Differences in the quasi-biennial oscillation response to stratospheric aerosol modification depending on injection strategy and species

Franke, Henning; Niemeier, Ulrike; Visioni, Daniele

doi:https://doi.org/10.5194/acp-21-8615-2021

Articles | Volume 21, issue 11

https://doi.org/10.5194/acp-21-8615-2021

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

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https://doi.org/10.5194/acp-21-8615-2021

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

Articles | Volume 21, issue 11

Research article

|

08 Jun 2021

Research article |

| 08 Jun 2021

Differences in the quasi-biennial oscillation response to stratospheric aerosol modification depending on injection strategy and species

Henning Franke, Ulrike Niemeier, and Daniele Visioni

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

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RC1: 'Review of “Differences in the QBO response to stratospheric aerosol modification depending on in section strategy and species” by Franke et al.', Anonymous Referee #1, 07 Dec 2020
RC2: 'Review for 'Differences in the QBO response to stratospheric aerosol modification depending on injection strategy and species' by Franke et al. (2020)', Anonymous Referee #2, 12 Dec 2020
RC3: 'Review of "Review of Differences in the QBO response to stratospheric aerosol modification depending on injection strategy and species"', Anonymous Referee #3, 21 Dec 2020
AC1: 'Answer to the reviewers', Henning Franke, 05 Feb 2021

Peer-review completion

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

AR by Henning Franke on behalf of the Authors (05 Feb 2021) Author's response Author's tracked changes

ED: Referee Nomination & Report Request started (28 Feb 2021) by Timothy J. Dunkerton

RR by Anonymous Referee #1 (10 Mar 2021)

Suggestions for revision or reasons for rejection

Review of “Differences in the QBO response to stratospheric aerosol modification depending on injection strategy and species” by Franke et al.

I highly appreciate the authors’ effort to address my comments. I generally agree with the authors that the thermal wind relationship in the lower stratosphere is the root cause for the differences in the QBO responses, but I am not fully convinced by the processes proposed by the authors to link the lower stratospheric aerosols to the QBO throughout the stratosphere. On the other hand, I do think the manuscript deserve publication even with some unclear reasoning. I am suggesting the authors to soften the tone a little bit and to simply acknowledge that some of the processes need further investigation. Below are my detailed comments.

1. The modification of the residual circulation. The authors argued that w* changes lead to QBO changes, and w* changes come from the extratropical jets which is linked to tropical confinement of the aerosols. However, the extratropical jet should be mostly sensitive to the temperature gradient at the subtropics instead of near the equator. As shown in Fig. 5, the lower stratospheric temperature gradient is quite similar at ~30N/S among different injection scenarios, indicating that the direct radiative effect of the aerosol injections would lead to similar changes in the subtropical jets. Also from Fig. 5, there is little zonal wind changes at the subtropics. In addition, the w* changes is largely confined within 15N-15S, which is much narrower than the ascending branch of the Brewer-Dobson circulation (~40N-40S). This suggest to me that the w* changes in these simulation is largely driven by the equatorial waves that is linked to the QBO changes. Rather than a cause to the QBO changes, I think the w* changes works as a feedback to the QBO changes.

2. The ozone’s effect in CESM. The authors argued that the ozone depletion centered near 30 hPa partly compensate the aerosol heating between 40 and 80 hPa. I don’t think ozone’s radiative effect would make any significant contribution at the lower stratosphere given the altitude of ozone changes. One should be able to verify that by comparing shortwave heating rates as ozone’s radiative effect is mostly expressed in shortwave. I suspect that the difference in temperature curvature at the tropical lower stratosphere between ECHAM and CESM mostly comes from the dynamical heating rates. It would also be informative to compared the aerosols’ radiative heating rates between the two models. Though the aerosol burden shares similar meridional structure, difference may arise from the vertical distribution as well as radiative schemes.

3. Given the opposite response in ECHAM and CESM to the regional aerosol injection and the possible role played by the gravity wave parameterization, it is then questionable that the meridional distribution of aerosol determines the QBO responses. Even at the lower stratosphere, the direct radiative effect of aerosols may be masked by other processes and may not predict the sign of zonal wind and temperature curvature changes at the equator.

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RR by Anonymous Referee #2 (04 Apr 2021)

ED: Publish as is (03 May 2021) by Timothy J. Dunkerton

AR by Henning Franke on behalf of the Authors (10 May 2021) Manuscript

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Short summary

Stratospheric aerosol modification (SAM) can alter the quasi-biennial oscillation (QBO). Our simulations with two different models show that the characteristics of the QBO response are primarily determined by the meridional structure of the aerosol-induced heating. Therefore, the QBO response to SAM depends primarily on the location of injection, while injection type and rate act to scale the specific response. Our results have important implications for evaluating adverse side effects of SAM.