Role of wave breaking in the air–sea interaction - Breaking and Dissipation of Ocean Surface Waves - page 350

9
Role of wave breaking in the air-sea interaction
Wave breaking, apart from serving as the main dissipation source in the wave field, plays
a number of other roles both on the ocean surface, and away from the surface. Chapter 8
was dedicated to such breaking-related other-than-dissipation features in the surface-wave
system itself, and this penultimate chapter of the topic, prior to Conclusions will extend
the topic into a description of the roles wave breaking performs in air-sea interactions in a
broader sense.
Section 9.1 and subsections are dedicated to the breaking-related effects in the atmo-
spheric boundary layer. These are not limited to the wind-wave energy/momentum
exchanges which have been discussed throughout the topic. The breaking alters the sea
drag, which then affects the near-surface air flow in general. The breaking is a source of
spray, and the presence of the spray has a most essential influence on the boundary layer
again. And finally, all these features have their peculiarities or even new behaviours, to a
great extent unknown at this stage, in extreme conditions.
Section 9.2 also includes a number of subsections on important roles which the break-
ing plays in the upper-ocean dynamics and mixing. These cover descriptions of interface
momentum and gas transfer, of which the breaking is part. In particular, two subsections
are dedicated to the physical phenomena by means of which breaking facilitates such air-
sea exchanges and mixing, i.e. the wave-induced turbulence and injection of the air bubbles
under the water surface.
9.1 Atmospheric boundary layer
Like with any turbulent fluid flow over a boundary, the dynamic balance near the boundary
is very different from that of the free flow (e.g. Holton , 1962 ; Komen et al. , 1994 ). In the
boundary layer, the flow starts feeling the surface, and its dynamics changes essentially,
even if there are no interactions other than friction against the surface.
In the case of geophysical atmospheric flow, the boundary layer can be further subdi-
vided into sublayers, with different forces and their balances being important. Very close
to the ocean surface, where the friction dominates and other forces can be neglected, the
system of equations for the horizontal momentum reduces to
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