Latent and Sensible Heat Flux at the Spray-Laden Air-Sea Interface

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The air-sea interface in high-wind situations, like hurricanes, is an important topic that crosses boundaries between atmospheric sciences and oceanography. Sea spray droplets are known to affect the temperature and moisture distribution in the surface layer above the ocean, which in turn can affect associated atmospheric processes. This award will provide an opportunity for a researcher and his students to work on numerical modeling of these processes using direct numerical simulation, which allows researchers to follow individual droplets as they move along in the wind. The potential impact of this project is on improved prediction of tropical cyclones, but the numerical techniques developed could potentially have an impact across a variety of scientific disciplines. The work would also contribute to the future scientific workforce through the training of a graduate student and undergraduate student.The researcher plans to address the role of sea spray on the exchanges of heat, moisture, and momentum at the air-sea interface through a suite of numerical experiments. The role of sea spray on these exchanges at high winds is uncertain due to the difficulty in making measurements in these conditions. The researcher has developed a numerical technique to track individual Lagrangian droplets through a shear-driven turbulent flow, and two-way momentum coupling was enforced for each particle allowing for a direct calculation of the bulk moment flux modifications. This project would extend that work by implementing two-way thermodynamic coupling between the droplets and the surrounding flow, allowing for a direct evaluation of spray's influence on latent and sensible heat flux and the resulting profiles of temperature and moisture. The specific research questions to be answered include: 1) Do the vertical fluxes of sensible and latent heat (and enthalpy) in an environment laden with thermodynamically-coupled droplet particles exceed those of an unladen case? 2) To what degree is the flux of salinity into the ocean enhanced by droplet evaporation, and can this lead to enhanced mixing in the ocean boundary layer? 3) Do the mean profiles of heat and humidity change immediately above the air-sea interface? 4) What concentrations of water droplets are necessary to see any effects on heat and moisture fluxes? 5) What size distribution of spray droplets can be expected when in thermodynamic equilibrium immediately above the air-sea interface?