The urban effects on the planetary boundary layer (PBL) wind structures of landfalling tropical cyclones (TCs) have rarely been explored. In this study, numerical simulations for Typhoon Lekima (2019), with and without multilayer building effect parameterization (BEP) and urban land cover, were executed to investigate the urban effects on TC PBL wind structures. Validations against observations demonstrate that the simulation incorporating BEP and urban surface replicates the track, intensity and 10-m wind field of Lekima better. Based on the comparison between the simulations with and without urban land cover, urban effects were analyzed, and the possible mechanisms were examined from the perspective of turbulent transport. Results show that urban surfaces have a deceleration effect on TC wind fields overall. This deceleration effect is most pronounced near the surface and decreases with height under 1 km above ground level. Urban surfaces reduce tangential winds and radial inflow in the near-surface layer, leading to a slight decrease in TC intensity. This is primarily attributed to the enhanced downward transfer of tangential momentum and upward transfer of radial momentum within the PBL, which results in larger magnitudes of negative tangential wind tendencies and positive radial wind tendencies induced by the divergence of subgrid-scale (SGS) momentum fluxes. Additionally, stronger tangential winds and radial outflow above the elevated PBL height correspond well to the increased tangential and radial wind tendencies in nearby areas. The analysis illustrates that turbulent transport provides insights into how urban surfaces affect the PBL wind structures of TCs.

中文翻译：

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城市对台风利奇玛行星边界层风结构的影响（2019 年）


城市对登陆热带气旋 （TC） 的行星边界层 （PBL） 风结构的影响很少被探索。在本研究中，对台风利奇玛 （2019） 进行了数值模拟，有和没有多层建筑效应参数化 （BEP） 和城市土地覆盖，以研究城市对 TC PBL 风结构的影响。对观测的验证表明，结合 BEP 和城市表面的模拟更好地复制了 Lekima 的轨迹、强度和 10 m 风场。基于有和没有城市土地覆盖的模拟之间的比较，分析了城市影响，并从湍流传输的角度研究了可能的机制。结果表明，城市表面对 TC 风场总体具有减速效应。这种减速效应在地表附近最为明显，并且随着离地面 1 公里以下的高度而减弱。城市表面减少了近地表层的切向风和径向流入，导致 TC 强度略有降低。这主要归因于 PBL 内切向动量的向下传递和径向动量的向上传递的增强，这导致亚网格尺度 （SGS） 动量通量发散引起的负切向风趋势和正径向风趋势的幅度更大。此外，PBL 高度升高以上更强的切向风和径向流出与附近地区增加的切向风和径向风趋势非常吻合。该分析表明，湍流输运有助于了解城市表面如何影响 TC 的 PBL 风结构。