Parameterizing Thermodynamic Feedback of Sea Spray at the Air-Sea Interface: A small-scale perspective via Direct Numerical Simulations

Sea spray generated from the ocean consists of saline water droplets ranging from micrometers to centimeters. Under high winds, a massive amount of spray droplets are transported to the atmosphere, which brings attention to their potential roles in modifying air-sea heat and momentum fluxes. However, how much energy droplets contribute to the lower atmospheric boundary layer remain obscured due to the difficulties in measurements. In this presentation, we explicitly resolve the trajectories and evaporation of individual sea spray droplets in a turbulent flow via direct numerical simulations (DNS). With the high-fidelity DNS, we analyze the statistics of spray droplets and use our findings to assess strong but untested assumptions in bulk air-sea models. We observe the different roles droplets play in turbulence. The difference is because of the different ratio of droplet thermal response time to its residence time for different sizes. Neglecting the influence of droplet timescales could lead to a significant error when estimating spray-mediated heat fluxes. We also find that a negative feedback effect induced by spray evaporation may be necessary but missing in bulk models. Neglecting this negative feedback term leads to overestimates of the total heat flux when directly adding spray-meditated heat fluxes to the interfacial fluxes. Moreover, we observe the interactions between different spray size classes, which may further overestimate the total heat flux when directly applying bulk models if neglected. Regarding all discrepancies between our DNS results and bulk models, we put forward potential corrections and suggestions based on the droplet thermal and dynamic timescales.