Role of wave breaking in the air–sea interaction - Breaking and Dissipation of Ocean Surface Waves - page 404

of air injection deeper into the upper-ocean layer leads to supersaturation of the sea water
with the gases. McNeil & D'Asaro ( 2007 ) make a conclusion about the dominant role of
the bubble injection in gas transfer in such extreme conditions.
As intended, McNeil & D'Asaro ( 2007 ) proposed a parameterisation which spans the
entire range of natural wind speeds including hurricanes. This accounts for both under-
critical mechanisms of gas transfer, that is the turbulent diffusion of microbubbles through
the interface and direct ventilation by means of wave breaking, and the super-critical
supersaturating dissolution of the subducted bubbles.
Thus, to conclude this last section of Chapter 9 we should say that we have briefly reviewed
a very large topic of bubble production and air-to-sea gas transfer due to the breaking.
Three main issues were outlined, the structure of the bubble clouds, the dynamics of bubble
submersion and surfacing, and the role of the bubbles in gas transport to the upper ocean.
Overall, Chapter 9 is dedicated to the various roles the breaking plays in the broader sys-
tem of air-sea interactions. Section 9.1 describes these roles with respect to the atmospheric
boundary layer. These include the dependence of sea drag on the breaking, the production
of spray by the breaking, and discussion of the boundary-layer physics in extreme weather
conditions. While the effects of the breaking on the drag coefficient are secondary, that
is the breaking alters the sea drag which is due to turbulent fluxes from the wind to non-
breaking waves, the wave-breaking part in the generation of spray is primary. Most of the
spray is produced by the breakers. In extreme conditions, the physics of this generation and
the structure of the droplet distributions change and that is linked to other changes in the
boundary-layer physics. The significance of spray and aerosol production for other fields
of atmospheric sciences and applications is also discussed.
The upper-ocean section, 9.2 , apart from the topic of the present subsection, discusses
in some detail schemes of the momentum and energy transfer from the wind to the ocean
and of the water-turbulence generation. This is done in a more general context than just
the influence of the breaking, because without accounting for other effects of the dynamic
transfer and turbulence behaviour such a description would be incomplete. The roles of
breaking, however, are most essential in all these processes, and in the respective subsec-
tions they are identified and highlighted.