New sea spray generation function for spume droplets

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Abstract

[1] With increasing wind forcing and development of wind waves, more and more sea spray droplets are produced on the sea surface. On the basis of now available observational data from field and laboratories with 10-m wind speeds ranging from 8 to 41 m/s, it is shown that the traditional approach of using wind speed only fails to describe the increase of spume droplet production, owing to the neglect of effect of wave state. Instead, a nondimensional parameter RB = u*2pν called the windsea Reynolds number (Toba et al., 2006) is very good for characterizing the observational data from laboratories and field, where u* is the friction velocity of air, ωp the angular frequency spectral peak of wind waves, and ν is the kinematic viscosity of air. The windsea Reynolds number RB represents the coupling effect of wind forcing and wind wave state, and can be regarded as a measure of fluid dynamical conditions at the air-sea boundary layer. A new sea spray generation function for spume droplets is proposed as a function of RB. We conclude that spume droplets begin to be produced as RB exceeds 103. The effects of sea spray droplets on air-sea transfers are also estimated with the new model. It is found that the heat and momentum fluxes induced by sea spray droplets become comparable to the interfacial fluxes by bulk formulas when RB is greater than 105 and 106, respectively.

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