Effects of Sea Spray on Air-Sea Fluxes and the Wave Boundary Layer in High Winds

Benjamin Witten Barr and Shuyi Chen, University of Washington Seattle Campus, Atmospheric Sciences, Seattle, WA, United States
Abstract:
Sea spray droplets injected into the atmosphere in high winds provide avenues for air-sea exchange of heat, moisture, and momentum that are not available in calmer conditions. The physics of spray is complex, and assumptions made regarding spray generation and transport strongly modulate spray-mediated fluxes and the effects of spray on the near-surface wave boundary layer. In the case of spray generation, recent laboratory and theoretical work and the development of fully-coupled atmosphere/wave/ocean (AWO) numerical models have allowed replacement of traditional wind-based models for spray generation with physics-based, seastate-dependent models. These physics-based models explicitly treat wave breaking, dissipation, and droplet ejection rather than using wind as a proxy for spray production. However, the impacts of this replacement on air-sea fluxes and on the near-surface layer remain largely unexplored.

This study aims to connect the physical processes of spray to the resulting air-sea fluxes and near-surface changes by exercising wind and seastate-based spray generation models in realistic high-wind environments produced from coupled AWO simulations. Using the Unified Wave Interface-Coupled Model (UWIN-CM), we perform simulations of Hurricanes Dorian (2019), Michael (2018), Florence (2018), Harvey (2017) and Typhoon Fanapi (2010) and test the sensitivity of these storms to model assumptions across a range of high-wind conditions.

It is found that the efficiency of spray in transferring heat and moisture depends strongly on the size distribution of droplets generated, highlighting the importance of assumptions made by wind and seastate-based generation models. It is also found that variation in storm conditions (e.g. wind speed, wave height, humidity) strongly affects spray heat fluxes. Impacts of spray on the near-surface region, as well as generalization of our results to global high-impact weather systems, are a focus of ongoing analysis.