Energy dissipation across the wave spectrum - Breaking and Dissipation of Ocean Surface Waves - page 272

Figure 7.9 Ratio of incipient-breaking φ i ( f p ,θ) and post-breaking φ p ( f p ,θ) directional spectra of
Figure 7.8 at peak frequency f p . Figure is reproduced from Young & Babanin ( 2006a ) © American
Meteorological Society. Reprinted with permission

the fact that the overall directionally integrated rates are typically only of the order of a
few percent (e.g. Babanin et al. , 2001 ).
Such an investigation was conducted by Filipot (2010, personal communication) and
revealed an isotropic distribution for the breaking probability. In connectionwith the bimodal
directional function of the dissipation here, this implies a strongly bimodal behaviour of
the breaking severity. Such conjecture is still to be confirmed experimentally.
In this regard, a recent study by Kleiss & Melville ( 2010 ) has to be mentioned. They
investigated the directional distribution of

, the breaking crest length per unit area
(see Section 3.6 ), which relates both to the breaking probability and to the dissipation. They
found it predominantly unimodal and broadening towards smaller scales. For these slow
breakers under developing-wave conditions, a bimodal directional distribution of

( c ,θ)

( c ,θ)

was observed.

7.4 Whitecapping dissipation functions in spectral models for wave forecasting

Dissipation functions which are used to represent the spectral distribution of dissipation
in spectral wave-prediction models is a large topic and may well constitute a large review
paper in its own right. Many, if not most (to date) such terms are not based on strictly