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Clear-air turbulence (CAT) is the turbulent movement of air masses in the absence of any visual cues such as clouds, and is caused when bodies of air moving at widely different speeds meet.〔Stull, B. R., 1988 An introduction to Boundary Layer Meteorology, Kluwert Academic Publishers 666 pp.〕 The atmospheric region most susceptible to CAT is the high troposphere at altitudes of around as it meets the tropopause. Here CAT is most frequently encountered in the regions of jet streams. At lower altitudes it may also occur near mountain ranges. Thin cirrus cloud can also indicate high probability of CAT. CAT can be hazardous to the comfort, and, though very infrequently, even the safety, of air travelers. An increase in clear-air turbulence is an expected effect of global warming. In the journal ''Nature Climate Change'' Paul Williams of the University of Reading and Manoj Joshi of the University of East Anglia reported moderate to severe transatlantic turbulence would be 40 to 170 percent more frequent in a world that had twice as much atmospheric carbon dioxide as pre-industrial times did.〔(''Rising carbon dioxide means more air turbulence'' ) April 8, 2013 Vol.183 #9 Science News〕〔(''Climate Change Could Equal Teeth-Rattling Flights'' ) April 08, 2013 NPR〕〔(''Warming Planet Means Bumpier Flights'' ); "Climate models and turbulence algorithms forecast that, by mid-century, clear-air turbulence will be more violent and transatlantic flights will hit it twice as often" April 8, 2013 Scientific American 〕〔(''Transatlantic flights 'to get more turbulent'' ) 8 April 2013 BBC〕 == Detection == Clear-air turbulence is usually impossible to detect with the naked eye and very difficult to detect with conventional radar,〔John J. Hicks, Isadore Katz, Claude R. Landry, and Kenneth R. Hardy, "Clear-Air Turbulence: Simultaneous Observations by Radar and Aircraft" Science Science 18 August 1967:Vol. 157. no. 3790, pp. 808–809〕 with the result that it is difficult for aircraft pilots to detect and avoid it. However, it can be remotely detected with instruments that can measure turbulence with optical techniques, such as scintillometers, Doppler LIDARs, or N-slit interferometers.〔F. J. Duarte, T. S. Taylor, A. B. Clark, and W. E. Davenport, The N-slit interferometer: an extended configuration, ''J. Opt.'' 12, 015705 (2010).〕 Although the altitudes near the tropopause are usually cloudless, thin cirrus cloud can form where there are abrupt changes of air velocity, for example associated with jet streams. Lines of cirrus perpendicular to the jet stream indicate possible CAT, especially if the ends of the cirrus are dispersed, in which case the direction of dispersal can indicate if the CAT is stronger at the left or at the right of the jet stream. 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「Clear-air turbulence」の詳細全文を読む スポンサード リンク
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