the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jun 2026
Contrasting impacts of Asian sulfate aerosols on regional summer extreme precipitation under different climate backgrounds
Abstract. This study investigates the impact of Asian sulfate aerosols on regional summer extreme precipitation under both pre-industrial and pre-industrial +1 K climate states, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 (FORTE2) with Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce extreme precipitation, characterized by lower frequency and weaker intensity over East and South Asia in both climates, but the suppression is more pronounced over northern India in the +1 K climate. Atmospheric energy budget analysis reveals this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate state, an increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, reducing the meridional temperature gradient and thus diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses between the two climates results from the nonlinear effect between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that continued global warming alone will exacerbate Asian sulfate aerosols’ weakening of precipitation, including extremes, over northern India. This implies that future reductions in aerosol emissions may unmask or amplify extreme precipitation increases in this region.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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.- Preprint
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2026-3301', Anonymous Referee #1, 23 Jul 2026
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AC1: 'Reply on RC1', Feifei Luo, 12 Aug 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3301/egusphere-2026-3301-AC1-supplement.pdf
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AC1: 'Reply on RC1', Feifei Luo, 12 Aug 2026
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RC2: 'Comment on egusphere-2026-3301', Anonymous Referee #2, 12 Aug 2026
In " Contrasting Impacts of Asian Sulfate Aerosols on Regional Summer Extreme Precipitation under Different Climate Backgrounds ", Feifei Luo et al. use the coupled climate model FORTE2 to investigate the effects of Asian sulfate aerosols on regional summer extreme precipitation under two climate backgrounds: a pre-industrial climate state and a climate state 1 K warmer than pre-industrial conditions. The authors also compare FORTE2 results with simulations from the more comprehensive PDRMIP simulations. Overall, this is a valuable study that addresses an important and timely topic and has the potential to be of broad interest. However, the manuscript requires revisions before it can be considered for publication. In particular, it would benefit from substantial improvements in clarity, structure, and presentation. Many sentences are overly long and difficult to follow, which at times obscures the main message.
In addition, the model evaluation lacks a direct and consistent comparison framework, as the simulations being compared are conducted under different forcing and background climate conditions. This makes it difficult to assess the robustness of the FORTE2 results and weakens confidence in the conclusions. The authors should better justify the comparability of the evaluated simulations and provide a clearer assessment of model performance and result robustness.
Although a Results section and a separate Discussion section is provided later, several subsections move prematurely into interpretation and discussion without adequately presenting the underlying results. I recommend first describing the key findings shown in the figures and then reserving interpretation and broader implications for the Discussion section. This would improve the logical flow and make it easier for readers to distinguish between the reported results and their interpretation.
The manuscript structure would also benefit from placing the Discussion before the Conclusion. Furthermore, the current Discussion section reads more like a recommendation than a discussion of the study’s findings. Consider expanding the discussion of the key results, their implications, limitations, and relation to previous studies, while reserving recommendations and future work for the concluding remarks.
Line 42: The statement is somewhat ambiguous. Please clarify that the aerosol-induced reduction in precipitation is enhanced under a warmer climate background, rather than implying that global warming itself strengthens the aerosol effect.
Line 110: Could the authors provide more details on how the vertical layer thickness varies with depth? Additionally, please clarify the rationale and advantages of using progressively thicker layers at greater depths.
Lines 138–139: Could the authors explain the rationale for imposing the constraints σmin < 0.75 and pmin > 300 hPa over complex terrain? In particular, it would be helpful to describe their impact on the model performance and to provide references supporting the choice of these threshold values.
Lines 149–155: are somewhat lengthy and difficult to follow. Please consider rephrasing this section to improve clarity and readability.
Line 155 – 156: The wording is unclear. Do the authors mean that the first 50 years were treated as a spin-up period and excluded from the analysis? If so, please state this explicitly.
Fig. 1: The two panels are presented using different scales, which makes a direct comparison difficult. The authors state that the figure is intended to highlight differences in spatial patterns and signs; however, most regions appear positive in both panels. Would the authors consider including a direct comparison, such as a normalized difference or relative change, to better illustrate the differences?
Lines 193–197: The interpretation is largely left to the reader. Rather than only stating that the sign and spatial pattern can be compared, the authors should provide their own assessment of the model performance and discuss what the comparison with PDRMIP implies about the robustness and limitations of the FORTE2 results.
Section 2.1: SyRAP-FORTE2 is discussed as a version of the FORTE2 model; however, the term SyRAP-FORTE2 rarely appears beyond the model description and is not used consistently in the Results, Discussion, or Conclusion sections. It is therefore unclear whether the reported results are produced by SyRAP-FORTE2, FORTE2, or whether the two names are being used interchangeably. The authors should clarify the relationship between these model versions and consistently indicate which model is used throughout the manuscript to avoid confusion.
Lines 160–167: The large number of correlation coefficients is difficult to follow. Could the authors provide a brief summary of the key results, as a table?
Lines 260–262: Could the authors provide the corresponding figure or table of reference for these values to help readers locate the supporting results?
Line 258 and 263: "PDRMIP" and "MMM" appear to be used interchangeably. Please use consistent terminology to avoid confusion.
Lines 272 – 274: The model evaluation appears to compare simulations conducted under substantially different forcing setups and background climate states. For example, FORTE2 includes aerosol-free and P1k experiments, whereas the PDRMIP baseline is configured with present-day aerosol and greenhouse gas forcing. Could the authors justify why these simulations are considered sufficiently comparable for model evaluation?
Line 297: Please clarify what is meant by "shown here". Consider providing an explicit cross-reference to the relevant figure, table, or section.
Line 316: "East Asia and South Asia" A cross-reference to "Fig. 4a" would be helpful here, allowing readers to easily identify the regions discussed and relate the text to the spatial patterns shown in the figure.
Section 3.3: This section appears to move directly into interpretation and discussion without first presenting the results shown in the individual figures. I suggest first describing the main findings from Figs. 7 - 10 separately and then discussing their implications. As currently written, readers are expected to infer the results.
Section 3.4: Similar to Section 3.3, this section moves rapidly into interpretation without adequately presenting the results shown in Figs. 11–13. Please consider first summarizing the main findings from each figure before discussing their implications.
Lines 360–361: Since this is already the Conclusion section, the phrase "Our main findings are summarized as follows" is unnecessary and could be omitted for conciseness.
Lines 503–504: The statement " This study underscores the strong dependence of aerosol-precipitation relationships on the background climate" appears somewhat broader than what is directly demonstrated in the manuscript. Consider limiting this conclusion to the specific regions and climate scenarios examined in this study, rather than implying a more general relationship.
Line 503 – 508: While it is important to acknowledge model limitations. The wording in this paragraph sounds significantly to undermine confidence in the model and the study's conclusions.
Line 113: "adjustments" to adjustment
Line 153: “Fig. 1a” Is it the correct reference? Please verify the cross-reference.
Line 283: Please define the acronym "SST" at first use (i.e., "Sea Surface Temperature").
Citation: https://doi.org/10.5194/egusphere-2026-3301-RC2
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General comments:
The manuscript by Luo et al. investigates the impacts of Asian sulfate aerosols on regional summer extreme precipitation and their underlying physical mechanisms using the reduced-complexity climate model FORTE2. The authors compare a suite of SyRAP-FORTE2 simulations under two different background climate states (piC and p1K) with different aerosol treatments, and further compare their findings against the PDRMIP multi-model simulations. The results demonstrate that sulfate aerosols generally suppress extreme precipitation across some Asian regions, primarily driven by large-scale dynamic effects, and that a warmer climate background enhances this suppression by increasing lower-tropospheric static stability. The study also suggests a linear ARI-ACI combination under pre-industrial conditions and nonlinear interactions under a +1K climate.
The topic falls within the scope of ACP and holds scientific value. The experiments are well designed, and the paper is generally written in a clear way. However, the Abstract and Conclusion need to be more concise and focused to effectively convey the core findings and broader implications. Furthermore, several methodological and analytical details require clarification. Therefore, I recommend a major revision before its final publication.
A general suggestion for plots: Please maintain consistency in the colorbars throughout the paper. For instance, blue represents positive values in Figs. 4, 7, 9, 11, 13 but negative values in other figures, which may confuse readers.
Specific comments:
Line 23: The Abstract should begin with a brief background and introduction to the topic, followed by a clear statement of the main scientific challenges/gaps and research questions this study aims to address.
Line 65: Please briefly explain the physical mechanism by which greenhouse gases induce precipitation increases (e.g., thermodynamics).
Lines 57-84: The current literature review on anthropogenic aerosols is overly general. Given that the focus of this study is specifically on sulfate aerosols, I suggest tailoring the literature review to discuss how sulfate aerosols specifically impact regional extreme precipitation, thereby making the transition to your study's focus more natural for readers.
Line 85: It would be more natural to go to a new paragraph when you introduce what this study will do.
Line 97: Please clarify the response of “what” to Asian sulfate aerosol perturbations, e.g., precipitation?
Line 100: The heading "methods" is too broad; consider renaming it for better clarity.
Lines 138-139: Please provide references or physical justifications for the choice of the 0.75 (σmin) and 300 hPa (pmin) thresholds.
Lines 155-156: This sentence is ambiguous. Do you mean that the spin-up period is 200 years, and the last 51 years are selected for analysis? Please clarify.
Line 163: While you introduced the ACI parameterization, the ARI parameterization scheme is missing. Please provide a brief description of how ARI is implemented.
Line 185: Please define what "10×" stands for in this context.
Line 213: Please provide a reference or justification for the 1 mm/day wet-day threshold.
Lines 241-243: Please state the units for each symbol in the energy budget equations.
Line 294: Please clarify how the precipitation responses to sulfate aerosols were calculated. For instance, for Fig. 4e, is it the relative difference in PRCPTOT between p1K and SO4_p1K in FORTE2?
Lines 302 & 307: The figure subplot citations appear to be incorrect. In line 302, it likely refers to Fig. 4a, b, e, f, i, j; similarly, please check the subplot numbers cited in line 307 (e.g., Fig. 4c–l).
Line 308: Please provide statistical evidence to support the claim of "high agreement".
Lines 389-401: Section 3.3 focuses on the differences between the two climate scenarios. Therefore, the analysis (e.g., “Relative to SO4_piC, SO4_p1K exhibits weaker cold anomalies over northern India…”) should be the primary focus of this paragraph, and the detailed description of SO4_piC for Fig. 10a–d can be toned down. Additionally, it would be clearer to directly show the difference between SO4_piC and SO4_p1K for the variables in Fig. 10, moving the previous Fig. 10a–h to the supplement.
Line 403: Does "response" denote the difference between the aerosol-added experiment and the baseline scenario (e.g., (ARI_p1K - p1K) / p1K for PRCPTOT)? If so, please explicitly define this in the figure caption, and clarify the sub-panel titles (e.g., using "ARI_p1K" directly can be misleading).
Lines 414-425: Figs. 11c, f, i, l and Fig. 12, along with the corresponding text, actually focus on the differences between the two climate conditions. This material should either be restructured into Section 3.3 or streamlined.
Line 437: Please specify what kind of "moisture" is being referred to (water vapor?).
Line 449: Replace “adding” with “the additional”
Line 453: Since precipitation is also evaluated in Section 3.1, it should be mentioned briefly here as well.
Line 469 The discussion regarding resolution issues does not seem well-integrated here; consider moving it to the Discussion section.
Line 447: The Conclusion should be more concise and compact, while outlining clear directions for future research. Currently, it largely repeats the results without offering future perspectives. Please sharpen the summary and add forward-looking statements stemming from your findings.
Line 492: The Discussion section should appear before the Conclusion. Also, note that the Introduction states Section 4 provides a summary and discussion, but Section 5 is labeled as Discussion. Please ensure consistency.