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average enhancement plotted in
Figure 8.5
b is a more suitable measure for parameterising
the effect.
The second panel shows these corresponding results for the enhancement
E
.Again,if
there were no enhancement,
E
should be 1 because the relative contribution of the breaking
events to the total flux would be the same as their relative duration. We note, however, that a
significant mean enhancement of 1.87 was observed, highlighting the potential aerodynamic
consequences of wave breaking. Values of
E
for individual records vary from 1.4 to 2.7, that
is in the presence of breaking it is always that
E
1. The highest enhancement is exhibited
by the most-strongly forced waves. This is perhaps connected with the breaking severity
which further magnifies the effect of the breaking events as such, as discussed above.
Figure 8.6
presents further analyses of several key statistics related to breaking waves
and their relative contribution to the energy flux from the wind to the waves. Since a
>
Figure 8.6 Key breaking-wave statistics and their relative contributions to the energy flux from
the wind to the waves. In the top two panels, symbols denote breaking (pluses), non-breaking
(x-symbols) and non-segregated (circles) waves. a) Mean energy flux from the wind as a function
of the rear-face steepness. Energy flux to each individual wave was normalised by its steepness.
b) Statistics derived from counting the waves in each steepness group. c) Ratio of counted breaking
to non-breaking waves as a function of the steepness of the windward (rear) face of individual waves.
Figure is reproduced from
Babanin
et al.
(
2007b
) © American Meteorological Society. Reprinted
with permission
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