Effect of Surfactants on the Generation of Sea Spray During Tropical Cyclones

The hydrosphere and atmosphere are connected through the air-sea interface, a critical boundary that is altered as wind speed increases, such as in tropical cyclone conditions. Biological surfactants on the sea surface affect the air-sea interface as they alter surface tension, dampen short gravity-capillary waves, and suppress near-surface turbulence. Under tropical cyclone conditions surfactants may impact the generation of sea spray and spume. The size distribution of sea spray and spume may influence heat and momentum flux between the ocean and atmosphere under tropical cyclone conditions. Present understanding of the relationship between surfactants, wind speed, and sea spray generation remains limited. Using computational fluid dynamics tools, we model the effect of surfactants on sea spray generation under tropical cyclone conditions. Specifically, we use a Volume of Fluid to Discrete Phase Model developed by ANSYS Fluent, which converts water parcels to Lagrangian particles to represent sea spray and spume. Fluent’s Evaporation-Condensation model allows us to model sea spray evaporation.Preliminary model results suggest surfactants increase the overall abundance of spray under tropical cyclone winds. The relationship between the abundances of surfactants and spray appear to be positively correlated. Laboratory experiments conducted at the University of Miami show that surfactants alter sea spray generation by forming branch-like rather than finger-like structures, which fragment into sea spray or spume of various sizes. Biological surfactants brought to the surface from deeper in the water column potentially affect heat, energy, and momentum exchanges under tropical cyclone conditions due to altered size distribution and abundance of sea spray and spume. The effect of surfactants on sea spray generation may have consequences for tropical cyclone intensification or decline, especially in coral reef areas and areas affected by oil spills and dispersants.