Scale of Fujita improved

The Scale of Fujita improved , or EFF (according to English Enhance Fujita), is a scale of classification of the force of the tornadoes according to the caused damage. It used with the the United States to replace the original scale of Fujita since the summer season 2007. It was developed to mitigate the weaknesses noted in the original scale who showed uncertainties when with the force of the winds necessary to cause certain damage and with the evaluation of similar situations but having affected constructions of various solidities.

History

The scale of Fujita was developed by Tetsuya Theodore Fujita of the Université of Chicago, which was at the time the most famous expert in the field, in collaboration with the meteorologist Allan Pearson, today with the head of the Storm Prediction Center (center of forecast of the storms violent one) with the the United States. It was adopted in 1971 like operational instrument of classification of the intensity of the tornadoes. It comprises up to 12 categories but only the categories from 0 to 5 were noted in reality (F0 with F5). Speeds of winds communicated in this scale correspond to an estimate of the winds necessary to produce such damage, they are thus provided only as an indication since no experimental correlation between the speed of the winds and the damage had been carried out.

Very early, the scale has defendant certain limitations, as for example the fact that it does not take account of materials employed or the quality of construction of the damaged structures, or that it is satisfied with too a small number of indicators, so much so that in certain cases, these indicators are simplified to the extreme. The fact that foundations were swept class of office a tornado of F5 category, without to take account of the type of structure, nor the rate of horizontal travel of the tornado. It as frequently arrives as of the tornadoes having speeds of winds higher than F5 are classified all the same in this category, reason for which no tornado was recorded in a higher category to date. This is explained because of the physical constraints, but also of the resolution of the material of measurement used.

Because of the limitations of the original scale of Fujita, scientists and experts decided to establish of it a new version improved within the framework of the Fujita Scale Enhancement Project at the research center on the wind and the ingenery with the Université Texas Tech. They analyzed of 2000 to 2004 the studies of engineers published since the Années 1970 and the reports/ratios of damage noted by the meterologic senior ones comparing the effects of tornadoes and other damage by the wind on various structures.

The improved scale was officially revealed by the National Weather Service (NWS) the February 2nd 2006 with the annual conference of the American Meteorological Society with Atlanta in Georgia. It is coming into effect the 2007 for all the evaluations made by the NWS. One still uses the original scale in parallel for a certain time in order to note the differences in evaluation, if it of A. the NWS does not envisage there however to reclassify the tornadoes which occurred before the adoption of the new scale.

It was used the first time at the time of an event of multiple tornadoes to Greensburg, Kansas, the May 4th 2007.

Methodology

The scale of Fujita improved is based on 28 indicators of damage, which takes account of the types of buildings or structure, of materials employed, as well as quality of construction, and which comprises a greater number of graduations. It also uses the estimates of winds being able to be obtained by the weather Radars, the Photogrammétrie as well as the circles left in the cultures and on the ground.

The two scales are thus similar, only the more elaborate way to determine the intensity of the damage is different and the level from the winds necessary to produce them. The new scale comprises the same categories from 0 to 5 (EF0 with EF5) by adjusting the winds estimated according to the studies and comprises a mode of evaluation of the very precise damage. Indeed, the meteorologists had the impression that the winds estimated before to cause a certain level of damage were too high and the engineers theirs gave reason. Thus the total devastation of F5 caused by winds estimated at more than 420 km/h required only winds of 324 km/h what was given like level for EF5. At the time of an event, the investigator must:

to locate in the table the type of damage (ID);
to go then in the part of characterization of the attacks (CA) and to find what describes best the damage;
it draws lower and higher speed being able to produce them and connects that from it on scale EFF;
if there are several types of damage, it must remake the stages and make an average of the results;

Improved scale

The table below gives the six categories of Scale EFF by order of importance. The force of the winds and the examples photographic are updated compared to the old scale but description is rather similar to the latter. The more precise description in the way of evaluating this damage is found in the following section.

Indicators of damage and its intensity

Here various categories of damage and scales of intensity for each one:

Effects of the change

The fact of giving more guides to estimate the force of the tornadoes should make it possible to better compare situations different and thus to have less variability in the estimates from one event to another. Thus, a tornado passing in fields or an inhabited place could be difficult to compare with the old scale. This could carry out to under or over-estimate.

The NWS estimates that the relation between the old scale and the news is rather close so that one names only few displacements from one category to another. It is not thought either whom there will be more classified tornadoes EF5 even if the limit of estimated winds were decreased. Indeed, the best evaluation offered by the tables of the types of damage holds account of it. Moreover, category EF5 does not comprise higher limit of winds.

See too

External bonds

National Weather Service Improves Tornado System Rating by NOAA News
The Enhanced Fujita Scale (EFF Scale) (NOAA/SPC)
Fujita Scale Enhancement Project (Wind Science and Engineering Research Center At Texas Tech University)
has Guide for Conducting Convective Windstorm Surveys (NWS SR146)
The Tornado: Year Engineering-Oriented Prospect (NWS SR147)

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