Dear Authors

Thank you for providing the revised manuscript “Strong aerosol-cloud interaction in altocumulus during updraft periods: lidar observations over central Europe” as well as your responses to the issues raised during the reviews.

Based on the reviewer’s comments and my own assessment I have concluded to reconsider your manuscript for publication in Atmospheric Chemistry and Physics after minor revisions.

Most of the reviewer’s comments have been resolved in your response; however, I would kindly ask you to address some outstanding issues listed below.

I am looking forward to your revised manuscript.

Kind regards,

Philip Stier
Co-Editor
Atmospheric Chemistry and Physics


Major issues:

1. All reviewers raised the issue of statistical significance. I take note of your emphatic rebuttal of these requests. While I agree with you that there is very little that can be done about this experimentally and that there is still value in such analysis, this should not require this analysis to become qualitative. You write that if you performed the tests “most tests would tell us: most of the results are statistically not significant!” but that you still present “a statistical analysis of ACI values based on well-defined liquid-water cloud layers with a promising innovative approach”. If that is the case then I do not see a reason why one could not add some results and discussion on significance and move the argument you are making in your rebuttal to the actual paper, i.e. show that there is still merit in this. This is important as you drawing very strong general conclusions from your work that should probably be backed up with longer term statistics in the future, as you argue yourself in the conclusions.

2. Theoretically and experimentally there is little doubt that one would expect different values of ACI when sub-sampling different parts of the vertical velocity spectrum. However, that does not necessarily make one sampling superior (referred to in the manuscript as “necessary”, “important for a realistic estimation”, …) or other scales inferior (referred to as “must be generally interpreted with care”, “not be appropriate to guide climate modelling”) - they are different and may have different applications. To detect an effect in noisy data, updraft sampling is certain to give the strongest signal but for the actual radiative effect driving global mean forcing one could argue that the cloud mean effect (or even cloud regime / regional or global mean) is really what matters. So even if we had perfect satellite and lidar retrievals without sampling errors, ACI would differ simply because your proposed methodology preferentially samples area with the largest ACI values and satellite data would deliver larger-scale averages. This should be explicitly discussed and all judgemental statements in the manuscript as outlined above should be put in this context.

3. The literature overview presented in Fig. 7 and the discussion in section 4 is interesting but I was missing some differentiation based on the regime. Clearly ACI will depend on the cloud regime via the updraft pdf but it will also depend on the availability of CCN via saturation effects. Many of the discussed differences can probably be attributed to differences in the analysed (updraft or CCN) limited regime and the averaging scale (see above).

Specific issues:

1. Some parts of the manuscript make unnecessarily general statements that need to be substantiated, such as:
“For the first time, a detailed lidar-based study of the aerosol-cloud-dynamics relationship was conducted.”
You should provide an overview over previous area in this field in the introduction to substantiate this. “First time” is dangerous ground as it all depends on what you call “detailed”.
“There is no doubt that aerosols play a key role in the evolution of warm (pure liquid-water) and mixed- phase clouds and in the formation of precipitation and that anthropogenic and natural aerosols thus sensitively influence the atmospheric water cycle as a whole.”
This is not an uncontroversial statement and the verdict on the influence of aerosol on the water cycle is still out. Please be specific and substantiate.
“However, we are far away from a good representation of aerosols and their complex role in the climate system in computer models, especially with respect to aerosol vertical layering”
This is true but needs to be demonstrated either in the paper or through references.

2. Your introduction does not give an overview over lidar work regarding to aerosol cloud interactions other than your own. This should be extended, in particular in the light of your statement that this is the first work attempting to do a detailed anlaysis.

3. Line 260: “A distance of 300 m to the cloud layer base was usually sufficient to avoid that particle water-uptake effects influenced αp.”
How do you know?

4. You use aerosol “burden” often synonymously with concentration. In most of literature this refers to the column amount.

5. Line 544: Any statements referring to numbers, such as “Typical cloud scales of variabil- ity (process scales, 100–1000 m) are much smaller than the scales of variability in the aerosol properties (10–100 km).” should be backed up with references.

6. Line 716: “In summary, we may conclude from Fig. 7 that all CCN become activated at cloud base when injected into the cloud from below”
CCN is used very loosely here. What you may conclude is that all CCN that activate at the realised supersaturation (or can be detected by your sensor) may have activated. As you use mid-visible extinction the sensitivity is largest in the accumulation mode and smaller CCN requireing larger supersaturations may not be detected.

Dear Authors

Thank you for providing the revised manuscript “Strong aerosol-cloud interaction in altocumulus during updraft periods: lidar observations over central Europe” as well as your responses to the issues raised in the editor report.

Your responses and the revised manuscript have addressed all outstanding issues and I am happy to accept this manuscript for publication in ACP.

Thank you very much for choosing ACP!

Kind regards,
Philip Stier