The accuracy of typhoon track prediction has improved in recent years, whereas that of typhoon intensities prediction has not been improved yet. One of the main reasons is the difficulty of representing momentum and heat transfer mechanisms across the sea surface in typhoons. Momentum and heat transfer across the sea surface, which substantially influences intensities of typhoons, has not been well modeled.

The goal of this project is to develop accurate models for predicting the heat and momentum fluxes across the air-water surface under high wind-speed conditions similar to typhoons, using the world's largest typhoon simulation tank (Fig. 1), and to clarify possibility of typhoon control (weakening) numerically by using MSSG (Multi-Scale Simulator for the Geoenvironment) model (Fig. 2).

① Experiment on changing the water surface condition

We conducted experiments by introducing a surfactant solution into the tank and measuring significant wave heights under high wind speed conditions (Fig. 3). The surface tension of the water surface decreases due to the surfactant, suggesting changes in the shape of wind waves and the associated energy transport at the air-water interface.

② Numerical simulation of typhoons using the proposed flux models

We performed numerical simulations of tropical cyclones (e.g. typhoons) to confirm the influence of using the flux models proposed based on the experimental results, focusing on the tropical cyclone event, Irma (2017) (Fig. 4). Irma is a hurricane formed in the North Atlantic on August 30, 2017. Hurricane case is accepted to confirm the general responsivity of tropical cyclones.
We considered some surfactant models based on the flux model for the simulations. The results suggested that the changes of the air-sea surface due to surfactant can have significant impacts on the intensities of tropical cyclones.