Energy dissipation across the wave spectrum - Breaking and Dissipation of Ocean Surface Waves - page 320

On a broader scale, in this section, and throughout the topic, we concentrate on deep-
water waves which are typically treated in isolation from other oceanic processes. In and
The WISE Group ( 2007 ), however, interactions of surface waves with the vertical struc-
ture of the upper ocean are outlined as another source of the dissipation. These can be
interaction of surface waves with internal waves (e.g. Gargett & Hughes , 1972 ), or mixing
through the thermocline conducted by the surface waves (e.g. Qiao et al. , 2006 ), among
many others.
To summarise the entire chapter, we should say that it is one of the most important chap-
ters of the topic. The topic is dedicated to wave breaking, and while the breaking is an
interesting physical phenomenon in its own right, relevant across a broad range of scien-
tific and practical applications, the wave energy dissipation is one of its most significant
outcomes and applications. Such dissipation occurs non-uniformly across the wave spec-
trum, and its spectral distribution is still poorly understood, but is included in most of the
models which are used for forecast of the waves and plays a role in describing interaction
of the waves with the upper ocean and the atmospheric boundary layer.
In this chapter, analytical theories of the spectral dissipation are described in Section 7.1 .
They are broadly classified into probability, quasi-saturated, whitecap and kinematic-
dynamic model types in the respective subsections.
Phase-resolvent numerical models are outlined in Section 7.2 . They deal with a challeng-
ing task of simulating the wave-breaking phenomenon explicitly, based on first principles,
and therefore have to take into account the strongly turbulent nature of fluid flow, with air
bubbles embedded on the water side and spray emitted and suspended in the air. With the
advance of fast computing, this class of models has been rapidly expanding over the past
two decades, and a variety of clever mathematical and numerical means of treating this
two-phase dynamic medium are available these days. Potentially, this way of investigating
the wave breaking and associated wave-energy dissipation, which is not based on limiting
assumptions and conditions like the analytical theories, has a great future.
While analytical theories drive the understanding of physics and progress of numerical
simulations of phenomena, the ultimate judgment of validity, applicability, significance
and relative importance of the theories always belongs to the experiment and observations.
Section 7.3 is dedicated to measurements of the spectral dissipation. These are considered
both in the laboratory, where components of the phenomenon can be isolated and studied
separately, and for the real waves in the field. New features of the total-dissipation and
spectral-dissipation behaviour found, or rather re-discovered recently, are attended to in
detail. These are, first of all, the wave-breaking threshold and the cumulative effect. The
effects that the wind imparts on the dissipation process and its strength, as well as the
directional behaviour of the dissipation, are still in a blurred area at the present stage, but
they are important and highlighted in respective subsections.
This topic is on the physics rather than applications of the wave-breaking and wave-
dissipation knowledge, but without mentioning these applications it would be incomplete.
Therefore, a substantial Section 7.4 outlines past experience, present attempts, and updates
on the potential future progress with respect

to the dissipation terms employed in