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). However, conventional meteorological towers, satellite retrievals, and global reanalyses are each limited in vertical coverage or resolution, hindering fine-scale assessment from the near-surface to the mid-upper atmosphere. This study combines the kilometer-scale regional atmospheric reanalysis EARS1km with year-round L-band radiosonde observations from 2025 over the desert region of Alxa Left Banner, Inner Mongolia. We systematically evaluate the vertical structure and diurnal, monthly, and seasonal variations of wind speed, wind direction, and wind shear across 20-3000 m, with a focus on the 50-300 m layer critical for wind energy development. The main results are as follows. (1) EARS1km performs well against radiosonde observations, with correlation coefficients of 0.89 (wind speed) and 0.78 (wind direction) and RMSEs of $ 2.85 \mathrm{~m} \cdot \mathrm{~s}^{-1} $, and $ 39.40^{\circ} $, respectively. 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: rapid growth in the lower-layer, a slowdown in the mid-layer, and renewed strengthening aloft, with values of 5.70, 7.14, and $ 7.97 \mathrm{~m} \cdot \mathrm{~s}^{-1} $ at 20, 100, and 500 m, respectively, corresponding to wind power densities of 239.8, 461.1, and $ 682.8 \mathrm{~W} \cdot \mathrm{~m}^{-2} $. Wind shear is pronounced within $ 20-200 \mathrm{~m}(\alpha=0.11-0.15) $, which is 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) with directional concentration increasing 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 20 m) to autumn (around November) above 200 m and to winter above 1000 m, while the 20 m diurnal cycle peaks in the early morning (06: 00-08: 00 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 50-300 m layer is identified as the core layer for tall-tower wind power development over Alxa Left Banner, with 300-500 m as an extended-potential layer, and above 1000 m holding further potential. The systematic vertical offset in peak-wind timing provides a basis for temporal complementarity and coordinated multi-height wind farm development.