Comment on acp-2021-676

Using the ERA-Interim reanalysis, ENSO index, QBO observations, and solar cycle index, Lecouffe et al. calculated the metrics of the southern hemispheric stratospheric polar vortex at 50 hPa using the vortex elliptical diagnostics. The variable PV is used in the study due to its conservation property on the isentropic surface in the free atmosphere. The paper is interesting and provide some useful information to the community. However, I also found some minor shortcomings in the paper. The authors might need to well review the most recent publications in the literature, and build their work on the existing results in literature. For example, previous studies have confirmed that the ENSO does not have significant impact on the Southern Hemisphere polar vortex. But this paper still discusses the weak impact of the ENSO on the vortex edge. Due to those problems in the manuscript, I suggest a substantial revision before the paper could be published.


Summary
Using the ERA-Interim reanalysis, ENSO index, QBO observations, and solar cycle index, Lecouffe et al. calculated the metrics of the southern hemispheric stratospheric polar vortex at 50 hPa using the vortex elliptical diagnostics. The variable PV is used in the study due to its conservation property on the isentropic surface in the free atmosphere. The paper is interesting and provide some useful information to the community. However, I also found some minor shortcomings in the paper. The authors might need to well review the most recent publications in the literature, and build their work on the existing results in literature. For example, previous studies have confirmed that the ENSO does not have significant impact on the Southern Hemisphere polar vortex. But this paper still discusses the weak impact of the ENSO on the vortex edge. Due to those problems in the manuscript, I suggest a substantial revision before the paper could be published.

Major comments
Lack of a sufficient review on the most recent publications.
The impact of ENSO, solar cycle, and QBO on the polar vortex in both hemispheres has been widely and exhaustively studied in literature. However, this manuscript fails to provide a sufficient review on the most recent publications. The impact of the canonical ENSO on the SH polar vortex is insignificant in both observations and modeling studies ( In my understanding, the start date of the stratospheric polar vortex in both hemispheres are mainly forced radiatively due to the annual cycle, and it should be very stable. I checked the start date of the polar vortex in the NH using the zonal mean zonal wind at 60N and 10hPa as the threshold. I found that the start date of the NH polar vortex is very stable. In contrast, the final warming date in both hemispheres differs from year to year due to the dynamics associated with planetary wave activities. However, this study shows that both the start date and end date of the SH polar vortex have a large interannual variability. What forces such a strong variation of the start date of the stratospheric polar vortex. The authors also failed to mention the most recent studies on the final warming date in the SH (Rao and Garfinkel 2021CD, https://doi.org/10.1007/s00382-021-05647-6). They also discussed the possible impact of the ozone depletion and recovery on the polar vortex final warming date.

Minor comments
P1L18: This sentence should be supported by some citations. Please insert.
L24: The most recent report by Rao and Garfinkel 2021CD checked the interannual variation of the final warming date from CMIP5/6 models and JRA55 reanalysis. Explore if you missed more recent reports. P2L1: The reference put too much on the ozone depletion, but review on other aspects of the stratospheric polar vortex is insufficient.
L13: The ozone depletion events are also existing in the NH. The AUG organized one special issue for the NH ozone loss event in the 2019/2020 winter: https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)1944-8007.ARCTICSPV. Choose several references and discuss the ozone depletion in the NH (e.g., Garfinkel 2020Garfinkel , 2021Feng et al. 2021). The authors really should read more to enrich the introduction of the paper. This version is really not satisfactory.