Impacts of Seastate-Dependent Sea Spray Heat Fluxes on Tropical Cyclone Structure and Intensity Using Fully Coupled Atmosphere-Wave-Ocean Model Simulations

Air-sea fluxes of sensible and latent heat are fundamental to the energetics of tropical cyclones (TCs) and their intensity. The contributions of sea spray to high-wind air-sea heat fluxes and their impacts on TC structure and intensity are not well understood due to the difficulty of measuring spray and heat fluxes in high-wind TC environments and to the challenge of representing complex seastate-dependent spray physics in numerical models. In this study, we implement a new parameterization for air-sea heat fluxes with seastate-dependent spray into the Unified Wave Interface–Coupled Model, a fully coupled atmosphere-wave-ocean regional model, and perform simulations for four TCs to understand the interactions by which spray heat fluxes produce changes in model TC structure and intensity.

Our results show spray’s impact on our intensifying model TCs as progressing in three stages. These are: 1) When maximum azimuthal-mean 10-m windspeed is below 30–40 m s^-1, spray evaporation cools boundary layer (BL) inflow, suppressing eyewall deep convection and causing spray to weaken intensification. 2) Intensification beyond this threshold produces surface warming due to spray under the eyewall, which should promote intensification. However, spray-induced changes to the BL and secondary circulation reduce the efficiency of moist static energy transport into eyewall deep convection, and spray continues to oppose intensification overall. Further intensification may strengthen spray surface warming under the eyewall enough to overwhelm the influence of the structural inefficiency, and a transition occurs towards spray promoting intensification. 3) In the presence of strong warming due to spray under the eyewall, the eyewall contracts and spray promotes intensification. The magnitude of spray’s impact on minimum sea level pressure is at all times within approximately +/- 5 mb.