Abstract: The vertical structure and spatiotemporal variability of wind resources are central to the siting, capacity configuration, and coordinated dispatch of tall-tower wind power (core hub-height range 50~300 m), yet meteorological towers, satellite retrievals, and global reanalyses are each limited in vertical coverage or resolution and struggle to support fine-scale assessment from the near-surface to the mid-upper atmosphere. We therefore combine the kilometer-scale regional atmospheric reanalysis EARS1km with year-round L-band radiosonde observations in 2025 over the desert region of Alxa Left Banner, Inner Mongolia, and systematically evaluate the vertical structure and diurnal, monthly, and seasonal variations of wind speed, wind direction, and wind shear over 20~3000 m, focusing on the 50~300 m layer critical for wind energy development. The main results are as follows. (1) EARS1km performs well, with correlation coefficients of 0.89 (wind speed) and 0.78 (wind direction) against radiosonde observations and RMSEs of 2.85 m/s and 39.40°; its performance improves with height and is better in the cold season.(2) The annual mean wind speed increases with height in a multi-layer pattern of rapid lower-layer growth, a mid-layer slowdown, and renewed strengthening aloft, with speeds of 5.70, 7.14, and 7.97m/s at 20, 100 and 500 m and wind power densities of 239.8, 461.1, and 682.8 W/m². Wind shear is pronounced within 20~200 m (α = 0.11~0.15), the layer of most concentrated wind speed gains, weakens within 200~500 m with a winter-positive/summer-negative reversal, and the 300~400 m layer marks the transition from growth to saturation; wind directions are dominated by west-northwest (WNW), northwest (NW), and west (W) and concentrate further with height. (3) The temporal variability is strongly height-dependent: the timing of peak wind speed shifts from spring near the surface (April maximum at 20m) to around November above 200 m and to winter above 1000m, while the 20m diurnal cycle peaks in the early morning (06~08 LT), associated with momentum redistribution in the stable nocturnal boundary layer. Considering both the quantity (wind power density) and quality (shear stability) of the resource, the 50~300m layer is the core layer for tall-tower wind power development over Alxa Left Banner and 300~500 m an extended-potential layer, with above 1000 m holding further potential; the systematic offset in peak-wind timing across heights provides a basis for temporal complementarity and coordinated multi-height development.