## 5 Conclusions  
In this study, based on the high-precision remote-sensing measurements from May to July 2023 in a typical mountainous Shanghuang site in southeast China, we systemically evaluated the vertical accuracy of the ERA5 meteorological variables over mountainous areas, which corresponds well to the Doppler wind lidar observations, but there are still some discrepancies. The mountainous climate is extremely complex and changeable, especially at the summit, making it much more difficult for the ERA5 data to capture true  
Figure 7: Mean deviations of ERA5 and remote-sensing observations for (**a**) horizontal wind speed (HWS), (**b**) vertical wind speed (VWS), (**c**) wind direction (WD), (**d**) temperature (T), and (**e**) relative humidity (RH) for May–July 2023.  
values because of its relatively coarse resolution both at temporal and spatial scales. The horizontal wind speeds of ERA5 only deviate from the observed values below 400 m by about 8%, whereas above 400 m, there is an increasing negative bias as altitude increases. The difference between the vertical wind speeds in ERA5 and those observed by Doppler wind lidar is large, and the valley winds and heterogeneous topographic forcing in the mountains are important reasons. Thus, the ERA5 is not able to characterize the vertical wind speeds of the localities. Therefore, the coarse resolution and heterogeneous topographic forcing jointly result in poor representativeness of meteorological variables, especially in extreme weather such as heavy rainfalls and typhoons. In particular, there is a large deviation from the observations in the middle and lower vertical wind speeds and the horizontal winds. The maximum mean wind speeds of both the ERA5 reanalysis data and the observations occur in the westerly winds. Below 1800 m, the vertical wind speed of the ERA5 shows positive deviations from \(-150\%\) to \(-60\%\). Above 1800 m, the deviation is from \(-60\%\) to 40%. With prevailing westerly and northwesterly winds, the observed wind direction and ERA5 reanalysis data have fewer outliers, and they show a better correlation at a 100 m height, whereas larger biases exist at other altitudes. The reasons for the poor consistency of wind direction in the atmospheric boundary layer below 1500 m are the influences of the topography of the subsurface, the temperature, the convective weather processes, typhoons, etc. In addition, temperature data from the ERA5 agree well at low and medium levels over mountainous regions, with deviations of less than 0.5%, but systematic errors with higher deviations occur at altitudes higher than 2000 m, and the upper-level temperature data need to be optimized. The general trend of relative humidity variations in the ERA5 is similar to that observed by the MWR, but with larger deviations occurring during convective weather events. Below 200 m, the ERA5 relative humidity is similar to that observed by MWR, but at middle and upper levels, the ERA5 relative humidity is generally biased, higher than that observed by MWR, with larger positive deviations ranging from 30% to 110% from 500 to 2500 m. The results expand the application of the ERA5 reanalysis datasets in the mountainous areas of southeast China. More importantly, it provides credible reference data for the meteorological predictions and climate modelings in the southeast China mountainous region.