| 06 Feb 2026
Evaluating SCIAMACHY-retrieved and ECHAM-simulated stratospheric aerosol characteristics by their comparison after volcanic eruptions
Abstract. Satellite observations and global aerosol–micropysical model simulations are essential to study the impact of volcanic aerosols on stratospheric composition and dynamics. However, despite their continuous improvements, uncertainties remain in satellite retrievals and model outputs due to assumptions about aerosol size, composition, and simplified model parameterizations. The SCIAMACHY v2.0 PSD algorithm for obtaining stratospheric aerosol characteristics assumes a fixed particle number density profile representative of background conditions. MAECHAM5-HAM simulations employ parameterized aerosol microphysics and chemistry. Both approaches might be affected by increased uncertainties after volcanically perturbed situations. We compare SCIAMACHY v2.0 PSD aerosol extinction coefficient and effective radius profiles with MAECHAM5-HAM simulations following the Manam (2004/2005) and Sarychev (2009) eruptions to evaluate both data products. SCIAMACHY retrievals and MAECHAM5-HAM simulations show strong consistency for the Sarychev eruption in plume location, particle growth within the plume, and size reduction at plume boarder. In contrast, SCIAMACHY observes the Manam plume further north, with differences in aerosol size evolution compared to MAECHAM5-HAM simulations. Additional comparisons with SAGE II and alternative SCIAMACHY retrievals after the Manam eruption confirm that the v2.0 PSD approach provides the most realistic aerosol characteristics from SCIAMACHY. A model parameter study highlights the importance of accurate background aerosol size information, its parameterization, and vertical injection profiles for realistic simulations of volcanic plumes. Nudging MAECHAM5-HAM with ERA5 reanalyis data improves the simulated atmospheric dynamics and brings the simulation output closer to observations. Increasing the horizontal injection area compensates for under-represented chemical interactions involving OH and volcanic ash. These findings provide valuable insights for improving the simulations of volcanic eruptions with aerosol-microphysical models and enhancing the interpretation of satellite-based aerosol data.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.
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In the paper “Evaluating SCIAMACHY-retrieved and ECHAM-simulated stratospheric aerosol characteristics by their comparison after volcanic eruptions” the authors have looked at three different SCIAMACHY-retrieved aerosol data products (v2.0 PSD, SCIA PSD N_WY and v3.0), SAGE II measurements and multiple configurations of the ECHAM model with the goal of demonstrating the usefulness of the SCIAMACHY v2.0 PSD aerosol product. Retrieval of aerosol information in the stratosphere from limb looking instrumentation is challenging and this paper provides useful information related to both the v2.0 data product, and the ECHAM model and how it can be used alongside the measurements to inform on their quality. In the end the authors conclude “This makes the SCIAMACHY v2.0 PSD a valuable data resources, …”, and I agree. Although the work is not definitive, it belongs in the open literature as it adds yet another piece to the puzzle. Because they speak truth, the last two sentences of the paper explain very nicely why I agree with the value attributed by the authors to the data product. I suggest this paper be accepted with a few revisions/suggestions that I feel are not onerous.Â
Suggestions
Although I like the synergistic use of the model and the measurements, it seems to me that it could be perceived that the outcome of the study may have been predetermined and that the methodology and analysis were designed to get to the desired result. I would suggest that the authors spend a little time convincing the reader that tweaking the model parameters, so the model agreed well with the other two data products wasn’t the right way to go. I understand the authors feel more confident with the v2.0 data product, but the reader could maybe use a little more convincing that it was the clear choice.
I am not overly familiar with the model parameters that were tweaked and although I think the authors addressed the impact of changes to the parameters, I don’t have the background to fully understand these impacts. I would ask the authors to revisit this section with a view toward the measurement community. Is it possible to add a few more sentence, or a paragraph or two, to assure the measurement community that the model is not just being tweaked to make the measurements look better? The shortcoming may be with me, so I trust the authors to add these extra words only if they are necessary.
I am curious as to what was learned about the other two data products used within this study. If the authors have anything to say about future work with these products, a paragraph devoted to them in the Conclusions would be useful.
Summary
I would like to thank the authors for their contribution to an interesting and challenging area of research. Keep up the good work.