Stratospheric impact on the Northern Hemisphere winter and spring ozone interannual variability in the troposphere

Liu, Junhua; Rodriguez, Jose M.; Oman, Luke D.; Douglass, Anne R.; Olsen, Mark A.; Hu, Lu

doi:https://doi.org/10.5194/acp-20-6417-2020

Articles | Volume 20, issue 11

https://doi.org/10.5194/acp-20-6417-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-6417-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 11

Research article

|

04 Jun 2020

Research article |

| 04 Jun 2020

Stratospheric impact on the Northern Hemisphere winter and spring ozone interannual variability in the troposphere

Junhua Liu, Jose M. Rodriguez, Luke D. Oman, Anne R. Douglass, Mark A. Olsen, and Lu Hu

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Final revised paper (published on 04 Jun 2020)
Supplement to the final revised paper
Preprint (discussion started on 21 Oct 2019)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of "Liu et al., Stratospheric impact on the Northern Hemisphere winter and spring ozone interannual variability in the troposphere", https:doi.org/10.5194/acp-2019-825', Anonymous Referee #1, 16 Nov 2019
RC2: 'Review on ACP Manuscript No. ACP-2019-825', Anonymous Referee #2, 26 Nov 2019
RC3: 'Review of "Stratospheric impact on the Northern Hemisphere winter and spring ozone interannual variability in the troposphere"', Anonymous Referee #3, 18 Dec 2019
SC1: 'Comment by R. S. Williams et al. (2019)', Ryan Williams, 23 Dec 2019
AC1: 'Response to reviews', Junhua Liu, 15 Feb 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Junhua Liu on behalf of the Authors (15 Feb 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (24 Feb 2020) by Andreas Engel

RR by Anonymous Referee #1 (29 Feb 2020)

Suggestions for revision or reasons for rejection

1) Please include upfront a clear definition including one that is mathematical of what you mean by IAV
2) The paper needs to be grammar checked; in particular pay close attention to verb tense.
3) When introducing the model runs on line 77, make sure you note clearly this a specified-dynamics, or replay or nudged run
4) line 98/99 related to #3, Davis et al just published a paper detailing issues regarding STE and nudged climate model runs. (see DOI 10.5194/gmd-13-717-2020). Bottom line is that with at least some nudging techniques the vertical transport that is the input (ie, like the MERRA2 winds) is not what you get after the nudging occurs, and it can give incorrect trends. A comparison of what you call IAV in a free running model with what you have in the replay version (of course using the same chemistry) would be useful. This may be beyond the scope of this study, but could impact some of your results. I would strongly encourage the authors to consult Dr. Orbe (who's paper they cite) as to possible deficiencies in the results presented here.
5) StratO3: The description of the quantity needs to be improved. I don't understand how you are tagging stratospheric ozone and I also would like to see some statement as to how using E90 as a tropopause definition compares to using an actual tropopause definition (such as PV or the vertical temperature gradient).
6) line 131 (section 3); One of the other reviewers commented that there seems to be two topics, model validation and then the tropospheric ozone analysis. Is the issue that this way of running the model has not been validated with respect to tropospheric ozone? Perhaps there should also be a model validation paper, or if not, then this section might be better as supplementary material or as an appendix, because it distracts from the main science being presented.
7) line 167 and subsequent paragraph: What is impact? It needs some reworking. And, also on the line, are you referring to the mean flux of ozone from stratosphere to troposphere (or mass flux...ie see Appenzellar et al, 1996, JGR, 10.1029/96JD00821).
8) Some of the terminology is kind of confusing...specifically when you talk about explaining the variance of the IAV (which is already a variation). I think you're explaining the variance of ozone, not the ozone IAV. Giving a mathematical definition of IAV may help.
9) The paper really needs to have the language cleaned up in regards to the way it talks about variations and variance and changes. One example, the text states on line 232/233 "The IAV of StratO3 tracer in the troposphere reflects a combined effect of the changes in the lower stratospheric O3 concentrations and in the strength of stratosphere-to- troposphere (STE) mass flux." I think what you're saying is that variability in the amount of tropospheric ozone that was transported from the stratosphere is due to both variability in the lower stratospheric ozone reservoir and variability in the net downward mass flux. (and Albers et al, JGR, 2018, doi 10.1002/2017JD026890 would be a reasonable reference for that).
10) One comment: Line 271/272 says " The difference in the stratospheric O3 influence between North America and Europe is likely due to longitudinal difference in dynamics." I am not sure what that actually means. Perhaps better would be to say it is due simply to the existence of planetary scale waves (which are part of dynamics). I have a similar comment regarding line that states " Figure 7 illustrates the relationship of StratO3/O3 ratio at 400 hPa to dynamics ..." You are not illustrating a relationship to dynamics, but to specific quantities.

11) This is another sentence that is confusing: "The vertical airmass flux is calculated by multiplying w (the volume flow rate, which depends on the pressure difference) with the density of air." Isn't omega dp/dt? (I'm not sure what a volume flow rate means here) And, I would just refer to it as the downward mass flux (rather than vertical airmass flux). And, this is another confusing statement " The jet locations, approximated by the strongest winds". Jet locations are where the strongest winds are, they're not approximated. The rest of this paragraph (centered around line 315) needs to be rewritten. Make sure that all of the co-authors concur with these descriptions (Several of the paper's co-authors should be able to help make this much more understandable. They should also be able to help with the grammar issues that perhaps will also be dealt with by a copy editor.)
12) lines 358/259 states " Our analysis suggests that the IAV of wave disturbances in the westerlies likely affect the IAV of the regional distributions of prevailing wind patterns as well as the strength of STE flux. " Wave disturbances (or better, just waves) and wind are going to co-vary, and the location where tropopause folds occur will co vary with the waves too. This whole discussion needs to be rewritten.
13) The overall results of this study seem to be
a) from the first part, the model seems to do OK at reproducing means and variability as based on comparisons with SBUV and sondes (and this should be an appendix or supplement.)
b) temporal variability in tropospheric ozone in the NH mid latitudes is related to temporal variability in the transport of ozone from the stratosphere
c) there is a difference in the degree of influence of stratospheric ozone on tropospheric ozone between North America and Europe. This is essentially a function of the spatial distribution of regions of tropopause folding type events, which is really a consequence of the different synoptic patterns the occur over Europe and North America.
None of this is really new information, but the particular analysis they do with the stratospheric tracer is fine to publish. They acknowledge a significant number of past similar studies that were done with global scale models. Although they do reference the Lin et al. CalNex paper (however, they do need to fix the citation, the paper was published several years ago), they do not acknowledge that the western US air quality issue related to STE has been studied extensively with aircraft and ground fieldwork, and I would encourage the authors to take a look at some of the papers from the LVOS experiment led by Andrew Langford.
14) General impression; The authors need to reread all the original reviewer's comments, and respond to those comments in a more thorough manner.

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RR by Anonymous Referee #2 (04 Mar 2020)

Suggestions for revision or reasons for rejection

I would like to thank the authors for taking my comments into account and revising the manuscript accordingly. However, one of my comments did not came across well. I did not mean that the model evaluation is unnecessary. My point was that the weighting how the results were described was not done in the correct way. There was to much focus on the evaluation instead of the investigation of the IAV which was supposed to be the main focus of the paper. However, with the revisions done the manuscript reads now much better and I do not feel any mismatch any longer.

Nevertheless, I have several technical comments that should be considered before publication:

P2, L45: “replay simulations” → I would suggest to either skip here “replay” or you explain what is meant with replay simulations. Alternatively, you could also add the reference to the Orbe et al. 2017 paper if you do not want to skip replay.

P2, L63: I would suggest to skip “tropospheric” since this is confusing. Usually, CTMs simulate the entire atmosphere. If you want to emphasize that the simulation run had a focus on the troposphere it should be said more clearly.

P2, L73: Plural or singular? Thus, either “used a nudged CCM simulation” or “ used nudged CCM simulations”.

P3, L101: Sentence “More detailed information on replay methodology can be found in Orbe et al. (2917)” is obsolete since you refer to the replay simulation and the Orbe et al. reference already a few sentences before.

P4, L127: in UTLS → in the UTLS

P4, L150: Centers → Center

P4, L159: Model did not → The model did not

P5, L168: relatively weaker → I would suggest to either write “relatively weak” or “weaker”.

P5, L171: observed ozone → specify which observations

P5, L183: lost parentheses at the end of the sentence.

P5, L203: …..IAV is mall, only become significant…..→ sentence not clear, please rephrase

P7, L275: by Browell et al. (Browell et al., 1996) → by Browell et al. (1996)

P9, L350: shows the → shows a

P9, L355: weakend descending air → please rephrase, e. g. to “weak descending air”

P10, L376: N. America → North America

P10, L394: near surface → near the surface
P10, L398: show a similar → shows a similar

P10, L403: tropospheric O3 in the troposphere → repetition, please rephrase

P15, Table2: Ny Aleasund → Ny Alesund

P16, Figure 1: Ny Aleasund → Ny Alesund

P18, Figure 4 and Figure 5: Figures should be done in a consistent way. Here, the x-axis labeling is missing (add year) and the headers should be written in the same way (same font, same abbreviation for North America).

P19, Figure 6: Same here as for Figures 4 and 5. Additionally, remove the y-axis labeling in the middle of the figures. N. Am should be N. American toe be consistent and height of the right 4 figures should be adjusted to the left 4 figures.

P19, Figure 6 caption: top → Top, bottom → Bottom

P20 and 21, Figures 7 and 8: Increase space between the panels. What is the additional colour bar (light pink) for? Cannot this be skipped?

P20, Figure 7 caption: Do not start sentence with a number → sentence should be rephrased.

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ED: Publish subject to minor revisions (review by editor) (05 Mar 2020) by Andreas Engel

AR by Junhua Liu on behalf of the Authors (20 Mar 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (27 Mar 2020) by Andreas Engel

AR by Junhua Liu on behalf of the Authors (27 Mar 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (14 Apr 2020) by Andreas Engel

AR by Junhua Liu on behalf of the Authors (17 Apr 2020) Author's response Manuscript

ED: Publish subject to technical corrections (04 May 2020) by Andreas Engel

AR by Junhua Liu on behalf of the Authors (06 May 2020) Author's response Manuscript

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Short summary

Our paper quantifies and identifies the importance of stratospheric ozone influence on the tropospheric ozone IAV in Northern Hemisphere mid-high latitudes. Our analysis provides an in-depth understanding of how 3-D dynamics influences the O₃ redistribution in the troposphere. These findings are particularly important considering the potential changes in these dynamical conditions in the future as a result of climate change