Predicting Rogue Waves

Continued from page 1

By Bruce Gain

Thursday, March 01, 2007

A rogue wave, for example, likely sunk the German München cargo ship in the Atlantic in 1978. Scattered remains of the München's wreckage indicate the force of the wave that brought it down. The Bremen, a luxury ocean liner, is thought to have encountered a 30-meter wave in the South Atlantic in 2001; it was measured by the height of the impact against the ship's bridge. The Bremen's electronic controls and engines were momentarily shut down after the wave hit, which caused the ship to veer sideways against incoming waves. Had the ship's engines not been started shortly thereafter, the ship's captains reported, the ship would have almost surely gone down.

The researchers say this map of rogue waves won't change that much over time, which makes it all the more useful. Now that they've located where these huge monster waves have appeared, the researchers know where they are likely to occur again. With their real-time weather data and average-wave-height forecasts, the rogue-wave maps could help save lives. If forecasts showed that, for example, average wave heights were going to be 10 meters or more at a particular coordinate where rogue waves have been known to occur, the appropriate authorities could be alerted.

Some scientists remain cautiously skeptical, however. "Using SAR data to find wind and wave-height measurements is a good idea, and perhaps the only way you can get a global view of these parameters," says Kristian Dysthe, a mathematician with the University of Bergen, in Norway, who was not involved in the research project. "But uncertainties remain about the [equations] used."

The ultimate test to determine the accuracy of the German Space Agency's individual wave maps will depend on buoys and other moorings with sensors that can check and calibrate the results. That's why William W. Drennan, of the University of Miami, hopes to place buoys in the Southern Hemisphere off the coast of Australia, where, he says, "the waves tend to be the highest." The moorings will be sturdy enough to withstand the impact of waves up to 30 meters or more, Drennan says.

"I don't think [the German Space Agency's] data is incorrect, but you can't corroborate their measurements of individual waves with data now, because you would have really had to have been there at the right time and place," Drennan says. "But if you are in the right place long enough, like in the southern ocean, you can do that."

But where do rogue waves come from? Answering this question is one of the goals that the German Space Agency team shares with researchers at institutes and universities around the world. At present, several theories exist. Crossing seas and waves from different storms, currents and topographies, and what Lehner calls the "nonlinear interaction of different individual waves" are all thought to come into play.

In the meantime, the German Space Agency researchers say they will soon have more ESA satellite data available to add to their wave-atlas map. Images taken by ESA satellites from 2003 to 2007 could be available to complement their wave-measurement database within two years.