## 3 Results and Discussion
### PL Vertical Structure from CloudSat Measurements  
Detailed vertical structure of the PL3 cloudiness is illustrated by a cross-section of clouds radar reflectivity measured by the CPR radar onboard the CloudSat satellite at 14:34 UTC on 19 October (Figure 6c). The CPR sampled the PL3 from northeast to southwest about 25 km west of its center through the area of scattered clouds between two cloud spirals. CPR measurements are nearly synchronous with AMSR2 data at 14:25 UTC (Figures 5 and 6a,b) on 19 October. The location of the cross-section line is plotted on the fields of brightness temperature Tb(89H) and total cloud liquid water content Q (Figure 6a,b). Due to the higher spatial resolution (4 km \(\times\) 6 km) and the sensitivity of the measurements at a frequency of 89 GHz to variations in geophysical parameters, the Tb(89H) field provides the detailed structure of mesoscale atmospheric processes.  
In the Tb(89H) and Q fields (Figure 6a,b), as well as on satellite images, two PLs and the wave structure of the PL**3** inner boundary are clearly visible. The high Tb(89H) values of 200-220 K along this boundary within the 20-50 km swath correspond to vertically developed convective clouds. The Tb(89H) and Q fields illustrate the high correlation due to the sensitivity of the former to the areas of the PLs and convective cells with increased liquid water content and/or precipitations.  
The CloudSat measurements show that the PL**3** clouds are as high as 3 km in the south (about 72.2-72.4 N) and about 4 km in the north (72.7-74.4 N) of the cross-section (Figure 6c). It corresponds to the CloudSat measurements over the Okhotsk [33; 34] and Labrador [36] Seas, where the cloud top height of 4 km was observed in the PLs. In the Sea of Japan [34], in contrast, the higher SST results in penetration of convection up to 5-6 km.  
Figure 6: The brightness \(-\)175 temperature fields at the 89 GHz frequency in horizontal polarisation (**a**) and the total cloud liquid water content (**b**) from the AMSR2 measurements at 14:25 UTC, and vertical cross-section of the clouds close to the PL3 center from the CPR measurements at 14:34 UTC (**c**) on 19 October 2017. The arrows on (**a**) indicate segments of the cross-section on (**c**).  
Across almost the entire vertical extent of heavy cumulus clouds, the radar echo varies from 5 to \(\geq\)10 dB, except at the cloud top, where it sharply decreases to negative values. Within the swath of \(\approx\)45 km from the inner boundary of the northern part of the PL3 (between 72.7-73.1N) cloud spiral, the maximum CPR reflectivity is concentrated below the height of \(\approx\)1.5 km with a cloud height of 4 km. Further north along the cross-section, the cloud height remained roughly the same, but the reflectivity values sharply increased to 5-10 dB up to the height of 3 km up to 73.8N. High reflectivity values correspond to the increased Tb(89H) values of 200-220 K and Q of 0.1-0.25 kg/m\({}^{2}\). The only exception is observed for the swath marked by arrow **1** in Figure 6. Here, low values of the Tb(89H) and Q correspond to increased total water vapor content V (Figure 5b), high CPR reflectivity (\(\geq\)8-10 dB) and heavy convective clouds. A similar combination of the Tb(89H), Q and CPR reflectivity values was also found in the PL over the Sea of Japan [34] and can be explained by the predominance of ice crystals in the clouds with specific microphysics properties [46; 47].