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Jin Wu

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Jin Wu

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There are two sets of comprehensive measurements of sea spray: de Leeuw and Smith et al. Their data are interpreted to describe similar productions of film and jet drops by bursting bubbles. For measurements of Smith et al., those droplets associated with the second peak at large sizes of the production spectrum are shown to be spume drops generated by the wind tearing of wave crests. Together with physical understanding, representations of field data are deduced for film and jet drops and are discussed for spume drops.

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Jin Wu

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Experimental results of Blanchard and Syzdek and of Resch and Afeti on the production of film drops by bubbles bursting at the surface of seawater were parameterized earlier by Wu. More recently, comprehensive observations have been carried out by Spiel. All these measurements, covering different size ranges of film drops, are shown to quantitatively complement each other. Through combining these results, the production of film drops has been quantified, in terms of both number and size distribution, over the entire radius range 0.01–250 μm. The average size of film drops is about 25 μm in radius, which is much larger than the commonly cited radius for film drops of 5 μm. In addition, all the results are shown to follow a simple rule; that is, the ratio between the total surface area of film drops and the surface area of their parent bubble is a constant.

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Jin Wu

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Several empirical formulas were reported to describe the production of jet drops by bubbles bursting at the surface of seawater; they were, however, based on scanty data. Recent observations of Spiel have provided new data for intermediate-size bubbles; his results are further quantified here, aiming for their extrapolations to both small and large bubbles. A greater number of jet drops are shown to be produced by smaller bubbles; the production follows a combined exponential and linear decline for larger bubbles, rather than the exponential or linear decline proposed earlier. The largest number of jet drops produced by the smallest bubble may not exceed seven. The largest bubble that can produce jet drops may not exceed about 1.7 mm, a radius somewhat smaller than the analytical value. The ratio between the radius of jet drops and that of their parent bubble is always greater than the oft-quoted 1-to-10 value; it approaches a minimum value of 0.110 for zero bubble radius and reaches a maximum value of 0.147 for bubbles having a radius larger than 0.8 mm.

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Jin Wu

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Jin Wu

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Drift currents immediately below the water surface were systematically measured in a circulating wind-wave tank. The results confirmed the existence of a viscous sublayer at the air–water interface, with the current varying linearly with depth and the shear stress determined from the linear profile comparing very favorably with the wind stress. The thickness (δν) of the sublayer was found to be almost invariant with wind velocity. Its nondimensional thickness (δν u */ν) is smaller than that over a solid surface, having a value of 4 at low wind velocities and increasing with wind velocity toward the solid-surface value of 8 at high wind velocities.

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Jin Wu

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Jin Wu

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The fraction of wind stress consumed in driving aqueous flows has been estimated for various nondimensional fetches, derived from the wind velocity, fetch, and gravitational acceleration. The fraction is shown to vary with both fetch and wind velocity; at all fetches it is smaller at lower wind velocities, and for most wind it is smaller at shorter fetches.

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Jin Wu

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Features of observed radar sea returns are interpreted to provide evidence of widespread small-scale wave breaking over the sea surface. These breakings can extensively disrupt aqueous thermal and diffusion sublayers, greatly modifying present formulations on air–sea exchanges of heat and mass.

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Jin Wu

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The rate of air–sea gas transfer has been largely parameterized on the basis of studies performed in laboratory tanks: empirical formulas are proposed for three wind-velocity regions. Observed features of the transfer in these regions are associated with various wind, wave, and aqueous-flow conditions in straight and circulating tanks; some of these conditions do not even exist in the field. With these understandings, two formulas are proposed for the gas transfer: one for lakes and the other for the open sea; the rate is generally greater in the open sea.

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