The Wind Profile Characters in the Skyscrapers Region during Typhoon Muifa (2022): a Lidar Observation Study

On Sept 15 2022, Typhoon Muifa made landfall in Shanghai,the biggest city of China with the intensity 38m/s. During the period from Sept 13 to Sept 16,Typhoon Muifa caused significant wind and rain impacts in Shanghai. To study the boundary layer wind character in the urban region,researchers deployed two Doppler lidars in the downtown region(Luziazui) and coutrisde(Baoshan). These observations comprehensively captured the evolution of the boundary layer wind field structure and its characteristics during Typhoon Muifa ranging from the front periphery to the typhoon's core and eye, and then to the rear periphery.The minimum distance of the lidar observation which located in Lujiazui to typhoon center was about 3 kilometers.The observed maximum horizontal wind speeds exceeding 40 m/s. Overall, the evolution of the boundary layer wind field of Typhoon Muifa was well captured and was divided into four stages: the outer weak wind stage, the inner core strong wind and updraft stage, the eye calm wind stage, and the rear outer downflow stage. Significant changes in the boundary layer wind field were observed during different stages. The boundary layer height, calculated based on turbulence gradients, gradually decreased as the typhoon center approached and increased as the typhoon moved away. In the peripheral region of the typhoon, the boundary layer height calculated based on signal-to-noise ratio gradually approached the height calculated based on turbulence gradients.Interestingly, it was found that before the arrival of the typhoon, in the high-rise area of Lujiazui, near-surface wind speeds exhibited two instances of wind shear phenomena, first decreasing with height and then increasing, occurring at an approximate height of 150 meters. During the same period, the lidar in the suburban area of Baoshan did not observe this unusual phenomenon of two reversals in wind shear. This may suggest the presence of very strong near-surface gusty winds in the near-surface layer of the high-rise area of Lujiazui, possibly related to the presence of high-rise buildings.Simultaneously, in the near-surface layer of the front core area of the typhoon, very small-scale strong upward and downward oscillations with cross-distribution of fine structures were observed multiple times, accompanied by strong winds.Further study shows that research community should pay more attention to the effect of urban buildings to the wind profile of typhoon boundary layer.