The turbulent air-sea fluxes in high winds

In high winds, 20 m/s and above, spray droplets proliferate. These effectively increase the surface area of the ocean and may, therefore, enhance the transfer of any constituent normally exchanged across the air-sea interface. My particular interest is in how spray droplets mediate the normal turbulent surface fluxes of momentum and sensible and latent heat.

I will first review the rate at which spray droplets are created at the air sea interface and establish that this rate goes as the cube of the wind speed. That is, droplet numbers and, therefore, droplet effects become increasingly important as the wind speed approaches hurricane strength. I will next combine this knowledge of the spray generation function with microphysical theory to develop a framework for partitioning eddy-correlation measurements of the turbulent sensible and latent heat fluxes into interfacial and spray contributions. These "interfacial" fluxes are the ones normally parameterized with a bulk flux algorithm; the microphysical model parameterizes the "spray" fluxes.

Using data from HEXOS, the experiment to study Humidity Exchange over the Sea, and this theoretical framework, I partition the measured HEXOS turbulent heat fluxes into interfacial and spray contributions and thereby demonstrate what the signature of spray-mediated fluxes looks like. I find that, for the HEXOS data, essentially all heat fluxes measured in 10-m winds above 12 m/s include at least a 10% spray effect. Partitioning the HEXOS data leads next to a bulk surface flux algorithm that is appropriate for high-wind, spray conditions. I close by demonstrating how including spray affects, with this algorithm, in ocean storm simulations leads to improved simulations of storm intensity. Basically, this spray algorithm adds energy to the storm through theoretically sound processes that have been treated only with ad hoc tuning in previous storm models.