Polar stratospheric nitric acid depletion surveyed from a decadal dataset of IASI total columns

Wespes, Catherine; Ronsmans, Gaetane; Clarisse, Lieven; Solomon, Susan; Hurtmans, Daniel; Clerbaux, Cathy; Coheur, Pierre-François

doi:https://doi.org/10.5194/acp-22-10993-2022

Articles | Volume 22, issue 16

https://doi.org/10.5194/acp-22-10993-2022

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

https://doi.org/10.5194/acp-22-10993-2022

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

Articles | Volume 22, issue 16

Research article

|

30 Aug 2022

Research article |

| 30 Aug 2022

Polar stratospheric nitric acid depletion surveyed from a decadal dataset of IASI total columns

Catherine Wespes, Gaetane Ronsmans, Lieven Clarisse, Susan Solomon, Daniel Hurtmans, Cathy Clerbaux, and Pierre-François Coheur

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Final revised paper (published on 30 Aug 2022)
Preprint (discussion started on 04 Aug 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review', Anonymous Referee #1, 31 Aug 2020
- AC1: 'Response to anonymous Referee #1', Catherine Wespes, 15 Dec 2020
RC2: 'review', Anonymous Referee #3, 31 Aug 2020
- AC2: 'Response to anonymous Referee #3', Catherine Wespes, 15 Dec 2020
SC1: 'Short Comment from GL Manney and ML Santee', Gloria Manney, 28 Sep 2020
- AC3: 'Response to GL Manney and ML Santee', Catherine Wespes, 15 Dec 2020

Peer-review completion

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

AR by Catherine Wespes on behalf of the Authors (12 Jan 2021) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Jan 2021) by Michael Pitts

RR by Anonymous Referee #3 (01 Feb 2021)

RR by Anonymous Referee #1 (01 Feb 2021)

Suggestions for revision or reasons for rejection

In response to both reviews and the detailed comments by Gloria Manney and Michelle Santee, the authors have improved their manuscript considerably. However, I still have concerns about the correctness of their estimation on errors to be applicable within the dark Antarctic polar vortex. In this respect I do appreciate the addition of a comparison with MLS as new Figure 1. However, I don’t understand why the authors have stopped half way. It would have only been a small step to show a picture comparing total column amounts integrated from MLS to those of IASI and I would strongly recommend to do this. In the response to the review it is argued:

“…that we have preferred comparing IASI HNO3 columns with VMR measured by MLS at specific levels instead of integrated columns calculated from MLS, given the difference in the sensitivity profile between IASI and MLS, the non-negligible IASI sensitivity to HNO3 in the troposphere where MLS does not measure HNO3 etc, which makes the integrated columns from IASI vs MLS not directly comparable. It should be pointed out finally that part of the differences between IASI and MLS are likely due to the different number of co-located data within the 2.5x2.5 grid cells considered here for the comparison, with a much larger number of observations for IASI (through the quality filtering) than for MLS. “

It would just be easier to put forward and discuss these arguments when the column amounts derived from MLS are presented and quantitative differences shown. E.g. one could easily analyse how much the sensitivity of IASI applied to MLS vertical profiles would change the results. Since it is claimed that the IASI dataset is valuable for polar stratospheric studies as it is, one should do this, even when any tropospheric part would not be considered (in case of MLS). Further, the argument about “the non-negligible IASI sensitivity to HNO3 in the troposphere” is quite confusing, since all over the paper it is argued that the IASI HNO3 data well represent the stratospheric situation and that, e.g. a renitrification at lower levels cannot be captured well. Such a comparison could also help in understanding the problems of the IASI retrievals e.g. over Eastern Antarctica.

L120-122: ‘…(Ronsmans et al., 2016). The total columns are associated with a total retrieval error ranging from around 3% at mid- and polar latitudes to 25% above cold Antarctic surface during winter (due to a weaker sensitivity above very cold surface with a DOFS of 0.95 and to an poor knowledge of the seasonally and wavenumber-dependent emissivity above ice surfaces which induces larger forward model errors) .’

However, I think the error due to wavenumber-dependent emissivity has not been considered in the error estimation of ‘Ronsmans et al., 2016’. So I wonder why only the 25% from that paper is reported here. Further, might there be also an error contribution due to cloud-clearing over very cold Antarctic surfaces?

Technical:

L122: ‘an poor’ -> ‘a poor’ or only ‘poor’

L318: ‘explained’ -> ‘explain’

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ED: Reconsider after major revisions (17 Feb 2021) by Michael Pitts

AR by Catherine Wespes on behalf of the Authors (16 Aug 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (22 Aug 2021) by Michael Pitts

RR by Anonymous Referee #1 (30 Aug 2021)

RR by Michelle Santee (13 Oct 2021)

ED: Reconsider after major revisions (14 Oct 2021) by Michael Pitts

AR by Catherine Wespes on behalf of the Authors (25 Feb 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (28 Feb 2022) by Michael Pitts

RR by Anonymous Referee #1 (07 Mar 2022)

RR by Michelle Santee (06 Apr 2022)

ED: Reconsider after major revisions (06 Apr 2022) by Michael Pitts

AR by Catherine Wespes on behalf of the Authors (03 May 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (11 May 2022) by Michael Pitts

RR by Michelle Santee (26 May 2022)

ED: Publish subject to minor revisions (review by editor) (26 May 2022) by Michael Pitts

AR by Catherine Wespes on behalf of the Authors (08 Jun 2022) Author's response Author's tracked changes Manuscript

ED: Publish as is (10 Jun 2022) by Michael Pitts

AR by Catherine Wespes on behalf of the Authors (22 Jun 2022)

Short summary

The first 10-year data record (2008–2017) of HNO₃ total columns measured by the IASI-A/MetOp infrared sounder is exploited to monitor the relationship between the temperature decrease and the HNO₃ loss observed each year in the Antarctic stratosphere during the polar night. We verify the recurrence of specific regimes in the cycle of IASI HNO₃ and identify the day and the 50 hPa temperature (drop temperature) corresponding to the onset of denitrification in Antarctic winter for each year.