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Scientists Find Freak Wave Hot Spots

August 10, 2009

U.S. scientists believe they have made great headway in understanding what have been termed, freak waves.

These rogue waves are relatively large and spontaneous ocean surface waves that are a major threat to large ships and ocean liners. They have a height of more than twice the significant wave height (SWH). They are not necessarily the biggest waves at sea, but they are incredibly large compared to the state of the sea. 

U.S. oceanographers developed a computer simulation that might be able to predict where and when these monster waves are likely to happen.

According to the theoretical study, prime conditions for the phenomenon are in coastal areas with varying water depths and strong currents.

Throughout history, there have been many seafaring tales about rogue waves that could overtake a ship.

These waves are characterized as measuring about three times higher than other waves on the sea in the same time frame. They can hit up to 60 feet in height, which is comparable to a six-story building.

The change of a wave’s direction and speed may be caused by sandbanks and strong currents. This causes wave energy to be concentrated on one particular point, which oceanographers call a “wave focal zone”.

Co-developer of the computer simulation, Tim Janssen of San Francisco State University, compares the zone to burning glass. A hot spot is formed by the light coming in and focuses all the energy on a single point.

The same principle applies when a wave passes over a sandbank or a current. It causes the energy to focus on a single point.

Researchers now have reason to believe that these hot spots are much more likely to drive the formation of extreme waves.

“In a normal wave field, on average, roughly three waves in every 10,000 are extreme waves,” Dr. Janssen explained.

“In a focal zone, this number could increase to about three in every 1,000 waves.”

Data from real waves was entered into the scientists’ computer model. They then performed a single experiment over and over, using different data each time.

Dr. Janssen said he next hoped to go to places known for having freak wave hotspots, such as the Cortez Banks on the coast of California in order to test whether his simulations were accurate.

He told BBC News, “What’s really important about this research, is that it is easy to validate. We have a theory now, a prediction, and we can go to areas and actually measure whether this happens or not.” 

It is vitally important to know where and when freak waves are most likely to occur to help shipping and navigation in coastal areas.

This understanding could be used for marine weather forecasts and could also inform the design of offshore platforms.

“If you know that a certain area is very prone to freak waves, then you might wish to stay away from it,” Dr. Janssen said. “Anybody out in the ocean would like to [have this information].”

However, Dr. Janssen kept emphasizing that this was a theoretical study.

“We have tried to be as realistic as we could, but we are a long way away from making a prediction solid enough for people to actually use. However, it might be something to work towards,” he said.

Dr Janssen added that the term “freak wave” was unfortunate, because it indicates that these waves are unexpected. He went on to explain that the seemingly random nature of ocean waves means that any size of wave can happen at any given time.

These findings are published in the Journal of Physical Oceanography.

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