## 3 Results
### ERA5 Wind Assessment  
In Figure 4a-l, discrepancies between observed mean wind speeds and directions at various heights and the corresponding ERA5 reanalysis data are clearly illustrated. The wind rose diagrams (Figure 4a-l) compare mean wind speeds and directions at different heights, while the scatter plots (Figure 5a-l) demonstrate the alignment between observed and ERA5 reanalysis wind directions. At 50 m (Figure 4a), ERA5 tends to overestimate wind speeds, except for the northwest and southwest directions. This overestimation may be related to local terrain effects (such as buildings and land use) that influence near-surface wind speeds but are not fully captured by the ERA5 model. The alignment of observed and reanalysis wind directions is particularly strong in the northwest direction, although discrepancies are observed in the southeast direction, which could be due to local turbulence or wind deflection effects. At 100 m (Figure 4b), ERA5 overestimates mean wind speeds, especially in the west and south directions, with poor alignment of wind directions (Figure 5b) across all directions. This discrepancy may be linked to the relatively low resolution of ERA5, which fails to capture the small-scale terrain features and their influence on wind flow. At 200 m (Figure 4c), ERA5 underestimates wind speeds by 1 to 2 m/s in the east-southeast, northwest, and north directions, which may be due to localized wind channeling effects around the terrain in Kundulun District, Baotou, not fully represented by ERA5. However, as the height increases, the wind speed becomes less dependent on surface roughness, and the alignment of wind directions improves at this height compared to lower levels. At 500 m (Figure 4d), ERA5 overestimates wind speeds by 2 to 3 m/s in the east-northwest and west directions, possibly because the larger-scale atmospheric circulation dominates at this height, though local topographic features still cause some variation. Wind direction alignment is good, with fewer outliers in the northwest and northeast directions, indicating the dominance of larger-scale weather systems. At 1000 m (Figure 4e) and 1500 m (Figure 4f), ERA5 consistently overestimates wind speeds, especially in the west, west-northwest, and northwest-north directions, with errors ranging from 3 to 6 m/s. This could be due to ERA5 capturing the large-scale atmospheric circulation patterns well, but it still fails to fully account for the local terrain influences on wind flow in Kundulun District, Baotou. Wind direction alignment improves at these heights, with prevailing west and northwest winds, though occasional outliers are still observed, possibly due to short-term weather systems [18]. At higher altitudes (Figure 4g-l), the comparison of wind speeds and directions shows that ERA5 consistently overestimates wind speeds, although wind direction alignment improves with altitude as the influence of local terrain decreases. Seasonal variations make the analysis more complex. In winter, significant deviations in wind directions are observed below 200 m, which may be related to cold air accumulation and local atmospheric effects. In summer, poor alignment of wind directions is observed in the southwest direction below 500 m, likely due to local thermal effects, such as valley winds. Overall, discrepancies in wind direction alignment can be attributed to various factors, including underlying surface topography, temperature, and local weather conditions, particularly in Kundulun District, Baotou, where local topographic features have a significant influence on wind flow.  
Figure 4: Wind rose plots and scatter plots comparing wind speed and wind direction at various heights. (**a**-I) Wind rose plots comparing mean wind speed observations in 16 directions at different heights with ERA5 reanalysis data.