|I would like to sincerely thank the Authors for their work and revisions of their very interesting manuscript. I can see that most of my Specific Comments have been tackled and I’m very satisfied of the way this was addressed by the Authors. By the way, my main concerns have been mostly skipped, namely the model’s representation of secondary aerosols (Major Comment 1 and a few Specific Comments) and the role of evolving optical properties on the radiative impacts (Major Comment 2 and a few Specific Comments). To be clear, I honestly think that the paper should be published soon, as it deals with an important topic, but I would in any case require that these two points are better addressed before publication. This basically means: 1) smoothing many very strong statements (e.g. about the “certainly positive radiative forcing of the plume” or the “perfect optical properties simulated by the model” or the “secondary aerosols which are surely not formed”) and 2) adding a deeper and comprehensive discussion on the two issues. I strongly suggest the Authors to make this effort. A few more details are in the following.|
Thank you for the interesting work and discussion,
Major comments (#MC)
MC1) In Khaykin et al., 2020, it was supposed that one reason for the increasing trend of SAOD could be saturation of the OMPS-LP detector. This was the proposed reason at the time of publication of that paper (which I personally co-authored). By the way, following reflections and analyses since that publication, while keeping this as a possible explanation of this time evolution of the SAOD, led to other possible explanations: 1) the formation of secondary aerosol and aerosol mixing, (which, on the other hand is a known issue in terms of representation of biomass burning plumes in models like the one used in this work (Brown et al., 2020)) and 2) plume’s progressive lofting due to in-plume radiative heating. These aspects are further addressed and discussed in a recent preprint publication (https://egusphere.copernicus.org/preprints/egusphere-2022-42/) that I suggest checking. As a matter of fact, these two aspects cannot be excluded, and this certainly needs further discussion in the paper. Why are you so deterministic in this statement “Secondary aerosol formation appears unlikely to be the explanation considering the required amount of smoke.”? The progressively less absorbing aerosol properties seem to actually point at a progressive secondary aerosol formation and brown-carbonification of black carbon emissions. The LiDAR SSA inversions (by the way, please discuss briefly the inversion methodology in the Data and Methods section) that are now presented in the manuscript cannot actually demonstrate the fact that there is no secondary aerosol formation, and then progressive larger SSA and lesser absorption from plume’s aerosol, because: 1) if I got it right, these are measurements for January 2020 only, too early to have a marked secondary aerosol formed and a clear signature in the plume’s aerosols optical properties; 2) LiDAR inversions of optical properties have usually significant uncertainties and SSA variability is small (from 0.75-0.80, for black carbon; 0.85-0.90, for brown carbon, only 10-15% increase on SSA but sufficient to switch the RF sign from positive to negative). Also, the statement, P15 L3-4: “Ohneiser et al. (2022) show an SSA of 0.79 for the rotating smoke disk on 26 January above Punta Arenas in Chile, which is also representative for other smoke measurements” is not true: the vortex plume is an isolated patch of fresh smoke aerosols, isolated from the environment and absolutely not representative, in terms of optical properties, of the overall large-scale plume: please correct. It is necessary that you add a substantial discussion on these aspects in your manuscript and be more cautious in this respect in the Abstract and Conclusions.
MC2) First, please accept my apologies for my mistake: Yu et al. (2021) is also clear-sky RF estimations and not full-sky as I stated in the previous review round. By the way, it is undoubtedly true that optical properties of the aerosol layer have dramatic impacts on the radiative forcing of a given aerosol layer, which is even more important for biomass burning highly evolving plumes. The LiDAR observations and all discussion in the revised manuscript only deal with the young plume (in January), while the optical properties of biomass burning aerosols should evolve (e.g. SSA and g) at longer timescales and mostly visible, in case, starting from February-March. Thus, it cannot be accepted what you state: “This analysis, however, further supports that the optical properties of the fire aerosol are reasonably realistic for this case, and thus the positive instantaneous solar radiative forcing at TOA”. Again, yours is a valuable work and should be published but the limits of the model assumptions must be discussed, and the fact that the magnitude and sign of the radiative forcing depend on the modelled aerosol optical properties must be clearly stated. The strict certainty of a positive radiative forcing, that you suggest, should be avoided throughout the whole text. In the meanwhile, a preprint with sensitivity analyses of radiative forcing for this event to optical properties has been published (see MC1); please exploit, in your paper, these sensitivity analyses in the discussion of this aspect.