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describing these most important properties of the air-sea interactions has stagnated for
decades, unable to improve the large scatter of experimental data and parameterisations,
and it appears that the sensible way to progress here is to take into account multiple
influences which form such a drag, wave breaking among them.
Speaking generally, a proper account of the wave-breaking effects both in the dynamic
models of the atmospheric boundary layer and in mixing schemes of the upper ocean
should also be on the agenda. In this regard, not only the wave breaking, but the waves
in general, are an important player near the ocean surface, above and below, and negoti-
ate all the exchanges through the surface. This includes the large-scale air-sea interactions
too, all the way to the climate scale. The wave effects and influences are important, but
largely overlooked or underestimated by large-scale models, and coupling of them with
the wave models, which is already under way as mentioned throughout the topic, is the
reasonable and sensible way to advance modelling physics and improve the respective
forecasts.
Below the surface, the topic of bubbles generated by the breaking is also in need of
attention. Such bubbles are a major player both in the dynamics of the subsurface water
layer and in the air-sea gas and moisture exchange. On the technical side, they appear to be
a proxy for wave-energy dissipation, the most challenging property due to wave breaking
to measure and investigate.
In principle, the problems discussed so far should not take too long to solve. As dis-
cussed in
Chapter 3
and throughout, all the instrumentation, measurement techniques and
theoretical understanding are available, and it only requires attention and a concentrated
effort by the wave-breaking research community.
It is not so, however, with respect to wave breaking and breaking-related issues in
extreme weather conditions such as tropical cyclones. Here, change in the regime of the
air-sea exchanges is observed in every regard, with the wave breaking in the centre of it.
In the air, it generates spume which may slow down the momentum fluxes, affect the ther-
modynamics of the boundary layer and thus allow the cyclones to grow. Below the surface,
the new mechanisms of bubble submersion are produced which can enhance the air-to-sea
gas transfer. The wave breaking itself, with the wind directly tearing wave crests rather
than gradually leading to the water surface collapse, takes on another regime.
Three layers of difficulties seem to prevent solution of the extreme-weather problems in
the immediate future. Firstly, there is an apparent lack of instruments and techniques which
can operate, conduct measurements and collect data in such circumstances. As a result, the
observations are few and cannot support conclusive theoretical research. Secondly, there is
no clarity in what exactly should be measured, that is, what are the most essential properties
of wave breaking and its products which are needed for adequate physical modelling. In
some way, this field is now in the position in which the general wave-breaking field was
some 20-30 or even more years ago, that is we measure what we can measure and are
guided by these measurements. The choice of available analytical theories of extreme air-
sea interactions has been abundant in recent years, but it has not seemed to help to guide the
experiment consistently. This is the third difficulty: there is no leading recognised theory
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