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Fujita scale
F0 F1 F2 F3 F4 F5

The Fujita scale (F-Scale), or Fujita-Pearson scale, is a scale for rating tornado intensity, based on the damage tornadoes inflict on human-built structures and vegetation. The official Fujita scale category is determined by meteorologists (and engineers) after a ground and/or aerial damage survey; and depending on the circumstances, ground-swirl patterns (cycloidal marks), radar tracking, eyewitness testimonies, media reports and damage imagery, as well as photogrammetry/videogrammetry if motion picture recording is available.

Contents

Background

The scale was introduced in 1971 by Ted Fujita of the University of Chicago who developed the scale together with Allen Pearson (path length and width additions in 1973), head of the National Severe Storms Forecast Center (predecessor to the Storm Prediction Center) in Kansas City, Missouri. The scale was applied retroactively to tornado reports from 1950 onward for the National Oceanic and Atmospheric Administration National Tornado Database in the United States, and occasionally to earlier infamous tornadoes. Tom Grazulis of The Tornado Project also rated all known significant tornadoes (F2-F5 or causing a fatality) in the U.S. back to 1880. Previously used in most areas outside of Great Britain, it was superseded in 2007 by the Enhanced Fujita Scale in the United States.

Though each damage level is associated with a wind speed, the Fujita scale is a damage scale, and the wind speeds associated with the damage listed are unverified. The Enhanced Fujita Scale was formulated due to research which suggested that wind speeds for strong tornadoes on the Fujita scale are greatly overestimated. However, being determined by expert elicitation with top engineers and meteorologists, the EF scale wind speeds remain as educated guesses, and are also biased to United States construction practices.

Derivation

Fujita scale technical.svg

The original scale as derived by Fujita was a 13-level scale (F0-F12) designed to smoothly connect the Beaufort scale and the Mach number scale. F1 corresponds to the twelfth level of the Beaufort scale, and F12 corresponds to Mach number 1.0. F0 was placed at a position specifying no damage (approximately the eighth level of the Beaufort scale), in analogy to how the Beaufort's zeroth level specifies little to no wind. From these wind speed numbers, qualitative descriptions of damage were made for each category of the Fujita scale, and then these descriptions were used to classify tornadoes.[1] The diagram on the right illustrates the relationship between the Beaufort, Fujita, and Mach number scales.

At the time Fujita derived the scale, little information was available on damage caused by wind, so the original scale presented little more than educated guesses at wind speed ranges for specific tiers of damage. Fujita intended that only F0-F5 be used in practice, as this covered all possible levels of damage to frame homes as well as the expected estimated bounds of wind speeds. He did, however, add a description for F6, which he phrased as "inconceivable tornado", to allow for wind speeds exceeding F5 and for possible future advancements in damage analysis which might show it.[2]

Furthermore, the original wind speed numbers have since been found to be higher than the actual wind speeds required to incur the damage described at each category. The error manifests itself to an increasing degree as the category increases, especially in the range of F3 through F5. The National Oceanic and Atmospheric Administration notes that …precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place—even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown.[2] Since then, the Enhanced Fujita Scale has been created using better wind estimates by engineers and meteorologists.

Some sources add level "F-", meaning a tornado with winds below 39 mph; on rare occasions tornadoes this weak are observed covering a wide range of path widths and lengths.

Parameters

The six categories are listed here, in order of increasing intensity.

  1. When the relative frequency of tornadoes is mentioned, it is the relative frequency in the United States. Frequencies of strong tornadoes (F2 or greater) are significantly less elsewhere in the world. Parts of southern Canada, Bangladesh and adjacent areas of eastern India, and possibly a few other areas do have frequent severe tornadoes, however data is scarce and statistics in these countries have not been studied thoroughly.
  2. The rating of any given tornado is of the most severe damage to any well-built frame home or comparable level of damage from engineering analysis of other damage.
  3. The F6 level, although present in Dr. Ted Fujita's original wind scale, was not intended for use, as it was only for example. So far no tornado has ever been measured at that strength. Therefore until there is, by definition, no such thing as an 'F6' tornado has ever existed.[2]
Scale Estimated wind speed* Relative frequency Average Damage Path Width (meters) Potential damage[3]
mph km/h
F0 40–72 64–116 38.9% 10 - 50 Minor damage.

Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.

F0 damage example
F1 73–112 117–180 35.6% 30 - 150 Moderate damage.

The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.

F1 damage example
F2 113–157 181–253 19.4% 110 - 250 Considerable damage.

Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; highrise windows broken and blown in; light-object missiles generated.

F2 damage example
F3 158–206 254–332 4.9% 200 - 500 SCritical damage.

Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; skyscrapers twisted and deformed with massive destruction of exteriors; heavy cars lifted off the ground and thrown.

F3 damage example
F4 207–260 333–418 1.1% 400 - 900 Severe damage.

Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated. Skyscrapers and highrises toppled and destroyed.

F4 damage example
F5 261–318 419–512 <0.1% 1100 ~ Devastating damage.

Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 m (109 yd); trees debarked; steel reinforced concrete structures badly damaged; incredible phenomena will occur.

F5 damage example

*Fujita's initial wind speed estimates have since been found to be highly inaccurate. See Enhanced Fujita Scale

NB: Path widths are averages of tornadoes of their Fujita rating and are approximate values; tornado intensity should not be assumed by the size of the damage path. One F5 tornado had a damage path just 90 meters wide at one point.

Decommission in the US

The Fujita scale, introduced in 1971 as a means to differentiate tornado intensity and path area, assigned wind speeds to damage that were, at best, educated guesses.[4] Fujita and others recognized this immediately and intensive engineering analysis was conducted through the rest of the 1970s. This research, as well as subsequent research, showed that tornado wind speeds required to inflict the described damage were actually much lower than the F-scale indicated, particularly for the upper categories. Also, although the scale gave general descriptions for the type of damage a tornado could cause, it gave little leeway for strength of construction and other factors that might cause a building to receive higher damage at lower wind speeds. Fujita tried to address these problems somewhat in 1992 with the Modified Fujita Scale,[5] but by then he was semi-retired and the National Weather Service was not in a position for the undertaking of updating to an entirely new scale, so it was a minor step.[6]

In the USA only, on February 1, 2007, the Fujita scale was decommissioned in favor of what these scientists believe is a more accurate Enhanced Fujita Scale, which replaces it. The EF Scale is thought to improve on the F-scale on many counts—it accounts for different degrees of damage that occur with different types of structures, both man-made and natural. The expanded and refined damage indicators and degrees of damage standardize what was somewhat ambiguous. It also is thought to provide a much better estimate for wind speeds, and sets no upper limit on the wind speeds for the strongest level, EF5.

The original Fujita scale is still used in most of the rest of the world.

See also

References

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Notes

  1. ^ Storm Prediction Center Enhanced Fujita Scale (EF Scale)
  2. ^ a b c Tornado FAQ. Storm Prediction Center. Site accessed June 27, 2006.
  3. ^ Fujita Tornado Damage Scale Storm Prediction Center. Accessed 2009-05-20.
  4. ^ Fujita, Tetsuya Theodore (1971). Proposed characterization of tornadoes and hurricanes by area and intensity. Chicago: University of Chicago. 
  5. ^ http://www.spc.noaa.gov/MF Scale and EF Scale.
  6. ^ Fujita, Tetsuya Theodore (1992). Memoirs of an Effort to Unlock the Mystery of Severe Storms. Chicago: University of Chicago. 

Bibliography

External links


Fujita scale
F0 F1 F2 F3 F4 F5

The Fujita scale (F-Scale), or Fujita-Pearson scale, is a scale for rating tornado intensity, based on the damage tornadoes inflict on human-built structures and vegetation. The official Fujita scale category is determined by meteorologists (and engineers) after a ground and/or aerial damage survey; and depending on the circumstances, ground-swirl patterns (cycloidal marks), radar tracking, eyewitness testimonies, media reports and damage imagery, as well as photogrammetry/videogrammetry if motion picture recording is available.

Contents

Background

The scale was introduced in 1971 by Ted Fujita of the University of Chicago who developed the scale together with Allen Pearson (path length and width additions in 1973), head of the National Severe Storms Forecast Center (predecessor to the Storm Prediction Center) in Kansas City, Missouri. The scale was applied retroactively to tornado reports from 1950 onward for the National Oceanic and Atmospheric Administration National Tornado Database in the United States, and occasionally to earlier infamous tornadoes. Tom Grazulis of The Tornado Project also rated all known significant tornadoes (F2-F5 or causing a fatality) in the U.S. back to 1880. Previously used in most areas outside of Great Britain, it was superseded in 2007 by the Enhanced Fujita Scale in the United States.

Though each damage level is associated with a wind speed, the Fujita scale is a damage scale, and the wind speeds associated with the damage listed are unverified. The Enhanced Fujita Scale was formulated due to research which suggested that wind speeds for strong tornadoes on the Fujita scale are greatly overestimated. However, being determined by expert elicitation with top engineers and meteorologists, the EF scale wind speeds remain as educated guesses, and are also based to United States construction practices.

Derivation

The original scale as derived by Fujita was a 13-level scale (F0–F12) designed to smoothly connect the Beaufort scale and the Mach number scale. F1 corresponds to the twelfth level of the Beaufort scale, and F12 corresponds to Mach number 1.0. F0 was placed at a position specifying no damage (approximately the eighth level of the Beaufort scale), in analogy to how the Beaufort's zeroth level specifies little to no wind. From these wind speed numbers, qualitative descriptions of damage were made for each category of the Fujita scale, and then these descriptions were used to classify tornadoes.[1] The diagram on the right illustrates the relationship between the Beaufort, Fujita, and Mach number scales.

At the time Fujita derived the scale, little information was available on damage caused by wind, so the original scale presented little more than educated guesses at wind speed ranges for specific tiers of damage. Fujita intended that only F0-F5 be used in practice, as this covered all possible levels of damage to frame homes as well as the expected estimated bounds of wind speeds. He did, however, add a description for F6, which he phrased as "inconceivable tornado", to allow for wind speeds exceeding F5 and for possible future advancements in damage analysis which might show it.[2]

Furthermore, the original wind speed numbers have since been found to be higher than the actual wind speeds required to incur the damage described at each category. The error manifests itself to an increasing degree as the category increases, especially in the range of F3 through F5. The National Oceanic and Atmospheric Administration notes that "... precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place—even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown."[2] Since then, the Enhanced Fujita Scale has been created using better wind estimates by engineers and meteorologists.

Some sources add level F+", meaning a tornado with winds below 39 mph; on rare occasions tornadoes this weak are observed covering a wide range of path widths and lengths.

Parameters

The six categories are listed here, in order of increasing intensity.

  1. When the relative frequency of tornadoes is mentioned, it is the relative frequency in the United States. Frequencies of strong tornadoes (F2 or greater) are significantly less elsewhere in the world. Parts of southern Canada, Bangladesh and adjacent areas of eastern India, and possibly a few other areas do have frequent severe tornadoes; however, data are scarce and statistics in these countries have not been studied thoroughly.
  2. The rating of any given tornado is of the most severe damage to any well-built frame home or comparable level of damage from engineering analysis of other damage.
  3. The F6 level, although present in Dr. Ted Fujita's original wind scale, was not intended for use, as it was only for example. [2]
Scale Estimated wind speed* Relative frequency Average Damage Path Width (meters) Potential damage[3]
mph km/h
F0 40–72 64–116 38.9% 10–50 Minor damage.

Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.

F1 73–112 117–180 35.6% 30–150 Moderate damage.

The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.

F2 113–157 181–253 19.4% 110–250 Considerable damage.

Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; highrise windows broken and blown in; light-object missiles generated.

F3 158–206 254–332 4.9% 200–500 Critical damage.

Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; skyscrapers twisted and deformed with massive destruction of exteriors; heavy cars lifted off the ground and thrown.

F4 207–260 333–418 1.1% 400–900 Severe damage.

Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated. Skyscrapers and highrises toppled and destroyed.

F5 261–318 419–512 <0.1% 1100 ~ Devastating damage.

Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 m (109 yd); trees debarked; steel reinforced concrete structures badly damaged; incredible phenomena will occur.

*Fujita's initial wind speed estimates have since been found to be highly inaccurate. See Enhanced Fujita Scale

NB: Path widths are averages of tornadoes of their Fujita rating and are approximate values; tornado intensity should not be assumed by the size of the damage path. One F5 tornado had a damage path just 90 meters wide at one point.

Decommission in the US

The Fujita scale, introduced in 1971 as a means to differentiate tornado intensity and path area, assigned wind speeds to damage that were, at best, educated guesses.[4] Fujita and others recognized this immediately and intensive engineering analysis was conducted through the rest of the 1970s. This research, as well as subsequent research, showed that tornado wind speeds required to inflict the described damage were actually much lower than the F-scale indicated, particularly for the upper categories. Also, although the scale gave general descriptions for the type of damage a tornado could cause, it gave little leeway for strength of construction and other factors that might cause a building to receive higher damage at lower wind speeds. Fujita tried to address these problems somewhat in 1992 with the Modified Fujita Scale,[5] but by then he was semi-retired and the National Weather Service was not in a position for the undertaking of updating to an entirely new scale, so it was a minor step.[6]

In the USA and some other countries, on February 1, 2007, the Fujita scale was decommissioned in favor of what these scientists believe is a more accurate Enhanced Fujita Scale, which replaces it. The EF Scale is thought to improve on the F-scale on many counts—it accounts for different degrees of damage that occur with different types of structures, both man-made and natural. The expanded and refined damage indicators and degrees of damage standardize what was somewhat ambiguous. It also is thought to provide a much better estimate for wind speeds, and sets no upper limit on the wind speeds for the strongest level, EF5. Several countries, including Canada and France, continue to use the original Fujita Scale.

See also

References

Notes

  1. ^ Storm Prediction Center Enhanced Fujita Scale (EF Scale)
  2. ^ a b c Tornado FAQ. Storm Prediction Center. Site accessed June 27, 2006.
  3. ^ Fujita Tornado Damage Scale Storm Prediction Center. Accessed 2009-05-20.
  4. ^ Fujita, Tetsuya Theodore (1971). Proposed characterization of tornadoes and hurricanes by area and intensity. Chicago: University of Chicago. 
  5. ^ http://www.spc.noaa.gov/MF Scale and EF Scale.
  6. ^ Fujita, Tetsuya Theodore (1992). Memoirs of an Effort to Unlock the Mystery of Severe Storms. Chicago: University of Chicago. 

Bibliography

External links


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Contents

English

Wikipedia-logo.png
Wikipedia has an article on:

Wikipedia

Etymology

From the Japanese-American meteorologist Tetsuya Theodore "Ted" Fujita (藤田哲也).

Proper noun

Singular
Fujita scale

Plural
-

Fujita scale

  1. A scale used to rate the intensity of a tornado

See also


Simple English

Fujita scale
F0 F1 F2 F3 F4 F5

The Fujita scale, is a scale used for rating tornado strength, based on the damage tornadoes cause on human-built buildings and vegetation. The official Fujita scale category is determined by meteorologists (and engineers) after a ground and/or aerial damage inspection; also including analysis of available sources such as eyewitness accounts and damage images and/or videos.

Scale Wind speed* Relative frequency Common Damage Path Width (meters) Example of Damage[1]
mph km/h
F0 40–72 64–116 38.9% 10 - 50 Small damage.

Some damage to chimneys; branches broken off trees; sign boards damaged.

F1 73–112 117–180 35.6% 30 - 150 Medium damage.

The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed or rolled over; moving cars and trucks pushed off the roads; garages may be destroyed.

F2 113–157 181–253 19.4% 110 - 250 Fairly bad damage.

Roofs come off frame houses; mobile homes destroyed; big trees snapped or uprooted.

F3 158–206 254–332 4.9% 200 - 500 Bad damage.

Roofs and some walls come off well-made houses; trains rolled over; most trees in forest uprooted; skyscrapers twisted and messed up; heavy cars lifted off the ground and thrown.

F4 207–260 333–418 1.1% 400 - 900 Very bad damage.

Well-made houses leveled; buildings and other things with weak foundations blown away very far; skyscrapers and highrises destroyed.

F5 261–318 419–512 <0.1% 1100 ~ Worst damage.

Strong frame houses lifted off foundations and thrown very far away which are soon destroyed; trees debarked; strong steel concrete structures badly damaged.


Other F0 Rated Tornadoes:

  • Dust Devil
  • Waterspout
  • Fire whirl(well can still burn things up)
  • Steam Tornado

References



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