the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Jan 2026
Tropospheric Circulations Modulating the Boreal Winter Lower Stratospheric Polar Vortex
Abstract. Here we present an observational study of the variations in the lower stratospheric polar vortex (LSPV) associated with the main tropospheric circulation patterns in the Northern Hemisphere in winter (November to March). The LSPV is based on daily geopotential height at 100 hPa, and the circulation patterns are based on the empirical orthogonal function analysis of geopotential height anomalies at 500 hPa. The LSPV is found to strengthen with the Ural trough and the negative phase of the Pacific-North America (PNA-) pattern, and to weaken with the Ural ridge and the PNA+ pattern. These relations result first from the anomalous poleward, isentropic transport of oceanic air masses on the western flank of the positive tropospheric geopotential height anomalies, and of continental air masses on the eastern flank of the negative anomalies. Secondly, they result from troposphere-stratosphere propagation of anomalies, which may intensify or flatten the stationary anomalies in the stratosphere. In particular, the northeast Asia trough is deepened during the Ural ridge, and the Alaska ridge is enhanced during PNA+ regimes, which increase meridional fluxes of heat and cause a weakening of the polar vortex. This work thus supports wave-propagation-and-interferences based theory for polar vortex variations in previous studies, while highlighting the role of certain tropospheric circulation patterns. The large-scale anomalous advection of airmasses explain coherently tropospheric and stratospheric changes associated with the circulation patterns, and suggest covariations of the LSPV with clouds, latent heating, precipitation, and radiative feedbacks in the Arctic atmosphere.
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- RC1: 'Comment on egusphere-2025-6381', Judah Cohen, 30 Jan 2026
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RC2: 'Comment on egusphere-2025-6381', Anonymous Referee #2, 10 Feb 2026
This study relates patterns of mid-tropospheric geopotential height variability across the Pacific–North America and Atlantic–Eurasian sectors with variability in the lower stratospheric polar vortex (100 hPa) using NCEP-DOE reanalysis data over extended winter 1979–2019. This is a relatively short study.
The concept of analysing the vortex response to tropospheric regimes [i.e., p(vortex state | regime) is probably less explored than the reverse p(regime | vortex state)], especially when not explicitly related to SSWs, which seems to be the main point of this study. However, the depth of analysis presented here and its integration with the existing literature seems too thin and preliminary to justify its publication in this journal. The concept is interesting and I would encourage the authors to pursue it in a suitably revised and expanded study.
Causality and contextualisation:
It is not clear what the motivation for considering the 100 hPa vortex is. The text around L43 mentions that the 10 hPa and 100 hPa vortex can be out-of-phase, but it is not clear how that motivates the present work, nor are the details of this shown. Typically, patterns in the troposphere can be precursors for upward propagating wave activity that decelerates the upper stratospheric vortex with subsequent downward propagation of NAM anomalies (e.g., Cohen and Jones 2011 J. Climate https://doi.org/10.1175/2011JCLI4160.1) – what is the mechanism here? Are we considering a case where these circulation patterns affect the lower stratosphere but not the upper stratosphere (and why would that be the case)? Figure 7 doesn’t clearly answer this because the sign of the anomalies appears to change everywhere in both cases.
It is extremely difficult to determine the direction of causality with the 100 hPa vortex. The downward influence of the stratospheric vortex strength on the surface is mediated by the 100 hPa vortex and anomalies at 100 hPa influence tropospheric weather regimes almost instantaneously. Several studies have looked at this previously using regimes frameworks over the domains here: Charlton-Perez et al. (2018, QJRMS https://doi.org/10.1002/qj.3280), Lee et al. 2019 (GRL https://doi.org/10.1029/2019GL085592), White et al. (2020, J Climate https://doi.org/10.1175/JCLI-D-19-0697.1). That the dominant North Atlantic pattern in this study resembles the NAO supports this point, as this is the expected response to the LSPV anomalies rather than necessarily causal. Ultimately, a key missing factor in this manuscript – particularly for a journal like Weather and Climate Dynamics – is a lack of dynamics: the readers are presented with many different composites, but very little in the way of diagnostics commonly used to identify the dynamical interaction between the troposphere and stratosphere such as eddy heat flux/EP flux.
Fig 1b, Atlantic–Eurasia EOF2 closely resembles the Scandinavian Pattern, which has been previously extensively linked to vortex variability (e.g., Pang et al. 2021, J. Climate https://doi.org/10.1175/JCLI-D-21-0331.1). Figs 1c and d resemble the Pacific Trough and Alaskan Ridge weather regimes (see above literature).
Data:
The authors have chosen to use the now outdated NCEP-DOE reanalysis over 1979–2019. The results of the SPARC Reanalysis Intercomparison Project (S-RIP) strongly discouraged the use of the NCEP reanalyses https://s-rip.github.io/pubs/index.html. It’s not clear why such an old and coarse reanalysis has been used rather than a modern, high-resolution reanalysis like ERA5, MERRA-2 or JRA-3Q. Furthermore, why does the analysis stop at 2019? It should be extended to present, given this is a relatively short period and the additional 6 years could be significant.
Treatment of uncertainty:
There is a lack of detailed treatment of statistical significance/uncertainty in this manuscript, which needs to be addressed, including any effects arising from the strong autocorrelation of the 100 hPa vortex state (e.g., Baldwin et al. 2003, Science https://doi.org/10.1126/science.1087143). L429/430 mention standard errors, but this would be a weak test (not the usual 95%), while L459 claims 99% significance but does not mention the test or whether it is appropriate given the data. The authors should also consider the effect of multiple testing of spatial data through an approach like the False Discovery Rate as outlined in Wilks (2016, BAMS) https://doi.org/10.1126/science.1087143.
Line-specific comments:
L40: it is highly correlated, to the point that it’s unclear if the NAM and NAO are actually distinct modes e.g. Feldstein and Franzke 2006 JAS https://doi.org/10.1175/JAS3798.1
L49: does this “horizontal elongation” have a preferred axis to induce these effects? How does this occur?
L53-55: perhaps this is a personal style point, but I don’t think it’s good practice to simply say “previous studies” and then list 10 studies across three lines. This isn’t helpful to the reader nor does it clearly show why these have been cited. It is more helpful to cite a few studies next to the relevant statement.
L59: yes, this additional upward wave flux can cause SSWs but it isn’t necessary for SSWs to occur, e.g. de la Cámara et al. 2018 https://doi.org/10.1175/JCLI-D-19-0269.1
L81: does this mean 1979/80 to 2018/19 for each NDJFM? Please make this clear.
L83: have you accounted for mean state trends in geopotential height due to thermal expansion/contraction?
L109: this classification of a “regime” needs some justification or linkage with the existing literature, or some sensitivity analysis. You might also wish to link these patterns to existing literature on North American and North Atlantic/European weather regimes, and justify why you have chosen a different method.
L115: but this ‘variable durations’ aspect makes it difficult to interpret. The supposed ‘impact’ of a 30 day regime versus a 5 day regime on the vortex is very different.
L188: misspelled citation to Domeisen et al. 2018.
Citation: https://doi.org/10.5194/egusphere-2025-6381-RC2 -
AC1: 'Reply on RC2', Songmiao Fan, 20 Feb 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6381/egusphere-2025-6381-AC1-supplement.pdf
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AC1: 'Reply on RC2', Songmiao Fan, 20 Feb 2026
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The manuscript presents an observational analysis of the variations in the lower stratospheric polar vortex (LSPV) associated with the main tropospheric circulation patterns in the Northern Hemisphere in winter. The authors focus on daily geopotential height at 100 hPa, and the tropospheric circulation patterns are based on the empirical orthogonal function analysis of geopotential height anomalies at 500 hPa. The authors found that the LSPV is found to strengthen with the Ural trough and the negative phase of the Pacific-North America (PNA-) pattern, and to weaken with the Ural ridge and the PNA+ pattern.
I do think that this is an important study with important results as I don’t feel that the community appreciates enough the importance of Ural ridging/troughing to polar vortex variability. However I do wish that the authors could have done more. Two analyses that I strongly suggest that the authors include are: Rossby wave energy propagation (wave activity flux) associated with all the different teleconnection patterns and the surface temperature pattern with each of the different teleconnection patterns. I would also be curious to see an analysis that shows which ridging patterns are associated with stretched polar vortex events and which are associated with sudden stratospheric warmings. Otherwise I feel that the manuscript is in good shape.
I have some more minor suggested edits below. I recommend that the manuscript be accepted pending minor revisions.
Minor comments:
Reference:
Kretschmer, J. Cohen, V. Matthias, J. Runge and D. Coumou,. 2018: The different stratospheric influences on cold extremes in northern Eurasia and North America, npj Climate and Atmospheric Science, doi: 10.1038/s41612-018-0054-4.
Judah Cohen