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Rogue waves (also known as freak waves, monster waves, episodic waves, killer waves, extreme waves, and abnormal waves) are relatively large and spontaneous surface waves that occur far out in open water, and are a threat even to large ships and ocean liners. Rogue waves present considerable danger for several reasons: they are rare, unpredictable, may appear suddenly or without warning, and can impact with tremendous force. A 12-meter wave in the usual "linear" model would have a breaking force of 6 million tons per square metre (MT/m2) and modern ships are designed to tolerate a breaking wave of 15 MT/m2, but a rogue wave can dwarf both of these figures with a breaking force of 100 MT/m2.〔 In oceanography, rogue waves are more precisely defined as waves whose height is more than twice the significant wave height (''H''s or SWH), which is itself defined as the mean of the largest third of waves in a wave record. Therefore, rogue waves are not necessarily the biggest waves found on the water; they are, rather, unusually large waves for a given sea state. Rogue waves seem not to have a single distinct cause, but occur where physical factors such as high winds and strong currents cause waves to merge to create a single exceptionally large wave.〔 Rogue waves can occur in other media than water. In particular, optical rogue waves allow study of the phenomenon in the laboratory. A 2015 paper studied the wave behavior around a rogue wave, including optical, and the Draupner wave, and concluded that "rogue events do not necessarily appear without a warning, but are often preceded by a short phase of relative order".〔(Predictability of Rogue Events ), Simon Birkholz, Carsten Brée, Ayhan Demircan, and Günter Steinmeyer, Physics Review Letters 114, 213901, 28 May 2015〕 == Background == Rogue waves are an open water phenomenon, in which winds, currents, non-linear phenomena such as solitons, and other circumstances cause a wave to briefly form that is far larger than the "average" large occurring wave (the significant wave height or 'SWH') of that time and place. The basic underlying physics that makes phenomena such as rogue waves possible is that different gravity waves can travel at different speeds, and so they can "pile up" in certain circumstances - known as "constructive interference". (In deep ocean the speed of a gravity wave is proportional to the square root of its wavelength--the distance peak-to-peak.) However other situations can also give rise to rogue waves, particularly situations where non-linear effects or instability effects can cause energy to move between waves and be concentrated in one or very few extremely large waves before returning to "normal" conditions. Once considered mythical and lacking hard evidence for their existence, rogue waves are now proven to exist and known to be a natural ocean phenomenon. Eyewitness accounts from mariners and damage inflicted on ships have long suggested they occurred; however, their scientific measurement was only positively confirmed following measurements of the "Draupner wave", a rogue wave at the Draupner platform in the North Sea on January 1, 1995, with a maximum wave height of (peak elevation of ) . During that event, minor damage was also inflicted on the platform, far above sea level, confirming that the reading was valid. Their existence has also since been confirmed by satellite imagery of the ocean surface. A rogue wave is a natural ocean phenomenon that is not caused by land movement, only lasts briefly, occurs in a limited location, and most often happens far out at sea.〔 Rogue waves are considered rare but potentially very dangerous, since they can involve the spontaneous formation of massive waves far beyond the usual expectations of ship designers, and can overwhelm the usual capabilities of ocean-going vessels which are not designed for such encounters. Rogue waves are therefore distinct from tsunamis.〔 Tsunamis are caused by massive displacement of water, often resulting from sudden movement of the ocean floor, after which they propagate at high speed over a wide area. They are more or less unnoticeable in deep water and only become dangerous as they approach the shoreline and the ocean floor becomes shallower; therefore tsunamis do not present a threat to shipping at sea (the only ships lost in the 2004 Asian tsunami were in port). They are also distinct from megatsunamis, which are single massive waves caused by sudden impact, such as meteor impact or landslides within enclosed or limited bodies of water. They are also different from the waves described as "hundred-year waves", which is a purely statistical prediction of the highest wave likely to occur in a hundred-year period in a particular body of water. In February 2000, a British oceanographic research vessel, the RRS ''Discovery'', sailing in the Rockall Trough west of Scotland encountered the largest waves ever recorded by scientific instruments in the open ocean, with a SWH of and individual waves up to .〔Holliday, NP, MJ Yelland, RW Pascal, VR Swail, PK Taylor, CR Griffiths, and EC Kent (2006). (Were extreme waves in the Rockall Trough the largest ever recorded? ) Geophysical Research Letters, Vol. 33, L05613〕 "In 2004 scientists using three weeks of radar images from European Space Agency satellites found ten rogue waves, each or higher." Rogue waves have been cited in the media as a likely cause of the sudden, inexplicable disappearance of many ocean-going vessels. One of the very few cases in which evidence exists that may indicate a rogue wave incident is the case of the freighter MS ''München'', lost in 1978. 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「Rogue wave」の詳細全文を読む スポンサード リンク
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