Review of “Heterogeneous freezing in synoptic cirrus enables subsequent homogeneous freezing” by Kasper Juurikkala et al.

In this paper Juurikkala et al. use a large-eddy model to show that early heterogeneous ice nucleation can lead to a depletion of ice nucleating particles and later instances of homogeneous freezing as a result. Data from a NASA study, MACPEX, were used for this work. This is largely in agreement with other recent field studies. It is noteworthy that the model result  – showing that initial heterogeneous freezing can lead to later homogeneous freezing – has been previously shown in a number of other model studies (as referenced here, e.g., Spichtinger et al., etc.). None the less, this is an important addition to the literature and one that should be published in ACP given some minor changes.

My major comment is that the overall length of the paper, 30 pages, is far in excess of what is needed for the treatment of what is essentially a single cloud case study. This is specifically true of section 3, the case study (6 pages), 4, the model setup (4 pages) and 5, the comparison of model and observations (9 pages). Since this paper contains supplementary information, I would highly encourage the authors to move as much of this as possible to the SI. I believe the text in these sections could easily be reduced by half without loss of content. The tables and half the figures (in section 3 Figures 2 overlaps greatly with 3 and 6, ideally just retain 3 and move the others to SI, in the later sections all contain 2 panels of which 1 can easily move to SI) could also be moved to SI. The use of so many sub-sections which seem to be small scale breaks in content also makes what should be a short and focused paper seem very chopped up. My recommendation is also that comparison to the field studies and the model description could largely rely on published results without the need for the repetition here. I hope the authors consider this as the paper will lose a lot of readers in the great length. Pulling out and focusing on the novel material – by eliminating or moving to SI the non-critical content - would increase readability a great deal.

I also encourage the authors to clarify from the abstract and introduction that the paper is a single cloud case from MACPEX, as treated by Jensen et al. 2013(b in the reference list), not an overview of the whole field mission. The ice residual measurements described in Cziczo et al., 2013 (also referenced), for the whole mission, indicate the prevalence of supersaturations and ice residuals consistent with heterogeneous freezing (not in this case but overall). This distinction is unfortunately not clearly stated until the Conclusions and so appears contradictory unless one reads all the reference materials in detail; the paper would therefore benefit from a statement in the abstract and a short paragraph in the introduction. I believe this would both help motivate and clarify their paper.

Another missing element is a couple paragraphs of treatment of previous modeling studies in the introduction, specifically those that considered the interplay between homogeneous and heterogeneous freezing. The absence of description of previous work – which, conversely, is done for field measurements - leads one to believe this is the first time it has been done, which is clearly not the case. There are some statements that discuss comparison to other studies but they are imbedded in the Case Study and Model Setup sections. Ideally these should be gathered to the Introduction, as is done for comparisons of these data to previous field measurements. Therefore, inclusion of a paragraph or two on previous work should be straightforward.

Overall, this paper, after significant shortening, will be a solid addition to the literature on the contemporary important topic of ice nucleation m