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.