## 3 Results
### Vertical Structure and Temporal Evolution of the Orographic Clouds as Observed by Radars
#### 3.1.2 Characteristics of Cloud Observed by Cloud Radar
The highest layer of cloud, observed above the higher level of wind shear (Figure 8c), formed because the moist cross-ridge flow was lifted by the lower dry northerly flow (Figure 8d) and was possibly related to the lee wave of the cross-ridge flow as well; however, this cannot be verified using radar data alone. The cloud base had a similar shape compared to the structure of the vertical wind shear. At 3.5 km, a thin cloud layer formed along the lower wind shear level and the shape of the cloud top was consistent with the lower southerly flow, again revealing the importance of the vertical wind shear for the cloud formation and evolution. There was a third layer of cloud near the surface, with a few weak cells generated due to local convergence. The upper two cloud layers were mostly decoupled from the surface, and the precipitation was mainly generated by the warm rain process. This pattern continued (Figure 8e,f) until the cloud dissipated and the rain stopped (Figure 4). The warm cloud rarely exceeded the vertical wind shear level above its top, suggesting an inhibiting impact on the cloud vertical development. Figure 7: RHI measurements of (**a**,**c**,**e**) reflectivity and (**b**,**d**,**f**) radial velocity conducted by the cloud radar for Segment 2. S and N below each panel indicate south and north of the cloud radar. The blue color in the panels of radial velocity indicates flow towards the radar, while red indicates flow away from the radar. The temporal evolution of clouds can be described using the time series of the composite reflectivity (i.e., the maximum reflectivity in each vertical column) along the RHI cross-section. Figure 9a is the composite reflectivity for all heights, and Figure 9b,c are for the heights below 3.9 km and above 4.2 km, which represent the clouds below and above the vertical wind shear level. It can be seen from the figure that that cloud evolution was very different above and below the wind shear level. Between 7:00 and 9:40 UTC (corresponding to the first precipitation segment), the temporal variation in precipitation (Figure 9a) was controlled by the warm rain process below the wind shear level (Figure 9b) and the maximum reflectivity was approximately 35 dBZ. The observed clouds moved northwards. Scattered non-precipitating warm clouds and upper-level clouds were observed before 8:00 UTC. Two convective cells were generated at about 8:00 UTC and produced warm rain at the observational site from 8:50 to 9:40 UTC. The second precipitation segment (9:45-10:40 UTC) was dominated by a warm rain process as well. Clouds were rarely seen above the wind shear level (Figure 9c), suggesting the presence of a dry cross-ridge southwesterly flow and a lack of strong convection. The composite reflectivity was much lower than that in Segment 1, indicating a weaker warm rain process. In Segment 3 (10:55-12:10 UTC), clouds both above and below the wind shear level contributed to the overall composite reflectivity. The low-level clouds contributed relatively more to the echoes stronger than 30 dBZ, but they were more scattered and short-lived. The clouds  
Figure 8: RHI measurements of (**a,c,e**) reflectivity and (**b,d,f**) radial velocity conducted by the cloud radar for Segment 3. S and N below each panel indicate south and north of the cloud radar. The blue color in the panels of radial velocity indicates flow towards the radar, while red indicates flow away from the radar. covered similar areas above and below the vertical wind shear level, but the clouds were more homogeneous above the wind shear level, while clouds below the shear level had a higher variability. We can see from Figure 9 that the precipitation processes were quite different in the three segments. Although all the clouds in the three segments were related to theabatic winds over the Tian Shan Mountains, the ambient conditions changed significantly with time, since the prevailing wind was westerly in this case.