Rogue wave

Rogue waves are massive, unpredictable surface waves found in the open ocean.

They are much larger than the waves surrounding them. Scientists use a specific mathematical definition to identify them. They look at the significant wave height, or SWH. This value is the mean height of the largest third of waves in a specific record. A rogue wave is officially defined as a wave exceeding twice that SWH. These waves are distinct from tsunamis. Tsunamis result from the displacement of water, often due to earthquakes or ocean floor movement. While tsunamis travel fast over wide areas, rogue waves occur spontaneously in limited locations. They are often far from land and can be extremely dangerous to ships and lighthouses.

There is no single cause for these waves, but several physical processes can create them. One method is through linear superposition. This happens when high winds or strong currents cause different waves to move at different speeds. When these waves merge, they combine into a single, much larger wave. Another process involves nonlinear effects. One theory involves modulational instability. This is a phenomenon where a "normal" wave begins to draw energy from nearby waves. This causes the wave to briefly become very large. Researchers also study the Peregrine soliton. This is a type of nonlinear wave that can reach three times the height of the surrounding sea.

Scientists have discovered different types and variations of these extreme sea states. In laboratory water-wave tanks, researchers have observed a "super rogue wave." This is a specific type of breather that can be five times higher than the surrounding waves.

They have also identified "rogue holes." These are the inverse of rogue waves. In a rogue hole, the water depth drops to more than twice the significant wave height. While many thought these only existed in experiments, a recording from a North Sea oil platform confirmed they occur in nature. Some researchers also study the "Three Sisters," which is a pattern of three successive large waves.

For a long time, rogue waves were considered mythical. Sailors reported them, but the scientific community was skeptical. In 1826, Jules Dumont d'Urville reported waves 30 meters high in the Indian Ocean. However, he was publicly ridiculed by other scientists. At that time, many believed no wave could exceed 25 meters. This disbelief likely came because few people survived such encounters to tell the stories. This changed as technology improved. The first scientific evidence came in 1984 from the Gorm platform in the North Sea. However, the most famous proof arrived on January 1, 1995.

The Draupner wave was recorded at a gas-pipeline support complex in the North Sea. A downward-pointing laser sensor measured a maximum wave height of 25.6 meters. The peak elevation was 15.6 meters above the still water level. This wave was more than twice the height of the surrounding sea. It even caused minor damage to the platform. This event provided the digital proof needed to convince the scientific community. Since then, many other tools have confirmed their existence. These include satellite imagery, radar, and pressure transducers on the seafloor.

Extreme wave measurements have continued to push scientific boundaries. In February 2000, the British research vessel RRS Discovery encountered massive waves. It was sailing in the Rockall Trough west of Scotland. The ship recorded an SWH of 11.8 meters. Individual waves reached heights of up to 30 meters. In 2004, scientists used European Space Agency satellites to study the ocean. They analyzed three weeks of radar images. From this data, they identified ten rogue waves that were 20 meters or higher. These numbers show that rogue waves are far more powerful than standard statistical models predict.

Understanding rogue waves is vital for ocean safety and engineering. These waves can overwhelm ships that were not designed for such sudden energy. They have been implicated in the loss of several vessels. The freighter MS München was lost in 1978. The Ocean Ranger, a drilling unit, sank in Canadian waters in 1982. In 2007, NOAA compiled a catalog of over 50 historical incidents likely caused by rogue waves. Even famous art may reflect this reality. Hokusai's "The Great Wave off Kanagawa" is often called a tsunami, but it likely depicts a large rogue wave.

Modern research continues to explore how waves interact. Studies at TU Delft have looked at cross-swell waves. They found that waves coming from multiple directions can grow much steeper than expected.

These studies help engineers build safer structures for the ocean. The math used to describe these waves, such as the nonlinear Schrödinger equation, is also studied in other fields. Scientists look at similar patterns in liquid helium and nonlinear optics. This shows that the physics of rogue waves connects to many different parts of science.