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Tornado Alley is a colloquial term for the area of the United States (or by some definitions extending into Canada) where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in parts of Texas, Oklahoma, Kansas, South Dakota, Iowa, Missouri, New Mexico, Colorado, North Dakota, and Minnesota only. It is largely a media driven term although tornado climatologists distinguish peaks in activity in various areas〔 and storm chasers have long recognized the Great Plains tornado belt. Although the boundaries of Tornado Alley are not clearly defined, its core extends from northern Texas, Oklahoma, Kansas, into Nebraska. Some research suggests that tornadoes are becoming more frequent in the northern parts of Tornado Alley where it reaches the Canadian prairies.〔http://www.usask.ca/water/news-and-events/news/news43.php〕 Active tornado regions have also been discovered in other areas of the world, such as in parts of Europe and especially in the Pampas lowlands of Argentina extending into adjacent areas of Paraguay and extreme southern Brazil. The Pampas has a high consistency of tornadoes, whereas Bangladesh and adjacent East India have the highest frequency of violent tornadoes outside the central and southern US. == Tornado alley geographical area == Over the years, the location(s) of Tornado Alley have not been clearly defined. No definition of tornado alley has ever officially been designated by the National Weather Service (NWS).〔 Thus, differences of location are the result of the different criteria used.〔 According to the National Severe Storms Laboratory (NSSL) FAQ,〔 "Tornado Alley" is a term used by the media as a reference to areas that have higher numbers of tornadoes. A study of 1921–1995 tornadoes concluded almost one-fourth of all significant tornadoes occur in this area. Though no state is entirely free of tornadoes, they occur more frequently in the Central United States, between the Rocky Mountains and Appalachian Mountains. Texas reports the most tornadoes of any state due to its large size. Per , Kansas and Oklahoma rank first and second respectively in the number of tornadoes. Florida also reports a high number and density of tornado occurrences, though tornadoes there rarely approach the strength of those that sometimes occur in the southern plains. Regionally, the frequency of tornadoes in the United States is closely tied with the progression of the warm season when warm and cold air masses often clash.〔 Another criterion for the location of Tornado Alley (or Tornado Alleys) can be where the strongest tornadoes occur more frequently. Tornado Alley can also be defined as an area reaching from central Texas to the Canadian prairies and from eastern Colorado to western Pennsylvania.〔 It has also been asserted that there are numerous Tornado Alleys.〔 In addition to the Texas/Oklahoma/Kansas core, such areas include the Upper Midwest, the lower Ohio Valley, the Tennessee Valley and the lower Mississippi valley.〔 Some studies suggest that there are also smaller tornado alleys located across the United States. The tornado alleys in the southeastern U.S., notably the lower Mississippi Valley and the upper Tennessee Valley, are sometimes called by the nickname "Dixie Alley", coined in 1971 by Allen Pearson, former director of the National Severe Storms Forecasting Center (NSSFC).〔Gagan et al. (2010), page 147.〕 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 Alley」の詳細全文を読む スポンサード リンク
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