# Wind Characteristics in Mountainous Valleys Obtained through Field Measurement
## 4 Conclusions  
In this study, 2D ultrasonic anemometers and 3D Doppler radars were installed on the southwest and northeast sides of a selected site to observe and record the wind environment in the horn-shaped terrain for more than a year. The mean wind characteristics and turbulence wind characteristics, including turbulence intensity, spectral analysis, and turbulence integral scale, were comprehensively analyzed. Statistical analysis of the measured data and local weather station observations revealed that some of wind parameters are almost consistent with the specifications, such as turbulence intensity. Moreover, some of the wind parameters at the observation site differed significantly from the normative recommendations, and the following conclusions were drawn:  
1. The results indicate that the wind profile index \(\alpha\) is about 0.21, and the measuring locations are near the gentle hilly terrain. According to the Chinese specifications, the surface roughness coefficient for this terrain is 0.22, which is close to the measured value of 0.21. However, due to the influence of the complex topography of the area, the wind profile index \(\alpha\) cannot fully indicate the surface roughness of the area. As shown in Figure 5, the wind profile data were divided into six forms. This does not match the exponential law. The distribution of wind attack angle in the measured low-altitude range is discrete, even reaching 20\({}^{\circ}\), which is much larger than the \(\pm 3^{\circ}\) recommended by the specifications. The frequency of negative wind attack angle is greater than that of positive wind attack angle. As height increases, the tendency toward negative tapping angles becomes more obvious. There is a strong correlation between the wind speed profile and the wind direction angle in the observed area. The distribution of wind speed with height in the main wind direction (NW) is well  
Figure 31: Relationship between turbulence integral scale and mean wind speed: (**a**) the northeast side; (**b**) the southwest side. \begin{table}
\begin{tabular}{c} **Southwest** \\ **Side** \\ **Frequency** \\ \end{tabular} \\ \hline
[0–50] & 36.99 & 33.26 & [400–450] & 0.56 & 0.65 \\ \hline
[50–100] & 39.29 & 37.95 & [450–500] & 0.39 & 0.48 \\ \hline
[100–150] & 10.78 & 14.33 & [500–550] & 0.17 & 0.22 \\ \hline
[150–200] & 4.78 & 5.78 & [550–600] & 0.11 & 0.09 \\ \hline
[200–250] & 2.96 & 3.00 & [600–650] & 0.11 & 0.13 \\ \hline
[250–300] & 1.75 & 2.04 & [650–700] & 0.07 & 0.00 \\ \hline
[300–350] & 1.03 & 1.04 & [700–750] & 0.05 & 0.09 \\ \hline
[350–400] & 0.92 & 0.87 & [750–800] & 0.03 & 0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Frequency distribution of integral scale interval on the northeast and southwest sides. in accordance with the exponential law, while the distribution of wind profile data in other directions is disorganized and irregular. 2. The downwind turbulence intensity degree \(I_{u}\) on both sides of the river channel is about 13%, slightly greater than the 12% recommended value in the norm. However, the ratio of crosswind and downwind turbulence intensity \(I_{p}/I_{u}\) is 0.46, only 52% of the recommended value of the specification (0.88). This may be due to the topography resulting in the main wind direction (NW and WNW), accounting for a larger component of the incoming wind direction, which in turn results in a reduced degree of crosswind pulsation. We found a strong linear correlation between the gust factor \(G_{u}\) and the turbulence \(I_{u}\) during the observation period, with \(G_{u}\) increasing with the increase in \(I_{u}\). There is a high turbulent component in the incoming wind velocity in these areas. The high-frequency energy is relatively large, while the low-frequency energy is relatively small. The existing empirical spectra do not provide an accurate description of the measured spectrum. Therefore, the Von Karman spectrum was used to fit the spectrum expressions with good applicability to the wind characteristics. 3.