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Concept
Tornado climatology
Résumé
Tornadoes have been recorded on all continents except Antarctica. They are most common in the middle latitudes where conditions are often favorable for convective storm development. The United States has the most tornadoes of any country, as well as the strongest and most violent tornadoes. A large portion of these tornadoes form in an area of the central United States popularly known as Tornado Alley. Canada experiences the second most tornadoes. Ontario and the prairie provinces see the highest frequency. Other areas of the world that have frequent tornadoes include significant portions of Europe, South Africa, Philippines, Bangladesh, parts of Argentina, Uruguay, and southern and southeastern Brazil, northern Mexico, New Zealand, and far eastern Asia.
Tornado reports in the U.S. have been officially collated since 1950. These reports have been gathered by the National Climatic Data Center (NCDC), based in Asheville, North Carolina. A tornado can be reported more than once, such as when a storm crosses a county line and reports are made from two counties. The severity of tornadoes is measured by the Enhanced Fujita Scale, which measures tornado intensity on a scale of EF0 to EF5 based on wind speed and intensity of destruction. The ratings are made after the tornado has dissipated and the damage trail is carefully studied by weather professionals. A series of continuous tornado outbreaks is known as a tornado outbreak sequence.
Not every thunderstorm, supercell, squall line, or tropical cyclone will produce a tornado. Precisely the right atmospheric conditions are required for the formation of even a weak tornado. Tornadoes can form in any month when conditions are favorable. 1,000 or more tornadoes a year are reported in the contiguous United States. The high frequency of tornadoes in North America is largely due to geography, as moisture from the Gulf of Mexico is easily advected into the midcontinent with few topographic barriers in the way.
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Concepts associés (3)
Chasseur d'orages
L'activité du chasseur d'orages consiste à traquer un orage générant des tornades ou pas, dans le but de le photographier et de l'observer. Cette traque – qui a de plus en plus d'adeptes dans le monde – a permis à des chercheurs bien équipés de mieux connaître ces phénomènes météorologiques. Cependant, la plupart des chasseurs d'orages le font seulement pour assister aux phénomènes violents associés au cumulonimbus : foudre, grêle, rafale descendante et tornade.
Tornado climatology
Tornadoes have been recorded on all continents except Antarctica. They are most common in the middle latitudes where conditions are often favorable for convective storm development. The United States has the most tornadoes of any country, as well as the strongest and most violent tornadoes. A large portion of these tornadoes form in an area of the central United States popularly known as Tornado Alley. Canada experiences the second most tornadoes. Ontario and the prairie provinces see the highest frequency.
Tornado Alley
thumb|upright=1.5|Conditions météorologiques créant les tornades dans la Tornado Alley en couleur saumon au centre La Tornado Alley (en français, l'allée des tornades) est un terme commun pour désigner une région centrale des États-Unis couvrant plusieurs États ou parties d'États et où se produisent fréquemment des tornades. Elle comprend les basses terres des fleuves Mississippi, Ohio et les vallées du bas Missouri aussi bien que le sud-est des États-Unis.