the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Mar 2025
The Diurnal Susceptibility of Subtropical Clouds to Aerosols
Abstract. The diurnal susceptibility of clouds to aerosols is examined during the transition from subtropical stratocumulus to shallow cumulus regimes. Using large-eddy simulations, a six-day air mass evolution along a 3800-km observed trajectory from the coast of Peru toward the equator is analyzed. Pristine and polluted scenarios are simulated with forcing imposed from weather reanalysis. The polluted scenario exhibits stronger diurnal variations in cloud water, cloud fraction, and albedo, with enhanced entrainment and suppressed precipitation. The overall response of cloud properties and outgoing shortwave radiation to droplet number concentration follows a distinct diurnal pattern: strong positive adjustments dominate at night and in the morning, while weak negative adjustments prevail in the afternoon. This cycle is driven by the competition between precipitation suppression, which enhances cloud water and coverage, and entrainment drying, which depletes them. In polluted conditions, enhanced entrainment leads to a deeper and more decoupled boundary layer that cannot be sustained by surface fluxes in the afternoon, resulting in negative cloud adjustments. This entrainment enhancement is mediated by the sedimentation of cloud and precipitation water from the entrainment zone. While the Twomey effect dominates the diurnal average albedo response, the diurnal variation in the competing cloud adjustments lead to a near-neutral net adjustment effect, highlighting the critical role of diurnal processes in aerosol-cloud interactions.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
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
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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
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- BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-714', Anonymous Referee #1, 17 Mar 2025
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AC1: 'Reply on RC1', Marcin J. Kurowski, 07 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-714/egusphere-2025-714-AC1-supplement.pdf
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AC1: 'Reply on RC1', Marcin J. Kurowski, 07 Aug 2025
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RC2: 'Comment on egusphere-2025-714', Anonymous Referee #2, 30 Apr 2025
OVERALL COMMENTS:
This manuscript presents Lagrangian LES simulations of marine cloud transitions along a six-day trajectory. I recommend its publication after the following comments are adequately addressed.
MAJOR COMMENTS:
The discussion of the physical processes influencing the results is somewhat underdeveloped. For instance, in Figure 4, entrainment, coupling, and radiative heating are shown in different units, which makes direct comparisons between them challenging. While these processes can be qualitatively associated with the evolution of LWP, the relative importance of each remains unclear, weakening the overall argument. The role of precipitation is neglected. In particular, a relevant mechanism to consider is the evaporation of drizzle below the cloud base, which dampens buoyancy flux, weakens turbulence, and reduces entrainment. Seee the Introduction section in Uchida et al. (2010, doi:10.5194/acp-10-4097-2010) for a summary of this mechanism. How does this process influence the results presented in this study?
As the authors noted, there have been many papers on the ACI in marine shallow clouds. It would greatly benefit the readers and strengthen and current paper if the authors can more clearly connect their new findings to the existing body of work. This is not about advertising any previous studiy, but about highlighting the novel aspects of the current paper through thoughtful comparison. For example, the diurnal LWP pattern, higher at night and lower during the day, is reminiscent of the results in Sandu et al. (2008), who proposed an explanation for this behavior. While a comprehensive literature review or exhaustive testing of all previous hypotheses is not necessary, a deeper and more explicit discussion of how this study builds upon or diverges from past work would be highly valuable.
MINOR COMMENTS:
I found it concerning that some well-established ideas are cited using only recent publications, rather than the original sources. For example, citing Wall et al. for ERFaci and Hoffmann et al. (2023) for Eq. 6. Even a quick check of the cited papers would tell references to the original sources, which the authors should cite directly to properly acknowledge the historical development of these concepts.
Please clarify the connection between Eqs. 7-9 and Eq. 1. Are these equations intended as proxies for specific terms in Eq. 1? Please state clearly.
Line 149: Why does the current work focus only on two aerosol scenarios? More specifically, did the authors observe any indication of the previously reported "inverted-V" shape in the LWP-N relationship? If not, it is worth noting. This comment is not meant to cast doubt on the results, but rather to encourage a more complete discussion of their implications.
Line 180: The term "similar" seems too vague here. Please be more specific about the particular features the authors intended to highlight.
TECHNICAL ISSUES:
Line 129: It seems that LWP refers to the sum of LWPc (cloud LWP) and RWP. If this is the case, please state it explicitly.
Line 169: Should this refer to panel e instead of d? Please double-check.
Since Section 2 is titled "Methodology," Subsection 2.4 should be moved to a new section for clarity and consistency in the manuscript structure.
Citation: https://doi.org/10.5194/egusphere-2025-714-RC2 -
AC2: 'Reply on RC2', Marcin J. Kurowski, 07 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-714/egusphere-2025-714-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Marcin J. Kurowski, 07 Aug 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-714', Anonymous Referee #1, 17 Mar 2025
-
AC1: 'Reply on RC1', Marcin J. Kurowski, 07 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-714/egusphere-2025-714-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Marcin J. Kurowski, 07 Aug 2025
-
RC2: 'Comment on egusphere-2025-714', Anonymous Referee #2, 30 Apr 2025
OVERALL COMMENTS:
This manuscript presents Lagrangian LES simulations of marine cloud transitions along a six-day trajectory. I recommend its publication after the following comments are adequately addressed.
MAJOR COMMENTS:
The discussion of the physical processes influencing the results is somewhat underdeveloped. For instance, in Figure 4, entrainment, coupling, and radiative heating are shown in different units, which makes direct comparisons between them challenging. While these processes can be qualitatively associated with the evolution of LWP, the relative importance of each remains unclear, weakening the overall argument. The role of precipitation is neglected. In particular, a relevant mechanism to consider is the evaporation of drizzle below the cloud base, which dampens buoyancy flux, weakens turbulence, and reduces entrainment. Seee the Introduction section in Uchida et al. (2010, doi:10.5194/acp-10-4097-2010) for a summary of this mechanism. How does this process influence the results presented in this study?
As the authors noted, there have been many papers on the ACI in marine shallow clouds. It would greatly benefit the readers and strengthen and current paper if the authors can more clearly connect their new findings to the existing body of work. This is not about advertising any previous studiy, but about highlighting the novel aspects of the current paper through thoughtful comparison. For example, the diurnal LWP pattern, higher at night and lower during the day, is reminiscent of the results in Sandu et al. (2008), who proposed an explanation for this behavior. While a comprehensive literature review or exhaustive testing of all previous hypotheses is not necessary, a deeper and more explicit discussion of how this study builds upon or diverges from past work would be highly valuable.
MINOR COMMENTS:
I found it concerning that some well-established ideas are cited using only recent publications, rather than the original sources. For example, citing Wall et al. for ERFaci and Hoffmann et al. (2023) for Eq. 6. Even a quick check of the cited papers would tell references to the original sources, which the authors should cite directly to properly acknowledge the historical development of these concepts.
Please clarify the connection between Eqs. 7-9 and Eq. 1. Are these equations intended as proxies for specific terms in Eq. 1? Please state clearly.
Line 149: Why does the current work focus only on two aerosol scenarios? More specifically, did the authors observe any indication of the previously reported "inverted-V" shape in the LWP-N relationship? If not, it is worth noting. This comment is not meant to cast doubt on the results, but rather to encourage a more complete discussion of their implications.
Line 180: The term "similar" seems too vague here. Please be more specific about the particular features the authors intended to highlight.
TECHNICAL ISSUES:
Line 129: It seems that LWP refers to the sum of LWPc (cloud LWP) and RWP. If this is the case, please state it explicitly.
Line 169: Should this refer to panel e instead of d? Please double-check.
Since Section 2 is titled "Methodology," Subsection 2.4 should be moved to a new section for clarity and consistency in the manuscript structure.
Citation: https://doi.org/10.5194/egusphere-2025-714-RC2 -
AC2: 'Reply on RC2', Marcin J. Kurowski, 07 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-714/egusphere-2025-714-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Marcin J. Kurowski, 07 Aug 2025
Peer review completion
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Marcin J. Kurowski
Matthew D. Lebsock
Kevin M. Smalley
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1458 KB) - Metadata XML
Please find my review attached below.