the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Using OMPS-LP color ratio to extract stratospheric aerosol particle size and concentration with application to volcanic eruptions
Mark Schoeberl
Ghassan Taha
Daniel Zawada
Adam Bourassa
Abstract. We develop an algorithm that uses the aerosol extinction at two wavelengths (color ratio) to derive the size and number density for stratospheric aerosols. We apply our algorithm to Ozone Mapping Profiler Suite Limb Profiler (OMPS-LP) L2 and Stratospheric Aerosol and Gas Experiment (SAGE) data. We show that the color ratio between two wavelengths (e.g. 510 nm/869 nm) is insensitive to aerosol concentration and thus can be used to derive aerosol size assuming a log-normal size distribution. With the size and the extinction, we can compute a number density consistent with both wavelengths. Our results compare favorably to balloon borne particle size and concentration measurements. Our results are also consistent with SAGE solar occultation measurements. Finally, we show the background distribution of stratospheric aerosols and the changes in those distributions during the Reikoke and Hunga Tonga-Hunga Ha’apai volcanic eruptions. We also show the evolution of the size and number density of aerosols following both of those eruptions.
Yi Wang et al.
Status: open (until 22 Apr 2023)
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CC1: 'Comment on amt-2023-36', Pasquale Sellitto, 25 Feb 2023
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Dear Yi,
thank you for the interesting paper on this simple but effective new methodology. I have a couple of quick questions and comments:
1) It is "Raikoke", not "Reikoke"
2) L25: "dust": do you rather mean "meteoritic dust"?
3) L78-79: "Figure 1a shows...869 nm": what are your assumptions in terms of composition in these Mie calculations (I guess it is sulphates but in case please mention this explicitely"
4) Linked to my previous question, one fundamental question that I have on this method: how do you cope in your method with aerosol mixing, i.e. aerosol layers with particles of different composition? In this case, I imagine that CR is no more insensitive to size. This is quite critical for first stages of some volcanic eruptions, like Raikoke (there was a significant fraction of ash in the early sulphate plume).
5) For Hunga Tonga, there are size distribution measurements shown in Kloss et al. 2022 (https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL099394), that are ideally perfect correlative data for your method.
6) For the rapid formation of sulphate aerosol in Hunga Tonga plume (which is linked to their size evolution), you cite model studies of Zhu et al 2022 (L234) but this is also show with observations in Sellitto et al. 2022 (https://www.nature.com/articles/s43247-022-00618-z), as well as hypothese of why observed SO2 emissions where small (L228) and estimations of the radiative impacts of Hunga Tonga plume (L227), and should then be cited in your discussion.
My best regards,
Pasquale Sellitto
Citation: https://doi.org/10.5194/amt-2023-36-CC1 -
CC2: 'Comment on amt-2023-36', Travis N. Knepp, 06 Mar 2023
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The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-36/amt-2023-36-CC2-supplement.pdf
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CC3: 'Comment on amt-2023-36', Peter F. Bernath, 18 Mar 2023
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This is an interesting paper, but some improvements should be implemented.
- The interpretation of the color ratio depends entirely on Mie scattering calculations carried out with SASKTRAN. These calculations depend on input parameters and assumptions, which need to be explicitly stated. In particular, the results depend on the assumed composition (weight % of sulfuric acid) and the optical constants used. What is the temperature of the optical constants and was there any effort to match the optical constant temperature to the atmospheric temperature? The assumption of 1.6 for the width of the log-normal distribution is noted, but the systematic error on the median radius from this assumption is not estimated. Some discussion of systematic errors introduced by these various assumptions should be included.
- Two recent papers on the properties of stratospheric sulfate aerosols from Raikoke, Tonga and Nabro volcanic eruptions based on ACE-FTS spectra have been overlooked [1,2]. These papers can help with point 1 above and with particle size comparisons with independent measurements.
- The plume from the Raikoke volcanic eruption traveled both northwards and southwards, not just South [2,3]. “The eruption cloud is initially at 50° N and moves southward so the aerosols are detected at more southerly latitudes at a later time.”
References
- Bernath, C. Boone, A. Pastorek, D. Cameron and M. Lecours, Satellite characterization of global stratospheric sulfate aerosols released by Tonga volcano, J. Quant. Spectrosc. Rad. Transfer 299, 108520 (2023). Doi: 10.1016/j.jqsrt.2023.108520
- D. Boone, P. F. Bernath, K. LaBelle and J. Crouse, Stratospheric Aerosol Composition Observed by the Atmospheric Chemistry Experiment Following the 2019 Raikoke Eruption, J. Geophys. Res.: Atmospheres 127, e2022JD036600 (2022). Doi: 10.1029/2022JD036600
- D. Cameron, P. Bernath and C. Boone, Sulfur Dioxide from the Atmospheric Chemistry Experiment (ACE) Satellite, J. Quant. Spectrosc. Rad. Transfer 258, 107341 (2020). DOI: 10.1016/j.jqsrt.2020.107341
Citation: https://doi.org/10.5194/amt-2023-36-CC3
Yi Wang et al.
Yi Wang et al.
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