Physics-Resolving Simulations of Spray Fluxes in the High-Wind Tropical Cyclone Boundary Layer

The large uncertainty in air-sea fluxes momentum, heat, and moisture at high winds in the marine boundary layer is a longstanding problem, despite their pivotal role in hurricane dynamics. In particular, the role of sea spray on air-sea transfer remains largely unconstrained, owing to the difficulty of measuring spray influence directly, and the untested assumptions that must be made in various spray parameterizations. In this work, we aim to close this gap by conducting large eddy simulations of the high-wind marine boundary layer, while explicitly resolving spray generation and feedback via a Lagrangian method (the so-called “superdroplet” or Lagrangian cloud model). This explicit treatment avoids the need for making ad hoc assumptions about the spray dynamics and thermodynamics, and naturally incorporates the complex interplay between the boundary layer turbulence and the suspended droplets. We find that spray has a negligible effect on the drag coefficient, but can have potentially large impacts on the thermodynamic flux coefficients. As the boundary layer adjusts to the spray-mediated fluxes, however, the flux coefficients relax back to the spray-free values, but this is a strong function of the boundary layer properties. In this talk we will show the results of the large eddy simulations, and discuss prospects for parameterizing the effects of spray in numerical weather prediction models.