the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 May 2023
Rapid saturation of cloud water adjustments to shipping emissions
Abstract. Human aerosol emissions change cloud properties by providing additional cloud condensation nuclei. This increases cloud droplet numbers, which in turn affects other cloud properties like liquid water content, and ultimately cloud albedo. These adjustments are poorly constrained, making aerosol effects the most uncertain part of anthropogenic climate forcing. Here we show that cloud droplet number and water content react differently to changing emission amounts in shipping exhausts. We use information about ship positions and modelled emission amounts together with reanalysis winds and satellite retrievals of cloud properties. The analysis reveals that cloud droplet numbers respond linearly to emission amount over a large range (1–10 kg h−1), before the response saturates. Liquid water increases in raining clouds, and increases are constant over the emission ranges observed. There is evidence that this is due to compensating effects under rainy and non-rainy conditions, consistent with suppression of rain by enhanced aerosol. This has implications for our understanding of cloud processes and may improve the way clouds are represented in climate models, in particular by changing parameterizations of liquid water responses to aerosol.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(953 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(953 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
- RC1: 'Comment on egusphere-2023-813', Anonymous Referee #1, 29 May 2023
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RC2: 'Comment on egusphere-2023-813', Anonymous Referee #2, 16 Jun 2023
The study presented in this manuscript uses satellite together with ship position and emission data to identify so-called invisible ship tracks, and exploit changes in emission regulations to evaluate droplet number and liquid water path changes in ship tracks compared to out-of-track data as a function of SOx emission and time since emission. While it builds on a previous study published in Nature by the same authors, it is not just an extension of the dataset, but focusses on an effect not covered in the previous work: While the Nd perturbation scales with emission, the LWP changes do not. This hints at a non-linear threshold behaviour which is highly relevant for the evaluation of aerosol indirect effects from observations and their representation in climate models.
The paper is well-written with clear graphics. The fact that the entire methods section is in the appendix appears unusual, but is in line with the requirements for an ACP Letter. Given the clear storyline , the conciseness of the manuscript, and the relevance of the results, I support publication as a letter subject to minor revisions.
Detailed comments:
- 3/Line 163: the region of study is specified as “(-50°S,50°N)” and “(-90°W, 20°E)”, but in Fig. 3, the southernmost row of this domain is partly white. Is this because data is missing here? Or are the values all 0%? Please indicate.
- How are the out-of-track regions defined? I was not able to find details on this. Line 145 mentions 30 km distance, but this is not further explained in the methods section. Line 213 mentions control regions, which I assume is the same as out-of-track regions, but it would be good to use consistent terminology.
- Only one year of post-IMO regulation change data is available (2021). Please discuss in how far this may introduce an uncertainty when pre- and post-IMO conditions are compared.
- Line 175 mentions “best-matched tracks”. What does this mean and how is it tested?
Technical comments:
- Sometimes the position of the parentheses for references is not correct, e.g. in line 39, where it should read: “As in Manshausen et al. (2022), …”
- Line 118: add “their” before Fig. 6 to make clear that this is referring to Gryspeerdt et al.’s figure.
- Line 171: positons -> positions
Citation: https://doi.org/10.5194/egusphere-2023-813-RC2 - AC1: 'Comment on egusphere-2023-813', Peter Manshausen, 19 Jul 2023
Interactive discussion
Status: closed
- RC1: 'Comment on egusphere-2023-813', Anonymous Referee #1, 29 May 2023
-
RC2: 'Comment on egusphere-2023-813', Anonymous Referee #2, 16 Jun 2023
The study presented in this manuscript uses satellite together with ship position and emission data to identify so-called invisible ship tracks, and exploit changes in emission regulations to evaluate droplet number and liquid water path changes in ship tracks compared to out-of-track data as a function of SOx emission and time since emission. While it builds on a previous study published in Nature by the same authors, it is not just an extension of the dataset, but focusses on an effect not covered in the previous work: While the Nd perturbation scales with emission, the LWP changes do not. This hints at a non-linear threshold behaviour which is highly relevant for the evaluation of aerosol indirect effects from observations and their representation in climate models.
The paper is well-written with clear graphics. The fact that the entire methods section is in the appendix appears unusual, but is in line with the requirements for an ACP Letter. Given the clear storyline , the conciseness of the manuscript, and the relevance of the results, I support publication as a letter subject to minor revisions.
Detailed comments:
- 3/Line 163: the region of study is specified as “(-50°S,50°N)” and “(-90°W, 20°E)”, but in Fig. 3, the southernmost row of this domain is partly white. Is this because data is missing here? Or are the values all 0%? Please indicate.
- How are the out-of-track regions defined? I was not able to find details on this. Line 145 mentions 30 km distance, but this is not further explained in the methods section. Line 213 mentions control regions, which I assume is the same as out-of-track regions, but it would be good to use consistent terminology.
- Only one year of post-IMO regulation change data is available (2021). Please discuss in how far this may introduce an uncertainty when pre- and post-IMO conditions are compared.
- Line 175 mentions “best-matched tracks”. What does this mean and how is it tested?
Technical comments:
- Sometimes the position of the parentheses for references is not correct, e.g. in line 39, where it should read: “As in Manshausen et al. (2022), …”
- Line 118: add “their” before Fig. 6 to make clear that this is referring to Gryspeerdt et al.’s figure.
- Line 171: positons -> positions
Citation: https://doi.org/10.5194/egusphere-2023-813-RC2 - AC1: 'Comment on egusphere-2023-813', Peter Manshausen, 19 Jul 2023
Peer review completion
Journal article(s) based on this preprint
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- 1
Peter Manshausen
Duncan Watson-Parris
Matthew W. Christensen
Jukka-Pekka Jalkanen
Philip Stier
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(953 KB) - Metadata XML