Assessing stratospheric transport in the CMAM30 simulations using ACE-FTS measurements

Kolonjari, Felicia; Plummer, David A.; Walker, Kaley A.; Boone, Chris D.; Elkins, James W.; Hegglin, Michaela I.; Manney, Gloria L.; Moore, Fred L.; Pendlebury, Diane; Ray, Eric A.; Rosenlof, Karen H.; Stiller, Gabriele P.

doi:https://doi.org/10.5194/acp-18-6801-2018

Articles | Volume 18, issue 9

https://doi.org/10.5194/acp-18-6801-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-18-6801-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 18, issue 9

Research article

|

16 May 2018

Research article |

| 16 May 2018

Assessing stratospheric transport in the CMAM30 simulations using ACE-FTS measurements

Felicia Kolonjari, David A. Plummer, Kaley A. Walker, Chris D. Boone, James W. Elkins, Michaela I. Hegglin, Gloria L. Manney, Fred L. Moore, Diane Pendlebury, Eric A. Ray, Karen H. Rosenlof, and Gabriele P. Stiller

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Final revised paper (published on 16 May 2018)
Preprint (discussion started on 23 May 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Good validation of CCM versus satellite measurements', Anonymous Referee #1, 17 Jun 2017
- AC1: 'Response to Reviewer #1', Kaley Walker, 30 Oct 2017
RC2: 'Review', Anonymous Referee #2, 20 Jun 2017
- AC2: 'Response to Reviewer #2', Kaley Walker, 30 Oct 2017
RC3: 'Review', Anonymous Referee #3, 21 Jun 2017
- AC3: 'Response to Reviewer #3', Kaley Walker, 30 Oct 2017

Peer-review completion

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

AR by Kaley Walker on behalf of the Authors (31 Oct 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (02 Nov 2017) by Martin Dameris

RR by Matthew Toohey (17 Nov 2017)

Suggestions for revision or reasons for rejection

I commend the authors for successfully addressing so many of the reviewers comments and suggestions.

One (relatively minor) issue still remains unfilled in my eyes, and it concerns the explanation of differences brought about by the three different sampling strategies presented in Sec. 3.3. According to text there:
- The ‘basic’ sampling method involved selecting a vertical column based on the nearest neighbour grid point to the 30 km tangent point location with no interpolation and no consideration of the vertical extent of the profile.
- The ‘intermediate’ level of sampling extracted the vertical column based on a bilinear interpolation of the four closest grid points to the 30 km geometric tangent point but
with no consideration of the variation in geographical location of the tangent points above or below 30 km.
- The ‘advanced’ sampling method improves on the intermediate level of sampling by performing the bilinear interpolation at each level of the ACE-FTS profile using the distinct geographic locations derived from the refraction model for the respective level.

So, based on these descriptions, the differences in mean N2O zonal mean cross-sections (Fig 4) based on sampling can be understood as follows:
- Advanced-Intermediate represents the impact of including the variation of the geographical location of tangent point with height.
- Advanced-Basic represents the combined impact of including the variation of geographical location of tangent point with height (as in Advanced-Intermediate) plus the impact of simply interpolating to the location of the 30 km tangent point (in other words, not using the nearest-neighbour as done in Basic).

The impact of including the variation of the geographical location of tangent point with the height of the retrieved profile, shown by the Advanced-Intermediate plot, is zero at ~30 km, as per definition, and pretty small otherwise (~2%). The Advanced-Basic plot shows differences that are much larger (reaching ~10%), which, by elimination, must be mostly the result of performing the horizontal interpolation and not using the nearest-neighbour.

This is a long-winded explanation for why I find the statement at pg 14, l13-14, and the discussion following, to be incorrect, or at least misleading. The main reason for differences between the Advanced and Basic methods must be mostly due to the horizontal interpolation to the 30 km tangent point. The horizontal variation of tangent point with altitude plays a relatively smaller role. The discussion here should make that clear.

Minor corrections:
pg15, l16: there doesn't appear to be a difference in the scale of Fig 7c.

pg16, l19: "tropical upwelling occurs"

pg 17, l24: most-> mostly ?

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ED: Publish subject to minor revisions (review by editor) (08 Dec 2017) by Martin Dameris

AR by Kaley Walker on behalf of the Authors (18 Dec 2017) Author's response Manuscript

ED: Publish as is (20 Dec 2017) by Martin Dameris

AR by Kaley Walker on behalf of the Authors (27 Dec 2017) Manuscript

Short summary

We used satellite observations and model simulations of CFC-11, CFC-12, and N₂O to investigate stratospheric transport, which is important for predicting the recovery of the ozone layer and future climate. We found that sampling can impact results and that the model consistently overestimates concentrations of these gases in the lower stratosphere, consistent with a too rapid Brewer–Dobson circulation. An issue with mixing in the tropical lower stratosphere in June–July–August was also found.