the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Jan 2026
Regulation of Cloud Particle Spectra and Vertical Structure by Sub-Cloud Aerosols: Insights from Aircraft Observations and Numerical Simulations
Abstract. Aerosol–cloud interactions are key processes affecting cloud microphysics, precipitation formation, and climate system energy balance. Using aircraft observations from Hebei and parcel model simulations, the spectral characteristics, vertical structures, and response of cloud particles to aerosols are systematically analysed. In liquid and mixed-phase clouds, droplet number concentration peaks occur at 5–7 μm and 14–15 μm, whereas ice and mixed-phase clouds exhibit ice crystal peaks near 125 and 1550 μm. Regarding ice crystals, high aerosol concentrations enhance number concentrations at both small and large sizes, whereas concentrations within the intermediate range are lower than those under low aerosol loadings. High sub-cloud aerosol loading effective droplet diameters in the lower part of liquid and mixed-phase clouds are 2.4 and 2.8 μm larger, respectively, than those in the upper part, accompanied by higher droplet number concentrations and broader size distributions. Under low-aerosol conditions, the upper part of liquid and mixed-phase clouds contains droplets that are 2.7 μm and 4.4 μm larger than those in the lower part, respectively. The droplet number concentrations are higher in the upper layers for both cloud types. In ice clouds, high sub-cloud aerosol concentrations yield decreasing ice crystal number concentrations with height and effective radius that first increase but then decrease. Sensitivity experiments reveal that increasing aerosol concentrations cause a monotonic increase in droplet number concentrations. At low aerosol concentrations. High aerosol concentrations amplify vapor competition and latent heat release, increasing temperature and reducing supersaturation, reducing the effective radius.
- Preprint
(2708 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on egusphere-2026-249', Anonymous Referee #1, 20 Feb 2026
- AC1: 'Reply on RC1', Honglei Wang, 21 Mar 2026
-
RC2: 'Comment on egusphere-2026-249', Anonymous Referee #2, 22 Feb 2026
Review for “Regulation of Cloud Particle Spectra and Vertical Structure by Sub-Cloud Aerosols: Insights from Aircraft Observations and Numerical Simulations” by Liu et al.
Summary:
This study examines the impact of sub-cloud aerosol concentrations in different size ranges on cloud particle properties in liquid, mixed-phase, and ice clouds. The introduction and data sections are well-written. The numerical simulations are particular insightful and lend useful context to the process-level hypotheses made by the authors. The inclusion of the adiabatic cloud model in addition to analyzing flight data from numerous flights across hydrometeor phases is commendable and a step beyond studies that solely use either observational or modeling datasets.
That said, I have major concerns about the presentation and discussion of observations shown in Figure 2 and 3. More context on the flights (such as flight maps; context on where different phases were sampled), dataset classification (definitions of upper and lower layers, examples/highlights of an individual case or two), and objective analysis back by figures (see some brief comments on figure 2, 3) are sorely needed before the results are properly reviewed. In its current form, I am struggling to properly evaluate the conclusions drawn by the authors given the discrepancy between the figures and some of the text and the difficulty in examining the figures.
I recommend the authors rework the discussion and presentation of Figures 2 and 3 significantly before the manuscript can be considered for publication. In addition, there are some minor comments provided below.
Major comments:
Abstract:
- The authors compare particle size/number in the upper and lower parts of the cloud layer. Firstly, “upper” and “lower” need to be defined objectively. Secondly, while differences in particle diameters are quantified, differences in droplet number concentration and spectral width (defined as ‘broader size distributions’) are not. From these results, it follows that the liquid/mixed-phase hydrometeor mass was considerably higher under high aerosol loading conditions? This should be clarified.
- The authors should specify here if the quantitative comparisons are based solely on aircraft data or numerical simulations also.
- Please review ACP submissions guidelines for authors at https://www.atmospheric-chemistry-and-physics.net/policies/guidelines_for_authors.html. State importance and implications of the results in the abstract. The abstract ends abruptly with a result statement.
The two key figures in section 3 need some work to be better interpretable:
Figure 2: This figure needs better labels and an explanation of why two rows represent ice clouds. The discussions in text refer to upper and lower layers of clouds whereas the labels indicate “low, mid, high”?
Figure 3:
- This forms a key figure in the authors’ analysis and interpretation of the aerosol impacts on particle distributions. As such the panels are very noisy and it is difficult to objectively analyse the results and their claims. Maybe a binning approach would be better – bin data over the upper, mid, and lower layer of the cloud profile?
- Line 208: Apart from maybe panel m, I’m really struggling to see how high aerosol conditions have higher particle concentrations. In fact, near cloud base, panel a shows low droplet concentrations near cloud base under conditions of high aerosol concentrations.
- Line 210: I’m struggling to see this claim represented in Fig. 3a, e. In fact, I see the opposite trend in Fig. 3a as blue colors representing low aerosol concentration conditions have lower values near cloud top.
- Line 216: I don’t see an increase in Ed with height for low aerosol concentrations.
- Panels o, p should be reversed as dispersion is in column 3 in the preceding rows.
Minor comments:
Abstract:
- Please maintain consistency in terminology. Authors use the terms “sub-cloud aerosol loading”, “low-aerosol conditions”, and “sub-cloud aerosol concentrations”, in three consecutive sentences to mean the same thing (I assume).
- Is there a difference between “mixed-phase clouds” and “ice clouds” on line 21?
- Is the full stop before “at low aerosol concentrations” intended?
Line 14-15: Please specify radius or diameter.
Line 17: Please rephrase and/or break sentence into two parts, it is hard to understand.
Line 50: Can the authors list a couple of the findings corresponding to these citations?
Line 54: “Jae et al. (Yeom et al. (2025)” needs to be corrected.
Line 76: Some of the uncertainties, specifically those the authors intend to address in this work should be mentioned here.
Line 87: There needs to be consistency in the information provided for different probes – please provide size range, number of bins (channels), range of particle sizes used in the study, uncertainty estimates if available, for each probe. Also please delineate between primary measurement and derived quantities. Perhaps a table with all these details might be suitable.
Line 98: I’m very confused on how many flights were used in this study because the introduction states 21 flights, then here the authors state 35 flights but the paragraph ends with a total of 29 flights, and Table 1 describes “sorties” which are not defined yet and there are only 16 sorties with multiple sorties on a single date.
Table 1: Previously, it was mentioned that data from two flight platforms were used but Table 1 only lists K350 flight sorties?
Line 105: “number concentration distribution” is awkward, I believe you mean to say the “number distribution function”, which is a term used in previous studies using airborne cloud probe datasets.
Line 117: should “n_i” be replaced by “N_i times delta r_i”? and does d_i not represent the central diameter for the ith size channel as stated previously? “droplet diameter” is misleading given that the diameter for individual droplets is not estimated.
Line 118: what is the value of n?
Line 125: mention that m is the number of channels? What is the value of m?
Line 128: the parameter “effective radius” was defined much earlier in a study by Hansen and Travis, 1974, which may be an appropriate reference here. Again, the authors may want to maintain consistency across the equations (this is the first equation that has the i subscript for the Greek symbol for summation).
Line 141: The authors need to define N_c and N_i first. The acronym “N_i” has already been used as a variable in an equation above, so I recommend using “N_ice”. Was there no “N_ice” threshold used to define liquid clouds? Why not include LWC and IWC as determinates of cloud phase? For an ice cloud threshold for temperature, I would imagine that for values up to 5 C, there may be some mixed phase segments. Please clarify.
Line 143: Sections 2.3 and 2.4 have the same heading, please adjust appropriately.
Technical corrections:
Line 56: ( 2025) -> (2025). Similar error repeats throughout the manuscript. Please edit following the journal’s recommended format.
Line 61: do you mean ice nucleating particle concentrations?
Line 69: Please define E3SM as was done for other models.
Line 117: “channel” is written twice.
Citation: https://doi.org/10.5194/egusphere-2026-249-RC2 - AC2: 'Reply on RC2', Honglei Wang, 21 Mar 2026
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 224 | 75 | 19 | 318 | 28 | 49 |
- HTML: 224
- PDF: 75
- XML: 19
- Total: 318
- BibTeX: 28
- EndNote: 49
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
My comments are included in the attached PDF.