Interhemispheric Anti-Phase Variability in Mesospheric Climate Driven by Summer Polar Upwelling During Solstice Months

Zhang, Liang; Liu, Zhongfang; Tinsley, Brian

doi:https://doi.org/10.5194/acp-25-13141-2025

Articles | Volume 25, issue 20

https://doi.org/10.5194/acp-25-13141-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-25-13141-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 25, issue 20

Research article

|

21 Oct 2025

Research article |

| 21 Oct 2025

Interhemispheric Anti-Phase Variability in Mesospheric Climate Driven by Summer Polar Upwelling During Solstice Months

Liang Zhang, Zhongfang Liu, and Brian Tinsley

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Final revised paper (published on 21 Oct 2025)
Preprint (discussion started on 19 May 2025)

Interactive discussion

Status: closed

RC1: 'Comment on egusphere-2025-2047', Anonymous Referee #1, 22 Jun 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2047/egusphere-2025-2047-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-2047-RC1
RC2: 'Comment on egusphere-2025-2047', Anonymous Referee #2, 15 Jul 2025

I consider that this paper presents an important contribution to mesospheric climate. It identifies a dynamical and chemical coupling mechanism that drives interhemispheric variability during solstice months. Using satellite datasets the authors assess how the summer polar upwelling affects H2O and O3 chemistry in both hemispheres. They identify what they call the "cold-trap effect" and distinguish it from "the freeze-drying effect", which I find very interesting.
The manuscript is well explained, in my opinion, based on the data analysis presented, with very clear figures and data analysis.
I have only a couple of question, which does not need to be addressed in the manuscript itself, as I consider the work suitable for publication.
(1) Can the results proposed in the paper be supported by atmospheric models such as WACCM-X for example?
(2) Regarding the observed interannual variability, is there a possibility that global circulation patterns, like the QBO, influence each hemisphere, during solstices, inversely at these altitudes?

Citation: https://doi.org/10.5194/egusphere-2025-2047-RC2
AC1: 'Comment on egusphere-2025-2047', liang zhang, 05 Aug 2025

Thanks the referees for taking the time to review our paper and providing valuable feedback. Please find attached file for the Authors' Response.

Citation: https://doi.org/10.5194/egusphere-2025-2047-AC1

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by liang zhang on behalf of the Authors (05 Aug 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (11 Aug 2025) by John Plane

RR by Anonymous Referee #2 (11 Aug 2025)

RR by Anonymous Referee #1 (24 Aug 2025)

Suggestions for revision or reasons for rejection

I would like to thank the authors for thorough responses to the referee comments and for the revised manuscript. I am generally happy with the revisions and I find the manuscript almost ready for publication.

I am still uneasy regarding the authors’ distinction between freeze-drying (involving vertical transport of PMC particles) and cold trap (not involving vertical transport of PMC particles). I understand that there is a “companion manuscript” by Zhang et al. under review at ACP. It seems that that review process is almost completed, and I suggest to refer to the companion manuscript (discussion paper) in the present manuscript. Once the companion paper will be published, I assume that future studies will need to address the suggested distinction and the relative importance of the PMC freeze drying and PMC cold trap mechanisms. In any case, the focus of the present manuscript is on the role of upwelling for the mesospheric chemistry, and I would argue that the conclusions of the present manuscript are actually not critically dependent on the distinction between freeze-drying and cold trap. Maybe the authors want to comment on that. So, as of now, I am satisfied with the description of both processes in the current manuscript.

However, there is one related issue that must be clarified in order to avoid potential confusion for readers not familiar with water vapour in the middle atmosphere:

The main reason why the upper mesosphere and thermosphere are dry (“dehydrated”) is the photolysis of water vapour by solar UV radiation. This is particularly prominent in the polar summer mesosphere because of the permanent solar irradiation. This basic fact should be clearly stated in the manuscript when mesospheric water vapour is discussed (sections 1.1, 2.2 (point 1), and 4.1).

In the polar summer, PMC add to this dehydration of the upper mesosphere and thermosphere, but they are not the major cause. The manuscript uses wordings like “ice particle growth that blocks upward H2O transport, causing de-hydration above PMC in the summer hemisphere” (line 259-260). Such wordings are potentially confusing as a reader may understand that PMC are the major cause of low water concentrations at higher altitudes.

An instructive reference is e.g. Siskind et al. (2018) “Understanding the effects of polar mesospheric clouds on the environment of the upper mesosphere and lower thermosphere”. This paper is already cited in the present manuscript, albeit only as an example of PMC effecting odd hydrogen chemistry. The more important message from that paper is how much PMC actually affect the global water vapour budget water in the mesosphere (based on WACCM model simulations). See in particular their Figure 1, comparing the global distribution of water vapour in a world with PMC and without PMC. I suggest to add this to the discussion with an explicitly reference to this paper.

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ED: Publish subject to minor revisions (review by editor) (01 Sep 2025) by John Plane

AR by liang zhang on behalf of the Authors (02 Sep 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (16 Sep 2025) by John Plane

AR by liang zhang on behalf of the Authors (17 Sep 2025) Manuscript

Short summary

Using multi-satellite datasets, the interannual climate variability in upper mesosphere is demonstrated to be anti-phase between the summer and winter hemispheres during solstice months. Summer polar upwelling bottom-up drives opposite water vapor variability between the two hemispheres. Subsequently, mesospheric ozone is negatively modulated by water vapor through ozone chemistry, which further influences temperatures above 90 km via radiative and chemical heating.