Vertical Transport of Sea Spray and Spume Droplets in High-Wind Marine Atmospheric Boundary Layer

Through analyzing the observational data obtained during high-wind conditions over the South China Sea, our results have shown that:(a) The 10-min average horizontal wind speed u is almost independent of height; (b) the 10-min average vertical velocity w is almost always positive; (c) there exists strong coherent gusty wind with low-frequency ( v _g, between 1/600 Hz and 1/60 Hz), and nearly random and isotropic turbulent fluctuations with high-frequency ( v _t, larger than 1/60 Hz). The vertical velocity w and the characteristics of the gusty wind and turbulence can be well parameterized through the horizontal wind speed u. Using the observations of (u, w) and the parameterized gusty wind and turbulence, the Lagrangian stochastic model is implemented to study and simulate vertical transport of spume droplets. The results show that a quite high proportion of spray and spume droplets (the radius is between 10 and 500 μm) teared from the breaking waves can reach the 100 m height in ABL (Atmospheric Boundary Layer) and contribute to the sea salt aerosol flux. The coherent gusty wind during high winds plays an important role in the vertical transport of droplets. Besides, we also parameterize the uplifting fraction of spume droplets that can reach the 100 m height in the ABL by using a nondimensional factor u²/(r_qg), where r_p is the radius of droplet and g is the gravitational acceleration.