What are the different types of rogue waves? Where does physics fit into the equation, and what is the criteria for determining if a wave is "rogue" or "tame"?

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### Types of Rogue Waves

Though there is not yet an agreement on the different types of rogue waves, researchers have come up with some preliminary categories.

Rogue waves are currently classified into three main types:

- Large Walls: Several large walls of water traveling through the ocean.

- Three Sisters: Groups of three waves at a time, where two of them are very large waves followed by a monster wave.

- Single Wall: A single wall of water that can reach several stories high such as that seen in the film The Perfect Storm.

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### A Rogue Wave Equation

There is a consensus on the basic equation used to define rogue waves, and it is based on the

**significant wave height**. Oceans have waves of varying sizes. Oceanographers look at several of them, choose one third of the largest ones they can find, and obtain the significant wave height by calculating their average size. For example, an oceanographer may gather wave heights for several minutes and out of this choose a particular three-minute stretch. If there are 90 crests, 30 of the largest ones are picked, and their average height is then calculated.The traditional equation used to define rogue waves is:

H

_{max}/H_{s}> 2where H

_{max}stands for the maximum wave height, and H_{s}is the significant wave height. This equation defines rogue waves as at least twice the size of the significant wave height. This is one reason why even a wave as small as three feet, such as that which drowned the three young men in California mentioned in part two, can be considered a rogue wave.Figure 2, courtesy of the Math Department at the University of Oslo, shows an actual 25.6-meter (84 foot) rogue wave that hit the Draupner Oil Platform in the North Sea off Norway on January 1, 1995. The significant wave height is 10.8 meters (35 feet). The monster even has a name: it is officially called the Draupner Wave or the New Year Wave.

In the next article we will examine current research on monster waves.

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### References

Introduction to Physical Oceanography by Robert H. Stewart

Elements of Oceanography by J. Michael McCormick and John Thiruvathukal

Are there Different Kinds of Rogue Waves? by Liu and MacHutchon

**Image Credits***Wave Heights from**Introduction to Physical Oceanography**Daupner Wave Department of Mathematics at the University of Oslo*