Conclusions. What else do we need to know about wave breaking? - Breaking and Dissipation of Ocean Surface Waves - page 425

or even set of theories for waves and wave breaking under extreme wind forcing, and for
air-sea interactions in such situations, which means there is no clear understanding of the
physics.
In the meantime, this physics must be something very special and must be strongly
coupled across all the ocean-interface environments. As highlighted in this topic, through
discussions in Sections 3.3 , 9.1.3 , 9.2.3 and in this conclusion, at wind speeds U 10 ∼
30-35m s a change in the dynamic regimes occurs in the atmospheric boundary layer

(saturation of the sea drag), on the surface (saturation of wave asymmetry and alteration
of the breaking mechanism) and below the surface (dynamics of bubble submersion).
The latter also leads to a change in the regime of gas transfer. It is time for a combined
effort/approach across the different air-sea-interaction sciences to address this issue which
apparently needs a complex coupled insight.
Another change in the regime observed in this topic should also be pointed out. This
may not seem as exciting as the new set of air-sea interactions in hurricanes just men-
tioned, but it may signify a new set of physical relationships in the wave system in benign
and moderate conditions, which are much more typical compared to the tropical cyclones.
This is the transition of the dynamic behaviour within the wave spectrum, at wave scales
which can be characterised by forcing U 10 / C

/

45, as discussed in Sections 5.3.4 and
8.2 . At these scales, alteration of the spectrum-tail behaviour happens, from the tail-level
being constant on average to becoming wave-age-dependent. At such wind forcing, the
highest dimensional transitional frequency between the f − 4 and f − 5 subintervals occurs.
And at the same dimensionless frequency, the transition from the inherent-breaking to
induced-breaking dissipation is observed. Each of the three features has importance and
needs attention in its own right, but the fact that the respective transitions all occur at
the same dynamic wind-forcing and frequency range can hardly be incidental and implies
some interesting coupled physics which is still to be understood.
Overall, in spite of the difficulties and gaps in understanding, we would like to conclude
on an optimistic note. The wave-breaking research and knowledge is much better struc-
tured today compared to even ten years ago. The physical picture of wave breaking is still
not complete, but a consistent image of this interesting and challenging phenomenon is
emerging.

≈ 1 .