Refined Empirical Model of Typhoon Wind Field and Its Application in China

Severe tropical cyclones or typhoons (hurricanes) cause significant damage in the coastal regions of China, Japan, and the United States. Estimating the wind speed accurately and efficiently is important for hazard mitigation and risk management. This study developed a refined empirical model of a typhoon wind field. The gradient wind field is obtained based on the gradient equilibrium equation and the variable pressure field. Then the relation between the gradient speed and surface speed is established using Arya's boundary layer model, which is integrated in the planetary boundary layer (PBL) wind field model. To facilitate engineering practice, a set of closed-form formulas was developed to simplify the original complex relation between the gradient speed and surface speed. Instead of solving the dynamic equation numerically as does the PBL model, the surface wind speed is derived directly from the gradient wind speed using the proposed model, which makes wind speed prediction much more efficient. Additionally, the proposed model is more accurate than previous empirical models, which use the simple reduction factor. The comparison of the measured wind speed and simulated counterpart validated the refined empirical model. Based on the proposed model, the typhoon hazard analysis for nine cities in China was performed. The circular subregion method was adopted to estimate the extreme wind speed for return periods of 50 and 100 years. Results show that the refined model has good performance in terms of the accuracy and efficiency.