## 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 cloud radar better shows the fine structures of the orographic clouds and precipitation; thus, it can be used to investigate the characteristics of clouds above and below the wind shear level at a height of approximately 4 km. Figure 6 shows the RHI measurements of cloud radar for Segment 1, including the reflectivity and radial velocity. The blue color of the panels of radial velocity indicates flow towards the radar, while red indicates flow away from the radar. As shown by the figure, strong wind shear existed at a height of about 4 km (Figure 6b,d,f), with a low-level northerly upslope wind and higher-level cross-ridge southwesterly wind; this confirms the wind field modeled by WRF (Figure 2b). The cloud top height was approximately 9 km, corresponding to a cloud top temperature of \(-\)30 \({}^{\circ}\)C. It can be seen that the cloud structure was very different above and below the wind shear level. Below 4 km, a convective cell was formed at 8:36 UTC to the south of the radar, along the boundary of the cross-ridge southwesterly flow and the upslope northerly flow. The cell intensified as it moved gradually to the north (shown by the black circles in Figure 6a,c,e). At 8:46 UTC, light precipitation occurred below the convective cell, and the precipitation intensified as the cell matured. An important aspect to note was that the cell top rarely exceeded the wind shear level. The clear separation between the cell and upper-level clouds  
Figure 5: (**a**–**c**) Drop size distributions and (**d**–**f**) profiles of drop concentration (black) and volume mean diameter (red) below the melting layer for the three precipitation segments. suggests that the precipitation was mainly due to warm rain rather than mixed-phase cloud. Falling ice did occur, as seen from the bright band on the north side of the radar at about 3.8 km at 8:56 UTC (Figure 6e), but the rainfall from the melted snow was much weaker than the warm rain generated by the convective cell. The convective cell dissipated after 9:10 UTC (not shown), meaning that the observed precipitation was weakened (Figure 4a). Figure 7 shows the RHI measurements from the cloud radar for Segment 2. The cloud structures remained different above and below the shear level. The radar echo was mostly weak above 4 km, indicating non-precipitating clouds, although ice particles might exist in regions with a reflectivity exceeding 10 dBZ. Below the wind shear level, the warm rain process was still efficient, generating light to moderate precipitation (Figure 4). The radar reflectivity was relatively high (>20 dBZ) in the convergence regions, such as that 10 km north of the radar at a \(\sim\)3 km height in Figure 7a,b. At 10:32 UTC, the wind field changed, as can be seen from the radial velocity measured by the cloud radar (Figure 7f); the wind near the surface turned to the south; between 3 km and 4 km, the wind was still northerly; and above 4 km, the wind was southerly. Therefore, two vertical wind shear levels were present. This limited most of the warm clouds between 3 km and 4 km at 10:32 UTC, as seen from the radar echoes (Figure 7e); the reflectivity was 5-20 dBZ within the cloud, but low both near the surface and above the shear level. Figure 6: RHI measurements of (**a**,**c**,**e**) reflectivity and (**b**,**d**,**f**) radial velocity conducted by the cloud radar for Segment 1. 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. In Segment 3 (Figure 8), the wind field became more complicated. At 11:17 UTC, the reflectivity was mostly weak, except a few isolated echoes exceeding 20 dBZ, associated with weak convergence zones. At 11:47 UTC, there were two clear vertical wind shear levels, as shown in Figure 8d, which resulted in multiple layers of clouds.