The peak period or peak frequency is considered to be an important quantity in characterizing ocean surface waves, including wave models [e.g., 1]. But practically, why are we interested in modelling the peak period accurately?

I'm thinking the peak frequency directly translates to how fast the dominant waves propagate, and so is important to predicting when the waves will reach coastal locations of interest. Is this thinking correct?


2 Answers 2


The peak period is only one of multiple parameters that is used to describe the spectral shape of ocean waves. Most commonly used parameters are significant wave height, mean period, and dominant (peak) period. Significant wave height is proportional to the square-root of total wave energy and it tells us how much bulk wave energy is there at any given location. Mean period tells us how long are waves on average, and peak period indicates how long are the waves with maximum energy. These are just statistical parameters describing the shape of the spectrum. In reality, accurate prediction of the whole spectrum is important for wave prediction.

What happens if we vary the peak wave period while keeping the total wave energy, and thus significant wave height, constant? These are some of the effects that can expect with longer peak period:

  • Swell propagates faster and reaches the shore sooner, as you mentioned in your question;

  • Because swell propagates faster, wave dissipation from swell outrunning wind will increase;

  • Longer waves are more dissipated due to bottom friction, i.e. longer waves will feel the bottom sooner as they propagate toward shallow water;

  • Longer waves induce Stokes drift that decays more slowly with depth compared to that of shorter waves, inducing stronger Lagrangian transport at depth and enhanced Langmuir circulations;

  • Longer waves with same wave energy are less steep, effectively decreasing the dissipation of short waves that "ride" on the forward faces of swell waves;

  • Different interaction with structures, as mentioned by Wolfgang Bangerth.

Because of the above physical processes, waves at peak period affect the evolution of the spectral shape both locally and along their propagation line.

  • $\begingroup$ Thanks for this @milancurcic. A follow up question on the second last point - why would there be less dissipation of short "rider" waves when the long waves are less steep? Is it because when the long waves are less steep, the short waves don't break as much? $\endgroup$ Jan 28, 2016 at 4:25
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    $\begingroup$ Yes, in general waves break when they reach some critical steepness. Imagine a short wave on a forward face of a long swell wave. When the forward face is steeper, this makes the short wave on that face become steeper as well and is more likely to break. $\endgroup$ Jan 28, 2016 at 6:04

The peak period is also important in evaluating the interaction of waves and human-built structures such as drilling platforms. If the frequencies of resonance of a drilling platform coincide with the peak frequency of waves, you will get rather sea sick occupants or, more seriously, structural failure. All platforms are designed to tune their resonance frequencies away from common wave frequencies.


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