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Rogue wave (oceanography)

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This article discusses deep ocean freak waves which occur far out at sea. For tsunami ("tidal" waves) and megatsunami (single giant waves due to impact or landslide in confined areas), see those articles.

The Draupner wave, a single giant wave measured on New Year's Day 1995, finally confirmed the existence of freak waves, which had previously been considered near-mythical Rogue waves, also known as freak waves, are relatively large and spontaneous ocean surface waves which can sink even large ships and ocean liners. In oceanography, they are more concisely defined as waves that are more than double the significant wave height (SWH), which is itself defined as the mean of the largest third of waves in a wave record.

Once thought to be only legendary, they are now known to be a natural ocean phenomenon, not rare, but rarely encountered. Anecdotal evidence from mariners' testimonies and damages inflicted on ships suggested they occurred; however, their scientific measurement was only positively confirmed following measurements of 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 may be evidence for rogue waves. Further research is underway to verify the method that translates the radar echoes into sea surface elevation.

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. <ref name="Rockall">Holliday, NP, MJ Yelland, RW Pascal, VR Swail, PK Taylor, CR Griffiths, and EC Kent (2006). Were extreme waves in the Rockall Trough the largest ever recorded? Geophysical Research Letters, Vol. 33, L05613</ref>

Contents

[edit] History

Image:Wea00800,1.jpeg It is common for mid-ocean storm waves to reach 7 metres (23 feet) in height, and in extreme conditions such waves can reach heights of 15 metres (50 feet). However, for centuries maritime lore told of the existence of vastly more massive waves — veritable monsters up to 30 metres (100 feet) in height (approximately the height of a 12-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 100 tonnes/m2 (980 kPa) exerted by the weight of the breaking water, and would almost certainly be sunk in a matter of seconds. Usual ship design allows for rounded storm waves up to 15 m and pressures around 15 tonnes/m2 (147 kPa) without damage, and somewhat more (around 20 m) if some deformation is allowed for.<ref>According to traditional linear models, a 12 meter wave has a force of about 6 MT/m, and ships are therefore designed to withstand around 15 MT/m. However a rogue wave may have a force of around 100 MT/m. [1] (PDF)</ref>

Scientists long dismissed such stories, asserting that mathematical models indicated that ocean waves of greater than 15 metres in height were likely to be rare "once in 10,000 years" events. However, satellite imaging has in recent years confirmed that waves of up to 30 metres in height are much more common than mathematical probability would predict based on a linear model of wave size. 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 rogue waves are believed to be responsible for the sinking of the Edmund Fitzgerald in November 1975.

These localized rogue waves are not the same as tsunami or megatsunami. Tsunami are displacement waves which travel at high speed and are more or less unnoticeable in deep water; they only become dangerous as they approach the shoreline. In the deep sea, tsunami do not present a threat to shipping. Megatsunami are also rare events, but only arise in confined spaces, such as inlets and river valleys. Freak waves, by contrast, are localized, short-lived water phenomena that most frequently occur far out to sea.

[edit] Occurrence

The MaxWave project studied the ocean surface with radar over a 3-week period in 2001. They took 30,000 images each of a 10 x 5 km section of ocean in that time, resulting in a total imaged area of 1.5 million km². Giant waves were detected in 10 of these, or one per 150,000 km². A short-lived wave in a section of ocean this size is an extremely rare occurrence in its own right.<ref>Freak waves spotted from space. BBC News (22 July, 2004). Retrieved on May 8, 2006.</ref>

[edit] Causes

The phenomenon of rogue 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 by, perhaps, coast shape or seabed shape
  • Constructive interference — In this theory, several smaller wave trains meet in phase. Their crest heights combine to create a freak wave.<ref NAME=OPC>Rogue Waves. Ocean Prediction Center. National Weather Service (April 22, 2005). Retrieved on May 8, 2006.</ref>
  • 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.<ref NAME=OPC>Rogue Waves. Ocean Prediction Center. National Weather Service (April 22, 2005). Retrieved on May 8, 2006.</ref>
  • Nonlinear effects — It seems possible to have a rogue wave occur by natural, nonlinear processes from a random background of smaller waves.<ref>Freak Wave - programme summary. BBC (14 November 2002). Retrieved on May 8, 2006.</ref> 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.<ref NAME=OPC>Rogue Waves. Ocean Prediction Center. National Weather Service (April 22, 2005). Retrieved on May 8, 2006.</ref>
  • 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 (1957, J. Fl. Mech.) provide some insight into the problem, though it still remains a tricky one.

The spatio-temporal focussing seen in the NLS equation can also occur when the nonlinearity is removed. In this case, focussing 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 focusses 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:

A comprehensive paper describing the ways that rogue 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, all of a sudden can 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.<ref>P. K. Shukla, I. Kourakis, B. Eliasson, M. Marklund och L. Stenflo: Instability and Evolution of Nonlinearly Interacting Water Waves nlin.CD/0608012, Physical Review Letters (2006)</ref>

[edit] Encounters

  • On the 10th of 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 50 feet high and she 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, a Canadian was fatally injured and several other passengers were hurt, but luckily there were no more fatalities.
  • In 1933 in the North Pacific, the Navy oiler USS Ramapo encountered a huge wave. The crew triangulated its height at 112 feet (34 meters). <ref name="broad">Broad, William J (July 11, 2006). Rogue Giants at Sea. New York Times</ref>
  • In 1942 while carying 15,000 American troops 700 miles from Scotland during a gale, RMS Queen Mary was broadsided by a 28-meter wave and nearly capsized. Queen Mary listed briefly about 52 degrees before the ship slowly righted itself.
  • In 1966, the Italian cruise ship Michelangelo was steaming toward New York when a giant wave tore a hole in its superstructure, smashed heavy glass 80 feet (24 meters) above the waterline, and killed a crewman and two passengers. <ref name="broad"/>
  • SS Edmund Fitzgerald was a lake freighter that sank suddenly during a gale storm on November 10, 1975, while on Lake Superior, on the U.S. and Canadian border. The ship went down without a distress signal in 530 feet (162 m) of water in Canadian waters about 17 miles (15 nm; 27 km) from the entrance to Whitefish Bay (at 46°59.9′N 85°6.6′W). All 29 members of the crew perished.
  • The Wilstar, a Norwegian tanker, suffered structural damage from a rogue wave in 1974. <ref name="broad"/>
  • 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 22-meter bridge deck. <ref name="Petersen">Petersen, Karsten (December 8, 2003). [http://www.geocities.com/kp_diver/index111TheStorm.html The Storm: Stolt Surf in the North Pacific, 1977. Retrieved July 11, 2006.</ref>
  • The six-year-old, 37,134-ton barge carrier MS München, lost at sea 1978. At 3am on 12 December 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 20m 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. [2]
  • Draupner wave (North Sea, 1995): first confirmed scientific evidence
  • RMS Queen Elizabeth 2 (North Atlantic, 1995), 29 meters, during bad weather in the North Atlantic.
The Master said it "came out of the darkness" and "looked like the White Cliffs of Dover." [3] (PDF) Newspaper reports at the time described the cruise liner as attempting to "surf" the near-vertical wave in order not to be sunk.
Bridge windows on both ships smashed, 30 meters above sea level, and all power and instrumentation lost. No adverse currents exist in that part of the world to explain the wave. The First Officer of the Caledonian Star stated it was "just like a mountain, a wall of water coming against us." [4] (PDF)
"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."


Several sources (including those below) repeat the claim that around 200 large ships have been sunk in recent years by 'freak' waves. That claim is a myth.<ref name="200_ships_myth" /> 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 200m and over sunk in the past 20 years". According to Lloyd's Register, only 143 ships of this size were lost from 1981-2001. 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 below).

[edit] Freak waves in literature and film

  • In Paul Gallico's 1969 novel The Poseidon Adventure, and in the 2006 film Poseidon, based on the novel, a rogue wave capsizes an ocean liner. (In the 1972 film, The Poseidon Adventure, the wave is described as a tsunami generated by a sub-sea earthquake).
  • Early in the 2000 movie The Perfect Storm, a "rogue wave" washes over the protagonists' fishing vessel, but does not sink the boat. It is merely treated as a bad omen of what is to come in the story. However, it is possible that the giant wave that finally sinks the boat is a similar rogue wave, only much larger.
  • Freak waves are a major theme in Clive Cussler's novel Polar Shift.
  • Stephen Colbert listed rogue waves in one edition of his Threat Down.
  • The Apocalypse by Tim Bowler also has freak waves crashing upon the island of Skaer.

[edit] See also

[edit] References

<references/>

[edit] External links

[edit] MaxWave report and WaveAtlas

[edit] Other

de:Monsterwelle fr:Vague scélérate it:Onda anomala nds:Kaventsmann pl:Fala wyjątkowa ru:Блуждающие волны sv:Monstervåg th:คลื่นยักษ์

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