The paper analyzes observations and models the Raikoke eruption in June 2019 in the Kuril Islands. The authors use the state-of-the-art general circulation model with the well-developed aerosol and stratospheric chemistry module in combination with the best available observations. They argue that the existing observations are still insufficient to describe the essential elements of the volcanic cloud evolution reliably. The model simulations help to better understand the overall evolution of the volcanic cloud, e.g., the simulated optical depth is twice higher than the observed one, but simulated SO2 loadings are significantly lower than that observed by OMPS-NM. The results are presented in a somewhat qualitative way. More quantitative information would help.

The paper is generally well-written and logically organized. However, it requires a more rigorous description of physical processes and how they are parameterized in the model.

The literature review is complete. I suggest the authors look at two recently published papers that consider the ash radiative heating and lofting effect in detail and ash coating by sulfate and heterogeneous chemistry.

Stenchikov, G., Ukhov, A., Osipov, S., Ahmadov, R., Grell, G., Cady‐Pereira, K., ... & Iacono, M. (2021). How Does a Pinatubo‐Size Volcanic Cloud Reach the Middle Stratosphere? Journal of Geophysical Research: Atmospheres, 126(10), e2020JD033829.

Abdelkader, M., Stenchikov, G., Pozzer, A., Tost, H., & Lelieveld, J. (2022). The effect of ash, water vapor, and heterogeneous chemistry on the evolution of a Pinatubo-size volcanic cloud. Atmospheric Chemistry and Physics Discussions, 1-49.

Specific comments:

L100: Please formulate the objectives and science questions you are targeting in this study

L147-160: CALIOP should be discussed separately in line with ONPS-NM and OMPS_LP

Section 3.1: You have to provide a more detailed description of the model physics, especially microphysical parameterizations.

Section 3.2: Please discuss the size distribution of emitted ash explicitly. What was the refractive index of ash? The deposition of dust particles should be corrected to be applicable to the stratospheric conditions.

Section 3.3 is out of context. It is better to reference Mie calculations in the place where they are used.

L222: "logical timeline" ?

Figure 1: The simulated SO2 loadings are more dispersed than in observations. Could you please comment on this? Could you provide statistical scores for the analysis?

Figure 4: Please label the panels in figure 4.

L391: Statistically significant at what confidence level?

L439: "Figure 7 begins to illustrate" - could you say it better?

L450-459: These are pretty vague explanations. Could you please clarify?

Figure 7: The e-folding time for SO2-only simulations is more consistent with observations than SO2+ash simulations, which decay faster than observed. Could you please comment on this?

L556-558: What additional analysis?

Section 4.7: Do you talk about SW clear sky radiative forcing at the top of the atmosphere? Please make it clear. Is the LW forcing negligible? How do you compare Sarychev and Raikoke's forcings? Do you compare them at the month when they are at maximum? Please clarify this.

Section 5: You added ash in simulations and did not show any figure that would characterize ash evolution. How fast does ash deposit? What is its optical depth? There should be almost no ash (if it is not pumice) in the volcanic cloud two weeks after the eruption. Please elaborate on this. Also, what about water vapor injections? Are there any estimates of injected water vapor?

L602: In the model, SO2 disperses faster than in the real world. What is the conclusion from this?

L614-616: It isn't easy to compare with the point observations in MLO, as the cloud is far not uniform at that latitude.

L634-635: The model overestimates the observed sAOD two times. This has to be acknowledged and explained.

L652-655: Why do Sarychev and Raikoke SW clear sky radiative forcings not scale with the amount of injected SO2? Both forcings are obtained in the model, so you can analyze them and tell why it happens. This type of analysis would be helpful.

General comments

The paper analyses simulations with a state of the art earth system model including chemistry and satellite observations concerning the effects of a medium size volcanic eruption. It considers 2 satellite instruments providing information on the vertical distribution of aerosol but still focuses too much on the horizontal distribution of vertical integrals in the initial phase where the uncertainty is largest due to lack of observations. Possible interactions with smoke from forest fires are mentioned but not included in the simulations.  

The model description is too short. Concerning radiative effects, the standard quantities and notations  (e.g. radiative forcing) should be used and not only subsets.  

The parts on MLO-AERONET might be skipped because of large uncertainties.

The quality of the figures should be improved. The selected color scheme is almost as bad as a grey-scale. The paper should be published after revision.

Specific comments

Line 38ff: Here again only estimates for total injections of SO₂ are cited. Satellite observations (e.g. Glantz et al., 2014, Höpfner et al., 2015) show that  stratospheric aerosol optical depth  and SO₂ concentration of Sarychev are larger than that of Kasatochi, because Kasatochi has a larger fraction staying in the troposphere (despite of the opposite behavior of the total).

Line 90: Here already 'pumice' should be mentioned, section 5 is too late.

Line 102:  Heating by soot from forest fires might be mentioned here, especially if a sensitivity study is included. 

Line 173: At Mauna Loa can be effects of local volcanoes. Also a possible signal might be dominated by Ulawun.

Line 188: Here more details on the aerosol module (modal or sectional, microphysics) should be provided. The sentence in the abstract (2 moments for what?) is not enough.

Line 192: Is CNTL without explosive volcanoes only or without any volcano including the ones outgassing into the troposphere?

Line 194ff: Here is a big source of uncertainties. Are the injections equally distributed in a slab like assumed by Mills et al. (2016)? Or is there a vertical distribution derived from observations? If yes, mention instrument. How thick is the slab in the upper troposphere? More details please, for SO₂ as well as for ash.

Line 214ff: Section 3.3 should be merged with section 3.1, also with respect to the assumed size distribution.

Line 229f: Please provide a figure for the OMPS-NM background and the background SO₂-burden in CNTL in an electronic supplement. 

Line 293ff and Figure 3: Don't expect agreement for  the initial peak in burden.  The e-folding time for OMPS-NM looks smaller than the number in the legend because of the secondary peak. Is OMPS-LP used for the vertical separation? Averaging over half of the northern hemisphere might introduce a lot of artifacts from data gaps (and maybe a mismatch in convection patterns when subtracting results of 2 simulations, depending on the calculation method). What causes the spike at day 60? It might be useful also to show averaged vertically integrated values from OMPS-LP. Please provide more information on the "background" (extra lines here or a figure in a supplement).

Line 368 and Figure 5: Provide a number or a curve for the longtime background to allow for quantitative comparisons. Unfortunately that is often a problem in the literature.

Table 1: Is there something wrong with the presentation of the CALIOP-data here? You may remove the column since it is said in the text that CALIOP sees no signal.

Line 421: This is not valid for the latitude of MLO, see Table 1.

Figure 6: Can the bias between the left and right columns be related to background removal?

Line 430ff: This is difficult to understand. How are limits applied? By scaling or truncating of a model quantity, e.g. sAOD? Or by sampling only the regions with data? The jumps in Figure 7 at the time of switching between the instruments look odd. Linear interpolation of what? More details and clarification please.

Line 506: This points to the presence of pumice or soot particles.

Line 525: 'and longitude' or 'half of the northern hemisphere'.

Line 564ff: This is something like clearsky radiative forcing. However, by subtracting results of 2 GCM-simulations you have always some kind of cloud feedback. Allsky forcing is smaller but difficult to derive by such an approach. Also infrared is not negligible. Please expand on that and use the proper notation. For the global results for 2019 the number represents the combined effect of Raikoke and Ulawun. Concerning Sarychev and Raikoke/Ulawun you may compare with the instanteneous allsky forcing of Schallock et al. (2021).

Line 597: and OMPS-LP.

Line 602f: It might not be worth, to repeat this uncertain difference here. Please shorten.

Line 630ff: There should be also important contributions from Canadian forest fires as indicated in Osborne et al. (2022). A sensitivity study with volcanic ash and forest fire soot would be of interest, also in the light of the CALIOP observations in the contribution to the discussion by Ohneiser, but maybe in a separate paper if that causes a too long delay. At least mention findings of Osborne et al., (2022) on the effect of soot.

Line 647: Caution with these statements. That might be in contradiction to other shown results. 

Technical corrections

Line 49: What 'REFS'? Insert citations.

Line 69: Typo in citation.

Line 205: Typo.

Line 318: zonally averaged or averaged over longitude. Include a-f in Figure.

References

Glantz, P., Bourassa, A., Herber, A., Iversen, T., Karlsson, J., and Kirkevåg, A.: Remote sensing of aerosols in the Arctic for an evaluation of global climate model simulations, Journal of Geophysical Research: Atmospheres, 119, 8169–818, 2014.

Höpfner, M., Boone, C. D., Funke, B., Glatthor, N., Grabowski, U., Günther, A., Kellmann, S., Kiefer, M., Linden, A., Lossow, S., Pumphrey, H. C., Read, W. G., Roiger, A., Stiller, G. P., Schlager, H., Von Clarmann, T., and Wissmüller, K.: Sulfur dioxide (SO₂) from MIPAS in the upper troposphere and lower stratosphere 2002–2012, Atmospheric Chemistry and Physics, 15, 7017–7037, 2015.

Mills, M. J., Schmidt, A., Easter, R., Solomon, S., Kinnison, D. E., Ghan, S. J., Neely, R. R., Marsh, D. R., Conley, A., Bardeen, C. G., and Gettelman, A.: Global volcanic aerosol properties derived from emissions, 1990–2014, using CESM1(WACCM), Journal of Geophysical Research, 121, 2332–2348, 2016.

Schallock, J., Brühl, C., Bingen, C., Höpfner, M., Rieger, L., and Lelieveld, J.: Radiative forcing by volcanic eruptions since 1990, calculated with a

chemistry-climate model and a new emission inventory based onvertically resolved satellite measurements, Atmospheric Chemistry and Physics Discussions, Preprint, doi:10.5194/acp-2021-654, 2021.