the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Sep 2025
Observations of stratospheric streamers and frozen-in anticyclones in aerosol extinction
Abstract. When the polar vortex meanders and shifts towards the equator, air masses from the tropics and subtropics can be transported towards the pole in so-called tropical-subtropical streamers. These large-scale structures are areas of low potential vorticity and high pressure, containing dry air with a high ozone mixing ratio. The presence of these streamers can also be seen in changes in stratospheric optical properties. Satellite instruments such as OMPS-LP measuring the limb scattering of these aerosols are capable of observing an increase in the aerosol extinction coefficient in the mid-stratosphere at the edge of the vortex. The high spatial sampling of the limb instrument ensures that the trajectory of the streamer can be accurately monitored. Following a displacement and deformation of the vortex, aerosol transport to high latitudes occurred in the Northern Hemisphere in spring 2017. The additional stratospheric aerosol mass of around 1,000 t at an altitude of 24–38 km remained at middle and high latitudes for just under a month this year. This aerosol mass increase resulted in an estimated 70 % rise in the total mass within this altitude range at high latitudes. Frozen-in anticyclones, in which low latitude air is trapped in the circulation at high latitudes after the end of the polar vortex, can also be observed in the aerosol extinction coefficient. The observation of a particularly long-lived anticyclone in 2005, which is visible in the aerosol extinction coefficient, is presented. This is the first study documenting streamer events and frozen-in anticyclones in stratospheric aerosols.
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Status: open (until 17 Oct 2025)
- CC1: 'Comment on egusphere-2025-3984', Lynn Harvey, 10 Sep 2025 reply
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RC1: 'Comment on egusphere-2025-3984', Daniele Visioni, 10 Sep 2025
reply
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 -
CC2: 'Comment on egusphere-2025-3984', Farahnaz Khosrawi, 17 Sep 2025
reply
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
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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