The phrase ''rogue wave,'' calls to mind certain powerful images: Gigantic walls of water rise from the deep and crash down upon you, then disappear as fast as they emerged. The scariest part, really, is that there's no warning. But now, physicists think they may have found a way to predict rogue waves and other rogue events before they strike.
Scientists doubted rogue waves' existence until just 20 years ago, when a 26-meter-high rogue wave struck the Draupner oil platform in the North Sea on New Year's Day in 1995. (Mariner lore, on the other hand, has for centuries accepted the existence of rogue, or ''freak,'' waves.) That event made it clear that a rogue wave isn't just a big wave or a tsunami. As the National Ocean Service puts it, a rogue wave is ''large, unexpected, and dangerous.'' ''Large'' being at least twice as large as the significant wave height, which is the average of the top 33 percent of recorded wave heights. And by ''unexpected,'' they mean exactly that: Rogue waves are rare and as a result hard to study, so no one was sure whether they could be predicted, let alone how to do it.
That was the state of things for more than a decade after the Draupner wave, but in 2007 something weird happened: Physicists reported finding rogue waves in specially prepared light waves. Since then, rogue events have been detected in other physical systems as well, meaning that there's now enough data to at least begin speculating about whether rogue waves can be predicted.
That's exactly what physicists Simon Birkholz, Carsten Breé, Ayhan Demircan, and Günter Steinmeyer set out to do. They first gathered data on the Draupner wave, originally collected by a laser-ranging device that recorded the height of the ocean roughly every half second. The team also included data from several more recent experiments that had detected optical rogue waves. To examine whether the rogue waves in each example could have been predicted, the researchers first re-shuffled the data, effectively randomizing the time sequence of wave heights.
Comparing the re-shuffled data sets to the originals, the researchers discovered that there is some kind of repeating pattern in the minutes before a rogue wave emerges — a series of deja-vus, as the team puts it — that doesn't appear in the randomized data. In other words, there's something about the way the ocean rises and falls in the minutes before a rogue wave strikes that observers could pick up before — and indeed after — all that water comes crashing down.
Unfortunately, given the small sample of rogue events and the statistical methods the team used, it's hard to say what the pattern is — only that there is one. Further study might reveal what it is and what physical mechanisms are behind it. At the very least, the physicists write in Physical Review Letters, ''this finding appears to contrast the statement that 'rogue waves appear from nowhere and disappear without a trace.'''
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