Observations of stratospheric streamers and  frozen-in anticyclones in aerosol extinction

Löns, Christian; Eixmann, Ronald; Pohl, Christine; Rozanov, Alexei; von Savigny, Christian

doi:10.5194/acp-25-18209-2025

Articles | Volume 25, issue 23

https://doi.org/10.5194/acp-25-18209-2025

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

https://doi.org/10.5194/acp-25-18209-2025

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

Articles | Volume 25, issue 23

Research article

|

11 Dec 2025

Research article |

| 11 Dec 2025

Observations of stratospheric streamers and frozen-in anticyclones in aerosol extinction

Christian Löns, Ronald Eixmann, Christine Pohl, Alexei Rozanov, and Christian von Savigny

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Final revised paper (published on 11 Dec 2025)
Preprint (discussion started on 05 Sep 2025)

Interactive discussion

Status: closed

CC1:
'Comment on egusphere-2025-3984', Lynn Harvey, 10 Sep 2025

The authors should cite this study in the background section: Harvey, V. L., M. H. Hitchman, R. B. Pierce, T. D. Fairlie (1999). Tropical aerosol in the Aleutian High, JGR, https://doi.org/10.1029/1998JD200094

Citation: https://doi.org/10.5194/egusphere-2025-3984-CC1
- AC1: 'Reply on CC1', Christian Löns, 13 Oct 2025
  
  The comment was uploaded in the form of a supplement.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3984-AC1
RC1:
'Comment on egusphere-2025-3984', Daniele Visioni, 10 Sep 2025

In this paper, Löns et al use anomalies in stratospheric aerosol extinction, detected using multiple satellite products, to track the transport of air towards the poles, in particular through streamers – persistent ozone-rich masses of air coming from sub-tropical latitudes – and in particular look at the behavior of one identifiable event using this methodology in 2017. I found this paper extremely interesting and well written, and the analyses robust, and therefore recommend publication after some comments I attach below are addressed.
L. 9: “in that year” rather than “this year” (might be confusing)
L. 43: define what the “tape recorder” is, a reader might not necessarily be familiar with this term.
L. 185: this section title shouldn’t be “ECMWF”, that’s just the name of the Center.
L. 187: the dataset needs to be cited following Copernicus, not just with the long title, and the reference (with its own DOI) needs to be added to the Data Availability section.
Related to ERA5, it would be useful to include some references that validate ERA5 stratospheric transport. Here are a few suggestions, which the authors should try to include and talk about in Section 2.3:
Vogel, B., Volk, C. M., Wintel, J., Lauther, V., Clemens, J., Grooß, J.-U., Günther, G., Hoffmann, L., Laube, J. C., Müller, R., Ploeger, F., and Stroh, F.: Evaluation of vertical transport in ERA5 and ERA-Interim reanalysis using high-altitude aircraft measurements in the Asian summer monsoon 2017, Atmos. Chem. Phys., 24, 317–343, https://doi.org/10.5194/acp-24-317-2024, 2024.
Ploeger, F., Diallo, M., Charlesworth, E., Konopka, P., Legras, B., Laube, J. C., Grooß, J.-U., Günther, G., Engel, A., and Riese, M.: The stratospheric Brewer–Dobson circulation inferred from age of air in the ERA5 reanalysis, Atmos. Chem. Phys., 21, 8393–8412, https://doi.org/10.5194/acp-21-8393-2021, 2021.
Xiaozhen Xiong, Xu Liu, Wan Wu, K. Emma Knowland, Qiguang Yang, Jason Welsh, Daniel K. Zhou, Satellite observation of stratospheric intrusions and ozone transport using CrIS on SNPP, Atmospheric Environment, Volume 273, 2022, 118956, ISSN 1352-2310, https://doi.org/10.1016/j.atmosenv.2022.118956.
L. 295: it would be useful to add some more details (and a reference here to a volcanic dataset) where a reader can see the location and magnitude of the mentioned eruptions. I also think the claim that only Hunga reached the mid-stratosphere is a bit stretched, and the authors could provide some more details: in Li et al. (2023) for instance, the aerosols from La Sourfrier are clearly shown to reach 22-23 km.
Lastly on this point, it would be useful to acknowledge that Hunga was a peculiar eruption with a large stratospheric moistening, and discuss what this means for the air parcel and for the assumptions beyond the PSD.
Fig. 3 and Fig. 4 and Fig. 7, 8: The colors in these two figures are essentially impossible to understand when overlaid with the gray shading of the continents. Please only leave the countours of the continents and make the color constrat a bit sharper, or use black contour lines like the third row of Fig. 4.
L. 310: not sure “bins” is the right word here. Gridboxes?
L. 321: with all due respect to the Grainger PDF, which I’ve used often as well, as a reference with no permanent identifier is not really suitable for a journal. The internet often forgets…
Finally, I found the Conclusions particularly brief and dry. It seems to include some points that are more suitable for the Discussion section, and is lacking a final section that discusses future directions and an explanation of what this research contributes.
References
Li, Y., Pedersen, C., Dykema, J., Vernier, J.-P., Vattioni, S., Pandit, A. K., Stenke, A., Asher, E., Thornberry, T., Todt, M. A., Bui, T. P., Dean-Day, J., and Keutsch, F. N.: In situ measurements of perturbations to stratospheric aerosol and modeled ozone and radiative impacts following the 2021 La Soufrière eruption, Atmos. Chem. Phys., 23, 15351–15364, https://doi.org/10.5194/acp-23-15351-2023, 2023.

Citation: https://doi.org/10.5194/egusphere-2025-3984-RC1
- AC2: 'Reply on RC1', Christian Löns, 13 Oct 2025
  
  The comment was uploaded in the form of a supplement.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3984-AC2
CC2:
'Comment on egusphere-2025-3984', Farahnaz Khosrawi, 17 Sep 2025
I have read this manuscript with great interest. The authors present important new results that deserve to be published. However, I was quite disappointed about the presentation of the results (in terms of quality of the figures) and the text itself (too confusing, in some parts too lengthy and many statements without providing references). I will provide detailed comments below.
Major comments:
Introduction: 3.5 pages for an article introduction is much too long. I would suggest to shorten the introduction to 1.5-2 pages.

Figures: It would really be worth to increase all figure sizes, especially for the figures which consist of several panels and stereographic projections (Fig. 3, 4, 7 and 8). I also had trouble with the color scale. Therefore, I would suggest also to improve/change the color scales for some of them.

Discussion: In my opinion it would also be worth to shorten the discussion. This section was also too lengthy and in some parts confusing since it was not clear why specific things are discussed. See also my specific comments below.

Section 5: This section rather belongs to the method section or to an appendix.

Specific comments:
P2, L41: Dividing the atmosphere into three regions is useful only not only for understanding transport processes in the polar stratosphere, but also for understanding transport processes in the entire stratosphere.
P2, L41ff: Mention also how Plumb (2002) came up with the idea of dividing the stratosphere into three regions. Which method did he use? PDFs or tracer-tracer correlations?
P2, L54 or L70: Here, you could also add the reference of Khosrawi et al. (2005) who investigated the development of a streamer as measured by CRISTA and modeled with CLaMS and KASIMA. Also the study of Eyring et al. (2003) could be worth to be cited.
P2, L55ff: Add “e.g.” before the given reference since there are much more and you are providing here only some examples.
P3, L67-72: Add here some more newer references, too.
P3, L80f: References? I guess the stratospheric aerosol distribution in the vortex has previously been documented in the literature.
P3, L80: The connection between filaments in trace gas distribution and in aerosol distribution is not clear. This paragraph needs a better transition.
P4, L120-122: Don’t mention here each subsection, just summarize what is presented in Sect. 3.
P5, L127ff: This paragraph rather belongs to the introduction.
P5, L154: The first sentence of this paragraph is rather obsolete.
P6, L184: What do you do to overcome this? Is the affected SAGE III data still usable?
P6, L186: I would suggest to rephrase this sentence to be more clear. The ERA5 data itself is also data of a model simulation where observations have been assimilated into.
P7, L195: Add the time period.
P7, L198: Add references that document these volcanic eruptions.
P8, L204: When exactly was the maximum reached? Add the year or exact time period.
P8, L216: Why was there a higher background aerosol level? Has this been documented in the literature? References?
P8, L221-224: First, you mention less pronounced peaks and then a twofold increase. How does this fit together?
P9, Figure 2: I was wondering about your marking of the SSWs. I would have them expected during other times looking at this graph. While doing a quick search in the internet I found the paper by Roy and Kuttipurath (2022) where it is stated that the warmings in 2016/217 were in early January and early February.
P10, Figure 3: Increase the figure size and adjust color scale so that the differences in the aerosol distribution between the considered time periods become more obvious.
P11, Figure 4: Please increase the figure size and use a different color schemes than the current ones for PV and O3. Add also the time periods considered in the figure caption (or write a note that this are given in the plot title).
P12, 272: The transport barrier is between “air masses” not “air parcels”.
P12, in general: I had trouble to understand how you can investigate mixing processes while considering profiles. This needs more explanations and guidance for the reader.
P12, 275-276: “The agreement between anticyclone and subtropics…..” This does not make any sense for me.
P12, L282: Refer to the respective figure or add a reference.
P12, L285: This is not visible for me, even when I zoom into the figure.
P14, L307ff: This paragraph rather belongs to the method section.
P14, L327: How do you know that the mixing barrier was strong?
P14, L333: Why are you suddenly in this section focus on 2005? A motivation or transition between the sections is missing.
P15, Figure 7: Increase figure size and improve color scale.
P15, L345: Add the date and a reference.
P16, Figure 8: Increase figure size and use another color scheme for PV and O3.
P17, L360: To my knowledge, filaments do not necessarily occur in connection with anticyclones. I may be wrong, but this statement should be better elaborated.
P17, L361: Please check the dates for warmings again. See Roy and Kuttipurath (2022) who write that these were in early January and early February.
P17, L380: What is the connection between tropical-subtropical streamers and the polar vortex? To my knowledge streamers can also occur when there is no polar vortex (thus in other seasons than solely in winter time).
P17, L384: Add a reference.
P18, “observed signal”? Which exactly? Which parameter? Which figure are you referring to? Your study is using a completely different approach than previous studies, how can these then be compared?
P18, L401: Which model?
P18, L411: Add a reference. For me it is not clear how QBO phase is related to the results presented in your study. Why are you discussing this?
P17-19: The discussion is too lengthy and to confusing and should be shortened. Focus only on the important points and discuss these.
P19, Section 5: This section rather belongs to the method section or should be in an appendix.
P20, L485: Isn’t this a contradiction? If you have a streamer from the tropics to the subtropics, how is this then related to the polar region and the polar vortex?
P20, L465: In which direction is the flow of the streamer? From high to low latitudes or from low to high latitudes?
Technical corrections:
P2, L46 and 47: For better readability, instead of “it” it should be clearly mentioned what is meant.
P3, L80: Add this sentence to the previous paragraph.
P5, L144: remove comma and add “as”.
P6, L172: Instead of “several times” I would suggest to write “previously” or “in other studies”.
P6, L186: Add “meteorological” before “reanalyses”.
P8, L208: Add this sentence to the previous paragraph.
P10, L256: Chose a different term than “material”. Just name what exactly it is, either the respective trace gas or the aerosols.
P10, L258 and 259: Don’t write “it”, clearly state what exactly.
P12, L282: Add this sentence to the previous paragraph.
P14, L337: Add “e.g.” before the reference of Sonkaew et al.
P17, L372: Chose another term than “material”.
P17, L382: “structure’s trajectory” I would suggest to rephrase this.
P19, L426-428: Add these sentences to the previous paragraph.
P20, L470ff: Combine these sentences to one paragraph instead of several small paragraphs.

References:
Eyring, V., Dameris, M., Grewe, V., Langbein, I., and Kouker, W.: Climatologies of subtropical mixing derived from 3D models, Atmos. Chem. Phys, 3, 1007–1021, https://doi.org/10.5194/acp-3-1007-2003, 2003.
Khosrawi, F., Grooß, J.-U., Müller, R., Konopka, P., Kouker, W., Ruhnke, R., Reddmann, T., and Riese, M.: Intercomparison between Lagrangian and Eulerian simulations of the development of mid-latitude streamers as observed by CRISTA, Atmos. Chem. Phys., 5, 85–95, https://doi.org/10.5194/acp-5-85-2005, 2005.
Roy, R. and Kuttipurath, J., The dynamical evolution of Sudden Stratospheric Warmings of the Arctic winters in the past decade 2011–2021, SN Applied Sciences, https://doi.org/10.1007/s42452-022-04983-4, 2022.
Citation: https://doi.org/10.5194/egusphere-2025-3984-CC2
- AC3: 'Reply on CC2', Christian Löns, 13 Oct 2025
  
  The comment was uploaded in the form of a supplement.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3984-AC3
RC2:
'Comment on egusphere-2025-3984', Anonymous Referee #2, 01 Oct 2025

This article presents satellite observations of stratospheric steamers and frozen-in anticyclones in the enhancement of aerosol extinction at mid and high latitudes. This is the first study to document these phenomena using observations of stratospheric aerosols. The article demonstrates that these events can contribute significantly to the transport of sulphuric acid aerosols to the stratosphere at mid- and high-latitudes. The article is well-written and well documented. It provides new information on stratospheric air transport between tropical and higher latitudes following major SSWs. It is worthy of publication in Egusphere after a few minor revisions, as detailed below.

Line 32: The definition of major SSWs by the reversal of zonal wind at 60°N-10 hPa was first proposed by Labitzke (1981), well before Charlton and Polvani (2007).
Line 165: The phrase “vertical resolution greater than 7 km” may be confusing. I suggest “vertical resolution better than 7 km”.
Lines 180-184: It is true that the possibility of negative values for extinction can lead to a negative mean value, but conversely, the exclusion of negative values can lead to a positive bias in the mean value.
Figure 2: The zonal wind reaches a value close to 0 for the SSW event occurring at the end of February. I wonder if it should be classified as a major SSW.
Section 5: Sources of error: it would be preferable to place this section before the Discussion section.
Line 468-469: the sentence on the non-significant contribution of increased aerosol on the radiative transfer in the conclusions is not supported by any results in the text of the paper. It should be removed from the conclusions or supported by some argumentation in the core of the paper.

Citation: https://doi.org/10.5194/egusphere-2025-3984-RC2
- AC4: 'Reply on RC2', Christian Löns, 13 Oct 2025
  
  The comment was uploaded in the form of a supplement.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3984-AC4

Peer review completion

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

AR by Christian Löns on behalf of the Authors (22 Oct 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (03 Nov 2025) by Michael Pitts

RR by Farahnaz Khosrawi (06 Nov 2025)

Suggestions for revision or reasons for rejection

appreciate that the authors have taken my comments into account and revised their manuscript accordingly. Before publication I would like to ask the authors to consider the following technical corrections:

- P1, L3: ratio -> ratios
- P2, L23: What is meant with “frequently occuring zonal indicator”? Please revise.
- P2, L26: Here it needs to be shortly explained what the surf zone is.
- P2, L34: instead of “it” write clearly “the stratosphere” or write “ suggest a devision into three....” to avoid repetition of “stratosphere” in this sentence.
- P2, L39: Latest here it should be explained what the surf zone is (see my comment on L26).
- P3, L79: Mention/explain what the Junge layer is. At least the altitude where the Junge layer is found should be added.
- P3; L83: Here you should clearly state that the dynamic effects and meteoric or space debris contribute to particle formation. Otherwise the sentence is not clear and rather misleading. You could simply write “particle formation due to dynamic effects, meteoric or space, debris”.
- P3, L85: Also here for clarity a short explanation what the subduction zone is would be useful.
- P3, L103: add “instrument” so that it reads “remote sensing instruments”.
- P5, L130: height -> altitude
- P6, L181: Add this sentence to the next paragraph to avoid having a paragraph consisting of one sentence.
- P6, L188 and throughout the manuscript: Omit space between figure number and panel label, e.g. Fig. 1 e should read Fig. 1e.
- P7, Fig 1 caption and throughout the manuscript: Check the Copernicus guidelines, if I remember it correctly northern and southern hemisphere is written beginning with small letters.
- P10, L245: it -> be more clear. What exactly?
- P10, L252: “Fig.” before figure number missing. It should read “Fig. 4l”.
- P12, Fgure 5 caption: omit “0” and just write “4” and “5” March.
- P13, Figure 6 caption: same here as fo P12 Figure 5, omit the “0”.
- P13, L292: Has the abbreviation “PSD” been introduced? If the term is only used for a few occasion I would suggest to rather skip using this abbreviation for better readability.
- P18, L373: depend -> depends
- P19, L425: Add also respective altitude in km.
- P19, L436: Omit “of the atmsopheric state”.
- P20, L444: Here zyou write “sulphuric”, before you wrote “sulfuric”. Use a consistent writing.
Reference list: The reference of Khosrawi is imcomplete. The co-authors as well as the journal number and doi are missing.

Hide

RR by Anonymous Referee #1 (07 Nov 2025)

ED: Publish subject to minor revisions (review by editor) (21 Nov 2025) by Michael Pitts

AR by Christian Löns on behalf of the Authors (26 Nov 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (26 Nov 2025) by Michael Pitts

AR by Christian Löns on behalf of the Authors (27 Nov 2025) Author's response Manuscript

Short summary

During the polar vortex season, so-called streamers can transport tropical air towards the pole in the middle stratosphere. This tropical air can get trapped in high-pressure areas at high latitudes after the polar vortex breaks down. In this study, remote sensing instruments are used to observe the course of such streamers by measuring the scattered solar radiation. Aerosols get transported to high latitudes at an altitude of about 25–35 km, increasing the aerosol mass there significantly.