Fujita scale

Fujita scale, Beaufort scale and speed of sound (Mach)

The Fujita scale was developed by Tetsuya Theodore Fujita in 1971 . It is used to classify damage for strong winds such as tornadoes and downbursts . In 2007, a further development of the F-scale, the Enhanced Fujita Scale  (EF, 'improved Fujita scale'), was introduced in the USA and is becoming increasingly popular.

F scale

The F-scale is a 13-step mathematical interpolation between the Beaufort scale and the speed of sound ( Mach 1). The speed v can be represented as a function of the Fujita scale value F as follows:

${\displaystyle v[\mathrm {m/s} ]=6{,}3\cdot (F+2)^{3/2}}$ or. ${\displaystyle v[\mathrm {km/h} ]=22{,}68\cdot (F+2)^{3/2}}$

The following empirical relationship exists between F and the Beaufort wind force B:

${\displaystyle F\approx 0{,}2601\cdot B-2}$ or. ${\displaystyle B\approx 3{,}845\cdot (F+2)}$

Because precise measurements of wind speed are often not available, tornadoes are often classified according to the damage they cause. It happens again and again that experienced meteorologists determine different F-classes for the same tornado based on the damage or that tornadoes are subsequently upgraded or downgraded.

The transfer of the F-scale to Europe is another problem, as the European construction of houses and the size of mobile homes differs considerably from the American one. In view of these regional differences in construction, a scale was developed by TorDACH , taking into account vegetation damage , which is based on the TORRO scale, which is twice as fine as the Fujita scale and can be viewed in the web links.

Occasionally, subcritical tornadoes, i.e. those that cause no damage and whose intensity is therefore below F0, are also classified with negative values ​​on the F scale, i.e. as F-1 or F-2 tornadoes. Similarly, negative values ​​for subcritical tornadoes are also used on the TORRO scale.

Classification of the Fujita scale

step	Wind speed		Damage
	in m / s	in km / h
F0	≤ 32.5	63-117	There is slight damage to chimneys, broken branches and tree tops, uprooting of shallow-rooted trees and overturned billboards. F0 was introduced to prevent tornadoes below Bft. Class 12.
F1	32.5-50	118-180	Corrugated iron or roof tiles are lifted off, mobile homes overturned, moving cars are shifted.
F2	50-70	181-253	Roofs are covered as a whole, mobile homes are completely destroyed, large trees are uprooted, light objects become dangerous projectiles. Example: Tornado in the Viersen district on May 16, 2018
F3	70-92	254-332	Roofs and light walls are being removed, trains derail, most of the forest is being uprooted, trucks and cars are overturned or moved, cars can be lifted. Example: Tornado in Bützow
F4	92-116	333-418	Wooden houses with weak anchoring are moved, heavy objects turn into dangerous projectiles. Example: Tornado over Pforzheim
F5	116-142	419-512	Wooden houses are torn from their foundations, shifted widely and dismantled. An F5 tornado can peel asphalt from the road. Example: Tri-State Tornado
F6	142-170	513-612	Officially, no F6 tornado has yet been observed. On May 3, 1999, Oklahoma recorded the strongest tornado in US history. The upper error tolerance of the measured wind speeds was in the F6 range. It is controversial whether this event was an F6 tornado. It is officially classified as F5.
F7	170-199	612-717	Theoretical values ​​that have not yet been observed.
F8	199-230	717-827
F9	230-262	827-943
F10	262-295	943-1063
F11	295-330	1063-1188
F12	> 330	> 1188	These wind speeds cannot be achieved on earth. (Wind cannot exceed the speed of sound.)

Enhanced Fujita Scale

While tornadoes are classified according to the TORRO scale in Europe and the Fujita scale is not officially recognized, in the USA the classification of tornadoes using the Fujita scale is very common. There the Fujita scale was expanded to the so-called Enhanced Fujita Scale (abbreviated EF scale), which has replaced the original Fujita scale since February 1, 2007. It was also supplemented by 28 damage indicators or types in order to allow a more precise classification.

The scale includes levels from EF0 to EF5, with the steps between the individual levels being smaller than in the Fujita scale; so one speaks of an EF5 tornado from a speed of 322 km / h (F3 / T7) or 200  mph . There is therefore no longer any distinction between an F4 and F5 tornado, since, for example, with the widespread lightweight construction , no difference in intensity can be determined based on the damage caused.

However, some tornado researchers are critical of the EF scale; Bernold Feuerstein , for example, is of the opinion that it is very possible to differentiate on the basis of the damage above 320 km / h. The EF scale is not recognized outside of the US, partly because it relies too much on American construction . In addition, measurements in Germany revealed that the wind speeds indicated on the scale do not quite match the speeds actually measured.

Enhanced Fujita Scale

step	Wind speed			Damage example
	in km / h	in mph	in m / s
EF0	104-137 km / h	65-85 mph	29-37 m / s
EF1	139–177 km / h	86-110 mph	38-49 m / s
EF2	178-217 km / h	111-135 mph	50-61 m / s
EF3	218–265 km / h	136-165 mph	62-74 m / s
EF4	267-322 km / h	166-200 mph	75-89 m / s
EF5	> 322 km / h	> 200 mph	> 90 m / s

See also

• Saffir Simpson hurricane wind scale
• Winch and wind systems
• Cyclone

Web links

Commons : Fujita scale  - album containing pictures, videos and audio files

• Damage description adapted for Central Europe (TorDACH)
• NCDC Educational Topics (English)
• Tetsuya Theodore Fujita (English)
• Enhanced F Scale for Tornado Damage (English)

Individual evidence

1. ↑ TORRO and Fujita scale Description, adapted for Central Europe ( Memento of the original from August 25, 2005 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
2. ↑ ^{a b} Enhanced F Scale for Tornado Damage
3. ↑ ^{a b c} What does the new tornado scale look like? ( Memento of the original from November 29, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
4. ↑ Destructive tornado in Oklahoma - also possible here? ( Memento of the original from November 29, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.