Subgrid-scale variability in clear-sky relative humidity and forcing by aerosol–radiation interactions in an atmosphere model

Petersik, Paul; Salzmann, Marc; Kretzschmar, Jan; Cherian, Ribu; Mewes, Daniel; Quaas, Johannes

doi:https://doi.org/10.5194/acp-18-8589-2018

Articles | Volume 18, issue 12

https://doi.org/10.5194/acp-18-8589-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-8589-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 12

Research article

|

19 Jun 2018

Research article |

| 19 Jun 2018

Subgrid-scale variability in clear-sky relative humidity and forcing by aerosol–radiation interactions in an atmosphere model

Paul Petersik, Marc Salzmann, Jan Kretzschmar, Ribu Cherian, Daniel Mewes, and Johannes Quaas

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Final revised paper (published on 19 Jun 2018)
Preprint (discussion started on 13 Nov 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'key details missing', Steven J Ghan, 20 Nov 2017
- AC1: 'Response to Steven Ghan', Paul Petersik, 11 Apr 2018
RC2: 'Comments on “Subgrid-scale variability of clear-sky relative humidity and forcing by aerosol-radiation interactions in an atmosphere model” by Petersik et al.', Anonymous Referee #2, 02 Dec 2017
- AC2: 'Response to Reviewer 2', Paul Petersik, 11 Apr 2018

Peer-review completion

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

AR by Paul Petersik on behalf of the Authors (11 Apr 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Apr 2018) by Kostas Tsigaridis

RR by Anonymous Referee #2 (05 May 2018)

Suggestions for revision or reasons for rejection

The authors revised the manuscript substantially following the comments/suggestions by the two reviewers. The manuscript was much improved in this revision. However, I still think this is a technical manuscript and more suitable for GMD or a technical note in ACP.

Comment on reply to major comment 1:
A main reason why I feel this is a technical manuscript is that it is not clear whether the improvement of the sub-grid treatment by the authors (e.g., stochastic treatment, consistency with the cloud scheme) is really scientifically important or not.

The authors describe that previous studies “make strong simplifications about the shape of the used probability density function (PDF) and are not consistent with the cloud cover scheme” (page 2, lines 16-17) and that they “do not consider variations of width and shape of the used distribution.” (page 2, lines 26-27). The authors also describe that the width of the PDF is a function of height and the sub-saturated part of the PDF is sampled from the cloud-cover scheme in the parameterization developed in this study. Please show and explain how important the improvement by the authors is in the RF estimation (compared with the previous studies).

I understand that 1) the importance of resolving sub-grid RH variability itself was already shown in the previous studies and 2) the treatment of sub-grid RH variability was updated in this study. Since the authors focus on the comparisons between the simulation with the stochastic parameterization and the simulation without the sub-grid RH variability, both effects (1 and 2) are included in the author’s comparisons. I think the importance of the second effect should be shown and explained if the authors want to show the improvement in this study is really important.

Comment on reply to major comment 3:
I think the volume-weighted average refractive indices for internally mixed aerosols will lead to an overestimation of absorption enhancement. However, the authors describe that “the refractive indices for black carbon were updated to reduce the negative bias due to aerosol absorption enhancement” (page 3, lines 30-31). Please explain more about the consistency of these points.

The description that “the absorption enhancement of BC due to mixing with hydrophilic aerosols is compensated by the lower life time and abundance of BC” (page 3, lines 31-32) should not be used in this part. This may be correct when both properties (absorption and CCN activity of BC) are changed simultaneously (e.g. aging in the real atmosphere). However, here we focus on the treatment of absorption enhancement only (BC lifetime is probably independent to the treatment of absorption enhancement in the author’s model). The author’s description cannot be used to support ignoring absorption enhancement in a model.

Other comments:
Page 2, line 25: “They show” is better than “In this study”.

Page 3, lines 1-2: the effect of?

Page 4, line 3: add “2.2 “ before “Hygroscopic growth HAM2”.

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ED: Publish subject to minor revisions (review by editor) (07 May 2018) by Kostas Tsigaridis

AR by Paul Petersik on behalf of the Authors (17 May 2018) Author's response Manuscript

ED: Publish as is (19 May 2018) by Kostas Tsigaridis

AR by Paul Petersik on behalf of the Authors (25 May 2018)

Short summary

Our study presents the first estimate of RFari using a global atmospheric model with a parameterization for subgrid-scale variability in RH that is consistent with the assumptions in the model. We find that the revision has a strong influence on the simulated radiative forcing (~ 31 %). In addition, we examine its effects on optical properties of the atmosphere and find an increase in AOD by about 7.8 %.