Spray-mediated sensible heat flux in shear-driven turbulence

The exchange of latent and sensible heat at the air-sea interface is a process which is routinely parameterized in large-scale meteorological and climate models. At low wind speeds (below roughly 15 m/s), sufficient data exist such that bulk flux models can be quantitatively evaluated against observed behavior. At high winds, however, the general lack of reliable observational or experimental measurements frustrates any attempt to faithfully model fluxes at the surface, which is detrimental to models which aim to forecast within such conditions (e.g. tropical cyclone forecast models). Furthermore, the large number of physical processes occurring at the high-wind ocean surface make interpreting the few existing measurements difficult.

The goal of the present study is to seek a process-level understanding of one such physical process: spray-mediated sensible heat flux. Direct numerical simulations of shear-driven turbulence are used in conjunction with Lagrangian point-particles (representing individual spray droplets) to elucidate the fundamental heat transfer couplings between spray and the surrounding flow. These idealized simulations aim to answer a basic question which remains unresolved in the modelling community: In a shear-driven turbulent flow, does the addition of thermally coupled droplets enhance the total flux of heat, and if so, what are the physical mechanisms governing this change? We find that due to the relatively large heat capacity of water, droplets moving through a background mean temperature gradient greatly enhance the total heat flux, and can account for a significant fraction of the total flux of sensible heat. Additional results, as well as the limitations and future extensions of this numerical approach will be presented.