## 4 Discussion  
First of all, the remarkable agreement between ground-based and satellite-borne lidar has to be commented on. Notwithstanding the different observing geometry of both lidars, as well as comparing observations of air masses at different times and locations, the  
Figure 8: The figure shows the PSCs observed by lidar over Concordia Station in 2021. The upper level shows the ground-based observations, while the lower panel represents the CALIOP data, considering a latitude–longitude range defined by the coordinates 73.1°S < lat < 77.1°S and 116.33°E < lon < 130.33°E centered on Concordia Station. The color codes indicate the different PSC classes; orange stands for STSs, green for NAT mixtures, blue for ice, and red for enhanced NAT mixtures. The small circles indicate that a measurement is available but no PSCs were observed. agreement shown in Figure 8 is rather good. We must note, however, that the ground-based lidar in general detects more PSCs, probably due to its better signal-to-noise ratio. In a previous study [8], a large number of quasi-coincident lidar observations by the ground-based lidar at Concordia Station and the satellite-borne CALIOP lidar demonstrated that in almost 80% of all observations, both lidars observe PSCs or do not observe PSCs when the observations were within a certain time and distance. In the other 20%, only one of the two lidars observed PSCs and the other did not. This is mainly due to the fact that Concordia Station is located on a plateau with few orographic features. This implies that the temperature is quite homogeneous over a large area. As a result, the PSC fields are also expected to be rather homogeneous over extended ranges, as was demonstrated by an analysis of CALIOP tracks passing at distances of a few hundred kilometers from Concordia Station [8]. The formation of PSCs due to orographic wave activity, occurring primarily over the Antarctic Peninsula, is practically absent on the plateau [20]. We tried to further explore the representativeness of the Concordia PSC observations for the whole Antarctic Plateau. Figure 9 was conceived in the same way as Figure 8 but considering a latitude-longitude range for the CALIOP data, defined by the coordinates 73.1 degS + lat < 77.1 degS and 100 degE + lon < 150 degE centered on Concordia Station. This extended zonal area increases the number of CALIOP profiles considered from 262 to 646, while the average distance becomes 360 km, and the maximum distance is 815 km. The agreement between ground-based and CALIOP observations is still reasonably good and confirms that Concordia Station has good approximation that is representative of the Antarctic Plateau. This confirms the importance of Concordia Station as a long time series observatory of PSCs in Antarctica while considering that CALIOP was decommissioned in 2023. The 2021 data are peculiar from a certain point of view; the ubiquitous presence of ice PSCs during most of the winter is a result of the cold temperatures in the polar vortex in 2021. Figure 10 shows a time series of when the air is colder than 195 K at 450 K potential temperature obtained from the Climate Prediction Center website (https:  
Figure 9: The figure shows the PSCs observed by lidar over Concordia Station in 2021. The upper level shows the ground-based observations, while the lower panel represents the CALIOP data considering a latitude–longitude range defined by the coordinates 73.1°S + lat < 77.1°S and 100°E + lon < 150°E centered on Concordia Station. The color codes indicate the different PSC classes; orange stands for STSs, green for NAT mixtures, blue for ice, and red for enhanced NAT mixtures. The small circles indicate that a measurement is available, but no PSCs were observed. //www.cpc.ncep.noaa.gov/ (accessed on 11 May 2024)) for 2021. It is evident that the 2021 SH vortex covered a larger area than on average. Furthermore, the 2021 polar stratospheric vortex was stable with consistently cold temperatures [42].