Investigation of the evolution of urban wind fields during typhoons using a wind LiDAR network: A case study of Super Typhoon Saola (2309)

Predicting the wind characteristics of the urban atmospheric boundary layer (UBL) over different landforms is challenging. Field measurements of typhoons within the UBL are constrained by the randomness of typhoon generation and the restricted spatial coverage of wind-measuring instruments. To refine the research on the vertical structure of typhoon fields in different urban areas, three LiDAR units were used in the Pearl River Delta urban area of China. The UBL wind fields were measured within a height of 512 m during Super Typhoon Saola (2309). This study analyzed the spatiotemporal evolution of wind speed and direction profiles considering the effects of underlying surfaces. Based on a linear height-resolving typhoon wind field model, a new method using LiDAR data in conjunction with meteorological data was proposed to assess key typhoon parameters. Furthermore, an improved typhoon field simulation approach is proposed to enhance the simulation accuracy of UBL wind profiles. The results suggest that in urban areas, as the wind speed at 10 m increases, both the roughness length and power law index decrease. During the typhoon, the statistical data of mean wind twist angle exhibits a clockwise veering trend with increasing height in the study regions. The mean twist angles at 512 m are <25 degrees, with less affected by variations in underlying surfaces such as buildings, mountainous terrains, and sea surfaces. The turbulent diffusivity coefficient (K) varies mainly between 10(0 )and 10(2 )m(2 )s(-1). Besides, the values of K are found to be strongly correlated with gradient wind speeds, exhibiting an exponential increase with increasing gradient wind speeds.