The multi-scale physics of ocean spray aerosols generation by breaking waves and bursting bubbles

Physical processes at the ocean-atmosphere interface have a large effect on climate and weather by controlling the transfer of momentum and mass. Without wave breaking, transport between the ocean and the atmosphere is through slow conduction and molecular diffusion, while wave breaking is a transitional process from laminar to turbulent flow. When waves are breaking, the surface experiences dramatic changes, with sea spray ejection in the atmosphere and air entrainment into the ocean water. In this talk I will discuss recent efforts towards improving our understanding and modeling of ocean spray aerosol production through a multi-scale approach. Ocean spray aerosol impact climate through radiative processes and while acting as cloud condensation nuclei. We combine detailed laboratory experiments and numerical simulations on turbulent multiphase flows, including wave breaking, bubble break-up in turbulence and spray production by bubble bursting together with a statistical description of breaking waves to develop a general theoretical framework. This framework aims to account for the very large range of scales involved in the process, from wave statistics scales of order of km, O(1m-1km), to wave breaking dynamics, O(1-10m), air bubble entrainment, bubble dynamics in turbulence and finally bubble bursting at the first surface, O(microns to mm). The resulting ocean spray aerosols emissions are evaluated globally and are in remarkable agreement with field observations, without being adjusted to match any existing datasets, in terms of magnitude of sea salt emissions and size distribution. The remarkable coherence between the model and observations of sea salt emissions therefore strongly supports the mechanistic approach and paves the way for improved modeling of atmospheric processes controlled by aerosols of oceanic origin.