Rogue Waves

TheQuixote

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Freak waves spotted from space

The shady phenomenon of freak waves as tall as 10 storey buildings had finally been proved, the European Space Agency (Esa) said on Wednesday.
Sailors often whisper of monster waves when ships sink mysteriously but, until now, no one quite believed them.

As part of a project called MaxWave - which was set up to test the rumours - two Esa satellites surveyed the oceans.

During a three week period they detected 10 giant waves, all of which were over 25m (81ft) high.

Strange disappearances

Over the last two decades more than 200 super-carriers - cargo ships over 200m long - have been lost at sea. Eyewitness reports suggest many were sunk by high and violent walls of water that rose up out of calm seas.

But for years these tales of towering beasts were written off as fantasy; and many marine scientists clung to statistical models stating monstrous deviations from the normal sea state occur once every 1,000 years.

Wolfgang Rosenthal, GKSS Research Centre, Germany
"Two large ships sink every week on average," said Wolfgang Rosenthal, of the GKSS Research Centre in Geesthacht, Germany. "But the cause is never studied to the same detail as an air crash. It simply gets put down to 'bad weather'."

To prove the phenomenon or lay the rumours to rest, a consortium of 11 organisations from six EU countries founded MaxWave in December 2000.

As part of the project, Esa tasked two of its Earth-scanning satellites, ERS-1 and ERS-2, to monitor the oceans with their radar.

The radars sent back "imagettes" - pictures of the sea surface in a rectangle measuring 10 by 5km (6 by 2.5 miles), which were taken every 200km (120 miles).

Around 30,000 separate imagettes were produced by the two satellites during a three-week period in 2001 - and the data was mathematically analysed.

Esa says the survey revealed 10 massive waves - some nearly 30m (100 ft) high.

"The waves exist in higher numbers than anyone expected," said Dr Rosenthal.
Wave map

Ironically, while the MaxWave research was going on, two tourist liners endured terrifying ordeals. The Breman and the Caledonian Star cruisers had their bridge windows smashed by 30m waves in the South Atlantic.

The Bremen was left drifting for two hours after the encounter, with no navigation or propulsion.

Now that their existence is no longer in dispute, it is time to gain a better understanding of these rogues.

In the next phase of the research, a project called WaveAtlas will use two years' worth of imagettes to create a worldwide atlas of freak wave events.

The goal is to find out how these strange cataclysmic phenomena may be generated, and which regions of the seas are most at risk.

Dr Rosenthal concluded: "We know some of the reasons for the rogue waves, but we do not know them all."


BBCi News 22/07/04
 

James_H

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This is exciting, and it's also interesting how such a literally big phenonemon has escaped scientific credence for so long. It's like the meteorites.
 

Stormkhan

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Taking into account the size of super-cargo carriers this is a very scary concept.
It surprises me that this satellite research didn't begin earlier.
 

brianellwood

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Typical. Eyewitnesses over the years have reported huge waves of water swamping vessels, but scientists have said "exaggeration, waves that high cannot be physically generated."
Well there you go, satellite cameras have seen them now so it must be so, "but of course, we don't understand the mechanism at present.":rolleyes:
Giant cetaceans? Rubbish!
 
A

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brian ellwood said:
Typical. Eyewitnesses over the years have reported huge waves of water swamping vessels, but scientists have said "exaggeration, waves that high cannot be physically generated."
Well there you go, satellite cameras have seen them now so it must be so, "but of course, we don't understand the mechanism at present.":rolleyes:
Giant cetaceans? Rubbish!
Watch just how quickly a classic Fortean phenomenon becomes seamlessly integrated into the fabric of scientific orthodoxy.

;)

Although the recent Horizon 'Freak Waves' programme on the subject did show that the theoretical mathematics do lead to a sort of harmonic, mega-wave version of "high C" on the high seas.
 

Sarah_P

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For some reason the thought of massive waves coming out of a calm sea scares the Bejaysus outta me *shudder*. Nature can be truly terrifying.
 

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Both my adult daughters have an irrational fear of tidal waves, arrived at independently.

We've never lived near the sea or been involved in any seagoing disaster. :confused:
 

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Monday, April 18, 2005 - Page updated at 12:00 a.m.

Freak wave damages cruise ship, injuring 4

By The Associated Pres

CHARLESTON, S.C. — A seven-story wave damaged a cruise ship returning from the Bahamas over the weekend, smashing windows, flooding more than 60 cabins and injuring four passengers.

The Norwegian Dawn was diverted from its route when the ship ran into rough weather on the way back to New York on Saturday.

The 965-foot-long vessel docked in the Charleston harbor for repairs, and departed for New York early yesterday after a Coast Guard inspection, officials said. It was expected back in New York by noon today.

"The ship was hit by a freak wave that caused two windows to break in two different cabins," Norwegian Cruise Line said in a statement. It said 62 cabins flooded and four passengers suffered cuts and bruises. The wave reached as high as deck 10 on the ship, company spokeswoman Susan Robison said yesterday.

James Fraley, who was taking a honeymoon cruise with his wife, said they called their loved ones as the wave pounded the boat because they thought the ship was going down.

"It was pure hell. We're talking ... waves hitting the 10th floor, knocking Jacuzzis on the 12th floor overboard, people sleeping in hallways in life jackets," Fraley told WCBD-TV in Charleston. "Just pure pandemonium."

The ship's hull was damaged, but the vessel was not taking on water, said Keith Moore of the Coast Guard Group Charleston.

"All the passengers had donned personal flotation devices as a precaution," Moore told The (Charleston) Post and Courier.

The cruise line said that passengers whose cabins were flooded were being flown home from Charleston and that the safety of the ship "was in no way compromised by this incident." Each passenger on the ship got a refund of half the trip's cost and a voucher for half the price of a future cruise, Robison said.

Fraley said cruise-ship employees also opened the bar. "They tried giving free alcohol away to make up for it," he said. "That's not going to do it."

The ship left New York last Sunday with 2,500 passengers aboard.

Robison said about 300 passengers decided not to return by boat. About 100 people were flown back to New York and the rest made their own arrangements, she said.

Copyright © 2005 The Seattle Times Company
http://seattletimes.nwsource.com/html/n ... ave18.html
 

Kondoru

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But Ive heard that cruises are not worth it anyway...

Read a book about those ships sinking many years back. Author put it down to metal fatigue which may contribute. (a ships not going to sink if the hull remains intact and it is able to retain positive bouyancy.) But also the fact that most sailors these days come from very poor nations, and so no one gets worked up when they die...
 

canwyl_corf

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Taking into account the size of super-cargo carriers this is a very scary concept.
It surprises me that this satellite research didn't begin earlier.
For some reason the thought of massive waves coming out of a calm sea scares the Bejaysus outta me *shudder*. Nature can be truly terrifying.
With regards to the first quote, its all very well considering the size of these super-carriers when paced in drydock with a human of "average" stature as a reference point. But put that same super-carriier in a body of water that covers roughly two-thirds of an entire planet... it's like trying to fill a fish tank with one piece of plankton!!

as to the second, with the greatest of respect, do give over :D. Mother Nature has been doing this a lot longer that we've been around. Its only we, as a species, that has the audacity to consider this a personal act of aggression against us.

Besides, given the amount of grief we've given her over the years, she has every right to be somewhat peeved :imo: .

I mean there's somewhere in the region of 7 billion people in the world and still growing!! :_omg: This wonderful, beautiful planet we live on has already just about reached saturation level. I say, lets have a MEGA superwave!! :grouphug:
 

lopaka

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Hi canwyll corf. I'm not sure that your views and the one's posted are mutually exclusive, though. I'm, as much as the next guy, all for a series of F5 twisters descending on Kansas this afternoon. :shock: :twisted: Doesn't mean I won't be really frightened when the tornado sirens go off. :)
 

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lopaka said:
The ship left New York last Sunday with 2,500 passengers aboard.

Robison said about 300 passengers decided not to return by boat. About 100 people were flown back to New York and the rest made their own arrangements, she said.
http://seattletimes.nwsource.com/html/n ... ave18.html
LOL, how could 2,100 people make their "own arrangments" to get back!!

I could see it now>> "Yeah we just happen to have friends with a cigarette boat roaming these waters at random." wtf?
 

lopaka

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Human_84, it is worded slightly akwardly, but I think the inference is that they rented cars, took trains, etc. from Charleston, South Carolina to their respective homes, rather than taking the Cruise Ship Company's offer of either being flown back to New York or waiting for the ship to be repaired.
 

Anome

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More to the point, I think you'll find that it is only 200 people who made their own arrangements. As only 300 didn't take the boat back, and 100 of them were flown back at the company's expense.
 

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The ten-storey Mexican wave

BY PAUL SIMONS AND ALAN HAMILTON

A new record has been set for the largest swell, American oceanographers report
WHEN seafarers described them in tones of awe, sceptical landlubbers dismissed them as fantasy. Now scientists believe that they have evidence of the largest wave yet recorded.
It happened on September 16 last year when Hurricane Ivan stormed across the Gulf of Mexico and tore into the coast of Alabama, accompanied by 130mph winds and storm surges 8ft high.

While still out at sea, oceanographers report, the hurricane also produced a series of giant waves, one of which stood 91ft (27m) from crest to trough, the height of a ten-storey building and a new world record for a wave recorded by instruments.

But science, like old salts’ tales, is fallible. The seabed instruments that measured the surge were turned off at the moment the winds reached their peak, and scientists from the Naval Research Laboratory at Stennis Space Centre, Mississippi, have had to employ a computer model to predict that, while they were not looking, at the height of the storm the wave reached 131ft.

By comparison, the tsunami wave that swept across the Indian Ocean last December stood about 30ft high as it hit shorelines, although in some parts of Indonesia it was reported to have reached 65ft.

The greatest wave of all is not yet upon us. Scientists predict that if a future volcanic eruption sends a large part of the island of La Palma in the Canaries into the sea, it could cause a wall of water 2,950ft high. Reassuringly, they do not expect the event this century.

The Alabama wave last year comfortably exceeded the previous record for a wave, of 86ft, measured by the ocean weather ship Weather Reporter in the Atlantic on December 30, 1972. Giant waves are difficult to record because measuring buoys floating on the surface of the sea are usually wrecked by the intense storms.

Luckily, the eye of Hurricane Ivan passed over an array of 14 water pressure sensors spread over 38 miles of seafloor 100 miles off the Alabama coast. They are intended to measure the rise and fall of tides but also capture the height of waves. Their results are used for tracking the spread of algal blooms, jellyfish or oil spills from wells in the Gulf of Mexico.

They missed the height of the Hurricane Ivan waves because their work requires them to operate only every few hours.

But they did record that the sea currents generated by the hurricane broke another world record: the maximum current on the seafloor was 2.25 metres per second, compared with the Gulf Stream, which reaches top speeds of about 1.5 metres per second.

“We didn’t expect to measure hurricane waves,” William Teague, of the oceanographic team, said. “We were amazed at the strength of the currents and the size of the waves. It has changed our whole thinking of what could happen out at sea and what structures, like oil rigs, could get wiped out.”

Seven oil rigs were sunk and another 24 badly damaged in the storm. But the worst damage was to submarine pipelines, ruptured by submarine landslides. The hurricane caused the deaths of 116 people across the Caribbean, and insurance claims totalled $28 billion, making Ivan one of the costliest natural disasters in history.

HIGH WATER

Previous highest recorded was 86ft (26.2m) recorded in Atlantic on December 30, 1972

In 1933 the US Navy ship Ramapo was hit by a wave estimated at 112ft in the North Pacific

Waves up to 100ft high are thought to have sunk more than 200 supertankers and container ships during the past two decades. It was such a wave that took star role in Sebastian Junger’s The Perfect Storm

On a crossing to New York the QE2 was hit by a huge wave in the North Atlantic estimated 95ft high from a hurricane on September 11, 1995. She survived after taking the wave directly over her bow. Her captain, Ronald Warwick, described it as “like going into the White Cliffs of Dover”

The tallest underwater wave was measured as a mammoth 558ft on March 28, 2001

HURRICANE IVAN
Hurricane Ivan blasted through much of the Caribbean as a Category 5 storm, the most powerful level of hurricane

After destroying most of Grand Cayman, it moved into the Gulf of Mexico. The warm waters of the Gulf re-energised the hurricane’s ferocious winds

With virtually wide open sea, the hurricane had a free run to build up the sea into a frenzy

As Ivan approached the Gulf coast of the US it had piled up the sea into monstrous waves

Taken from The Times
 

crunchy5

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Worrying wave developments

I pondered putting this in the Gulf Stream thread or Global Warming or even Pole Reversal, but then figured it deserved a thread of it's own.
It's a v interesting read 8)

http://service.spiegel.de/cache/interna ... %2C00.html

[Emp edit: I'm adding in the full text of the article for future generations: ]

SPIEGEL ONLINE - March 31, 2006, 04:25 PM
URL: http://www.spiegel.de/international/spi ... 53,00.html

Monster Waves

Vessel Measures Record Ocean Swells

By Markus Becker

A British research team has observed some of the biggest sea swells ever measured. A whole series of giant waves hammered into their ship that were so big, according to computer models used to set safety standards for ships and oil rigs, they shouldn't even exist.

When the RRS Discovery set out to sea, the crew was expecting stormy weather. Meteorologists had predicted a violent storm, and the scientists -- a team from Britain's National Oceanography Center -- wanted to observe it from up close. What they ended up experiencing went far beyond anything they could have imagined -- and could have cost them their lives.

Near the island of Rockall, 250 kilometers (155 miles) west of Scotland, enormous waves came racing toward the vessel. When they checked their measuring instruments later, the scientists discovered that the tallest of these monster waves had hit nearly 30 meters (98 feet) at wind force 9. And it didn't come alone. "We were shaken up these waves for 12 hours," said Naomi Holliday, the leader of the expedition. Entire sets of giant waves hammered the ship.

After the adrenaline levels of the scientists had fallen somewhat, astonishment spread among the crew. The standard computer programs had predicted stormy weather for February 8, 2000, but not such a tempest. Even more astonishing, the giant waves had not appeared individually, but in a group. Previously waves of such size were assumed to only appeared alone.

What Holliday characterized as a "dangerous situation" has turned out to be a spate of luck. The Discovery's crew witnessed the largest waves ever measured by a scientific instrument on the open sea, according to an article the scientists have only now published in the journal Geophysical Research Letters.

Biggest waves ever measured

With a height of up to 29.1 meters (95 feet) from trough to crest, the single waves are the highest ever measured. In terms of so-called significant wave height, they established a new record, according to the scientists: 18.5 meters (61 feet). Significant wave height is the median height of a wave's upper third. It corresponds roughly to the sea swell that experienced sailors can estimate with the naked eye.

More important than the record, however, is how the waves were born. "They were not caused by very strong winds," Holliday told SPIEGEL ONLINE. The strongest phase of the storm had already been over for a day when the largest water masses hit the RRS Discovery.

The scientists think a so-called resonance effect was responsible for the monstrous waves: waves and wind travelled across the Atlantic at practically the same speed. The storm was able to pump energy into the waves efficiently for a long time, building them up to giant size. According to the article published by Holliday and her team, the rapid increase in wave height at the beginning of the event supports this hypothesis.

Trouble for sailors and shipbuilders?

The new data may spell trouble for sailors and shipbuilders, the British scientists believe. Their research results suggest that giant waves may be much more common than previously believed. "Of course we can't make general claims about all the world's seas on the basis of the specific event we observed," Holliday said. "But computer simulation can do this for us."

According to Holliday, plugging the new data into the standard formulas shows that existing computer simulations are slightly off the mark -- at least as far as the formation of giant waves is concerned. "The waves we observed were not predicted by the computer simulation," Holliday explained. That has implications for the construction of ships and oil rigs. "The safety standards are partly based on the computer simulations."

Why was the difference between simulation and reality not noticed earlier? Because of the relative scarcity of measuring buoys and ships collecting scientific data, according to Holliday: "Direct wave height measurements are extremely rare." Cargo ships tend to avoid powerful storms, and oil rigs are so few and far between they hardly ever encounter giant waves.

For this reason alone, the measurements taken by the British research expedition are "spectacular," confirmed Wolfgang Rosenthal, a marine weather expert at a Geesthacht research institute associated with Germany's GKKS ship-building society. Waves of the sort observed by Holliday's team had already been analyzed theoretically, but the only practical knowledge about them came from vague reports. The new measurements confirm the theories that have been developed. "Nothing like this has ever been documented before," Rosenthal said.

Not freak waves

The significant wave height of 18.5 meters (61 feet) is particularly interesting, according to Rosenthal. "The giant 29 meter (95 feet) waves fit well with this statistically," Rosenthal said. He explains that the giant waves observed at Rockall are not the same as the notorious "freak waves" that appear out of nowhere during relatively mild weather, destroying even large vessels. Only those waves are considered freak waves whose overall height is at least twice their significant wave height. When the significant wave height is in the region of 18.5 meters (61 feet), giant waves roughly 30 meters (98 feet) tall become possible -- as they did near Rockall in 2000, and as Holliday and her colleagues were able to find out for themselves.

But Rosenthal doubts that the new data will have a significant effect on security standards in shipbuilding. "A single case doesn't render the existing computer simulations obsolete," he said. Nonetheless, questions about the accuracy of computer simulations have been raised for some time with regard to sea swells under extreme weather conditions. Rosenthal explained that this is partly a result of the weak measurements obtained by means of satellite-based radar. "The stronger the wind gets, the weaker and harder to measure the radar signal reflected by the waves," he said.

Holliday -- whose team includes an expert for computer simulations of sea swells -- is convinced her measurements will contribute to an improvement in computer models. "The existing models strongly underestimate maximal wave heights," she said. "The people in charge of simulations are going to have to find out what they're doing wrong."

-----------
© SPIEGEL ONLINE 2006
 

OldTimeRadio

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The extreme reluctance of orthodox Oceanography to accept "Monster Waves" until the past two or three years strikes me as Science as sacred cow, Science as a reverse religion with altar cloths and incense, at its very worst.

The "proper" way to study oceans, it seems, was to sit in an ivory tower and ignore or (better yet) ridicule the evidential accounts from thousands of sailors and seafarers down the long centuries and indeed millennia.

"I am a Scientist and I have spoken. If you speak differently than I you are drunk, crazy or a liar and very possibly all three at once. Especially if you believe that rocks can fall from the skies or that the seas can generate 75- or 100-foot waves."

P. S. No genuine RESEARCH scientist need be the least bit offended by the above, because these comments are most certainly NOT directed at you.
 

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New theory (and old equations) may explain causes of ship-sinking freak waves


A freak wave approached this oil freighter, the Esso Languedoc, near Durban, South Africa in 1980. The masts are about 82 feet above sea level, but the wave, which broke over the deck, caused only minor damage. Photo credit: Philippe Lijour.
On a stormy April day in 1995, the RMS Queen Elizabeth 2 was sailing in the North Atlantic when the ocean liner dipped into a "hole in the sea." Out of the darkness, a towering 95-foot wave threatened to crash down upon the vessel, which the 70,000-ton ship attempted to surf in order to avoid being pummeled to the bottom of the ocean.

Fortunately, the ship and passengers survived, but the instance occurred just months after the first scientific recording confirmed the validity of old sailors' tales once considered skeptical: the existence--and prevalence--of freakishly giant waves, also known as rogue waves.

Before the first laser measurement of a freak wave in January 1995, oceanographers and mathematicians predicted that such monster waves should only occur about once every 10,000 years. But as the occurrence inspired satellite measurements, scientists observed many more freak waves than theory predicted. In fact, observations imply that a handful of these waves is occurring at every moment somewhere on the ocean. Although it's controversial just how many ships and lives have been lost in modern times due to these fairly common giant waves, most ships today are only built to withstand waves up to 50 feet tall--while freak waves have been calculated to reach heights of up to 198 feet. Technically, a freak wave is defined as a wave that is twice the "significant wave height," which is the mean of the largest third of waves in an area.

Intrigued and terrified by freak waves and their potential for swallowing giant ships whole (from oil rigs to cruise ships), scientists are trying to formulate a theory or theories to describe the evolution of these mythical realities. Recently, scientists from Sweden and Germany, Padma Shukla et al., have presented the first analysis and simulation of its kind for the instability of nonlinear waves interacting in deep water. In the past, nonlinear theories have seemed capable of explaining the greater prevalence of rogue waves than previous theories which were linear.

"The basic reason for the occurrence of freak waves seems to be what is known as nonlinear wave interactions--by a certain mechanism there is an energy exchange between the waves resulting in a large growth in wave amplitude, much larger than what would be possible through ordinary linear superposition of waves," coauthor Mattias Marklund told PhysOrg.com.

Nearly all waves originate as ripples on the water's surface blown by the wind. (The exception is tsunamis, which are caused by seismic tremors on the ocean floor and only become dangerous when they reach the shore.) Most waves, however, die down due to viscosity in the water, unless heavy winds cause the swells to increase. Scientists believe that heavy winds--especially when blowing in the opposite direction of the water current--play a large role in forming freak waves. This idea may explain why locations with strong currents (e.g. the Agulhas off Africa and Gulf Stream off the U.S., including the Bermuda Triangle) have a history of reported freak waves.

"The freak wave a phenomenon is important to understand since it may be the cause of serious accidents involving oil platforms and ocean-going ships," said Marklund. "If a greater understanding of the mechanisms behind these waves is obtained, one may, for example, in the future combine this with observational and statistical tools in order to construct warning systems."

Shukla, Marklund and their colleagues built their theory on a two-wave system, where two waves interact nonlinearly, which is described by the Schrodinger equations. These quantum mechanics equations, originally developed to describe the wave-like behavior of electrons in atoms, have since been used for a variety of wave systems. The scientists found that two-wave cases behave much differently than single waves, which exhibit standard instabilities and dissolve into a wide spectrum of waves.

"We have presented a theoretical study of the modulational instabilities of a pair of nonlinearly interacting two-dimensional waves in deep water, and have shown that the full dynamics of these interacting waves gives rise to localized large-amplitude wave packets," wrote the scientists in a recent issue of Physical Review Letters. "[T]wo water waves can, when nonlinear interactions are taken into account, give rise to novel behavior such as the formation of large-amplitude coherent wave packets with amplitudes more than 3 times the ones of the initial waves."

Using the Schrodinger equations, the scientists studied the impact of different wave speeds and different angles at which two waves intersect. The team found that for a certain, relatively small angle, a new instability arises with a "maximum growth rate that is more than twice as large as the ones for the single wave cases," they report. Two waves meeting at such an angle would escape normal stabilizing effects and exhibit constructive interference that would result in a freak wave. Strong currents can help further by "focusing" waves, continually building them up to giant sizes.

"This particular piece of research describes a possible mechanism behind rogue wave formation," said Marklund. "In order to statistically predict their location, one will need further observations and analysis of such data using various methods, in particular statistical analysis and computer simulations."

Citation: Shukla, P.K., Kourakis, I., Eliasson, B., Marklund, M. and Stenflo, L. "Instability and Evolution of Nonlinearly Interacting Water Waves." Physical Review Letters. 97, 094501 (2006).

By Lisa Zyga, Copyright 2006 PhysOrg.com



http://www.physorg.com/printnews.php?newsid=77381892
 

Yithian

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Ok. Interesting but i'm not a physicist.

"The basic reason for the occurrence of freak waves seems to be what is known as nonlinear wave interactions--by a certain mechanism there is an energy exchange between the waves resulting in a large growth in wave amplitude, much larger than what would be possible through ordinary linear superposition of waves," coauthor Mattias Marklund told PhysOrg.com.
.

Is 'non-linear interaction' a catch-all term to explain that while there's clearly an interplay it's not one that's understood well enough to enable modelling and hence prediction?

If 'chaotic' is a brand of 'non-linear' what other things are? I have a rather imperfect grasp of the terminology here.
 

amester

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Ha, ha, wipeout! 8)
 

rynner2

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Re: Worrying wave developments

crunchy5 said:
I pondered putting this in the Gulf Stream thread or Global Warming or even Pole Reversal, but then figured it deserved a thread of it's own.
It's a v interesting read 8)

http://service.spiegel.de/cache/interna ... %2C00.html

[Emp edit: I'm adding in the full text of the article for future generations: ]
Ha Ha! Given this creaky MB's history of losing perfectly interesting threads down the cracks in the floor boards, that Emps remark should really go on the Irony thread! 8)

Yith asks:
Is 'non-linear interaction' a catch-all term to explain that while there's clearly an interplay it's not one that's understood well enough to enable modelling and hence prediction?
No. The surprise is that the process is able to be modelled accurately, but using the Schrodinger equations, which were formerly thought to refer only to the quantum world of the very, very small.

The fact that it has applications in the macro-world as well is rather startling, and may well lead to new surprises in science.

[peadant mode]
Linear in maths and science means that things add up simply - in this case (to simplify), wave A with a height of x metres meeting wave B with a height of y metres would be expected to give a wave of height (x + y) metres.

But non-linear means the relationship is more mathematically complex, so we might get a combined height involving powers or logs of x and y, or something even more complicated. So there's still a formula for predicting the height of A and B combined, but it's not linear.
[/pedant]
 

Yithian

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Thanks Rynner. And none of that struck me as pedantry.
 

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Thursday, March 01, 2007

Predicting Rogue Waves
Researchers have used satellite data to create a map showing where massive waves are likely to appear; they hope to use it to save lives.
By Bruce Gains

Scientists from the German Space Agency say they have mapped incidents of extremely large waves, known as rogue waves, using synthetic aperture radar (SAR) satellite data, and will soon publish a massive wave atlas for the first time. Such waves can mysteriously surge 100 feet (or about the height of a 12-story building) and sink massive cargo ships in their wake.


The scientific community has been slow to validate the existence of rogue waves, which are loosely defined as having an individual crest height that is more than twice the average height of surrounding waves. Besides sailors' eyewitness accounts and discernible ship damage, evidence of abnormally large waves, which are extremely rare, has been limited to only a few rare photos, ocean oil-platform readings, and very occasional buoy data readings.


Difficulties in detecting the phenomenon are posed by the limited areas that traditional wave-height-measuring systems cover. There are a relatively small number of buoys or oil platforms collecting such data, and they are rarely deployed in remote oceans and seas where rogue waves are thought to be more likely to appear. During the very rare circumstances when high waves do surge against buoys or oil platforms, wave-height sensors are often damaged. Buoys that can withstand the impact without being destroyed are often incapable of measuring freak waves that are twice the average crest heights. Measurements of rogue waves, instead, are often indicated as mistaken readings.


Now, with two years of data from European Space Agency (ESA) satellites in tow, German Space Agency scientists say they are able to offer a rogue-wave map by taking advantage of the satellites' global coverage. The researchers used data from two ESA satellites that orbited the earth 12 times a day and took SAR images every 200 kilometers for two years. SAR is a remote sensing radar system with which images are created by tracking how emitted radio waves bounce off the earth's surface.


Using data from more than one million images, the German Space Agency scientists then calculated ocean surface heights with equations and models they created. The researchers pinpointed rogue waves up to 30 meters tall in the North Atlantic Ocean near Rockall (an island off the southwest coast of Greenland), in the North Pacific, in the Pacific Ocean southwest of Australia, and near the Cape Horn.


Unlike spectral data emitted by satellites, which enable only average wave sizes to be determined, the German Space Agency research group's SAR data calculations are more precise, the researchers say. They have been able to determine individual wave heights around the world for the first time, says Susanne Lehner, who was involved in the research.


"Spectral analyses only give an average over an area," Lehner says. "We derived the surface areas, the wave heights from top to bottom, and crest heights of individual waves."


By using the German Space Agency's rogue-wave atlas pinpointing where the monster waves have appeared in the past, real-time weather forecasts could, in theory, help prevent many accidents and deaths on the open ocean by indicating when and where dangerously high rogue waves might occur. Indeed, ship sinkings and ensuing deaths caused by the phenomenon are probably more numerous than officially recorded, Lehner says, given the large number of vessels that simply disappear without a trace every year.



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.

http://www.technologyreview.com/Infotech/18245/
 

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Some big if not rogue waves here, with pics on the link:

Surfer defies giant waves alert

A Cornish surfer defied warnings to ride what are thought to be the biggest waves recorded off the west coast of Ireland.
Duncan Scott, 29, from Newquay, was surfing at Mullagmore Head in Donegal Bay as waves estimated at 55ft (16.7m) high lashed the coast.

Weather forecasters had warned of hazardous conditions for ships, fishing vessels and coastal walkers.

He said that he was safe because friends were on hand with a water bike.

Flood fears

He and three others, who have surfed some of the biggest breaks in the world, including Mavericks in Hawaii, used the water bike to tow them onto the waves.

Mr Scott said: "These were the biggest waves I have ever surfed, but I never felt in danger because we were using experienced riders who were on hand all the time.

"The jet skis have a platform at the rear so you can get back to safety."

It is understood that low pressure near Iceland is causing the high sea levels with waves growing for between 500 and 600 miles by the time they crash against the Irish coastline.

Dr Glenn Nolan, of the Marine Institute, said: "This is allowing waves to travel all the way uninterrupted to the Irish coast.

"It's quite unusual. The last time we would have had waves close to this height would have been in early 2005 and before that in 2000."

Dr Nolan warned that the entire west coast, from Cork up to Donegal, was affected.

Previously the biggest waves recorded by the Marine Institute's data buoys were to the west of Galway Bay in January 2005, when swells of 44ft (13.4m) were recorded.

The high seas come just weeks after the east coast of England braced itself for tidal surges, sparking flood fears and evacuations.

http://news.bbc.co.uk/1/hi/england/cornwall/7122844.stm
 

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The Real Sea Monsters: On the Hunt for Rogue Waves
www.scientificamerican.com/article.cfm? ... orecasting

Scientists hope a better understanding of when, where and how mammoth oceanic rogue waves form can someday help ships steer clear of danger
By Lynne Peeples

A near-vertical wall of water in what had been an otherwise placid sea shocked all on board the ocean liner Teutonic—including the crew—on that Sunday in February, more than a century ago.

"It was about 9 o'clock, and [First Officer Bartlett], as he walked the bridge, had not the slightest premonition of the impending danger. The wave came over the bow from nobody seems to know where, and broke in all its fury," reported The New York Times on March 1, 1901: "Many of the passengers were inclined to believe that the wave was the result of volcanic phenomena, or a tidal wave. These opinions were the exception, however, for had the sea been of the tidal order Bartlett would have seen it coming." The volcano theory was just as unlikely: "Absurd, absurd," one of the Teutonic's officers told the Times. "It was a giant sea, and there is no doubt of that."

This is just one of the many anecdotal accounts in maritime history of waves upward of 30 meters devouring ships, even swallowing low-flying helicopters. But what sea captains and scientists have long believed to be true only gained widespread acceptance after the first digitally recorded rogue wave struck an oil rig in 1995. "The seamen tales about large waves eating their ships are correct," says Tim Janssen, an oceanographer at San Francisco State University. "This was proof to everybody else, and a treat for scientists. They suspected it, but to see it and have an observation is something else."

Now that there is no longer a question of rogue waves' existence, other mysteries have arisen: How frequently do they occur? Just how do they come about? Are there areas or conditions where they are more likely? Janssen is among a growing group of researchers in search of answers to these questions, which could someday lead to safer seas.

Rogue waves by the numbers
Before any answers could be attempted, scientists first had to characterize a rogue (or freak) wave. The widely accepted definition, according to Janssen, is a wave roughly three times the average height of its neighbors. This is a somewhat arbitrary cutoff. Really, he notes, they are just "unexpectedly large waves." The wave that swept onlookers off the coast in Acadia National Park in Maine on August 23 may not fit the former definition, for example, because background waves were already quite large due to Hurricane Bill, and rogues typically occur in the open ocean. Yet that wave has still been readily referred to as a "rogue".

No one is certain yet just how frequently freak waves form; accurate numbers are extremely difficult to collect given the waves' rare and transient nature. With more sophisticated monitoring and modeling—and as first-hand accounts are taken more seriously—the waves' prevalence appears to be rising. "[Rogue waves] are all short-lived, and because ships are not everywhere, the probability that a ship encounters one is relatively small," says Daniel Solli, who studies the optical version of rogue waves at the University of California, Los Angeles. "But with increasing amounts of oceanic traffic in the future, the likelihood of encountering them is getting larger."

Some areas seem to breed the waves more than others. Janssen and his colleagues recently used computer models to determine that regions where wave energy is strongly focused could be up to 10 times more likely to generate a freak wave. He speculates that approximately three of every 10,000 waves on the oceans achieve rogue status, yet in certain spots—like coastal inlets and river mouths—these extreme waves can make up three out of every 1,000 waves. A paper describing these results was published last month in the Journal of Physical Oceanography.

Forming fearsome waves
Various theories exist for how rogue waves form. The simplest suggests that small waves coalesce into much larger ones in an accumulative fashion—a faster one-meter wave catches up with a slower two-meter wave adding up to a three-meter wave, for example. Janssen and his colleagues build on this with a more complex, nonlinear model in their recent paper. Waves might actually "communicate—sometimes in a bad way—and produce more constructive interferences," Janssen explains. By communicating, he means exchanging energy. And because the conversations aren't necessarily balanced, he says, "Communication can get amplified enough that a high-intensity large wave develops." In other words, one burgeoning wave can actually soak up the energy of surrounding waves.

Again, in those places where variations in water depths and currents focus wave energies, this line of communication can get especially busy. Janssen's models identified these rogue-prone zones. Certain conditions such as winds and wave dissipation, however, could not be included, limiting the simulation's predictive power.

Meanwhile, Chin Wu, an environmental engineer at the University of Wisconsin–Madison sees another likely scenario spurring the monster waves: "If a wave propagates from east to west, and the current moves west to east, then a wave starts to build up," says Wu, who studies wave–current interactions in a 15-meter pool. The wave basically climbs the current's wall, rising out of what appears to be nowhere. Rogue waves have in fact been more common in regions such as the east coast of South Africa where surface waves meet currents running in the opposite direction.

Focusing on forecasts
The only way to really know what is going on in the unpredictable oceans is to watch, Wu says. He acknowledges, however, that the investments in the instruments and time necessary for such fieldwork are immense. "We need to identify places where [rogue waves] are more likely to occur," he says, emphasizing the importance of numerical models—including the nontrivial accounting of wind and wave breaking—at this step, "and then focus on those areas."

Focusing on an optical wave analogue may actually help scientists limit where they need to look. Light waves travel in optical fibers similarly to water waves traveling in the open ocean. "In optics we're dealing with a similar phenomenon, but doing experiments on the tabletop and acquiring data in only a fraction of a second," says U.C. Los Angeles's Solli. Although he doesn't suggest that optical experiments should replace ocean research, he suggests it could be a guide. Mapping light-wave conditions to the ocean could uncover parallel parameters that give rise to water waves. "Instead of looking for a needle in a haystack in the water, you could benefit from some beginning wisdom and narrow down the range," adds Solli, who co-authored a paper on optical rogue waves in the December 2007 edition of Nature. (Scientific American is part of the Nature Publishing Group.)

Janssen agrees with the need for more direct observations of ocean behavior. "We can make a theoretical prediction," he says. "But then we have to go out and see if nature agrees." If it does, the results "could provide a prediction scenario—made visible on maps—of hot spots that could change day to day," Janssen says. This could work much like tornado forecasting.

Only two passengers were seriously hurt in the Teutonic incident—one suffered a broken jaw and the other a severed foot. They were fortunate. "Had it struck us later on in the day many passengers would have been promenading in the sunshine, without doubt," Officer Bartlett told the Times. "There is no telling how many of them would have been injured." Extreme waves do not always offer such merciful timing, however. Forecasts could be crucial in helping future ocean liners evade the voracious sea monsters.
 
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