Wave-breaking probability - Breaking and Dissipation of Ocean Surface Waves - page 178

feasible in the general case and has to be done in terms of wave-related properties. For
the dominant waves, spectral-peak steepness

peak (5.17) - (5.18) was suggested and suc-
cessfully used as such a parameter (see Section 5.2 , Figure 5.18 and eq. (5.19) ).
The above-mentioned wind forcing (5.20) and shear-current influences were further

shown to have a marginal effect on dominant-wave breaking and therefore they were
employed in the breaking parameterisation through secondary-importance parameters (see
also Figure 5.20 for dependence of b T on

γ

γ ). For the shear current, the parameter intro-

duced was

u s
u 0 =

0 . 01 U 10

= , (5.21)

c p

the ratio of the wind-induced surface current u s to maximum orbital velocity u 0 . The drift-
current velocity was adopted from Babanin ( 1988 )as

u s ∼ 0 . 01 U 10 , (5.22)

and the maximal orbital velocity used was that of a linear surface gravity wave with height
equal to the peak wave height (5.18)

u 0 = peak c p .

(5.23)

The Black Sea and Lake Washington breaking-wave data sets, plotted in Figure 5.21 a, b
for the b T -versus-

dependence, show that the breaking fraction increases with the shear
parameter, although with a far lower visual correlation than seen for the peak steepness.

Figure 5.21 Observed dominant wave-breaking probability b T (2.3) versus surface-shear parameter
(5.21) for two diverse field sites (a) Black Sea data (*), (b) Lake Washington data (+). The legend
shows the correlation coefficient based on a linear fit. Figure is reproduced from Banner et al. ( 2000 )
© American Meteorological Society. Reprinted with permission