Stratospheric and mesospheric HO<sub>2</sub> observations from the Aura Microwave Limb Sounder

Millán, L.; Wang, S.; Livesey, N.; Kinnison, D.; Sagawa, H.; Kasai, Y.

doi:https://doi.org/10.5194/acp-15-2889-2015

Articles | Volume 15, issue 5

https://doi.org/10.5194/acp-15-2889-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-15-2889-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 5

Research article

|

13 Mar 2015

Research article |

| 13 Mar 2015

Stratospheric and mesospheric HO₂ observations from the Aura Microwave Limb Sounder

L. Millán, S. Wang, N. Livesey, D. Kinnison, H. Sagawa, and Y. Kasai

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Final revised paper (published on 13 Mar 2015)
Preprint (discussion started on 08 Sep 2014)

Interactive discussion

Status: closed

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

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- Supplement

RC C7735: 'Referee Comment', Anonymous Referee #3, 06 Oct 2014
- AC C10240: 'Response to reviewer 3', Luis Millan, 16 Dec 2014
RC C7767: 'Review of manuscript "Stratospheric and mesospheric HO2 observations from the Aura Microwave Limb Sounder" by Millán et al.', Anonymous Referee #2, 07 Oct 2014
- AC C10231: 'Response to reviewer 2', Luis Millan, 16 Dec 2014
RC C7907: 'Review of Millan et al. (2014)', Anonymous Referee #1, 13 Oct 2014
- AC C10218: 'Response to reviewer 1', Luis Millan, 16 Dec 2014

Peer-review completion

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

AR by Luis Millan on behalf of the Authors (16 Dec 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Dec 2014) by Gabriele Stiller

RR by Anonymous Referee #1 (23 Jan 2015)

Suggestions for revision or reasons for rejection

Review of the revised version of ACP manuscript

'Stratospheric and mesospheric HO2 observations from the Aura Microwave Limb Sounder'

by Millan et al.

General comments:

In general the authors did a good job addressing the issues raised in the reviews of the previous manuscript version. The paper has improved and is really very well written. The only remaining concern I have is related to the comparison to the FIRS measurements, which – I still think – is not a valid comparison (see specific comment below). For most other comparisons you use the daytime – nighttime differences in HO2 in the 10 – 1 hPa pressure range, because of possible biases in the data. But for the FIRS comparison you average daytime and nighttime data and this obviously leads to a nice comparison. This strongly suggests that the day-night average is used for the FIRS comparison in order to improve the agreement between MLS and FIRS, which is not a legitimate approach at all. As long as this issue is not addressed I cannot recommend accepting this paper. Otherwise the paper is very nice.

Specific comments:

Page 3, line 3: ‘The presence of HOx family’ -> ‘The presence of THE HOx family’ ?

Page 7, line 14/15: ‘onto a vertical grid of 6 surface per decade change in pressure’
Something’s wrong here, please rephrase.

Page 7, line 25: ‘jointly’ -> ‘joint’

Same line: ‘as oppose to’ -> ‘as opposed to’

Page 8, line 5: ‘have shown’ -> ‘has shown’

Page 10, line 25: delete comma after ‘as well as’

Page 11, line 2: ‘its high’ -> ‘their high’

Page 11, section 4.1: In my last review I raised the point that this comparison is in my opinion not a valid comparison, and I still hold this opinion. The FIRS profile you compare to is a single profile and a daytime profile, right? The MLS profiles shown in Fig. 6 are day-night-mean profiles. Given the very large diurnal changes in HO2 within the pressure range used for the comparison, this is NOT a valid comparison. You need to compare averaged MLS daytime HO2 profiles with the FIRS daytime profile. If only daytime MLS profiles are used, the MLS HO2 mixing ratios and concentrations will be significantly larger than the FIRS values, but this is comparing apples to apples. Currently, this is not the case.
In addition, for some of the other comparisons you use the daytime-nighttime differences in the 10 to 1 hPa pressure range, because of possible biases of the nighttime profiles. This makes the use of day-night averages for the FIRS comparison even less justified.
Perhaps I’m missing a point here?

Page 12, line 4: ‘in the ISS’ -> ‘on the ISS’ ?

Page 12, last paragraph: I suggest mentioning in the text that daytime-nighttime differences in HO2 are shown in the 10 to 1 hPa pressure range in Fig. 7 and 8. This is mentioned in the Fig. caption, but it would be good to mention it in the text as well.

Page 13, last paragraph: I suggest mentioning in the text that daytime-nighttime differences in HO2 are shown in the 10 to 1 hPa pressure range in Fig. 9.

Page 14, line 7: ‘The zonal latitudinal gradient’
I’m not sure what is meant here. Suggest deleting ‘zonal’

Page 16, line 17: ‘smaller that’ -> ‘smaller than’

Page 18, line 23: ‘result that agrees’ -> ‘a result that agrees’ ? or remove ‘;’ and continue with ‘in agreement with .. but contradicting ..’

Brasseur and Solomon reference: add comma after ‘Aeronomy of the Middle Atmosphere’

Add commas after last names of first authors in case of: Haigh et al., Rottmann et al., Smith 2012

Summers et al.: ‘Preuse’ -> ‘Preusse’

Summers et al.: ‘for m(see Sect. 4.3 for the model description)iddle’ ??

Twomey reference: ‘Asss.’ -> ‘Assoc.

Caption Fig. 4: ‘for A daily .. offline data averaged over’
‘a’ is odd, suggest to rephrase the sentence

Caption Fig. 5, line: ‘corresponds to’ – ‘correspond to’

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ED: Reconsider after minor revisions (Editor review) (03 Feb 2015) by Gabriele Stiller

AR by Luis Millan on behalf of the Authors (05 Feb 2015) Author's response Manuscript

ED: Reconsider after minor revisions (Editor review) (17 Feb 2015) by Gabriele Stiller

Dear Dr Millan,

according to your last reply to reviewer comments you recommend to use MLS HO2 data from the offline retrieval between 10 and 1 hPa only after correction of a systematic bias. This bias is quantified by the volume mixing ratios/ number densities of the nighttime retrievals for this pressure range, since nighttime HO2 is expected to be virtually zero. Regarding this issue, I have some further comments/recommendations:
- the abstract needs to make clear that the nighttime data set is for pressure levels below 1 hPa only. Further the recommended bias correction should be mentioned in the abstract.
- a statement regarding the recommended bias correction should be added to the summary (Section 5).
- regarding the comparisons to the SMILES instrument, you do not make use of the recommended bias correction as far as I read your paper. It is not clear to me why the bias correction has not been applied for this comparison. The discussion is inconsistent here. I recommend for the MLS- SMILES comparison in the 10 to 1 hPa altitude range to show bias-corrected daytime comparisons only
- page 8, line 17/18: the restriction to above 1 hPa for nighttime values needs to be mentioned here.
- page 9, line 20 to the end of the section: the discussion on systematic errors is completely unrelated to the bias correction by nighttime values you recommend earlier. A link between the recommended bias correction and the assessment of systematic errors needs to be established in the text.
- section 4.3 (Comparison to WACCM): please make clear if the bias correction has been applied for this comparison as well, i.e. if day-minus-night MLS data are compared to WACCM for the daytime comparisons between 10 and 1 hPa.

It might be clearer to use the explicit term "day-minus-night differences" instead of "day-night differences" all over the paper, but this is up to you.

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AR by Luis Millan on behalf of the Authors (17 Feb 2015) Author's response Manuscript

ED: Publish as is (24 Feb 2015) by Gabriele Stiller

AR by Luis Millan on behalf of the Authors (24 Feb 2015)