Influence of complex geomorphology on low-level wind shear at airports on the Loess Plateau

Low-level wind shear (LLWS), characterized by sudden changes in wind speed/direction within 600 m off the ground, poses significant risk to aviation safety. This study investigates the mechanisms of topographic features and land-use types influencing the formation of LLWS at Lanzhou Zhongchuan International Airport (ICAO: ZLLL), a representative high-altitude airport (1,947 m above mean sea level). Using a coupled WRF (Weather Research and Forecasting)-CFD (Computational Fluid Dynamics) modeling framework for dynamic downscaling from mesoscale to microscale, systematic sensitivity experiments were conducted to quantify the effects of topographic elevation gradient and land-use type on the LLWS dynamics. Key findings include: (1) Simulations accurately reproduced LLWS evolution under northwest airflow conditions, with near-surface flow patterns primarily governed by convergence zones formed through interactions between opposing northwest and southeast winds. (2) Pronounced downward momentum transfer occurred along northwestern slopes, where turbulent transport emerged as the dominant mechanism for vertical momentum redistribution. (3) A shift from stable to near-surface unstable atmospheric stratification enhanced vertical momentum mixing, creating favorable conditions for LLWS development. (4) Terrain slopes modulated momentum descent and induced flow separation, generating microscale vortices strongly correlated with LLWS events; whereas land-use alterations spatially relocated convergence zones through modified surface roughness and thermal stability but exhibited negligible direct influence on microscale dynamics. These results underscore the interplay between topographic forcing and land-use heterogeneity in LLWS generation, offering insights for refining LLWS forecasting methodologies at high-altitude airports.