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A tornado is a violently rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as twisters or cyclones, although the word cyclone is used in meteorology, in a wider sense, to name any closed low pressure circulation. Tornadoes come in many shapes and sizes, but they are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust. Most tornadoes have wind speeds less than , are about across, and travel a few miles (several kilometers) before dissipating. The most extreme tornadoes can attain wind speeds of more than , stretch more than across, and stay on the ground for dozens of miles (more than 100 km). Various types of tornadoes include the landspout, multiple vortex tornado, and waterspout. Waterspouts are characterized by a spiraling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornadoes that develop over bodies of water, but there is disagreement over whether to classify them as true tornadoes. These spiraling columns of air frequently develop in tropical areas close to the equator, and are less common at high latitudes. Other tornado-like phenomena that exist in nature include the gustnado, dust devil, fire whirls, and steam devil; downbursts are frequently confused with tornadoes, though their action is dissimilar. Tornadoes have been observed on every continent except Antarctica. However, the vast majority of tornadoes occur in the Tornado Alley region of the United States, although they can occur nearly anywhere in North America. They also occasionally occur in south-central and eastern Asia, northern and east-central South America, Southern Africa, northwestern and southeast Europe, western and southeastern Australia, and New Zealand.〔 Tornadoes can be detected before or as they occur through the use of Pulse-Doppler radar by recognizing patterns in velocity and reflectivity data, such as hook echoes or debris balls, as well as through the efforts of storm spotters. There are several scales for rating the strength of tornadoes. The Fujita scale rates tornadoes by damage caused and has been replaced in some countries by the updated Enhanced Fujita Scale. An F0 or EF0 tornado, the weakest category, damages trees, but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes. Doppler radar data, photogrammetry, and ground swirl patterns (cycloidal marks) may also be analyzed to determine intensity and assign a rating.〔Edwards, Roger et al. (May 2013). ("Tornado Intensity Estimation: Past, Present, and Future." ) ''Bulletin of the American Meteorological Society.'' pp. 641-653. Retrieved 2013-12-18.〕 ==Etymology== The word ''tornado'' is an altered form of the Spanish word ''tronada'', which means "thunderstorm". This in turn was taken from the Latin ''tonare'', meaning "to thunder". It most likely reached its present form through a combination of the Spanish ''tronada'' and ''tornar'' ("to turn"); however, this may be a folk etymology. A tornado is also commonly referred to as a "twister", and is also sometimes referred to by the old-fashioned colloquial term ''cyclone''.〔〔(【引用サイトリンク】 title =Frequently Asked Questions about Tornadoes )〕 The term "cyclone" is used as a synonym for "tornado" in the often-aired 1939 film ''The Wizard of Oz''. The term "twister" is also used in that film, along with being the title of the 1996 tornado-related film ''Twister''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tornado」の詳細全文を読む スポンサード リンク
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