The Boundary Layer Wind Characteristics of Typhoon Muifa (2022) at Lujiazui, Shanghai Observed by A Ground-Based Doppler Wind Lidar

Abstract

Understanding wind characteristics of the tropical cyclone boundary layer (TCBL) over land is crucial for improving typhoon forecasts and designing wind-resistant structures. This study employs a ground-based Doppler wind radar (DWL) in Lujiazui, Shanghai, to examine the evolution of TCBL wind and turbulence during Typhoon Muifa (2022), focusing on the transition from the periphery to the eyewall. Observations reveal significant changes in wind characteristics, highlighting the eye region's unique features and the complex dynamics of landfalling typhoons. Before Muifa's passage, the horizontal wind speed exhibited a low-level C-shape, with minimum speeds at 100–200 m, deviating from the typical logarithmic increase, due to high friction velocity and urban terrain effects. The vertical wind profile showed alternating updrafts and downdrafts, indicating dynamic turbulence within the TCBL. Turbulent integral length scales for tangential ($L_v$) and radial ($L_u$) winds at 104–208 m were smaller before the typhoon passage than after, with $L_u$ notably less than $L_v$, reflecting the influence of typhoon rotation and localized shear. Streak and roll intensities revealed intensified turbulence and energy transport near the surface before Muifa's passage, potentially contributing to localized wind damage. These structures exhibited periodic interactions, weakening after the typhoon's passage, likely due to changes in typhoon intensity or structure. Spectral analysis of radial and tangential winds highlighted variations in low-frequency and inertial subrange regions, emphasizing the role of turbulence and scale interactions in modulating energy and momentum transfer. This study demonstrates DWL's effectiveness in detecting fine-scale structures within the TCBL, enhancing understanding of wind and turbulence dynamics during landfalling typhoons.