The intensity of tropical cyclones is sensitive to the air-sea fluxes of enthalpy and momentum. Sea spray plays a critical role in mediating enthalpy and momentum fluxes over the ocean’s surface at high wind speeds, and parameterizing the influence of sea spray is a crucial component of any air-sea interaction scheme used for the high wind regime where sea spray is ubiquitous. Many studies have proposed parameterizations of air-sea flux that incorporate the microphysics of sea spray evaporation and the mechanics of sea spray stress. Unfortunately, there is not yet a consensus on which parameterization best represents air-sea exchange in tropical cyclones, and the different proposed parameterizations can yield substantially different tropical cyclone intensities. This paper seeks to review the developments in parameterizations of the sea spray-mediated enthalpy and momentum fluxes for the high wind speed regime and to synthesize key findings that are common across many investigations.

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Abstract

Accurate estimates of air‐sea enthalpy and momentum fluxes are critically important for hurricane intensity predictions. However, calculating these fluxes is challenging due to the nature of the air‐sea transition region. At extreme wind speeds, a substantial amount of sea spray is lofted making it necessary to calculate the sea spray‐mediated enthalpy and momentum fluxes. These calculations rely on microphysical equations, which are sensitive to the details of the local environmental conditions. Here we use a microphysical model to show that there exists a threshold wind speed beyond which the net sea spray‐mediated enthalpy and momentum fluxes are well‐approximated by using the net sea spray mass flux alone. This result supports the hypothesis that at extreme wind speeds, the ratio of the air‐sea exchange coefficients becomes independent of wind speed, implying the air‐sea flux calculations can be substantially simplified.

<p>Despite the powerful influence that sea spray has on air-sea enthalpy and momentum fluxes, most state-of-the-art tropical cyclone forecast models do not incorporate the microphysics of sea spray evaporation into their boundary layer flux schemes. Since the air-sea enthalpy and momentum fluxes control a tropical cyclone’s intensification rate, increasing the accuracy of the associated bulk parameterizations is crucially important for improving forecast skill. New microphysics-based bulk parameterizations for enthalpy and momentum flux through the tropical cyclone boundary layer are developed from a set of prognostic evaporation equations and numerical simulations of evaporating, multiphase flow subject to extreme wind speeds. The microphysics-based parameterizations are computationally inexpensive and are functions of the local environmental conditions; these features allow forecast models to efficiently vary the air-sea enthalpy and momentum fluxes in space and time. By developing microphysics-based bulk parameterizations, the influence that sea spray exerts on tropical cyclone intensification can be more accurately simulated and intensity forecasts could be improved.</p>