Daytime variation in the aerosol indirect effect for warm marine boundary layer clouds in the eastern North Atlantic

Qiu, Shaoyue; Zheng, Xue; Painemal, David; Terai, Christopher R.; Zhou, Xiaoli

doi:https://doi.org/10.5194/acp-24-2913-2024

Articles | Volume 24, issue 5

https://doi.org/10.5194/acp-24-2913-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-24-2913-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 24, issue 5

Research article

|

06 Mar 2024

Research article |

| 06 Mar 2024

Daytime variation in the aerosol indirect effect for warm marine boundary layer clouds in the eastern North Atlantic

Shaoyue Qiu, Xue Zheng, David Painemal, Christopher R. Terai, and Xiaoli Zhou

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Final revised paper (published on 06 Mar 2024)
Supplement to the final revised paper
Preprint (discussion started on 23 Aug 2023)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-1676', Anonymous Referee #1, 25 Sep 2023

Very interesting work. Please find my comments attached.

Citation: https://doi.org/10.5194/egusphere-2023-1676-RC1
- AC1: 'Reply on RC1', Shaoyue Qiu, 17 Nov 2023
  
  Thank you for your questions and suggestions, which greatly help to improve the clarity and quality of this paper. Please find the point-by-point response to each comment and details of the modifications made to the text and figures to address these points attached to this reply.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1676-AC1
RC2:
'Comment on egusphere-2023-1676', Anonymous Referee #2, 26 Sep 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1676/egusphere-2023-1676-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-1676-RC2
- AC2: 'Reply on RC2', Shaoyue Qiu, 17 Nov 2023
  
  Thank you for your questions and suggestions, which greatly help to improve the clarity and quality of this paper. Please find the point-by-point response to each comment and details of the modifications made to the text and figures to address these points attached to this reply.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1676-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Shaoyue Qiu on behalf of the Authors (13 Dec 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (18 Dec 2023) by Paulo Ceppi

RR by Anonymous Referee #2 (01 Jan 2024)

Suggestions for revision or reasons for rejection

I greatly appreciate the efforts made by the authors to address my questions. Most of my concerns raised in the previous review have been sufficiently addressed.
After reading the revised manuscript, I have a few comments that I encourage the authors to consider:
1) Regarding CF susceptibility, your sensitivity test convinced me that the results you shown in Fig. 2c is qualitatively robust, but not quantitatively, as CF susceptibility is a function of cloud size. Moreover, the daytime evolution in CF susceptibility (Fig. 3c) suggests to me that not only the change of sign, but the determination of the sign of CF susceptibility is in general statistically insignificant. Could you indicate on the figures, especially for CF susceptibilities, when the value is statistically-significantly different from zero?

2) Since you investigated daytime cloud susceptibility evolution, I am surprised that shortwave absorption by cloud (a source for cloud dissipation) and its dependence on cloud LWP and Nd are not discussed at all when interpreting the results and formulating hypotheses. For example, thick clouds thin faster because of stronger SW absorption, compared to thin clouds. In other words, a key term in cloud LWP budgets during daytime is SW radiation, which is sensitive to LWP and Nd (e.g., Petters et al. 2012). I wonder how do SW absorption and its dependence on LWP and Nd affect your interpretation of the susceptibility evolution?

3) Regarding the “cloud memory of AIE or susceptibility” argument, my interpretation of your statement/hypothesis is still that clouds have memory of their past states, meaning their past rate of change in LWP (as in your words), which is governed by the environmental states they have been residing in for the past few hours. The separation between different cloud transition groups, such as thin to thin, thick to thin, etc., is probably set by boundary layer characteristics, e.g., BL depth and thermodynamics. Therefore, I think your classification of different cloud transition groups essentially represents different boundary layer conditions that dictate different cloud evolutions. I believe one can show this using large-scale meteorological conditions from reanalysis data.
To me, this is different from “cloud has a memory of its past susceptibility” as susceptibility in your study is simply a regression slope, and cloud cannot physically retain or “memorize” a statistical relationship. Therefore, I recommend rephrase how this hypothesis/argument is framed and discussed throughout the manuscript.

Reference
Petters, J. L., J. Y. Harrington, and E. E. Clothiaux, 2012: Radiative–Dynamical Feedbacks in Low Liquid Water Path Stratiform Clouds. J. Atmos. Sci., 69, 1498–1512, https://doi.org/10.1175/JAS-D-11-0169.1.

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RR by Anonymous Referee #1 (02 Jan 2024)

ED: Publish subject to minor revisions (review by editor) (03 Jan 2024) by Paulo Ceppi

AR by Shaoyue Qiu on behalf of the Authors (13 Jan 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (15 Jan 2024) by Paulo Ceppi

AR by Shaoyue Qiu on behalf of the Authors (20 Jan 2024) Author's response Manuscript

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Short summary

The aerosol indirect effect (AIE) depends on cloud states, which exhibit significant diurnal variations in the northeastern Atlantic. Yet the AIE diurnal cycle remains poorly understood. Using satellite retrievals, we find a pronounced “U-shaped” diurnal variation in the AIE, which is contributed to by the transition of cloud states combined with the lagged cloud responses. This suggests that polar-orbiting satellites with overpass times at noon underestimate daytime mean values of the AIE.