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.
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:
Hmax/Hs > 2
where Hmax stands for the maximum wave height, and Hs 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.
Elements of Oceanography by J. Michael McCormick and John Thiruvathukal
Are there Different Kinds of Rogue Waves? by Liu and MacHutchon
Wave Heights from Introduction to Physical Oceanography
Daupner Wave Department of Mathematics at the University of Oslo
This post is part of the series: Introduction to Rogue Waves
An introduction to rogue waves, including discussions on their composition, history, tragic consequences, and their appearances in art, film, music, and literature.