Rogue wave

Wikipedia, the free encyclopedia - Cite This Source

Rogue waves, also known as freak waves, monster waves or extreme waves, are relatively large and spontaneous ocean surface waves that are a threat even to large ships and ocean liners. In oceanography, they are more precisely defined as waves whose height is more than twice the significant wave height (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 at sea, they are, rather, surprisingly large waves for a given sea state. A wave, such as the one that probably caused the loss of the RV Ballena in Southern California, was a rogue wave that occurred in a rather calm sea state. Such a wave is nevertheless very small compared to the largest waves recorded by instrumented buoys, with significant wave height.

Once thought to be only legendary, they are now known to be a natural ocean phenomenon. Anecdotal evidence from mariners' testimonies and damages inflicted on ships suggested they occurred; however, their scientific measurement was only positively confirmed following measurements of the "Draupner wave", a rogue wave at the Draupner oil platform, in the North Sea on January 1, 1995. During this event, minor damage was inflicted on the platform, confirming that the reading was valid.

In the course of the Project MaxWave, researchers from the GKSS Research Centre, using data collected by ESA satellites, identified a large number of radar signatures that have been portrayed as evidence for rogue waves. Further research is under way to develop better methods of translating the radar echoes into sea surface elevation, but at present this technique is not proven.

Freak waves have been cited in the media as a likely source of the sudden, inexplicable disappearance of many ocean-going vessels. However, although this is a credible explanation for unexplained losses, there is to date little clear evidence supporting this hypothesis nor any cases where the cause has been confirmed, and the claim is contradicted by information held by Lloyd's Register. One of the very few cases in which evidence exists that may indicate a freak wave incident is the 1978 loss of the freighter MS München, detailed below. In February 2000, a British oceanographic research vessel sailing in the Rockall Trough west of Scotland encountered the largest waves ever recorded by scientific instruments in the open ocean.

History

It is common for mid-ocean storm waves to reach in height, and in extreme conditions such waves can reach heights of . However, for centuries maritime folklore told of the existence of vastly more massive waves — veritable monsters up to in height (approximately the height of a 10-story building) — that could appear without warning in mid-ocean, against the prevailing current and wave direction, and often in perfectly clear weather. Such waves were said to consist of an almost vertical wall of water preceded by a trough so deep that it was referred to as a "hole in the sea"; a ship encountering a wave of such magnitude would be unlikely to survive the tremendous pressures of up to 980 kPa (142 psi) exerted by the weight of the breaking water, and would almost certainly be sunk in a matter of seconds. Many years of research have confirmed that waves of up to in height are much more common than mathematical probability theory would predict using a Rayleigh distribution of wave heights. In addition, pressure readings from buoys moored in the Gulf of Mexico at the time of Hurricane Katrina also indicate the presence of such large waves at the time of the storm. In fact, they seem to occur in all of the world's oceans many times every year. This has caused a re-examination of the reason for their existence, as well as reconsideration of the implications for ocean-going ship design.

Rogue waves are also known to occur on the inland Great Lakes, which are more like large inland seas. Perhaps most famously such inland freak waves are believed, according to some reconstructions, to be responsible for the sinking of the SS Edmund Fitzgerald in November 1975 (see below). However other causes have been advanced; the matter is far from settled.

A rogue wave is not the same as a tsunami. Tsunamis are mass displacement generated waves which propagate at high speed and are more or less unnoticeable in deep water; they only become dangerous as they approach the shoreline and do not present a threat to shipping (the only ships lost in the 2004 Asian tsunami were in port). A rogue wave, on the other hand, is a spatially and temporally localized event that most frequently occurs far out at sea.

Occurrence

The MaxWave project studied the ocean surface with radar over a 3-week period in 2001. Researchers took 30,000 images each of a 10 km × 5 km (6.2 mi x 3.1 mi) section of ocean in that time, resulting in a total imaged area of 1.5 million square kilometres (580,000 sq mi). Giant waves were detected in ten of these, amounting to one per . A short-lived wave in a section of ocean this size is an extremely rare occurrence in its own right.

Causes

The phenomenon of freak waves is still a matter of active research, so it is too early to say clearly what the most common causes are or whether they vary from place to place. The areas of highest predictable risk appear to be where a strong current runs counter to the primary direction of travel of the waves; the area near Cape Agulhas off the southern tip of Africa is one such area. However, since this thesis does not explain the existence of all waves that have been detected, several different mechanisms are likely, with localised variation. Suggested mechanisms for freak waves include the following:

Diffractive focusing — According to this hypothesis, coast shape or seabed shape directs several small waves to meet in phase. Their crest heights combine to create a freak wave.
Focusing by currents — Storm forced waves are driven into an opposing current. This results in shortening of wavelength, causing shoaling (i.e., increase in wave height), and oncoming wave trains to compress together into a rogue wave.
Nonlinear effects — It seems possible to have a freak wave occur by natural, nonlinear processes from a random background of smaller waves. In such a case, it is hypothesised, an unusual, unstable wave type may form which 'sucks' energy from other waves, growing to a near-vertical monster itself, before becoming too unstable and collapsing shortly after. One simple model for this is a wave equation known as the nonlinear Schrödinger equation (NLS), in which a normal and perfectly accountable (by the standard linear model) wave begins to 'soak' energy from the waves immediately fore and aft, reducing them to minor ripples compared to other waves. Such a monster, and the abyssal trough commonly seen before and after it, may last only for some minutes before either breaking, or reducing in size again. The NLS is only valid in deep water conditions, and in shallow water an alternative such as the Boussinesq equation is used.
Normal part of the wave spectrum — Rogue waves are not freaks at all but are part of normal wave generation process, albeit a rare extremity.
Wind waves — While it is unlikely that wind alone can generate a rogue wave, its effect combined with other mechanisms may provide a fuller explanation of freak wave phenomena. As wind blows over the ocean, energy is transferred to the sea surface. Phillips and Miles provide some insight into the problem, though it still remains a tricky one.

The spatio-temporal focusing seen in the NLS equation can also occur when the nonlinearity is removed. In this case, focusing is primarily due to different waves coming into phase, rather than any energy transfer processes. Further analysis of rogue waves using a fully nonlinear model by R.H. Gibbs (2005) brings this mode into question, as it is shown that a typical wavegroup focuses in such a way as to produce a significant wall of water, at the cost of a reduced height.

There are three categories of freak waves:

"Walls of water" travelling up to through the ocean
"Three Sisters", groups of three waves
Single, giant storm waves, building up to fourfold the storm's waves height and collapsing after some seconds

A comprehensive paper describing and illustrating the ways that freak waves could form, complete with layman descriptions, photos and animations, can be found here

A research group at the Umeå University, Sweden in August 2006 showed that normal stochastic wind driven waves can suddenly give rise to monster waves. The nonlinear evolution of the instabilities was investigated by means of direct simulations of the time-dependent system of nonlinear equations.

Applications

The possibility of the artificial stimulation of rogue wave phenomena, for use as a weapon or for other purposes, has attracted research funding from DARPA, an agency of the United States Department of Defense. Bahram Jalali and other researchers at UCLA studied microstructured optical fibers near the threshold of soliton supercontinuum generation and observed rogue wave phenomena. After modeling the effect, the researchers announced that they had successfully characterized the proper initial conditions for generating rogue waves in any medium.

Reported encounters

On the 11th March 1861 at midday the lighthouse on Eagle Island , off the West coast of Ireland was struck by the sea smashing 23 panes, washing some of the lamps down the stairs, and damaging the reflectors with broken glass beyond repair. In order to damage the uppermost portion of the lighthouse, water would have had to surmount a seaside cliff measuring 40 m (133 feet) and a further 26 m (87 feet) of lighthouse structure.

On December 15, 1900, three lighthouse keepers mysteriously disappeared from the Flannan Isles Lighthouse in the Outer Hebrides of Scotland. Although there were no surviving witnesses, a rogue wave has been theorized to be responsible.
On 10 October 1903, RMS Etruria was only four hours out of New York when, at 2:30 p.m., the ship was struck by a freak wave. The wave was reported to be at least high and struck the ship on the port side. The wave carried away part of the fore bridge and smashed the guardrail stanchions. There were a number of first-class passengers sitting in deck chairs close to the bridge and they caught the full force of the water. One passenger was fatally injured and several other passengers were hurt.
In 1933 in the North Pacific, the U.S. Navy oiler USS Ramapo encountered a huge wave. The crew triangulated its height at .
In 1942 while carrying 15,000 American troops from Scotland during a gale, RMS Queen Mary was broadsided by a wave and nearly capsized. Queen Mary listed briefly about 52 degrees before the ship slowly righted herself.
In 1966, the Italian liner Michelangelo was steaming toward New York City when a giant wave tore a hole in its superstructure, smashed heavy glass above the waterline, and killed a crewman and two passengers. The matter is related by Daniel Allen Butler in his book The Age of Cunard and by Walter Ford Carter in No Greater Sacrifice, No Greater Love.
The Wilstar, a Norwegian tanker, suffered structural damage from a rogue wave in 1974.
SS Edmund Fitzgerald was a lake freighter that sank suddenly during a gale storm on November 10, 1975, while on Lake Superior, on the Canada–United States border. The ship went down without a distress signal in Canadian waters about from the entrance to Whitefish Bay (at ). At the location of the wreck the water is deep. All 29 members of the crew perished. A coast guard report blamed water entry to the hatches, which gradually filled the hold, or alternatively errors in navigation or charting causing damage from running onto shoals. However, another nearby ship, the Anderson, was hit at a similar time by two rogue waves, and this appeared to coincide with the sinking around ten minutes later — or at least contributed to the sinking if the Edmund Fitzgerald was already in trouble as suggested. A Discovery Channel reconstruction pointed towards freak waves as the cause.
In October 1977, the tanker Stolt Surf ran into a rogue wave on a voyage across the Pacific from Singapore to Portland, and the engineer took photos of a wave higher than the bridge deck.
The six-year-old, 37,134-ton barge carrier MS München was lost at sea in 1978. At 3 a.m. on 12 December 1978 she sent out a garbled mayday message from the mid-Atlantic, but rescuers found only "a few bits of wreckage." This included an unlaunched lifeboat, stowed above the water line, which had one of its attachment pins "twisted as though hit by an extreme force." The Maritime Court concluded that "bad weather had caused an unusual event." It is thought that a large wave knocked out the ship's controls (the bridge was sited forward), causing the ship to shift side-on to heavy seas, which eventually overwhelmed it. Although more than one wave was probably involved, this remains the most likely sinking due to a freak wave.
The Ocean Ranger (North Atlantic, 1981), a semi-submersible mobile offshore drilling unit sank with all hands after a rogue wave flooded the platform's ballast control room.
Draupner wave (North Sea, 1995): The freak wave first confirmed with scientific evidence, it had a maximum height of .
RMS Queen Elizabeth 2 (North Atlantic, 1995), , during bad weather in the North Atlantic.

The Master said it "came out of the darkness" and "looked like the White Cliffs of Dover." ''Newspaper reports at the time described the cruise liner as attempting to "surf" the near-vertical wave in order not to be sunk.

On November 4, 2000, Channel Islands Sanctuary research vessel R/V Ballena was hit by a rogue and capsized near Point Conception in Santa Barbara, California. The ship was long, and the wave estimated at high. Although the two USGS crew members were trapped briefly inside the ship, they were rescued by the captain and all three managed to swim to shore. The boat, operated by NOAA at the time, was a total loss.
Bremen and Caledonian Star (South Atlantic, 2001) encountered freak waves. Bridge windows on both ships were smashed, and all power and instrumentation lost.
Naval Research Laboratory ocean-floor pressure sensors detected a freak wave caused by Hurricane Ivan in the Gulf of Mexico, 2004. The wave was around high from peak to trough, and around long.
Norwegian Dawn, (three waves in succession, off the coast of Georgia, 16 April, 2005):

"The sea had actually calmed down when the 21 meter wave seemed to come out of thin air… Our captain, who has 20 years on the job, said he never saw anything like it."

"The water exerted enough force to shear off the welds for the aluminum rail supports on the [ninth and tenth level] balconies of two cabins, allowing the teak balcony rails to break loose and crash into the cabin windows. The broken glass filling the drains compounded the water damage by allowing a large amount of water to enter the two cabins and damage the carpets in 61 other cabins. The ship’s operating at reduced speed when the waves hit probably limited the damage."

Aleutian Ballad, (Bering Sea, 2005)

Footage of the rogue wave appears on an episode of Deadliest Catch. The wave cripples the vessel, causing the boat to tip onto its side. The boat manages to right itself; some of the crew suffers minor injuries.

Norwegian Spirit, (off the coast of Tortola, January 2006)
In March 2007, Holland America's cruise ship MS Prinsendam was hit by a tall rogue wave in the Antarctic segment around the tip of South America.

It has also been suggested that these types of waves may be responsible for the loss of several low-flying aircraft, namely U.S. Coast Guard helicopters on Search and Rescue missions.

The claim that around 200 large ships have been sunk in recent years by 'freak' waves is incorrect. There are a tiny number of cases in recent years where no obvious explanation has been found, but according to the Lloyd's Register–Fairplay casualty database, fire or poor maintenance are more likely causes. The claim first appeared in the terms of reference for the EU's Max Wave project in 2001, without any supporting evidence. It was phrased as "200 supertankers or containerships of and over sunk in the past 20 years". According to Lloyd's Register, only 124 ships of this size were lost from 1981–2001, the majority being due to the Iran Iraq war. The claim achieved wider currency after it was picked up by the European Space Agency in its 2004 press release about freak waves observed from space (see External Links below).

Rogue waves in popular culture

The film Poseidon from 2006 explores the capsizing of an ocean liner by a rogue wave and the struggle of passengers to survive. The film is a remake of The Poseidon Adventure from 1972, itself an adaptation of Paul Gallico's novel, which was published in 1969. In the original novel and film, the ship was hit by a tsunami, which raised some criticism since these are only a few inches high in open sea and could never overturn a vessel. A 2005 remake addressed this issue by substituting a terrorist attack.

New York alternative rock band Brand New references rogue waves in "Play Crack The Sky", a track on their second album , Deja Entendu. The exact line is "They call them rogues, they travel fast and alone; one hundred foot faces of God's good ocean gone wrong."

References

External links

MaxWave report and WaveAtlas

Other

Wikipedia, the free encyclopedia © 2001-2006 Wikipedia contributors (Disclaimer)
This article is licensed under the GNU Free Documentation License.
Last updated on Tuesday March 11, 2008 at 05:41:47 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation