Wavelets and Air-Sea Transferby G. T. Csanady, Old Dominion Univ, Norfolk, United States,
Document Type: Proceeding Paper
Part of: Air-Water Mass Transfer
Newly acquired insight into the mechanism of air-sea momentum transfer has also resolved some long-standing questions on air-sea transfer of gases of low diffusivity. Sharp-crested wavelets carrying viscous shear layers cause air flow separation, which in turn leads to form drag and shear stress 'spikes' on the wavelets. Concomitant flow separation in water, and variable shear, cause surface divergence, and thereby keep the surface diffusion boundary layer thin. An important unresolved question is the precise role of the shear stress spikes in the momentum transfer process: do they increase wavelet momentum in the first instance, or does their momentum go directly into the viscous surface shear layer? If the former, then the surface divergences important for gas transfer arise only from flow separation, otherwise also directly from the variable acceleration of the surface shear layer. The latter answer implies more intense gas transfer. In an attempt to find the answer to this question, an idealized model of wave generation by an isolated shear stress distribution has been analyzed. The result shows unequivocally that nonuniform shear stress is not an efficient wave generator, and that in a typical situation more than 99% of the momentum input is absorbed by the surface shear layer.
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