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  1. Abstract

    We experimentally investigate the depth distributions and dynamics of air bubbles entrained by breaking waves in a wind‐wave channel over a range of breaking wave conditions using high‐resolution imaging and three‐dimensional bubble tracking. Below the wave troughs, the bubble concentration decays exponentially with depth. Patches of entrained bubbles are identified for each breaking wave, and statistics describing the horizontal and vertical transport are presented. Aggregating our results, we find a stream‐wise transport faster than the associated Stokes drift and modified Stokes drift for buoyant particles, which is an effect not accounted for in current models of bubble transport. This enhancement in transport is attributed to the flow field induced by the breaking waves and is relevant for the transport of bubbles, oil droplets, and microplastics at the ocean surface.

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  2. Abstract

    Laboratory measurements of droplet size, velocity, and accelerations generated by mechanically and wind‐forced water breaking waves are reported. The wind free stream velocity is up to 12 m/s, leading to wave slopes from 0.15 to 0.35 at a fetch of 23 m. The ratio of wind free stream and wave phase speed ranges from 5.9 to 11.1, depending on the mechanical wave frequency. The droplet size distribution in all configurations can be represented by two power laws,N(d) ∝ d−1for drops from 30 to 600 μm andN(d) ∝ d−4above 600 μm. The horizontal and vertical droplet velocities appear correlated, with drops with slower horizontal speed more likely to move upward. The velocity and acceleration distributions are found to be asymmetric, with the velocity probability density functions (PDFs) being described by a normal‐inverse‐Gaussian distribution. The horizontal acceleration PDF are found to follow a shape close to the one predicted for small particles in homogeneous and isotropic turbulence, while the vertical distribution follows an asymmetric normal shape, showing that both acceleration components are controlled by different physical processes.

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  3. Reliable estimates of the fluxes of momentum, heat and moisture at the air–sea interface are essential for accurate long-term climate projections, as well as the prediction of short-term weather events such as tropical cyclones. In recent years, it has been suggested that these estimates need to incorporate an accurate description of the transport of sea spray within the atmospheric boundary layer and the drop-induced fluxes of momentum, heat and moisture, so that the resulting effects on atmospheric flow can be evaluated. In this paper we propose a model based on a theoretical and mathematical framework inspired from kinetic gas theory. This approach reconciles the Lagrangian nature of spray transport with the Eulerian description of the atmosphere. In turn, this enables a relatively straightforward inclusion of the spray fluxes and the resulting spray effects on the atmospheric flow. A comprehensive dimensional analysis has led us to identify the spray effects that are most likely to influence the speed, temperature and moisture of the airflow. We also provide an example application to illustrate the capabilities of the model in specific environmental conditions. Finally, suggestions for future work are offered. 
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