Summer aerosol measurements over the East Antarctic seasonal ice zone

Simmons, Jack B.; Humphries, Ruhi S.; Wilson, Stephen R.; Chambers, Scott D.; Williams, Alastair G.; Griffiths, Alan D.; McRobert, Ian M.; Ward, Jason P.; Keywood, Melita D.; Gribben, Sean

doi:https://doi.org/10.5194/acp-21-9497-2021

Articles | Volume 21, issue 12

https://doi.org/10.5194/acp-21-9497-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-9497-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 12

Research article

|

23 Jun 2021

Research article |

| 23 Jun 2021

Summer aerosol measurements over the East Antarctic seasonal ice zone

Jack B. Simmons, Ruhi S. Humphries, Stephen R. Wilson, Scott D. Chambers, Alastair G. Williams, Alan D. Griffiths, Ian M. McRobert, Jason P. Ward, Melita D. Keywood, and Sean Gribben

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Final revised paper (published on 23 Jun 2021)
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Preprint (discussion started on 26 Nov 2020)
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Interactive discussion

Status: closed

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

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RC1: 'Review of Simmons et al., "Summer aerosol measurements over the East Antarctic seasonal ice zone"', Anonymous Referee #1, 21 Dec 2020
- AC1: 'Reply on RC1', Jack Simmons, 30 Mar 2021
RC2: 'Review of "Summer aerosol measurements over the East Antarctic seasonal ice zone” by Simmonds et al.', Anonymous Referee #2, 28 Dec 2020
- AC2: 'Reply on RC2', Jack Simmons, 30 Mar 2021

Peer-review completion

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

AR by Jack Simmons on behalf of the Authors (01 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (02 Apr 2021) by Lynn M. Russell

RR by Anonymous Referee #3 (12 Apr 2021)

Suggestions for revision or reasons for rejection

This manuscript by Simmons et co-authors presents a new set of aerosol observations during a summer cruise from Tasmania to East Antarctica. Given the scarcity of observational data in this region, the manuscript will be a nice addition to the literature. The authors have significantly improved the quality of the manuscript and addressed most of the concerns raised by the two reviewers. However, I think some more work is needed before it can be accepted for publication in Atmospheric Chemistry and Physics.

Main comments:

- The structure of the discussion must be revised. The description of categorization by wind direction and absolute humidity should be part of the Methods section. Another option is to start the Results and Discussion section with this description. Lines 223-292 should be moved further down, after the description of the categorization method. Figure 2 does not make any sense when referred to and discussed before this description. My recommendation is to start with the description of this method, and then, to present and discuss aerosol results.

- SIPEX-II / PCAN comparison:

1. while the authors highlight the difference in sea-ice extent in Figure 1, this is not mentioned later in the discussion. Could the different environmental conditions explain part of the differences during the two campaigns?
2. In addition, the authors do not fully address the point made by reviewer #2 about the description of the inlet system. The description of the sampling inlet and associated inlet losses on the Investigator are a welcome addition to the manuscript. However, it does not explicitly tell how the two systems compared. The authors mentioned in their response that the inlet system used on Aurora Australis was characterized separately. A few lines about that in the Methods section and later in the discussion would be appreciated.
3. Lines 549-551: Did Humphries et al. 2016 use the same method to categorize measurements? It is unclear to me if that’s the case and thus how concentrations in Polar cells during the two campaigns can be directly compared.

- In the abstract, and later in the discussion, the authors mention “seasonal differences in atmospheric circulation including potentially more significant katabatic outflow in summer”. How robust is this assumption? According to Parish and Cassano (2003), “summertime winds cannot be expected to contain a significant katabatic component, owing to enhanced solar heating of the ice slopes”.

- The authors mention that “southern measurements are separated from the Polar/Ferrel classification in an attempt to isolate the known influence of katabatic outflow on near-coast measurements”. While I fully support this initiative, Table S2 shows that there’s more measurements with low AH in the polar vs. southerly category. I’m concerned this method is not entirely successful here.

- I found a number of typos (see line-by-line comments), a thorough proofreading step would have been appreciated.

Line-by-line comments:

Line 21: Please indicate where the cruise started, something like: “(…) during a summer 2017 voyage from Hobart, Tasmania, to the East Antarctic seasonal sea ice zone”.

Figure 1, caption: the sentence “Measurements from the southward transit are excluded due to instrument malfunction” is mentioned twice (line 139-140 and line 140-141). In addition, a portion of the sentence is missing and we don’t know what is supposed to indicate the voyage period for which measurements were analyzed. In addition, could you add ground-based stations on the map, e.g., Casey and Dumont d’Urville, to help the readers orientate themselves?

Line 228-229: “it has been necessary to limit this analysis has been limited to the time period of the shortest dataset”. Please rephrase.

Line 274-275: “A median size distribution plotted (….) has a bimodal shape”. Are the authors referring to a specific figure here? See main comment above on the structure of the discussion, it is currently quite confusing.

Line 276: typo “close to 70 nm..”

Figure 2: I would replace “No_cat” by “Other”. “No_cat” seems to suggest missing wind data, which is not the case. Also please give more detail in the caption, e.g., explain what the low, mid, and high AH categories refer to (give the thresholds in gH2O/m3). The caption should be self-explanatory. Finally, can you use different colors for “No_cat” and “southerly”? (I know I’m being picky here).

Figure 3: same as above, the caption should be self-explanatory. Explain what the 56.6 S latitude threshold is, something like: “Wind rose for wind measurements south of 56.6 S, i.e., excluding homebound transit to Hobart, Tasmania”. In addition, “Frequency histogram of wind measurements plotted in 2b”, should be 3b.

Lines 321-323: “The southern edge of the Ferrel cell is expected to display a dominant NW wind, and the northern edge of the Polar cell is expected to be associated with a dominant SE wind”. Can you cite a few papers here to back this up?

Line 447: typo. “in the differences in difference”.

Figure 5, Fig S2 and S3: I’d appreciate having the southerly category plotted here as well.

References

Parish, T. R. and Cassano, J. J.: The Role of Katabatic Winds on the Antarctic Surface Wind Regime, Mon. Weather Rev., 131, 317–333, https://doi.org/10.1175/1520-0493(2003)131<0317:TROKWO>2.0.CO;2, 2003.

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RR by Anonymous Referee #1 (13 Apr 2021)

ED: Publish subject to minor revisions (review by editor) (13 Apr 2021) by Lynn M. Russell

AR by Jack Simmons on behalf of the Authors (29 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (03 May 2021) by Lynn M. Russell

AR by Jack Simmons on behalf of the Authors (06 May 2021)

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Short summary

Aerosols have a climate forcing effect in the Earth's atmosphere. Few measurements exist of aerosols in the Southern Ocean, a region key to our understanding of this effect. In this study, aerosol measurements from a summer 2017 campaign in the East Antarctic seasonal ice zone are examined. Higher concentrations of aerosols were found in dry air with origins from above the Antarctic continent compared to other periods of the voyage.