## 3 Results
### Comparative Analysis of Wind Directions from 50 to 1500 m  
Figure 4 shows the applicability of ERA5 wind direction at various heights. Figure 4(a1-f1) shows the wind rose plots of the mean wind speed observations in 16 directions at each height compared to the ERA5 reanalysis data. Figure 4(a2-f2) shows the corresponding scatter plots of the wind direction at each height between the observations and the ERA5 reanalysis data. Overall, the maximum mean wind speeds for both ERA5 reanalysis data and observations occur in the westerly direction, and the best concordance is also found between the two datasets at each height, as shown in Figure 4(a2-f2). Figure 4(a1) shows that the 50 m ERA5 values indicate a larger south-southeasterly wind than the actual observed values, which may be caused by the influence of local circulation and other factors. Figure 4(a2) illustrates a notable agreement in the northeast and south-southwest directions, and the mean wind speeds of the ERA5 in the northwest and northeast directions are smaller than the observations, while the winds in the west-northwest direction of the ERA5 are worse, and the difference is more than a few times. In Figure 4(b1), the mean wind speed of the ERA5 reanalysis data is 4 m/s higher than the observations in the south-southeast direction at 100 m, while it is 2 m/s smaller in the west-northwest and northeast directions, with more outliers and poorer concordance. In Figure 4(c1), the mean wind speed of ERA5 is 2 m/s higher than the observations in the south-southeast direction at 200 m, while the mean wind speeds in the west-northwest and north-northeast directions are 2 m/s lower than the observations. In Figure 4(c2), with prevailing westerly and northwesterly winds, the observed wind direction and ERA5 reanalysis data have fewer outliers and have a better correlation at 100 m height, whereas larger biases exist at other altitudes. In Figure 4(d1), the mean wind speed of the 500 m ERA5 values is 3 m/s higher than the observations in the southerly direction, while the mean wind speed in the west-northwest direction is 3 m/s lower than the observations, and the mean wind speed in the south-southwest, south-southwest, and west-northwest directions is about 1-2 m/s lower than the observations. In Figure 4(d2), the wind directions between the observations and the ERA5 reanalysis data are poorly attuned at 500 m, with more outliers observed in the ERA5 reanalysis data in the north-westerly and north-easterly directions. In Figure 4(e1), the mean wind speed of the ERA5 data is 4 m/s higher than the observations in the southeast wind at 1000 m. The deviation of the mean wind speed in the east-southeast wind shows the maximum value, which is 5 m/s higher than that of the observed value, and the mean wind speeds of the west-southwest wind, west-northwest wind, and south-southeast wind are lower than the observed mean wind by 1-2 m/s. In Figure 4(e2), the wind direction between the observations and the ERA5 reanalysis data is poorly correlated at 1000 m, with more outliers in the north and northwest directions. In Figure 4(f1), the mean wind speeds of the 1500 m ERA5 data are 3 m/s lower than the observations in the northeast, east-northeast, and west-northwest directions, the mean wind speeds in the west, east, and north-northeast directions are 1-2 m/s lower than the observations, and the mean wind speeds in the west, east, and north-northeast directions are 1-2 m/s lower than observations. There are fewer outliers of westerly winds, which are more correlated with the prevailing westerly and northwestern winds. There are various reasons for the poor wind data. Due to the influence of the topography of the subsurface, temperature, and weather, the difference between the observations and ERA5 reanalysis data will be significant. Therefore, the ERA5 does not accurately reproduce the wind direction in the mountainous area, and the deviation is large.