The impact of spume droplets induced by the bag-breakup mechanism on tropical cyclone modeling

Abstract

Spume, large-radius seawater droplets that are ejected from the ocean into the atmosphere, can exchange moisture and heat fluxes with the surrounding air. Under severe weather conditions, spume can substantially mediate air-sea fluxes through thermal effects and thus needs to be physically parameterized. While the impact made by spume on air-sea interactions has been considered in bulk turbulent air-sea algorithms, various hypotheses in current models have resulted in uncertainties remaining regarding the effect of spume on air-sea coupling. In this study, we extended a classic bulk turbulent air-sea algorithm with a “bag-breakup” physical scheme of spume generation parameterizations to include spume effects in a complicated numerical model. To investigate the impact of spume on air-sea coupling, we conducted numerical experiments in a simulation of Tropical Cyclone Narelle. We observed a significant improvement in the ability to model minimum central pressure and maximum sustained surface wind speed when including the bag-breakup spume scheme. In particular, the impact of the bag breakup–generated spume is observed in the intensity, structure, and size of the tropical cyclone system through the modulation of local wind speed (U10), wave height (Hs), and sea surface temperature.

Tropical Cyclone Modeling With the Inclusion of Wave‐Coupled Processes: Sea Spray and Wave Turbulence

“…(2017) and Xu et al. (2023): $$${H}_{s}=\rho {c}_{p}{C}_{h}U\left({\theta }_{l}-{\theta }_{b}\right)+{H}_{(s,sp)}$$$ $$${H}_{L}=\rho {L}_{v}{C}_{e}U\left({q}_{l}-{q}_{b}\right)+{H}_{(L,sp)}$$$ where H s and H L are the air‐sea interfacial sensible and latent heat fluxes. The ρ is the air density in the surface layer, c p is the specific heat capacity of air at certain pressure, L v is the latent heat of vapourization, C h and C e are the exchange coefficient for heat and moisture, respectively.…”

“…Sea spray droplets contribute to the air-sea interaction mainly through increasing the air-sea heat exchange. This surface process can be considered and implemented into the air-sea surface layer model in WRF system through additional air-sea turbulent heat fluxes resulted from the sea spray, following Zhao et al (2017) and Xu et al (2023):…”