While this paper has improved there are still significant difficulties in the presentation of the material which prevent a publication recommendation. All of these issues can be, or could have been, fairly easily addressed. A number of them were mentioned in the first review. The authors need to make a decision to bring the manuscript up to publication quality, or withdraw it until they have the time do so.
The authors do not do justice to one of their stated objectives, lines 114-116, “Additionally, SAGE III/ISS observations at 756 nm are employed to validate aerosol plume signatures detected by optical particle counters (OPCs), ensuring consistency across measurement techniques.” If the authors were serious about this statement, they would calculate OPC extinction coefficients at the wavelengths of the corresponding satellite observations. They don’t do this, but rather calculate OPC extinctions at 500 nm, use OMPS extinctions at 675 nm, and SAGE III extinction coefficients at 756 nm. A good compromise wavelength to allow the comparison of all three would be 675 nm. SAGE III has measurements at 676 nm. Is there a reason not to do that? Additionally if the authors were serious about their validation objective they could show a single plot with extinctions coefficients from OPCs and satellites in October 2022 when there is an impact from Hunga. Such a figure would be of great interest and would not detract from the point of this paper, but rather put the various extinction coefficient measurements in context.
Further detailed comments on these points and others follow here by line/figure number. Some of these comments are redundant to what was just said about instrument comparison since they were written as the manuscript was read.
Abstract: It would be helpful to know the wavelength assumed for the AOD estimates.
62 “… measurements of aerosol size distributions from 200 nm to 50 μm and partial aerosol concentrations corresponding to the measured size range …” The authors do not explain either here or in the response to review what they mean by partial aerosol concentrations, nor how that is different than aerosol size distributions, which can either be cumulative or differential. Some instruments measure the cumulative and some the differential, but with either one, the other can be derived. What does one do with a partial aerosol concentration, and what is it? The word partial implies there are parts of the aerosol concentration which are not measured. Clearly that part of the distribution outside of the size range covered would be one. But the authors do not state that this is implied, and anyway that is already clear from the statement about the size range of the instrument.
Same question applies to the text on line 81. But at least on line 82 we find that the authors actually mean differential distribution, which is well known in the community, and thus not sometimes, but always, called such. Why use language not familiar to the aerosol community and thereby obscure what is really measured by these instruments ?
If an instrument measures the cumulative size distribution it can easily be used to derive the differential size distribution and vice versa. Instruments don’t measure one and also the other at the same time. Depending on how they are designed they measure one or the other. It doesn’t make sense to state they measure both.
69 The time sampling … to end of paragraph is redundant to the statements just above where it was stated much more clearly. There is no need for this text, which is a holdover from the first version.
114-116 The OPC data are used to calculate extinction at 500 nm, according to their introduction, yet here the SAGE III data to be used are at 756 nm, even though the authors state, “Additionally, SAGE III/ISS observations at 756 nm are employed to validate aerosol plume signatures detected by optical particle counters (OPCs), ensuring consistency across measurement techniques.” Right good idea. So why don’t the authors used 521 nm from SAGE III so that these two data sets can be more carefully compared? In fact why don’t the authors calculate extinction coefficient at the SAGE III wavelengths they are going to use for the comparison? There several choices, 521, 676, 756 nm. If 676 was used it would allow OMPS to be included in the comparison. While such a comparison may be a little off the main point of this paper, it would add additional interest and confidence in the data sets used, which would enhance the points of this paper, and add to the stated objective above.
122 Supplementary figure A3 is called out before A1 and A2. Why aren’t the supplementary figures organized according to their call outs in the manuscript?
Figure A1. How is this figure useful for this manuscript? What is the reason to expand the extinction coefficient to 4 orders of magnitude and include the profile from the surface? The discussion of this figure only focuses on the large extinction coefficients below the tropopause which are attributed to a cirrus cloud. Is the reason so that the authors can show the LOAC is sensitive to cirrus clouds? But this is off the paper’s topic. The interest here is in the stratosphere. There is no additional information provided for the satellite measurements in this figure, and panel F show measurements in December 2021 before the Hunga eruption, and what does MAGIC at the top of this profile and in Figure A3 mean?
For the second time, why are the authors trying to squeeze measurements from an unknown instrument into this manuscript, particularly as the measurements have nothing to do with the Hunga plume in the NH. Figure A1 should be removed.
Then there is this statement, “The good comparability between the POPS and POPC profiles gives confidence in the reliability of the POPS and LOAC measurements.” How does it do that? LOAC is not compared in panel F. What could really help establishing reliability of the LOAC and POPS would be for them to be plotted together on the same graph. Didn’t they make measurements on the same day from the same location? And adding to that would be a SAGE III profile on the same graph to get a better sense of the correspondence of these three different instruments’ estimates of extinction coefficient, which would strongly test one of the authors’ stated goals of establishing “…the reliability and confidence in the POPS and LOAC measurements.” Certainly they won’t agree perfectly, but perhaps within known uncertainties in the measurements.
Figure A2. For the second time, why isn’t this figure added to Figure 2? It’s a sounding measurement at the same location as the POPS and LOAC and the timing is very interesting, showing no impact of Hunga on 10/10/22, one week before the Hunga plume was observed by POPS and LOAC at the same location. And then COBALD shows that the Hunga plume was still observable with in situ instruments two months later. This timing is also consistent the the CALIPSO data shown in Figure 5, where a dotted line could be added to show the COBALD sounding.
199-206 Why is there a call out to Figure 5 when Figures 3 and 4 have not been discussed? Reorder the figures and call them out in order for the sake of the reader if not for a logical progression of the manuscript! Or do the authors mean Figure 3 which is the back trajectories referenced in the discussion here, but the discussion also says that backscatter ratio was calculated along the back trajectory, but that is not shown. Backscatter ratios from CALIPSO are shown in Figure 5, but the discussion here does not mention CALIPSO. This paragraph needs to be straightened out. At this point it is inconsistent with the text, discussing data which are not shown.
Figure 3 caption. Don’t the authors mean that the air parcels culminate in a box 48-50 N? The air parcels in the figure originate between 24 and 28 N.
208 After the paragraph above the discussion shifts to Figure 6, skipping any discussion of Figure 4 and either Figure 3 or 5, depending on what figure the previous paragraph was referring to.
Fig. 6 caption states the OMPS data are from January 2022 – 2024, but what is shown only extends to September 2024. Why the discrepancy?
Table 1. It would be interesting to include in Table 1 the equivalent quantities from the lognormal fit to the LOAC data, even though there would be only one mode for LOAC. Equally interesting would be effective radius and aerosol extinction from both instruments and from the two POPS modes. Even though the two distributions are somewhat different such a comparison would provide an indication of how important these differences are.
280-284 Why do the authors express the range of a quantity as high to low rather than low to high, which is more customary? High to low forces the reader to reread a sentence to insure it is understood, an unnecessary complication.
287 For the second time, what is a theoretical Angstrom exponent? An Angstrom exponent just describes the relationship between extinction coefficients at two wavelengths, to allow extinction coefficient at an intermediate wavelength to be estimated. So does a theoretical Angstrom exponent imply extinctions from a theory, or are they from a model, which is quite different than theoretical? There are many ways models can provide an aerosol size distribution which is required to obtain an extinction coefficient. And, again for the second time, what two wavelengths are used to obtain the Angstrom exponent quoted?
289 What satellite observations provide these size distributions? They should be mentioned here.
Table 2 has problems. The extinction coefficient has a range from 1.1 e-3 to 8.5 e3. That’s a range of 6 orders of magnitude. The Angstrom exponent listed does not indicate the wavelengths involved.
304 Where is this 50% increase in extinction observed? According to Table 2, comparing row 3 with row 1, the increase is more like 30%, e.g. 1.7/6.9 at 384 nm, 1.1/3.1 at 756 nm, and 0.7/1.6 at 1020 nm. |
Thank you very much for authors' work regarding the cross-hemispheric transport of the Hunga aerosol plume. Please find some supplement informations in the uploaded file.