An analytical model of a typhoon wind field based on spiral trajectory

In typhoon risk assessment and warning, a critical component is a good representation of the typhoon wind field model. In this study, a new analytical model based on the logarithmic spiral trajectory model is developed to simulate the surface wind speed distribution of a typhoon. The logarithmic spiral trajectory model could overcome the limitation of the parametric gradient wind model. A slab surface layer of constant depth is used to solving the tangential equilibrium equation, and the frictional drag at the upper boundary of the surface layer is considered correctly. Consequently, the theoretical method for determining the Holland β parameter is derived from the logarithmic spiral trajectory model. It is concluded that β increases with the surface layer depth or decreases with the radius to maximum winds. By analyzing the change in kinetic energy of the air particle, the interpretation of the relationship between β and the influencing factors is provided. The models are applied to the 17th typhoon NESAT and the 19th typhoon NALGAE of 2011. Through comparisons between the observed wind records and the simulation results, the logarithmic spiral trajectory model proposed in this study could accurately simulate the wind speeds.