Strong aerosol indirect radiative effect from dynamic-driven diurnal variations of cloud water adjustments

Li, Jiayi; Wang, Yang; Li, Jiming; Zhang, Weiyuan; Zhang, Lijie; Wang, Yuan

doi:10.5194/acp-25-17455-2025

Articles | Volume 25, issue 23

https://doi.org/10.5194/acp-25-17455-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-25-17455-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 25, issue 23

Research article

|

02 Dec 2025

Research article |

| 02 Dec 2025

Strong aerosol indirect radiative effect from dynamic-driven diurnal variations of cloud water adjustments

Jiayi Li, Yang Wang, Jiming Li, Weiyuan Zhang, Lijie Zhang, and Yuan Wang

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Final revised paper (published on 02 Dec 2025)
Supplement to the final revised paper
Preprint (discussion started on 16 Dec 2024)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-3601', Anonymous Referee #1, 27 Dec 2024
This study uses retrieved properties of marine low clouds based on the Himawari-8 satellite data to investigate the LWP adjustment to Nd during the full daytime part of the diurnal cycle. It claims a large positive effect of N_d on LWP, which was previously unaccounted for.
However, the methodology has a major flaw that causes an artifact to manifest as an indicated strong positive effect of N_d on LWP. After correcting this problem, the results are likely to be very different. Therefore, this paper has to be rejected or at least undergo a very major revision.

Specific comments:
The retrievals of cloud properties:

The native resolution of the AHI is 2 km. Why use a microphysical product of 4 km? The low resolution renders the retrieval very sensitive to errors due to partial pixel feeling in most cases, except for the fully cloudy scenes. Therefore, the effects of cloud cover are confounded with those on LWP.

Why sub-sampling the data? Why is it 8 km at the NH and 6 km at the SH?

There is no justification for the threshold of r_e < 14 um. While larger re allows more water loss by precipitation, it may be more than balanced by less water loss due to less evaporation of the larger cloud drops.

Furthermore, r_e increases with cloud geometrical depth (CGT) and LWP increases with CGT². Therefore, excluding scenes by their r_e values is incurring bias, rendering the whole study questionable

Line 131: The positive trend of LWP with N_d was previously documented to occur only at N_d<30 cm^-3 (Figure 2 of Gyspeerdt et al., 2019). The clouds have to be very shallow with respectively small LWP for r_e<14 in clouds with N_d<30 cm^-3.

In fact, the condition of r_e<14 um imposes an artifact of more LWP with larger N_d, because with larger N_d the cloud needs to grow deeper and have larger LWP for reaching r_e=14 um at the cloud top !!!
Indeed, this study's maximum LWP is shifted from 30 (Figure 2 of Gyspeerdt et al., 2019) to nearly 100 cm^-3. This is evident in Fig1 left panels, especially in the convective regime (AUW), where cloud thickness and, hence, LWP consistently increase with N_d. This artifact dominates the results of this study.

Given the realization that the paper's main result is demonstrated here as an artifact of the methodology, I found little point in continuing to review the paper beyond this point, so I stopped the review here.
Citation: https://doi.org/10.5194/egusphere-2024-3601-RC1
- AC1: 'Reply on RC1', Jiming Li, 03 Jan 2025
  
  We would like to express our sincere gratitude to Reviewer #1 for the insightful and professional comments. We provide the following response to Reviewer #1's comments regarding the data and methods. Overall, the changes to the methods do not significantly affect our final results if we do not use r_e < 14 µm as suggested. The revised results is attached at the end of the response for reviewer’s reference. Please see the detailed reponses in the supplement!
  
  Citation: https://doi.org/10.5194/egusphere-2024-3601-AC1
- AC2: 'Updated Reply on RC1', Jiming Li, 18 Apr 2025
  
  We would like to express our sincere gratitude to Reviewer #1 for the insightful and professional comments. We provide the following response to Reviewer #1's comments regarding the data and methods. Additionally, we have incorporated Reviewer #2's suggestions and further refined the results. To ensure consistent responses, we decide to reply to reviewer #1's comments again.Please see the detailed reponses in the supplement!
  
  Citation: https://doi.org/10.5194/egusphere-2024-3601-AC2
RC2:
'Comment on egusphere-2024-3601', Anonymous Referee #2, 16 Mar 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-3601/egusphere-2024-3601-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-3601-RC2
- AC3: 'Reply on RC2', Jiming Li, 18 Apr 2025
  
  We sincerely appreciate Reviewer #2’s insightful suggestions, which prompt us to clarify several points and strengthen the arguments. Overall, we have clarified the explanation of the mechanisms with more supporting evidences. Many detailed discussions as suggested for the conclusion have been provided in the revised manuscript. Furthermore, we have improved the language for greater accuracy and readability. Please see the detailed reponses in the supplement!
  
  Citation: https://doi.org/10.5194/egusphere-2024-3601-AC3

Peer review completion

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

AR by Jiming Li on behalf of the Authors (18 Apr 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (01 May 2025) by Yi Huang

RR by Anonymous Referee #2 (27 May 2025)

RR by Anonymous Referee #3 (16 Jun 2025)

Suggestions for revision or reasons for rejection

The paper investigates the relationship between LWP and Nd for 2 regions over the Himawari domain. It is not clear why the authors select these regions, nor the motivation to carry out a regional analysis instead of investigating the full Himawari domain. Also, the English and the writing needs substantial work beyond the suggestions I provide here.
It is relevant to note that the precipitation filtering based on GPM observations will not remove light precipitation nor drizzle, which is quite persistent in these clouds. This is because GPM can detect rather large hydrometeors more typical of convective systems. In other words, this study is not limited to non-precipitating clouds, so precipitation must be considered when interpreting the results.
The most interesting result of this study is the positive correlation between LWP and Nd for high values of Nd. The authors conducted a partial assessment of the relationship, but it is still a somewhat superficial analysis. A critical question is whether the finding is physical. To that end, it is recommended to analyze variability of Nd and LWP with cloud fraction because biases in broken scenes could well explain the relationship. Also the result might be dependent on the binning methods. Is the binning based on percentiles, that is, bins with the same number of samples?

Abstract, “Their reflectivity to solar radiation is highly sensitive to atmospheric aerosol concentrations because aerosols can serve as the cloud condensation nuclei (CCN) to modify the mediated variables (e.g. droplet number concentrations, Nd; effective radius, re) of aerosol-cloud interactions (ACI)”. The sentence does not make sense grammatically.

…while holding cloud liquid water content (the Twomey effect) (Twomey, 1977). What does it mean?

Line 60, it should be “non-precipitating”

Line 83: “Nd can be estimated”….be more specific, did you use Eq. (1)?, If the answer is YES, then say it: “Nd IS estimated”

Line 77: “Briefly, CLTH is estimated as the altitude where the cloud-top temperature (CLTT) occurs in the temperature profile.” This assertion is incorrect, SatCORPS does not directly use the profile and the retrieved temperature for deriving the cloud height. Instead, the method is based on a lapse rate approach. See Sun-Mack et al., 2014:

Sun-Mack, S., P. Minnis, Y. Chen, S. Kato, Y. Yi, S. C. Gibson, P. W. Heck, and D. M. Winker, 2014: Regional Apparent Boundary Layer Lapse Rates Determined from CALIPSO and MODIS Data for Cloud-Height Determination. J. Appl. Meteor. Climatol., 53, 990–1011, https://doi.org/10.1175/JAMC-D-13-081.1.

Line 74: “retrieve Nd” do you mean “calculate Nd”?

Line 76-77 The SatCORPS is based on the CERES Ed4 cloud retrieval algorithm, providing more accurate CLTH and H parameterizations (Minnis et al., 2011, 2021).” More accurate than what?

Line 79: “CLTT is derived from an empirical parameterization of cloud-top emissivity at channel 4 and cloud effective temperature.” This correction primarily applies to thin cirrus clouds. For boundary layer clouds, effective and cloud top temperature are identical. Remove the sentence.

Line 82: “The SatCORPS retrievals provide cloud effective radius (re) in the 3.9 μm near-infrared band”..Please, be accurate with your description. It is more clear to say: “SatCORPS cloud droplet effective radius (re) is primarily estimated from the 3.9um near-infrared band”
Line 86: “as Q relies less on the size parameter in near-infrared.” The sentence does not make sense. Do you mean that Q varies little with particle size?
Lines 106: “We followed the previous methods to filter cloud pixels. But this classification…”, Why classification? Please revise the sentence.
Line 106-108, Why do you say that departures from adiabaticity are different between cumulus and stratocumulus clouds? This is a speculative statement.
Line 115: “Consequently, the above uncertainties will not greatly affect the conclusions of this paper…” We do not really know. For instance, if retrievals uncertainties are a function of solar zenith angle, then uncertainties will change with local time… Also, hourly changes in entrainment rate can modify the Fad parameter.
Line 125: I disagree. I direct way to calculate the effects of aerosols on LWP is to actually use aerosol concentration rather Nd. True, we don’t have aerosol retrievals for doing these….Please, change the “direct way” sentence….perhaps you could say: “is the standard way to quantify LWP sensitivity to aerosol from satellite data”.

Line 144: “obtained or calculated by ERA5 reanalysis”….What does it mean? Just say that the atmospheric parameters are obtained from ERA5.

Line 176. “For non-precipitation clouds, both positive and negative LWP adjustments have been reported” This is correct but all these studies report an inverted-V shape, whereas this study show a V shape. This is a substantial difference, which needs to be further explored. Finding a V-shape is significant departure from previous studies and, thus, the authors should spend more time trying to understand these results and double test check the signature is real.

Line 344 why is unexpected that the AOD diurnal cycle is flat? This is absolutely expected, especially over oceanic regions. Variations in AOD should be minimal, especially away from the aerosol sources.

Line 437. The reference should be Painemal et al. 2017.

Section 3.3. Without considering diurnal variations in Nd and albedo, the whole sensitivity calculation has no validity.

Discussion section: The criticism of Qiu et al. (2024) does not make sense. I would argue that the methodology in Qiu et al. was more carefully crafted than the one in Li et al. 2025. Also the stratification by cloud thickness is flawed because both LWP and thickness are a function of optical depth, so both parameters are NOT independent.

What is the physical process that would explain the convective invigoration? Why is this the only plausible explanation. For example, postfrontal conditions and cold-air outbreaks could explain both an increase in both LWP and Nd. In my opinion, the convective invigoration explanation is not proved by the analysis. The use of LTS is not optimal because LTS explains a modest fraction of cloud variance, so not finding a relationship between cloud microphysics and LTS does not mean much.

Note: This is the first time I review this paper

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ED: Reconsider after major revisions (26 Jun 2025) by Yi Huang

AR by Jiming Li on behalf of the Authors (05 Aug 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (14 Aug 2025) by Yi Huang

RR by Anonymous Referee #3 (17 Sep 2025)

Suggestions for revision or reasons for rejection

The manuscript has been substantially improved. My major concerns has been addressed. However, with the inclusion of new material, there are a number of lingering suggestions the authors should consider before their manuscript is accepted for publication. My main concern is on the interpretation of the V shape. Based on the new material, even though the V shape is clear in the analysis, this is not the manifestation of physical processes, instead, the artifact of spatial variability included in the analysis. In other words, in an ideal observational system, where it is possible to compute statistics at domains smaller than 1deg, the V shape disappears.

NB: This is my second evaluation of this manuscript.

Line 11: “geostationary observations were conducted”? you mean “Himawari-8 retrievals were used to investigate ACI in 2 regions”?
Line 15: “…is driven primarily by diurnal-related boundary layer decoupling and cloud top entrainment” Since the entrainment was not directly estimated, the statement is speculative and should be modified accordingly.
Line 32: The Albrecht 1989 citation is incorrect in the context of the sentence.
Line 34: “…as the least understood…” the phrase is not needed.
Line54-61. Qiu et al. (2024) needs to be described here because the paragraph is misleading.
Line 130 where is the re=14 um threshold coming from?
Line 145-148. This justification doesn’t make sense. Could you clarify it please?
Page 7, first paragraph. The results for ECS do not contradict Grsypeerdt et al. (2019). Note that the Nd range in Gryspeerdt does not exceed 300 /cc. In contrast Fig 1b depicts datapoints > 300 /cc. And the increase in Nd with LWP in SatCORPS NASA retrievals occur for Nd>300. My interpretation is that the East China Sea region and its range of variability is not represented in previous studies, but, again, I don’t see necessarily a discrepancy. The question is whether this increase in Nd with LWP is also observed in regions over land, where one should expect high Nd values.
Page 7 second paragraph. Insisting in the same topic of Nd range; it appears plausible that the unique behavior over the East China Sea is contributed by heavy pollution advected from the continent. In other words, meteorology is not the single factors that can modulate the relationship.
Figure 2: This is an interesting analysis. It is also relevant because it explains 2 things: 1) The v-shape is the manifestation of spatial variability. In other words, the behavior is the consequence of aggregating data from different locations (Fig. 2a). If the analysis was constrained to a narrower region (e.g. the region west of 124˚W), the so called v-shape disappears, and would be replaced by a single regime: a linear increase of Nd with LWP. Second, the linear increase of Nd comes from winter observations (cold SST). All these aspects should be discussed in the paper. Lastly, I would like to emphasize that the v-shape is an artifact, as 2 different sub-domains contribute, individually, to this shape, but in reality, it does not represent the cloud behavior. Having said that, it is still interesting that Nd increases with LWP in winter for coastal clouds. Figure 2 warrants changes to the abstract and the discussion/conclusion section. The importance of this artificial v-shape ,attributed to spatial variability, should be deemphasized, while the rather unique increase of Nd with LWP over the East China Sea should be highlighted.
Page 9, line 244-246. CAO is an extreme manifestation of cold advection, but the idea remains the same, that is, surface fluxes in the cold season are strong, attributed to changes between air-sea temperature differences, which strongly modulate cloud variability.
I still find it unnecessary to use cloud thickness to constrain the analysis of LWP. First, as I said in my first review, both LWP and physical depth are functions of optical depth and, therefore, they are not independent variables. Second, there is no physical algorithm for deriving cloud physical depth and, thus,s any method is based on empirical relationships, which are highly uncertain. The fact that a remote sensing group provides a product it does not mean that this is suitable for atmospheric research.

Estimation of cloud height: It suffices to say that the estimation follow the method in Sun-Mack et al (2014).
Line 329: “indicating that entrainment drying originates from evaporation at the cloud base”. This explanation is unphysical. Moreover, in a mixed-layer model, cloud top entrainment is the strongest during the nighttime, because it is drive by turbulence enhancement.
Line 369, why should we expect a diurnal cycle in subsidence over the open ocean? It doesn’t seem realistic. Even if a diurnal cycle in subsidence was observed, it remains to be demonstrated that is meaningful or physical. I am not aware of any large-scale diurnal cycle in subsidence other than in coastal regions near mountainous terrain (e.g. west coast of South America).

Line 364: It should read “Meanwhile, the decoupling cuts off moisture…”
Line 387-388: “Apparently, LWP skewness is a more appropriate indicator to reflect cumulus coupling in this region”, What is the line of evidence for this?, why did you use the word “apparently”?
Line 402: “hypothesized” instead of “believed”
Line 484-486: This is also the conclusion of Qiu et al. (2024)

Line 540: “Cloud thickness in the AUW region serves as a confounder to separate the effects of meteorological covariations.” You have not demonstrated this.

Line 545: I disagree, Figure 2 clearly shows that the V shape is an artifact of confounding spatial variability with microphysical processes. In other words, the relationship

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ED: Reconsider after major revisions (27 Sep 2025) by Yi Huang

AR by Jiming Li on behalf of the Authors (13 Oct 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (22 Oct 2025) by Yi Huang

ED: Publish as is (14 Nov 2025) by Yi Huang

AR by Jiming Li on behalf of the Authors (14 Nov 2025)

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Short summary

A key challenge in climate projections is the uncertainty in cloud water response to aerosols, especially from unclear diurnal microphysical-dynamical mechanisms. Geostationary satellite shows that neglecting the diurnal variations leads to an underestimation (up to 89 %) of the cooling effect induced by changes in cloud albedo due to aerosol perturbations. The results provide new insights in aerosol-cloud interactions, verifying this is a significant yet often overlooked source of uncertainty.