the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Aug 2025
The impact of Sahara dust aerosols on the three-dimensional structure of precipitation systems of different sizes in spring
Abstract. Saharan dust aerosols interacting with clouds and precipitation in the Atlantic Ocean's intertropical convergence zone can significantly impact storm microphysical and thermodynamic processes. Previous satellite research often focused on individual, km-scale rain pixels, neglecting interconnections among different locations. This study innovatively employs a clustering method to group satellite precipitation radar-observed profiles into organized precipitation systems (PSs) of varying horizontal dimensions. Key features such as the mean storm top height, 85-GHz polarization-corrected microwave brightness temperature, and horizontal area with specific radar reflectivity per layer are analyzed to uncover system-level precipitation characteristics. Observations indicate that dust-laden PSs have higher storm tops, broader upper-level precipitation areas with more large particles, stronger ice scattering signals, and heavier surface rain rates than clean systems. These PSs also exhibit greater convective available potential energy (CAPE) and distinct differences in related dynamic and moisture conditions. Partial correlation and sensitivity analyses revealed that CAPE-induced changes are the primary confounding factor for dust aerosol effects. Notably, even after constraining CAPE and other thermodynamic factors, significant dust-related PS changes persist. This implies that, under comparable thermodynamic conditions, Saharan dust aerosols may enhance mid- and upper-level ice heterogeneous nucleation, thereby increasing the number of ice particles, releasing extra latent heat, and invigorating storms. Overall, this study offers a novel perspective on how dust aerosols affect organized precipitation systems.
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Status: open (until 29 Sep 2025)
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CC1: 'Comment on egusphere-2025-2799', Xiong Hu, 27 Aug 2025
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The authors utilized a variety of observational data and reanalysis data to study the impact of dust aerosols on the three-dimensional structure of precipitation systems of different sizes. Nevertheless, certain methodological and interpretive aspects warrant further elaboration and refinement.
Q1: As a spectral instrument, MODIS cannot directly observe aerosols beneath clouds. Although the authors employed a spatiotemporal interpolation method for aerosol matching, it is worth clarifying whether a cloud fraction threshold was applied during the interpolation process, particularly for PS regions with high cloud coverage.
Q2: The study categorizes PSs into small (<2000 km²), medium (2000-10000 km²), and large (>10000 km²) classes based on their horizontal area. Could the authors please specify if these area thresholds were defined with reference to the climatological characteristics of PSs commonly found in the tropical Atlantic ITCZ region?
Q3: The paper primarily focuses on the aerosol-cloud interaction process involving dust acting as ice nuclei. Could the authors elaborate on whether a more quantitative investigation was conducted regarding the associated water-phase processes? Furthermore, while the dust's radiative effect is not discussed in detail within the text, it is depicted in the Fig. 10. Could this aspect be explained more thoroughly?
Q4: Figure 5 shows a reduction in the 20 dBZ area below the freezing level for stratiform precipitation in small- and medium-sized PSs under dusty conditions, which the authors attribute to the evaporation effect associated with the Saharan Air Layer. Is there more direct evidence supporting this proposed mechanism? For instance, was a significant variety in low-level humidity co-observed?
Q5: In Table 5, the sample sizes across different CAPE bins are notably imbalanced (e.g., for large PSs in the CAPE5 bin: clean n=5, dusty n=14). The statistical reliability of results derived from such small sample sizes is a concern.
Citation: https://doi.org/10.5194/egusphere-2025-2799-CC1 -
RC1: 'Comment on egusphere-2025-2799', Anonymous Referee #1, 08 Sep 2025
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General Comments: The aim of this manuscript is to statistically understand the effect of dust aerosols on the three-dimensional structure of precipitation systems of different sizes. This is an interesting and valuable attempt, as it is not common to study aerosol effects based on a large number of observational samples with the whole precipitation system as the research unit. Also, the authors have carefully considered the influence of meteorological conditions and employed multiple approaches (e.g., partial correlation analysis, and CAPE constraint) for investigation. So I think this work is well-constructed and scientifically meaningful, hence can be accepted for publication after the minor issues are addressed.
Major Comments:
- L177-180: The authors categorized PSs into three types: small-sized (< 2000 km²), medium-sized (between 2000 km² and 10000 km²), and large-sized (> 10000 km²). Please clarify the reason for selecting these specific thresholds.
- Figure 3: Why do other characteristics of PSs significantly increase under dusty conditions, while the differences in PS areas between clean and dusty conditions are not apparent?
- Section 4: In the analysis of physical mechanisms, this manuscript mentioned both the CCN effect and the IN effect of dust, but failed to clearly distinguish between these two effects. A more explicit elaboration would be necessary and beneficial.
Minor Comments:
- L14: The term ‘dimensions’ in ‘varying horizontal dimensions’ may be misleading, as it refers to size rather than dimension here.
- L21: I would recommend rephrasing the sentence ‘significant dust-related Ps changes persist’ to ‘significant dust-induced changes in PS properties persist’ for greater clarity and precision.
- Figure 1: PS2 and PS4 have noticeably smaller areas compared with the other PSs. As stated in L109-110, only PSs larger than 80 km2 were selected. Therefore, these two PSs should be excluded from this part of the analysis to avoid potential misinterpretation.
- Figure 6: Why are the significance levels of the differences between maximum radar reflectivity profiles of PSs under clean and dusty conditions not marked, as was done in the other profile figures?
- Figure 10: Numerous shape markers are used to represent different hydrometeors in the cloud, but these markers are not clearly labeled. A legend explaining this should be added.
Citation: https://doi.org/10.5194/egusphere-2025-2799-RC1 -
RC2: 'Comment on egusphere-2025-2799', Anonymous Referee #2, 09 Sep 2025
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This manuscript investigatesthe impact of dust aerosols on the three-dimensional structure of precipitation systems of different sizes using a variety of observational data and reanalysis data. The authors employed a clustering method to group satellite precipitation radar profiles into organized precipitation systems, which is a novel and valuable approach.Studying precipitation from the system perspective provides deeper insights into aerosol–precipitation interactions and their coupling with environmental conditions.However, there remain a few minor issues that need further clarification and refinement, as outlined below.
Major Comments:
1.In section 2.1, since MODIS cannot detect aerosols below clouds, the authors used a spatiotemporal interpolationand extrapolation method to estimate the dustconcentration. It is noted that the spatial extent of the extrapolation varies with the size of PSs, and the size of PSs can reflect cloud coverageto some extent. However, this manuscript does not evaluate the impact of cloud coverage.I believe sensitivity experiments should be added.
2. In section 3.2,theauthors analyzed the influence of meteorological conditions on dust effects and found that CAPE plays a significant role. The author did not explain why CAPE emerges as a more prominent factor compared to otherdynamic andmoisture conditions(e.g., vertical wind shear, relative humidity).Such an explanation is critical for understanding of the complex interactions between precipitation, aerosols, and meteorology.
3.In section 4, although the radiative effect of dust can causewarming of the midtroposphere and cooling of the near surface, thereby suppressing convection, the influence of dust radiative effects cannot be ruled out. This manuscriptprovides a rather limited introduction to dust radiative effects, which requires further elaboration.
4. The PSs selected for this study primarily consist of deep convective cloud systems that exceed 6 km in height. This selection criterion may affect the statistical results. Therefore, this should be highlighted in the conclusion section, so readers are aware of its potential influence on the findings.
Minor Comments:
1.In line 38, 'with a temperature of between -5 and +2 ℃' should be corrected to 'with temperaturesbetween -5 and +2 ℃'.
2. In Table 5, the sample sizes of large-sized PSs across different CAPE bins appear too small, which raises concerns about the statistical reliability of the results.
3. In Figure 3, it would be more accurate to replace 'area' with 'near-surface precipitation area', since it is defined as the number of pixels with near-surface precipitation rates greater than 0 mm/h multiplied by the pixel area.
4. The expression 'meteorology conditions'should bereplacedwith 'meteorological conditions'throughout the manuscriptfor grammatical accuracy and consistency.
Citation: https://doi.org/10.5194/egusphere-2025-2799-RC2
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