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

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(12) variation of the wavy-surface properties at wave-group and wavelength scales;

(13) wave directionality;

(14) wave short-crestedness;

(15) coupled effects in the air/sea boundary layers.

The 16th and separate item would be that due to peculiarities of air-sea interaction in

extreme wind-forcing conditions which include an entire set of new features irrelevant

in moderate winds (see Section 9.1.3 below). Here, we would also include the sea sur-

face temperature explicitly, in addition to the stratification item (8) above (see argument

in Bortkovskii , 1997 ). Even then, this list is far from exhaustive, and does not mention,

for example, properties and processes which breach the validity of the constant-flux-layer

approximation, as in such circumstances the notion of the drag coefficient (3.8) becomes

uncertain. Since a significant number of large-scale processes in the atmosphere disrupt the

constant-flux physics, parameterisations for the drag coefficient are bound to have some

residual scatter.

This scatter, therefore, cannot be helped by the technological advances as it is not

necessarily due to insufficient accuracy of the measurements. The bulk of this scatter is

apparently due to the fact that, at the same wind speed, C D can vary due to influences

other than the wind as such. These influences are very many and the variations are very

substantial.

To support this perception, Babanin &Makin ( 2008 ) used the approach which combined

an experimental study with theoretical investigations conducted by means of the WOWC

model. Experiment, although an ultimate truth, is hardly able to separate the effects of

the multiple influences acting simultaneously. This can be done within the WOWC model,

by switching on and off different physical mechanisms. If, for particular conditions, the

experiment and the model produce identical or close results, it can be assumed that the

physics included in the model is adequate for the relevant field circumstances. If, on the

contrary, there are essential discrepancies between the measurement and the model, such

cases should be scrutinised to find the cause.

Out of the many properties listed, Babanin & Makin ( 2008 ) considered the behaviour of

C D in terms of wind speed U 10 and sea state U 10 /

c p and, in addition to these traditional

properties, looked at the effects that the rising and falling winds (6) and gustiness (7) (from

the list above) have on the C d parameterisations. The latter effects were found to be the

major source of disagreement between the experiment and the model.

The Lake George finite-depth field experiment is well-documented in the literature and is

also described in this topic in Section 3.5 . Here, we will only mention that an integrated set

of instruments was deployed in all four relevant environments: the atmospheric boundary

layer, the water surface, the water column and the bottom boundary layer. The waves were

recorded with a stationary directional eight-probe wave array and by a set of mobile one-

probe arrays which were used to record the short-scale spatial variability of wave trains.

Detection of breaking events was also carried out by multiple means ( Babanin et al. , 2001 ,