The role of sea spray evaporation in air-sea exchanges is of concern for tropical cyclone intensification. It has been well known for decades that the major source of energy for a tropical cyclone is the oceanic surface in the core region. As emphasised in the recent WMO International Workshop on Tropical Cyclones, an improved understanding of the spray region in the core of intense cyclones is essential to proper specification of this energy exchange and the forecasting of tropical cyclone intensity.
In this study, a bulk parameterisation of sea spray evaporation is incorporated in a very high resolution, full physics, numerical model of a tropical cyclone to explore the impact of spray on structure, intensification and maximum potential intensity of the tropical cyclone. Our preliminary results show that inclusion of sea spray evaporation leads to not only an earlier development of the storm, but also a more intense storm at the mature stage. The sea spray evaporation modifys the direct air-sea fluxes at the sea surface by moistening, and cooling the lowest layer of the atmosphere. The result is a generally enhanced air-sea exchange of energy, and increase of the maximum intensity of the cyclone.
Since the available bulk parameterisations are valid only for wind speeds below 40 m/s, it is uncertain whether our results can be extrapolated to extremely intense storms. Indeed, the calculation of air-sea fluxes in general is quite uncertain at extreme wind conditions. In addition, the air-sea energy exchange may also modify the ocean conditions, which may then modulate the energy exchange. Therefore, to understand and evaluate the impact of sea spray evaporation on tropical cyclones, an active ocean should be included as a component of a coupled system. This is being evaluated and will be reported at the conference