadoes
6 Tornadoes as a metaphor
7 Motion pictures with a tornado theme
8 See also
9 References
10 External links

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Terminology

The word "tornado" comes from the Spanish word for "turned", which in turn comes from the Latin word torqueo, meaning "to twist." Some common, related slang terms include: twister, whirlwind, wedge, funnel, willy-willy, finger of God, Devil's tail, or rope. However, willy-willy usually refers to a dust devil in Australia.

Cyclone is also another term for a tornado, although it must be noted that in parts of the world (notably Australia) a cyclone refers to what is more correctly known as a tropical cyclone (also known as a hurricane, or a typhoon), and meteorologists use the term cyclone to refer to a wide range of circular weather systems (using adjectives to disambiguate).

In general, mirim tornadoes are associated with a thunderstorm; however, National Weather Service in the United States considers all waterspouts—including "fair weather" waterspouts—to be tornadoes. Waterspouts commonly form from rapidly growing cumulus clouds that have not become thunderstorms. They grow by stretching an already existing vortex. USA Today The Weather Book helps in defining a "waterspout" as a tornado-like rotating column of air under a cumuliform cloud occurring over water; they are most common over tropical and subtropical waters and dissipate upon reaching shore/land. Some waterspouts, however, are thunderstorm-spawned, identical to other tornados except for their occurrence over water.

Larger vortices not associated with a thunderstorm over land are sometimes called landspouts.

Dust devils are small vortices that form near the ground, which are not considered tornadoes.

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Characteristics

Tornadoes normally rotate in a cyclonic (counterclockwise) direction in the northern hemisphere, as the warm air in which thunderstorms usually form sweeps north and jet streams come from the west, creating a situation in which the storms rotate. In the northern hemisphere, this rotation is counterclockwise, and in the southern hemisphere, clockwise. The tornadoes usually rotate the same way. Sometimes opposite direction swirls develop under a thunderstorm. About 1 in 100 tornadoes in the northern hemisphere rotate in an anticyclonic direction.

The most intense tornadoes can develop multiple vortices, all pinwheeling around the same axis. The additive wind velocity of the vortices' on the outer side of the pinwheel greatly increases the destructive power of this type of tornado.

Tornado funnels can range in width from a few feet to as much as one mile across. The latter can be particularly dangerous in that it may be mistaken for an area of rain or lowering of clouds.

No two tornadoes look exactly alike, nor have any two tornadoes behaved in exactly the same way. There are true incidents of tornadoes repeatedly hitting the same town several years in a row; however, forecasting the exact position a tornado will strike at a certain time is presently impossible.

Tornadoes can be nearly invisible, marked only by swirling debris at the base of the funnel. While tornadoes are invisible at night, some nocturnal tornadoes have been observed glowing diffusely due to lightning activity. Verified observations by Hall and others suggest a cellular structure inside tornadoes. In Utah tornados during the spring are sometimes called "white tornadoes", this happens when the funnel passes through snow-covered land, sucking the white snow into it. A tornado must by definition have both ground and cloud contact. Thus, the exclamation "Tornado on the ground!" is redundant.

Not every thunderstorm, supercell, squall line, or hurricane will produce a tornado. Luckily, it takes exactly the right combination of atmospheric variables (wind, temperature, pressure, humidity, etc.) to spawn even a weak tornado. On the other hand, 700 or more tornadoes a year are reported in the contiguous United States.

There are two general types of tornadoes, one of which forms in the outflow of air from a thunderstorm. These have shallow and more localized vortices and are generally weak storms that rarely exceed an F-2 on the fujita scale (about 157 mph/252 km/h). Waterspouts can be associated with this first kind of tornado.

The next type of tornado is the strongest and most dangerous. These are storms found where the surface air is flowing into the updraft area of a supercell. Tornadoes begin at the storm's middle levels and grow up into the storm and down towards the ground. These types generally form the categories F-4 and F-5 tornadoes which range from 207 mph/333 km/h to above 261 mph/420 km/h.

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Intensity

In the United States (and predominately worldwide), the intensity of a tornado is measured on the Fujita-Pearson Tornado Scale (also known simply as Fujita scale). The intensity can be derived directly with high resolution Doppler radar wind speed data, or empirically derived from structural and vegetative damage indicators compared to engineering data, as well as ground swirl patterns or photogrammetry / videogrammetry. Note that intensity does not refer in any way to the size, or width, of a tornado. The scale ranges from F0 for the weakest to F5 for the most powerful recorded tornadoes. The Fujita scale goes all the way up to F12 which represents mach level winds, though F5 is the highest ever recorded. The Fujita scale is effectively a damage scale, wind speeds are estimates and have never been confirmed or fully tested, and there is no upper bound wind speed in the Enhanced Fujita Scale which has replaced the original Fujita scale.

The TORRO scale, developed in the United Kingdom by the Tornado and Storm Research Organisation (TORRO) and used primarily in the U.K., covers a broader range with tighter graduations, and TORRO says it is based solely on wind speed, though in practice damage analysis is used to infer wind speeds. It ranges from a T0 to T11 for the most powerful known tornado in the United States.

Of all tornadoes formed in the U.S., F0 and F1 tornadoes account for a large percentage of occurrences. On the other end of the scale, the massively destructive F5s account for approximately 0.1% of all tornadoes in the U.S.

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Frequency of occurrence

Image:Tornado1884.jpg The United States experiences by far the most tornadoes of any country, and has also suffered the most intense ones. Tornadoes are common in most states in spring and summer, especially those east of the Rocky Mountains. There is a secondary peak in autumn, especially in the southeastern U.S. where tornadoes also occur more frequently during winter there than in other areas.

Tornadoes can occur in the West as well, although they are usually very small and relatively weak. Recently tornadoes have struck the Pacific coast town of Lincoln City, Oregon, in 1996 and downtown Salt Lake City, Utah, in 1999 (see Salt Lake City Tornado). The California Central Valley is an area of some frequency for tornados, albeit of weak intensity. More tornadoes occur in Texas than in any other US state. The state which has the highest number of tornadoes per unit area is Florida, although most of the tornadoes in Florida are weak tornadoes of F0 or F1 intensity. A number of Florida's tornadoes occur along the edge of Hurricanes. The state with the highest number of stronger tornadoes per unit area is Oklahoma. The neighboring state of Kansas is another particularly notorious tornado state. It should be mentioned that states such as Oklahoma and Kansas have much lower population densities than Florida and that tornadoes may go unreported.

On average, the United States experiences 100,000 thunderstorms each year, resulting in more than 1,200 tornadoes and approximately 50 deaths per year. The deadliest U.S. tornado on record is the March 18, 1925, Tri-State Tornado that went across southeastern Missouri, southern Illinois and southern Indiana, killing 695 people. More than six tornadoes in one day is considered a tornado outbreak. The biggest tornado outbreak on record—with 148 tornadoes, including six F5 and 24 F4 tornadoes—occurred on April 3, 1974. It is dubbed the Super Outbreak. Another such significant storm system was the Palm Sunday Tornado Outbreak, which affected the United States Midwest on April 11, 1965. A series of continuous tornado outbreaks is known as a tornado outbreak sequence, with significant occurrences in May 1917, 1930, 1949, and 2003.

Canada also experiences numerous tornadoes, although fewer than the United States. In Canada, an average of 80 tornadoes occurs annually, killing 2, injuring 20 and causing tens of millions of dollars in damage. The last killer tornado in Canada struck Pine Lake, Alberta, on July 14, 2000, killing 11.

Tornadoes do occur throughout the world as well; the most tornado-prone region of the world (outside North America), as measured by number of reported tornadoes per unit area, is the Netherlands, followed by the United Kingdom (especially England). Bangladesh, India, Argentina, Italy, Australia, New Zealand, Germany, Estonia, and portions of Uruguay also have pockets of high tornadic activity. Occasional strong tornadoes occur in Russia, France, Spain, Japan, and portions of Paraguay and Brazil. Tornadoes have recently hit South Africa and parts of Pakistan in 2001 as well. Approximately 170 tornadoes are reported per year on land in Europe. Perhaps the most notorious tornado of recent years was that which struck Birmingham, England in July 2005 which destroyed a row of houses though - amazingly - without fatalities.

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Social implications of tornadoes

Image:Saltlaketornado.jpeg

Tornado damage to man-made structures is a result of the high wind velocity and windblown debris. Tornadic winds have been measured in excess of 300 mph (480 km/h). Tornado season in North America is generally March through November, although tornadoes can occur at any time of year. They tend to occur in the afternoons and evenings; over 80% of all tornadoes strike between noon and midnight.

Trained weather spotters are often on alert to look for tornadoes and notify local weather agencies when severe weather is occurring or predicted to be imminent. In the United States, Skywarn spotters, often local sheriff's deputies and state troopers, fulfil this role. Additionally, some individuals, known as storm chasers, enjoy pursuing thunderstorms and tornadoes to explore their many visual and scientific aspects. Attempts have been made by storm chasers to drop probes in the path of oncoming tornadoes in an effort to analyze the interior of the storms, but only about five drops have been successful since around 1990.

Due to the relative rarity and large scale of destructive power that tornadoes possess, their occurrence or the possibility that they may occur can often create what could be considered sensationalism in their reporting. This results in so-called weather wars, in which competing local media outlets, particularly TV news stations, engage in continually escalating technological one-upsmanship and drama in order to increase their market share. This is especially evident in tornado-prone markets, such as those in the Great Plains.

According to Environment Canada, the chances of being killed by a tornado are 12 million to 1 (12,000,000:1). One may revise this yearly and/or regionally, but the probability may be factually stated to be low. Tornadoes do cause millions of dollars in damage, both economic and physical, displacement, and many injuries every year.

Some common myths about tornadoes which people should not rely upon to protect them are given in the article on The Super Outbreak of 1974, in which some of the most dangerous tornadoes formed near rivers and crossed them, and crossed over steep hills, mountains and deep valleys. Other misconceptions and science fiction, concerning tornado formation can be found at the article for tornado myths.

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Tornadoes as a metaphor

Image:OZ5-2-94.JPG The tornado has been used by cartoonists for over 100 years as a metaphor for political upheaval. For example, according to political interpretations of theThe Wizard of Oz, the tornado takes Dorothy to a utopia, the Land of Oz, and kills the Wicked Witch of the East, who had oppressed a little people, the Munchkins. The storm cellar has also been used as a metaphor for seeking safety, as shown in the cartoon from 1894 at right.

A 1960s advertising campaign for the household cleaner, Ajax, claimed the product, "Cleans like a white tornado".

Tornadoes in dreams can often be associated with fear, chaos, and upheaval. The location where one is during a tornado dream, such as at home, can often give clues as to the meaning.

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Motion pictures with a tornado theme

The Wizard of Oz, 1939
Mr. and Mrs. Bridge, 1990
Night of the Twisters (TV), 1996
Tornado! (TV), 1996
Twister, 1996
Atomic Twister (TV), 2001
The Day After Tomorrow, 2004
The Perfect Disaster: Super Tornado (Discovery Channel), premiered on March 19, 2006

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References

Thomas P. Grazulis (1993). Significant Tornadoes 1680-1991, A Chronology and Analysis of Events. The Tornado Project of Environmental Films. ISBN 1879362007

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