Charnock dynamics: a model for the velocity structure in the wave boundary layer of the air–sea interface |
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| Authors: | John A T Bye Jörg-Olaf Wolff |
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| Institution: | 1.School of Earth Sciences,The University of Melbourne,Victoria,Australia;2.ICBM,Universit?t Oldenburg,Oldenburg,Germany |
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| Abstract: | We present a unified model of the air–sea boundary layer, which takes account of the air–sea momentum exchange across the
sea surface. The recognition of the importance of the velocity shears in the water (which comprise a frictional shear and
the Stokes shear due to the wave motion) in determining the sea surface roughness is a distinctive feature of the analysis,
which leads to a prediction of the Charnock constant (α) in terms of two independent parameters, namely the wave age and the ratio of the Stokes shear to the Eulerian shear in the
water. This expression is used to interpret the large observational variability of the Charnock constant. The 10-m drag coefficient
can also be expressed using similar reasoning, and the introduction of a relation in which the ratio of the frictional shear
in the water to the frictional shear in the air decreases with the friction velocity yields predictive relations for the variation
of the 10-m drag coefficient at very high wind speeds both in the open ocean and in wind–wave tanks. The physical interpretation
of this relation is that the production of spray essentially returns momentum from the ocean to the atmosphere, and this process
becomes progressively more important as the wind speed increases. |
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| Keywords: | Air– sea momentum exchange 10-m Drag coefficient Inertial coupling |
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