## 4 Discussion
On the other hand, it might be an instrumental effect due to the presence of sunlight causing baseline fluctuations, which have a major effect on the weaker depolarized signal. Figure 11: The figure shows the frost temperature (in red) and the NAT formation temperature minus 3 K to show where ice PSCs, NAT and STSs, respectively, are probably formed. The green contours indicate where the local temperature is below the formation temperature of NAT minus 3 K. The formation temperatures were calculated from local pressure and water vapor and nitric acid mixing ratios were obtained from MLS data. **Author Contributions:** Conceptualization, M.S., L.D.L., and F.C. ([PERSON]); methodology, M.S., L.D.L., and F.C. ([PERSON]); software, F.C. ([PERSON]), M.S., and F.S. ; validation, L.D.L., A.B., and F.S. formal analysis, L.D.L., M.S., and F.S. investigation, F.C. ([PERSON]), A.B., and F.C. ([PERSON]); resources, M.S. and F.C. ([PERSON]); data curation, L.D.L. and M.S. ; writing--original draft preparation, M.S. and L.D.L. ; writing--review and editing, all authors; visualization, all authors; supervision, M.S. ; project administration, M.S. ; funding acquisition, M.S. and F.C. ([PERSON]). All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the Piano Nazionale della Ricerca in Antartide (PNRA) in the framework of the projects 2009/B.08, OSS-12. and LIDAROBS. **Data Availability Statement:** The raw ground-based lidar data are available from the NDACC website: [[https://www-air.larc.nasa.gov/missions/ndacc/data.html?station=dome.c/ames/lidar/](https://www-air.larc.nasa.gov/missions/ndacc/data.html?station=dome.c/ames/lidar/)]([https://www-air.larc.nasa.gov/missions/ndacc/data.html?station=dome.c/ames/lidar/](https://www-air.larc.nasa.gov/missions/ndacc/data.html?station=dome.c/ames/lidar/)) (accessed on 11 May 2024). The PSC special product has been made available by [PERSON], NASA. **Acknowledgments:** The authors acknowledge the financial support by PNRA in the framework of the projects 2009/B.08, OSS-12, LIDAROBS, and the SH-YOPP project. We also acknowledge the support of the ISSI-PSC initiative project. Logistical and winter-time technical support was provided by the Programma Nazionale delle Ricerche in Antartide (PNRA). The authors thank [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] for performing the ground-based lidar measurements at Dome C during the winter and [PERSON] and [PERSON] for their valuable technical support. A particular mention goes to [PERSON] in the winter of 2020 for enabling remote control via VPN, thus providing remote alignment of the lidar, which improved the quality of the measurements and the lidar-by-night picture. A special thanks goes to [PERSON], NASA, for supplying us with the CALIOP PSC special product data. **Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. Figure 12: The figure shows the water vapor mixing ratio in ppm as observed by MLS in 2021.