Understanding the Fate of Spray, Aerosols, and Fluxes in the Tropical Cyclone Boundary Layer Via a Lagrangian Superdroplet Method

It is well-established that air-sea interaction plays a fundamental part in the genesis, intensity, and maximum potential strength of tropical cyclones. The nature of the fluxes of heat, moisture, and momentum at high winds, however, remains notoriously uncertain both quantitatively and qualitatively. In extreme conditions, sea spray is produced in copious amounts by breaking waves and direct tearing from wave crests, and airborne spray is thought to contribute significantly to the uncertainty in our understanding of air-sea fluxes. These spray droplets are also suspended for long times and distances, populating the marine atmosphere with what ultimately become salt aerosols. As such, many past efforts have been dedicated to clarifying the role of spray in the high-wind boundary layer, though the vast majority of these are hampered by unverified simplifications or measurement uncertainty. This work takes a more direct approach: large-eddy simulation coupled with a Lagrangian droplet model framework, capable of tracking droplets from their inception near the surface, monitoring their interaction with turbulence in the surface layer, and determining the rate at which they fall back or become detrained from the boundary layer. Typically applied to clouds, this technique resolves the Lagrangian transport of droplets generated by realistic sea surface generation functions, capturing their evolution and complex feedback with the surrounding turbulent boundary layer. This presentation will describe the application of the Lagrangian framework to this challenging problem, and summarize some of the counterintuitive results regarding the thermodynamic fluxes.