the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Statistical analysis of observations of polar stratospheric clouds with a lidar in Kiruna, northern Sweden
Peter Voelger
Peter Dalin
Abstract. In the present paper, we analyze 11 years of lidar measurements to derive general characteristics of Polar Stratospheric Clouds (PSCs) and to examine how mountain lee waves influence PSC properties. Measurements of PSCs were made with a backscatter lidar located in Kiruna, northern Sweden, in the lee of the Scandinavian mountain range. The statistical analysis demonstrates that nearly half of all observed PSCs consisted of nitric acid trihydrate (NAT) particles while ice clouds were only a small fraction, supercooled ternary solution (STS) and a mixture of different components making up the rest. Most PSCs were observed around 22 km altitude. Mountain lee waves provide a distinct influence on PSC chemical composition and cloud height distribution. Ice PSCs were about 5 times as frequent and NAT clouds were about half as frequent under wave conditions. PSCs were on average at 2 km higher altitudes when under the influence of mountain lee waves.
Peter Voelger and Peter Dalin
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2022-1163', Farahnaz Khosrawi, 21 Nov 2022
Voelger and Dalin analyse 11 years of lidar measurements that were performed in Kiruna to derive the general characteristics of polar stratospheric clouds (PSCs) and to examine the influence of lee waves on the properties of the polar stratospheric clouds in this area. They find clear differences between PSC formed at wave conditions and PSC formed solely by synoptic cooling. This is a nice and interesting study and I have only suggestions for minor revisions before publication in ACP.
Specific comments:
P2, L32: Here, I am not sure if you generally refer to clouds or if you mean PSCs. You should rephrase the sentence to be more clear. In case you mean clouds in general you should provide more details. If you mean PSCs when you should replace “clouds” by “PSC”.
P2, L34: I would suggest to rephrase the sentence. As suggestion is as follows: “The statistic based on the CALIPSO data has resulted in a global PSC climatology.” You could also mention how long their data sets were that have been taken into account to derive the climatologies.
P2, L44: There is a recent study by Tence et al. (ACP discussions) analysing the Durmont d’Urville data which would be worth to be mentioned here additionally to Santacesaria et al. (2001).
P2, L54ff: You should provide a short explanation or measure for the different scale of these waves.
P3, L66: Also here it is not clear if you mean cloud in general or PSCs. Please clarify and rephrase accordingly.
P3, L68: Add here how they affect ozone depletion (thus by the reactions on the surface of the PSC particles).
P3, L78: Here some more recent publications from the e.g. RECONCILE (Dörnbrack et al. (2012), see https://acp.copernicus.org/articles/special_issue228.html) or POLSTRACC (https://acp.copernicus.org/articles/special_issue913.html) campaigns should be added.
P4, L95ff. It would be nice if you could add here more details on how many measurement days and how many hours of measurements you derived in the considered 11-year period.
P5, Sect. 3: It would be nice if you could give examples for cold and warm winters, respectively, and how these winters are reflected in your statistic shown in Figure 1.
P5, L135: Yes, this is indeed the peak season for PSCs in Kiruna. Indeed, most PSCs appeared in January since the vortex is then usually quite stable and it becomes sufficiently cold. Are these climatological features documented somewhere? It would be nice if you could add a reference.
P6, L149: You shouldn’t write it that simple with just one short sentence. As you write it it can easily be misunderstood and it does not reflect what Achert and Tesche (2014) actually concluded. You should add more details when which scheme performs best (or write it specific to your data) since Achtert and Tesche (2014) provided clear statement for which data which schemes is most suitable.
P6, L164: This statement is not correct. STS forms at much higher temperatures, namely already at 192-193 K (see Tritscher et al., they write at Tice+4 K, which with Tice at 188 K corresponds to 192 K). Thus, this does not explain really why you observe mostly NAT particles over Kiruna.
P7, Figure 2 caption: In the figure you use the abbreviations “NAT”, “STS” and “ice”, but in the caption you write “Type1a”, “Type 1b” and Type2”. You should be consistent and use only one way of writing (or add STS, NAT and ice in parentheses).
P8, Figure 4: Would it be possible to also plot the height distribution separated by PSC type? This would be quite interesting to see.
P9, Figure 5: Add here also in the legend STS, NAT, and ice (respectively).
P9, 198: Here you should add a sentence about the quality of the ER5 winds. How reliable are these?
P11, L226: The height difference between non wave clouds and wave clouds is a quite interesting result. However, do you have an explanation why the wave clouds are found at higher altitudes? I would rather have expected the opposite result.
P11, 229: Also here you should add some more recent references than just Fleming et al. (2011).
P11, L231: The relationship between PSCs and water vapour trends was investigated by e.g. Khosrawi et al. (2016) and Thölix et al. (2016). Both did not find any significant trend in H2O so far. Their results should be discussed as well.
P12, Figure 9: Also here it would be really nice if you could add this figure separated by PSC type.
Technical corrections:
P1, L14: “HNO3” should be written in an upright font.
P1, L13-15: I would suggest to more clearly write:”…...by the formation of nitric acid containing PSC particles and…….…”
P2, L27: multiyear → multi-year (?)
P2, L29: I would suggest to also already here to provide the references of Pitts et al. (2018) and Spang et al. (2018).
P2, L32: Better to write “PSC” instead of just “clouds”. See also my specific comment.
P2, L34: add “as e.g. MIPAS” after “techniques”.
P3, L62: “several years or more”. I would suggest to rewrite this to “at least several years, but rather a decade or more”.
P3, L73: groundbased → ground-based
P3, L85: I would suggest to rather name this section “Data and Method” than “Tools”.
P7, L181: Not the PSC has the temperature, it’s the air that has a certain temperature. Thus, the sentence should be rewritten. You could e.g write “…...PSCs at higher altitudes more likely encounter low temperatures”.
P14, L269: fomration → formation
P15, L309: poole → Poole
P16, L330: HNO3/H2O should be written in an upright font.
P16, L330: ER 2 → ER-2
P16, L332: typo in “role“
References:
Dörnbrack, A., Pitts, M. C., Poole, L. R., Orsolini, Y. J., Nishii, K., and Nakamura, H.: The 2009–2010 Arctic stratospheric winter – general evolution, mountain waves and predictability of an operational weather forecast model, Atmos. Chem. Phys., 12, 3659–3675, https://doi.org/10.5194/acp-12-3659-2012, 2012.
Tencé, F., Jumelet, J., Bouillon, M., Cugnet, D., Bekki, S., Safieddine, S., Keckhut, P., and Sarkissian, A.: 14 years of lidar measurements of Polar Stratospheric Clouds at the French Antarctic Station Dumont d'Urville, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2022-401, in review, 2022.
Thölix, L., Backman, L., Kivi, R., and Karpechko, A. Yu.: Variability of water vapour in the Arctic stratosphere, Atmos. Chem. Phys., 16, 4307–4321, https://doi.org/10.5194/acp-16-4307-2016, 2016.
Khosrawi, F., Urban, J., Lossow, S., Stiller, G., Weigel, K., Braesicke, P., Pitts, M. C., Rozanov, A., Burrows, J. P., and Murtagh, D.: Sensitivity of polar stratospheric cloud formation to changes in water vapour and temperature, Atmos. Chem. Phys., 16, 101–121, https://doi.org/10.5194/acp-16-101-2016, 2016.
Citation: https://doi.org/10.5194/egusphere-2022-1163-RC1 -
RC2: 'Comment on egusphere-2022-1163', Anonymous Referee #2, 06 Dec 2022
Review of ‘Statistical analysis of observations of polar stratospheric clouds with a lidar in Kiruna, northern Sweden’, by P. Voelger and P. Dalin.
Summary:
Voelger and Dalin use a ground-based lidar located in Kiruna to present a climatology of polar stratospheric cloud characteristics from 11 winters of observation. The authors note that their observing location is in the lee of a major mountain range, resulting in an influence on PSC composition and mean altitude seen above Kiruna. Specifically, the properties of PSCs are different in the presence of mountain waves than in their absence. Voelger and Dalin discuss their climatology in the context of results from other locations.
Overall, the paper is well written, informative, and contains information worthy of publication. The paper is however too succinct, in that more discussion and placing your results into previous studies (ground-based and satellites) is needed. You could either create a separate Discussion section to achieve this, or, add paragraphs at the end of each section discussing the figure. Further, inconsistencies in labelling (i.e Type1a / NAT etc) is noted throughout, and forms a major distraction from the manuscript. However, I suggest that these issues can all be satisfied following ‘minor revisions’.
Minor Comments:
Line 76: Readily noting that this is beyond the scope of your work, but I wonder whether the radar which Rao et al (2008) used can be used for a future study to combine mountain wave PSC observations seen with lidar (as per your paper) and vertical wave motion in the UTLS which should be readily observable with the VHF radar? Is it still operating? Such a study might help elucidate the perennial limitation with ground-based lidar observations of PSCs which can only be performed in clear weather, i.e. when do you observe strong mountain wave activity with the radar, but it’s too cloudy to observe with the lidar?
Figure 2 caption: Need to be consistent between your caption (Types Ia, Ib, II) and your figure (‘ice’, ‘NAT’,’STS’) and throughout the text (and in other figures, e.g. Figure 8). As most ground-based lidar papers refer to the ‘Types’, you could if you choose go with that in your text and figures. But I’d still recommend a discussion of how these relate to the satellite-derived PSC classes. On the other hand, Tritscher et al. (2021) note these ‘type’ classifications are outdated and are not recommended any more (their Section 1.3), and this is what I’d prefer to see (i.e. switch to NAT, STS, etc. throughout).
Figure 2; why not indicate lines for the boundaries rather than these ellipses, which don’t seem physically based?
Figure 2 and Figure 7: It might be worth considering plotting these as perpendicular backscatter vs scattering ratio (e.g. Tritscher et al 2021 Figure 2, or Pitts et al 2018 Figure 5b), as used for CALIOP v2 PSC observations? That should make discussions and comparisons easier (see comments above noting the need to have a much-expanded discussion of your results).
Figure 4 and 9 could (should) be normalised.
Line 155: The point could be made that while ‘hard’ boundaries between PSC types are used, in reality the boundaries are somewhat fuzzy (see discussion in Pitts et al 2018, their Section 3.3). The same point would apply to ground-based observations.
Line 220 and following: Essentially you are discussing here (or accounting for) differences between your climatology and the Arctic-wide satellite distributions. Perhaps an expanded discussion on ‘mother-cloud’ seeding is warranted here, and may help tie your point-source, ground-based results into the regional scale (i.e. over mountains and downwind of mountains) PSC satellite observations and more regional-scale aircraft observations (and modelling studies) above and downwind of the Scandinavian mountains (e.g Dörnbrack et al. 2002 JGR) and over polar mountains more generally.
Figure 6: Probably more useful to show these as a fraction of ‘conditions favorable for mountain waves’ rather than actual number of hours?
Figure 7: As for Figure 6, why not normalize these plots so you can quantify and compare the relative changes. Also, I suggest you add in the PSC type (or better, class) boundaries.
Figure 9: You could also include each PSC class as a function of altitude too.
Figure 9b: Temperature decreases in the cool phase of the wave should induce some PSC formation at lower altitudes. Do you find any examples of these in your time series?
Data availability: check that your ‘lidar data is available on request’ is consistent with the journal. A permanent doi linking to the data is, I believe, much preferred.
Citation: https://doi.org/10.5194/egusphere-2022-1163-RC2 -
AC1: 'Comment on egusphere-2022-1163', Peter Voelger, 07 Feb 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1163/egusphere-2022-1163-AC1-supplement.pdf
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AC2: 'Comment on egusphere-2022-1163', Peter Voelger, 07 Feb 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1163/egusphere-2022-1163-AC2-supplement.pdf
Peter Voelger and Peter Dalin
Peter Voelger and Peter Dalin
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