Sea-Spray-Generation Dependence on Wind and Wave Combinations: A Laboratory Study

International audienceWe investigate the effects of wind-wave interactions on the surface sea-spray-generation flux. To this end, the Marine Aerosol Tunnel Experiment (MATE2019) was conducted at the Pytheas Institute large wave-wind facility in Luminy (Marseille, France) over the period June-July 2019. A unique range of air-sea boundary conditions was generated by configuring the laboratory with four types of wave forcing and five wind speeds spanning 8-20 m s −1. Young and developed waves were included, with wave ages between 1.3 and 9.5 (defined in terms of phase speed and friction velocity). Vertical sea-spray-concentration profiles measured over the 0.1-47.5 µm radius range and a flux-profile method allowed estimation of the sea-spray-generation flux. Results show that the flux increases for increased wind-induced wave breaking, and is highest for steep and heavily-breaking waves. Scaling analysis shows that the sea-spray generation is best correlated with the wave-slope variance for larger droplets (20 µm and above, assumed predominantly spume droplets generated by surface tearing). For smaller droplets (7-20 µm, presumed predominantly jet droplets generated by bubble bursting), the highest correlation is found with a non-dimensional number combining the wave-slope variance with the friction velocity cubed. This is reflected in the formulation of two wave-state-dependent sea-spray-generation functions, each valid for wind speeds 12-20 m s −1 and droplet radii 3-35 µm, thereby covering jet and spume droplet production