the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Jul 2026
Post-SSW Quasi-Biweekly Oscillations Sustained by Wave-Mean Flow Feedback in the Southern Hemisphere
Abstract. A quasi-biweekly oscillation developed in the Southern Hemisphere following the 2024 sudden stratospheric warming (SSW) events, rather than a monotonic recovery. Although recurrent tropospheric planetary-wave activity preceded the warming episodes, the much stronger stratospheric response suggests that lower-level forcing alone cannot explain the oscillation. We show that planetary-wave propagation, the polar vortex, and the stratospheric waveguide were linked through a coupled feedback: enhanced upward wave propagation before the warming peaks weakened and contracted the polar vortex, shifting the strongest waveguide structure poleward and reducing its overlap with the main 50° S–70° S wave-activity region. The subsequent weakening of upward propagation allowed the westerly flow and polar vortex to partially recover, restoring favorable propagation conditions and enabling the next cycle. These results suggest that Antarctic post-SSW variability can be sustained from late winter into early spring by internally modulated wave-mean flow interactions.
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Status: open (until 13 Aug 2026)
- RC1: 'Comment on egusphere-2026-3774', Anonymous Referee #1, 31 Jul 2026 reply
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RC2: 'Comment on egusphere-2026-3774', Anonymous Referee #2, 02 Aug 2026
reply
General comments
This letter investigates the recurrent post-SSW warming episodes occurred in the Antarctic stratosphere during austral winter 2024. These warming episodes and the stratospheric background state in 2024 are unusual during past decades. The authors propose the stratospheric wave-mean flow feedback as the driver of post-SSW oscillations under favorable stratospheric background state. The paper is well written and the results are interesting and convincing. I have only a few minor comments that could help improve the manuscript. I recommend minor revisions before publication.
Specific comments
This stratospheric oscillation phenomenon and its interpretation in this study bring to mind the Holton-Mass vacillation. Holton and Mass (1976) studied the stratospheric vacillation cycles in a dynamics model. The authors could add a brief discussion of their relationship.
Holton, J. R., and C. Mass, 1976: Stratospheric vacillation cycles. J. Atmos. Sci., 33, 2218–2225.
Line 34: Recent studies have highlighted the role of vortex preconditioning in triggering the Antarctic weak polar vortex events.
Lim, E.-P., et al., 2021: The 2019 Southern Hemisphere stratospheric polar vortex weakening and its impacts. Bull. Amer. Meteor. Soc., 102, E1150–E1171.
Yang, P. et al., 2025: The role of vortex preconditioning in the occurrence of Antarctic weak polar vortex events. J. Climate, 38, 1319-1332.
It would be beneficial to include a discussion on the possible causes for the unusual stratospheric background state during 2024. Readers may be interested in learning about this.
Citation: https://doi.org/10.5194/egusphere-2026-3774-RC2
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Post-SSW Quasi-Biweekly Oscillations Sustained by Wave-Mean Flow Feedback in the Southern Hemisphere Yiran Pan https://zenodo.org/records/20838731
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- 1
Review of “Post-SSW Quasi-Biweekly Oscillations Sustained by Wave-Mean Flow Feedback in the Southern Hemisphere”
This paper considers the role of the stratosphere in modulating upward propagating waves from the troposphere, and thereby the subsequent recovery of the stratospheric polar vortex following a sudden warming. The paper is well written and clearly laid out. The figures are of good quality and the results support the conclusions.
My main comment is whether the results and conclusions are as novel as is made out. I would suggest adding further references as detailed below, and further clarifying what new science is included in the current study.
1.
Line 30: “Their effects can extend downward into the troposphere … and persist for weeks to months”. There are a few references included here, but there has been so much work on this topic I think there should be more – for example:
Kidston et al. (2015), Stratospheric influence on tropospheric jet streams, storm tracks and surface weather, Nature Geoscience, 8, 433–440, doi:10.1038/NGEO2424
Thompson et al. (2005), Stratosphere-troposphere coupling in the Southern Hemisphere. J. Atmos. Sci. 62, 708–715
Hitchcock and Simpson (2014), The downward influence of stratospheric sudden warmings. J. Atmos. Sci. 71, 3856–3876
Mitchell et al. (2013), The influence of stratospheric vortex displacements and splits on surface climate. J. Clim. 26, 2668–2682
Sigmond et al. (2013), Enhanced seasonal forecast skill following stratospheric sudden warmings. Nature Geosci. 6, 98–102
The first two of these explicitly consider the Southern hemisphere (and there are other references within).
2.
Line 38: “the evolving mean flow is not only a response to prior wave forcing but also a regulator of subsequent wave propagation”:
Holton and Mass (1976), Stratospheric Vacillation Cycles. J. Atmos. Sci., 33, 2218–2225
Scott and Polvani (2004), Stratospheric control of upward wave flux near the tropopause, Geophys. Res. Lett., 31, L02115
3.
Figure 1 panels (c) and (d) show the stratospheric zonal wind to lag the upward propagating eddy heat flux. A key reference here is:
Newman et al. (2001), What controls the temperature of the Arctic stratosphere during the spring?, J. Geophys. Res., 106(D17), 19999–20010
4.
Line 94: “Thus, enhanced tropospheric wave activity does not necessarily lead to an amplified stratospheric wave response”. This is known, for example:
Birner and Albers (2017), Sudden stratospheric warmings and anomalous upward wave activity flux. Sola, 13A (Special Edition), 8–12
5.
Line 178: “the post-SSW atmosphere remained dynamically active”. I think this is a key point, which is really interesting and should be emphasized. Some evidence of post-SSW vacillations has been previously seen, for example:
Lee et al. (2025), Two major sudden stratospheric warmings during winter 2023/2024. Weather, 80: 45-53
who do also consider the stratospheric eddy heat flux following the SSWs.
6.
Line 182: “indicates that tropospheric forcing alone cannot explain the variability”. This is well known - see many of the references above, but also:
Christiansen (1999), Stratospheric Vacillations in a General Circulation Model. J. Atmos. Sci., 56, 1858–1872
Scott and Haynes (2002), The Seasonal Cycle of Planetary Waves in the Winter Stratosphere. J. Atmos. Sci., 59, 803–822