Global seasonal distribution of CH2Br2 and CHBr3 in the upper troposphere and lower stratosphere

Jesswein, Markus; Fernandez, Rafael P.; Berná, Lucas; Saiz-Lopez, Alfonso; Grooß, Jens-Uwe; Hossaini, Ryan; Apel, Eric C.; Hornbrook, Rebecca S.; Atlas, Elliot L.; Blake, Donald R.; Montzka, Stephen; Keber, Timo; Schuck, Tanja; Wagenhäuser, Thomas; Engel, Andreas

doi:https://doi.org/10.5194/acp-22-15049-2022

Articles | Volume 22, issue 22

https://doi.org/10.5194/acp-22-15049-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-22-15049-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 22

Research article

|

25 Nov 2022

Research article |

| 25 Nov 2022

Global seasonal distribution of CH₂Br₂ and CHBr₃ in the upper troposphere and lower stratosphere

Markus Jesswein, Rafael P. Fernandez, Lucas Berná, Alfonso Saiz-Lopez, Jens-Uwe Grooß, Ryan Hossaini, Eric C. Apel, Rebecca S. Hornbrook, Elliot L. Atlas, Donald R. Blake, Stephen Montzka, Timo Keber, Tanja Schuck, Thomas Wagenhäuser, and Andreas Engel

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Final revised paper (published on 25 Nov 2022)
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Preprint (discussion started on 19 Jul 2022)
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Interactive discussion

Status: closed

RC1: 'Comment on acp-2022-472', Anonymous Referee #1, 12 Sep 2022

This paper discusses the global and seasonal distribution of two short lived brominated compounds based on multiple aircraft measurement campaigns as well as two global models. The data compilation and discussion of the main features are well done and the comparison with the model output reveals some shortcomings in our ability to accurately model these compounds in certain seasons and hemispheres. The data discrepancy between instrument data sets in the fall SH lowermost stratosphere is significant and hampers the ability to make conclusions about transport differences between the SH and NH LMS. But this is important to point out as clearly as is done here since it shows the data are also not perfect and that we need more measurements in data poor regions to help us understand how models perform throughout the atmosphere.

Overall, I find this paper is acceptable for publication in ACP with consideration of the few minor comments listed below. In particular, Section 4.3 is far too heavy on the specific listing of mixing ratio values at various parts of the profiles to the detriment of reader comprehension of the main points of the section.

Specific comments:

Line 31: There’s an extra ‘to’ here, maybe remove the first one.

Lines 49-50: Add ‘tropospheric’ after ‘extratropical’ here.

Figure 4: This is important to show the uncertainty that can exist between data from different instruments and how it can defy easy explanation. It’s unfortunate that the discrepancy is so large in the region and time of interest but this makes it even more important to point out as you have done.

Line 261: ‘as’ should be ‘has’

Line 276: ‘tropospheric’ misspelled

Line 380: ‘close’ misspelled

Section 4.3: Starting at about line 370 I really had trouble staying focused while reading this section because there are far too many listing of exact ppt values for each species at various levels and seasons. This is in contrast to Sections 4.1 and 4.2 that were easy to follow and had many interesting features. I would suggest removing nearly all mention of exact mixing ratios in the text, the numbers are in the figures if anybody wants to see them, and stick with describing the main points you want to discuss.

Citation: https://doi.org/10.5194/acp-2022-472-RC1
RC2: 'Review comment on acp-2022-472', Anonymous Referee #2, 19 Oct 2022

General comments:

The manuscript “Global seasonal distribution of CH2Br2 and CHBr3 in the upper troposphere and lower stratosphere” written by Markus Jesswein, et al. presents seasonal cycles of CH2Br2 and CHBr3 in the global UTLS regions based on the combined analysis of multiple aircraft-campaign observation data and chemical transport models. The paper contains novel investigation to reveal seasonal cycles of CH2Br2 and CHBr3 in the UTLS of the northern and southern hemispheres and is generally well written, organized, and designed, but quantitative and clear descriptions are missing in some parts of the manuscript. It should be accepted for publication pending a modification of minor points. I provide general and specific comments that need to be addressed before moving forward publication processes below.

1. Please clarify what novel findings were made by integrating and analyzing data from the northern and southern hemispheres in the abstract and summary sections.

2. Can the limited temporal and spatial sampling, especially in the southern hemisphere, affect the conclusion of this paper? However, there is no quantitative discussion on such effects; could they be assessed using TOMCAT and CAM-Chem model data?

3. The methodology, especially the section on analytical methods, is insufficient. I would like additional explanation. Seems like different methods (e.g., with respect to equivalent latitude, sampling, etc.) were applied for observations and models, but I'm confused. Please sort them out.

Specific comments:

p. 1, l. 12: “the same emission inventory” What emission inventory?

p. 2, l. 18-19: “Thus, both models reproduce equivalent “flushing” in both hemispheres, which is not confirmed by the available observations.”ãWhat does it mean that the models are reproducing a phenomenon not confirmed by observation?

p. 6, l. 175: “with fixed emissions of the VSLS during the whole modeling period” What time resolution is the emission data, Annual or monthly climatology?

p. 7, l. 188-200: 1) It would be better to separate this section as analysis methods.

2) From what data were the equivalent latitudes and temperatures calculated for the observational and model data analysis, respectively?

3) Please clarify which sections latitude-altitude, θ, Δθ, and equivalent latitude coordinate systems are used for.

4) Please clarify how do you sample the model data, along the aircraft tracks or regional mean?

p. 8, l. 221: “While the distribution of CH2Br2 in hemispheric spring is quite similar, …” What is similar to what, the distributions of NH and SH?

p. 8, l. 222: “… differs with smaller values in the SH compared to the NH” How much is the difference?

p. 9, l. 258: “Ordonez et al. (2012) already identify some issues regarding…” Please clarify what issues were identified?

p. 9, l. 266: “Nonetheless, the NH shows larger values in autumn and winter compared to spring and summer …” How much?

p. 10, l. 308-309 “Both models quantitatively reproduce the larger CH2Br2 values in hemispheric winter and spring and smaller values in summer and autumn (see Fig. S3).” Which latitude bands does this statement refer? The models do not look like reproducing the observed seasonality of CH2Br2 in low latitudes.

p. 12, l. 382: “hemispheric autumn profiles of CH2Br2 and CHBr3 are less similar than in hemispheric spring.” What is less similar, profiles of CH2Br2 and CHBr3 or profiles in the NH and SH?

p. 13, l. 386; “Differences between the hemispheres become larger on lowest levels above the dynamical tropopause, i.e., in the ExTL.” Compared to what, do the inter-hemispheric differences become larger?

Figures 2 and 3: What is the reason for missing values in the lower stratosphere in the TOMCAT model? (Second row).

Figures 5 and S1: description of line colors are missing.

Citation: https://doi.org/10.5194/acp-2022-472-RC2
AC1: 'Responses to referees', Markus Jesswein, 03 Nov 2022

We would like to thank both reviewers for their comments on our manuscript. Please find attached our responses and a mark-up version of the manuscript.

Citation: https://doi.org/10.5194/acp-2022-472-AC1

Peer review completion

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

AR by Markus Jesswein on behalf of the Authors (03 Nov 2022) Author's response Author's tracked changes Manuscript

ED: Publish as is (05 Nov 2022) by Aurélien Dommergue

AR by Markus Jesswein on behalf of the Authors (08 Nov 2022) Author's response Manuscript

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Short summary

This study presents the global and seasonal distribution of the two major brominated short-lived substances CH₂Br₂ and CHBr₃ in the upper troposphere and lower stratosphere based on observations from several aircraft campaigns. They show similar seasonality for both hemispheres, except in the respective hemispheric autumn lower stratosphere. A comparison with the TOMCAT and CAM-Chem models shows good agreement in the annual mean but larger differences in the seasonal consideration.