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was conducted from an aircraft. Statistical estimates for the wave breaking and related
ocean-mixing characteristics, as well as for the breaking parameter b br were obtained. In
the traditional framework of relating the breaking properties directly to the wind, it was
found that the distribution of
(
c
)
is proportional to
10 4 U 10
10
3
(
c
) =
3
.
3
·
exp
(
0
.
64 c
).
(3.31)
(note that the fit is quantitative and is not dimensionally consistent, that is, the dependence
will only provide a value of
in m if the wind and phase speeds substituted are in m/s).
It was also found that the main impact of the wave-breaking mixing effect comes from
short waves which is consistent with observations that most of the wave energy/momentum
input, which is supported by the shorter waves in the spectrum, is lost locally (e.g. Donelan ,
1998 ). This work has now essentially been extended and has even included the directional
distribution of
( Kleiss & Melville , 2011 , 2010 ).
Dulov et al. ( 2002 ) performed the video recording from an observational tower, com-
bined with collocated records of waves by means of a wave array. Their study was intent
on investigation of whitecapping coverage and was mentioned in Section 3.1 . It high-
lighted the cumulative effect of wave breaking and clearly demonstrated the induced nature
of short-scale breaking. Overall, however, this kind of optical observation of breaking
dynamics is far from being routine or even common.
Among the optical means of remote-sensing, infrared methods of probing the breaking
waves are also most promising ( Jessup et al. , 1997a , b ; Jessup & Phadnis , 2005 ). Here, we
quote Jessup et al. ( 1997a ):
(
c
,θ)
“Under most circumstances, a net upward heat flux from the ocean occurs primarily by molecular
conduction through a thermal boundary layer, or skin layer, at the ocean surface. As a result, the
“skin temperature” at the top of this layer is a few tenths of a degree Celsius cooler than the bulk
temperature immediately below the skin layer ( Katsaros , 1980 ; Robinson et al. , 1984 )”.
Wave breaking disrupts the skin layer, exposes the bulk waters to the surface, and their
temperature can readily be detected by the infrared-sensing devices. Thus, the wave-
breaking process can be quantified in terms of the occurrence of breaking events and
areal coverage of the turbulent breaking wake. In this way, the infrared technique can be
employed to study not only the breaking statistics and probability, but also all sorts of tur-
bulent subsurface mixing and air-sea interactions due to the breaking, such as heat and gas
exchanges (e.g. Jessup et al. , 1997b ).
Infrared sensing can also be used to investigate remotely the most elusive property of
wave breaking, the breaking strength ( Section 2.7 and Chapter 6 ). This strength deter-
mines the extent and intensity of the turbulent wake, and therefore the recovery rate of
the skin layer as the breaking wake subsides and the surface cools, and correlates with the
dissipation rate due to the breaking event ( Jessup et al. , 1997b ).
Thus, the infrared-sensing probing is an all-in-one technique for investigation of wave
breaking and its consequences. It allows us to detect breaking occurrence, to investigate
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