Definitions for wave breaking - Breaking and Dissipation of Ocean Surface Waves - page 12

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Definitions for wave breaking

Following the intuitively familiar concept of wave breaking discussed in Section 1.2 ,
a variety of phenomenological definitions can be formulated. Wikipedia suggests such a
definition, applicable across the range of wave processes, including water waves as well as
electromagnetic waves, waves in plasmas and in other physical media:

“In physics, a breaking wave is a wave whose amplitude reaches a critical level at which some process
can suddenly start to occur that causes large amounts of wave energy to be dissipated. At this point,
simple physical models describing the dynamics of the wave will often become invalid, particularly
those which assume linear behavior” (http://en.wikipedia.org/wiki/Wave_breaking).

The Glossary of Meteorology of the American Meteorological Society defines the breaking
of ocean surface waves more specifically:

“A complex phenomenon in which the surface of the wave folds or rolls over and intersects itself.
In the process it may mix (entrain) air into the water and generate turbulence. The causes of wave
breaking are various, for example, through the wave steepening as it approaches a beach, through
an interaction with other waves in deep water, or through the input of energy from the wind caus-
ing the wave to steepen and become unstable” (http://amsglossary.allenpress.com/glossary/browse?
s = w&p = 11).

As discussed above, a more explicit physical, yet only mathematical definition of the
wave-breaking phenomenon is hardly possible. Wave breaking can occur due to a number
of different causes which will result in different appearances of the wave breaker, different
physics of wave energy dissipation in the course of breaking and different outcomes in
terms of the impact on the wave field, on the subsurface water layer and even on the solid
bottom in finite-depth environments. While breaking, a wave and the associated underwater
motion go through a number of different stages, with different dynamics, different surface,
acoustic, void-fraction, optical and other signatures. It is these stages that we will classify
in this chapter which will help us to avoid ambiguity throughout the rest of the topic. We
will also define here the main quantitative characteristics used to describe the frequency
of occurrence of wave breaking and the strength of breaking, and will describe breaking
types and breaking criteria.

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