Energy dissipation across the wave spectrum - Breaking and Dissipation of Ocean Surface Waves - page 271

Figure 7.8 Non-normalised incipient-breaking φ i ( f p ,θ) (solid line) and post-breaking φ p ( f p ,θ)
(dashed line) directional spectrum (7.33) at peak frequency f p . Units of the MLM directional
distributions are arbitrary. Figure is reproduced from Young & Babanin ( 2006a ) © American
Meteorological Society. Reprinted with permission

of the breaking occurrence. As has been discussed on a number of previous occasions,
the dissipation consists of contributions of both the breaking probability and the breaking
severity.
It is interesting to notice here that the frequency distribution of the breaking severity
is also smallest at the spectral peak ( Figure 6.6 and discussion in Section 6.2 ). That is,
the breaking appears to narrow down the spectral peak, both in the frequency and in the
directional domains.
In order to obtain the angular distributions of the breaking occurrence directly, it would
be necessary to combine one of the methods able to detect individual wave-breaking events,
e.g. one of the acoustic techniques described in Section 3.5 , with a method suitable for
detecting a direction of propagation of these individual waves, for example, the wavelet
directional method (WDM) of Donelan et al. ( 1996 ) or some of the remote-sensing tech-
niques of Section 3.6 . This is, however, a very demanding experimental exercise as it would
require very long observations in order to obtain reliable statistics. Even if the directional
plane is subdivided into reasonably broad bins, i.e.

20 ◦ , there will be
required many hours of continuous stationary wave-breaking records, particularly given

10 ◦ or even ± ±