## 3 Results
### Comparative Analysis of Vertical Wind Speed Profiles from 50 to 1500 m  
Figure 3 shows the applicability of ERA5 vertical wind speeds at various heights. Figure 3(a1-f1) shows the observed vertical wind speeds at various heights compared with the ERA5 reanalysis data values, and the zoomed-in time series on 2 and 3 June 2023 were selected for comparison. Overall, the vertical wind speeds from the ERA5 reanalysis data differ significantly from the observed vertical wind speeds from the Doppler wind lidar, and they illustrate a poor correlation, as shown in Figure 3(a2-f2). Although the spatial resolution of the ERA5 data is relatively high, it falls short in mountainous areas with complex terrain. Simultaneously, it is crucial to acknowledge the potential presence of data gaps during specific time intervals and in particular geographical regions, especially those characterized by pronounced terrain undulations. These impact factors contribute to the deviations observed between the vertical wind speeds in the ERA5 reanalysis data and the actual observations obtained from mountainous areas in southeast China.  
The wind speed at heights between 50 and 200 m is shown in Figure 3(a1-c1). Due to the valley winds, the sudden increase in observed vertical wind occurs from 1 May to 18 June. The Doppler wind lidar is located in the top of the sunrise slope at Shanghaiung site, so the valley wind is obvious in the observation. Due to the influence of solar radiation, the air on the slopes of the mountain will increase in temperature during the daytime. However, the air at the same altitude over the valley floor is farther away from the ground, so it receives less radiation than the air near the slopes and increases in temperature to a lesser extent. As a result, the warm air on the slopes of the mountain rises and circulates between the upper slopes and the valleys, the air in the valleys replenishes itself along the slopes to the tops of the mountains, thus forming a thermal circulation between the slopes and the valleys, with the lower wind blowing from the valleys to the slopes. On the contrary, due to the difference in specific heat capacity, the heat in the mountain slopes dissipates faster, and the air becomes cooler compared to the air in the valleys. Cold air on the slope of the mountain will sink down along the slopes because its density is lower than the warm air, and warmer air in the valleys is forced to lift and replenish the air at the tops of the mountains, so they form a circulation. As a result, upward vertical winds occur during the day and downward vertical winds during the night. Moreover, strong convective weather often occurs during the main season in southeast China, especially in May and June. For example, the convective weather caused the deviation between the ERA5 reanalysis data and the observed data on 17-19 May, and the heavy rainfall also caused the deviation of the vertical wind speed on 23-24 June. Due to the Typhoon Doksuri on the 24-31 July, extreme weather conditions such as heavy rain and high winds occurred over a wide area in southeast China, and the vertical wind speeds of the low-level ERA5 showed large errors compared with the observations. Thus, the climate on the mountain tops is unpredictable during the typhoon weather conditions. It is very important to improve the accuracy and resolution of ERA5 reanalysis data. The effects of topography and local circulation also need to be taken into account.  
Figure 3: Same as Figure 2, but for vertical wind speeds at different heights. Time series (**a1–f1**) and scatter plots (**a2–f2**) of the observed vertical wind speeds at various heights compared with the ERA5 reanalysis data values. The zoomed-in time series of 2 and 3 June 2023 were selected for comparison, with the red and blue lines representing the vertical wind speeds from ERA5 and Doppler wind lidar, respectively. The areas circled by ellipses are the locations of vertical wind speed changes during extreme weather.