Sea-State-Dependent Sea Spray and Air–Sea Heat Fluxes in Tropical Cyclones: A New Parameterization for Fully Coupled Atmosphere–Wave–Ocean Models

Abstract

Abstract Air–sea exchange in high winds is one of the most important but poorly represented processes in tropical cyclone (TC) prediction models. Effects of sea spray on air–sea heat fluxes in TCs are particularly difficult to model due to complex sea states and lack of observations in extreme wind and wave conditions. This study introduces a new sea-state-dependent air–sea heat flux parameterization with spray, which is developed using the Unified Wave Interface–Coupled Model (UWIN-CM). Impacts of spray on air–sea heat fluxes are investigated across a wide range of winds, waves, and atmospheric and ocean conditions in five TCs of various sizes and intensities. Spray generation with variable size distribution is explicitly represented by surface wave properties such as wave dissipation, significant wave height, and dominant phase speed, which may be uncorrelated with local winds. The sea-state-dependent spray mass flux is substantially different than a wind-dependent flux, especially when wave shoaling occurs with enhanced wave dissipation near the coast during TC landfall. Spray increases the air–sea enthalpy flux near the radius of maximum wind (RMW) by approximately 5%–20% when mean 10-m wind speed at the RMW reaches 40–50 m s−1. These values can be amplified significantly by coastal wave shoaling. Spray latent heat fluxes may be dampened in the eyewall due to high saturation ratio, and they consistently produce a moistening and cooling effect outside the eyewall. Spray strongly modifies the total sensible heat flux and can cause either a warming or cooling effect at the RMW depending on eyewall saturation ratio. Significance Statement Fluxes of heat and moisture from the ocean to the atmosphere are important for hurricane intensification, but the impact of sea spray generated by breaking waves on these fluxes is not well understood. We develop a new model for heat fluxes with spray that accounts for how waves control spray, and we apply this model to a set of five simulated hurricanes to better understand the broad range of ways that spray impacts heat fluxes in high wind conditions. We find that spray significantly affects heat fluxes in hurricanes and that impacts are strongly controlled by waves, which are not always correlated to winds. This research improves our understanding of how spray affects heat fluxes in hurricanes and provides a foundation for future studies investigating sea spray and its impacts on high-impact weather systems.