Geoscience Reference
In-Depth Information
the depth of themodulation and breaking severity. Significant scatter of the data points shows
the importance of other mechanisms superimposed over the observed trend and the complex-
ity of the problem, even in the absence of the wind. The influence of the wind on the depth
of the modulation, if added, further contributes to this complexity as it is most essential.
Since spectral models of wave forecast are one of the main consumers of dissipation-
function knowledge, it should be mentioned that the modulation depth will be a difficult
property to account for in such models where information on the wave-group properties
is basically lost, let alone on the depth of the modulation and development of instability
modes. Such relevant properties, e.g. rate of instability growth, will have to be param-
eterised through the characteristics of the wind forcing and available wave properties, for
example, the steepness of appropriately bandpassed waves.
The last three chapters of the topic are new compared to the review. These chapters
almost doubled the volume of the original review by considering breaking-related topics in
addition to the research on the wave breaking itself in the previous chapters. Their inves-
tigations and significance are in many regards equivalent to the wave-breaking research as
such, and the separation of the wave-breaking studies and wave-breaking-related studies is
in fact quite superficial. For example, topics of whitecapping dissipation of surface-wave
energy, spray generation in the atmospheric boundary layer, and bubble production in the
upper ocean are inseparable from the topic of wave breaking itself.
Indeed, research on the whitecapping dissipation routinely stands as almost a synonym
for wave-breaking studies. The wave-breaking chapters looked in detail at the breaking
probability and breaking severity, and these two features combined basically define the
dissipation. As it happens, however, the dissipation research is not a straightforward amal-
gamation of the two topics, but has rather taken on its own direction of investigations.
A variety of innovative analytical, statistical, probabilistic, numerical, experimental and
observational approaches have been developed to deal specifically with the whitecapping
dissipation. Effectively, this is a research area in its own right which constitutes a large
volume of knowledge, and had to be reviewed separately in
Chapter 7
, particularly given
its great applied importance with respect to wave-forecast modelling.
Chapter 7
started with a brief review of analytical theories which have tried to explicitly
investigate the wave-energy dissipation (
Section 7.1
). These interpret pre-breaking and
post-breaking features of the wave fields, bypassing the stage of individual waves as such.
Here, we have added a new type of such analytical models, the kinematic-dynamic model,
to the classifications available in previous reviews of these modelling issues.
Explicit modelling of the breaking in progress is a complex problem of fluid mechan-
ics, where a two-phase turbulent medium has to be simulated based on first principles,
with the strongly nonlinear wavy air-water interface, filled with air bubbles and cavities
at and below the water surface, and with spray droplets in the air. Such a task is demand-
ing analytically and expensive computationally. It is, however, possible nowadays and has
been a subject of active development over the past decade, predominantly with respect to
engineering applications ranging from the impact of breaking on structures to simulation
of breaking and its consequences in the surf zone. A variety of such models are available
Search WWH ::
Custom Search