the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 May 2024
High-resolution stratospheric volcanic SO2 injections in WACCM
Abstract. Aerosols from volcanic eruptions impact our climate by influencing the Earth’s radiative balance. The degree of their climate impact is determined by the location and injection altitude of the volcanic SO2. To investigate the importance of utilizing correct injection altitudes we ran climate simulations of the June 2009 Sarychev eruptions with three SO2 datasets, in the Community Earth System Model Version 2 (CESM2) Whole Atmosphere Community Climate Model Version 6 (WACCM6). We have compared simulations with WACCM’s default 1 km vertically resolved dataset M16 with our two 200 m vertically resolved datasets, S21-3D and S21-1D. The S21-3D is distributed over a large area (30 latitudes and 120 longitudes), whereas S21-1D releases all SO2 in one latitude and longitude grid-box, mimicking the default dataset M16.
For S21-1D and S21-3D, 95 % of the SO2 was injected into the stratosphere, whereas M16 injected only 75 % to the stratosphere. This difference is due to the different vertical distribution and resolution of SO2 in the datasets. The larger portion of SO2 injected into the stratosphere for the S21 datasets leads to more than twice as high sulfate aerosol load in the stratosphere for the S21-3D simulation compared to the M16 simulation during more than 8 months. The temporal evolution in AOD from two of our simulations, S21-3D and S21-1D, follows the observations from the space-borne lidar instrument CALIOP closely, while the AOD in the M16 simulation is substantially lower. This indicates that the injection altitude and vertical resolution of the injected volcanic SO2 substantially impact the model’s ability to correctly simulate the climate impact from volcanic eruptions.
The S21-3D dataset with the high vertical and horizontal resolution resulted in global volcanic forcing of -0.24 W/m2 during the first year after the eruptions, compared with only -0.11 W/m2 for M16. Hence, our study high-lights the importance of using high-vertically resolved SO2 data in simulations of volcanic climate impact, and calls for a re-evaluation of further volcanic eruptions.
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CC1: 'Comment on egusphere-2024-1448', Xue Wu, 24 May 2024
Thank you for providing an interesting study.
I have a few questions here:
- The title of the paper is featured in "high-resolution". Readers may expect that the differences in radiative forcing, etc., may be attributed to different resolutions. However, the major differences between the experiments M16 and S21-3D/S21-1D are not raised because S21-3D and S21-1D have a higher vertical resolution but because S21-3D and S21-1D assumed more sulfur was injected into the stratosphere. However, the title might make people think that S21-3D and S21-1D have the same integrated sulfur at the same vertical levels as M16, but only S21-3D and S21-1D have higher vertical resolutions. However, if we average S21-3D and S21-1D to a coarser vertical resolution than in M16, they still show more sulfur in the stratosphere than in M16.
- In our study, we calculated about 58% of the SO2 (0.81 Tg) was injected directly into the stratosphere during the eruption (Wu et al., 2017, ACP). (There might be further troposphere-to-stratosphere exchange that may transport a little more sulfur into the stratosphere later.) The number (58%) is actually closer to the 75% from the M16 experiment in your study. 95% is too much, which is not in agreement with observations.
- Fig.7 further demonstrates the above problem. The AOD from experiments S21-3D and S21-1D looks to have better agreements with the AOD from CALIOP, which proves the results from S21-3D and S21-1D have significantly overestimated the AOD caused by the sulfate aerosol from the Sarychev eruption. Because the AOD from CALIOP is composed of all kinds of aerosol information (NOT only sulfate aerosol) unless you have excluded the other aerosol species from the CALIOP AOD.
Regards,
Xue
Citation: https://doi.org/10.5194/egusphere-2024-1448-CC1 - AC1: 'Reply on CC1', Johan Friberg, 12 Sep 2024
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RC1: 'Comment on egusphere-2024-1448', Anonymous Referee #1, 07 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1448/egusphere-2024-1448-RC1-supplement.pdf
- AC2: 'Reply on RC1', Johan Friberg, 12 Sep 2024
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RC2: 'Comment on egusphere-2024-1448', Anonymous Referee #2, 19 Jul 2024
Review of the manuscript “High-resolution stratospheric volcanic SO2 injections in WACCM”, Axebrink et al
Dear Editor, dear Authors,
The manuscript “High-resolution stratospheric volcanic SO2 injections in WACCM” by Axebrink et al discusses large-scale modelling of the Sarychev eruption in 2009, with the aim of investigating the importance of input injection parameters and other model set-up aspects in the description of stratospheric volcanic eruptions, towards the estimation of radiative impacts of such events. The topic of the manuscript is important and of certain interest for the ACP readers. There is an active ongoing scientific debate, at the international scale, about how to represent volcanic plumes (stratospheric but also tropospheric), and their impacts, with numerical modelling. The consistency of confined plumes (volcanic emissions, wildfires, etc) observations and modelling is still to be achieved, to be honest. For this reason, this manuscript has the potential to be an important contribution to this debate. Unfortunately, I have fundamental concerns about the model set-up and cannot recommend this manuscript for publication as it is, see Specific Comments 20 and 23-29. Based on these comments, I rather recommend clarification or re-design of the experiments before I can fully evaluate this manuscript. For this reason, for the moment, I have not evaluated the Results section, and I’m waiting for such clarifications before going further in this review. In addition, I have found the manuscript severely lacking in text quality (i.e. different statements without justification) and the literature citation (knowledge?) is also to be strongly improved, see Specific Comments 1-22.
Please find Specific Comments in the following. Please address all these comments and I will be happy to review a further manuscript version, if the Authors decide to resubmit it to ACP.
I am sorry if I cannot be more positive this time but I strongly encourage the Authors to address my comments, improve the manuscript, re-design and re-run the simulations if needed, and then resubmit a new manuscript version.
Regards.
Specific Comments:
1) L22-23: why a full stop between the two sentences?
2) L23-24: "Aerosol emissions...greenhouse gases", please add one or more references for this statement.
3) L23: "These effects result in a net cooling...", not always! See the case of black carbon aerosols, e.g.: https://www.nature.com/articles/s41467-020-20482-9 or https://acp.copernicus.org/articles/22/9299/2022/ and others
4) L25: "...natural sources", why only natural aerosol sources? What about anthropogenic aerosol sources?
5) L28-29: Please rephrase: the SO2 emissions do not have a direct impact on the radiative balance, the subsequently formed sulphate aerosols have (it is said right after).
6) L29: the SO2 actually converts to binary solution droplets of sulphuric acid + water (e.g. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015RG000511). Maybe this sentence can be rephrased accordingly.
7) L30: "...which can create years of...", please mention the very long lifetime of sulphate aerosols in the stratosphere
8) L33: "explosiveness" --> "explosivity"
9) L33: "the SO2 mass" --> "the mass of the injected SO2"
10) L35: please state clearly that the cooling of the Earth's climate system from volcanic eruption is *transient*
11) L39-40: we are not at all in a background stratospheric aerosol condition, and the radiative effects of moderate stratospheric eruptions extends well beyond the "beginning of the 2000s": please mention, at least, more recent eruptions such as Raikoke 2019 (e.g. https://acp.copernicus.org/articles/21/535/2021/) and the very special case of the Hunga eruption 2022 (https://www.nature.com/articles/s43247-022-00618-z)
12) L44-46: This sentence sounds like a repetition of what already said before and can be suppressed.
13) L44: "SPA, 2006" is rather "SPARC, 2006"? This looks like too generic as a reference and the Authors can easily find more specific references
14) Please mention representative cases, like this one (plus others, in case): https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021JD035974
15) L48-49: please briefly state how satellite observations are used by modelers. Synergies studies can be cited, e.g.: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021JD035974 and https://acp.copernicus.org/articles/16/6841/2016/ and others
16) L49-50: "Most SO2..." "most" or "all"? How SO2 can be measured with active observations? Also, the question of the vertical resolution of satellite observations (especially in a nadir geometry) is complicated and should be briefly discussed here (e.g.: passive sensors do not lack vertical measurements but rather have limited vertical sensitivity, etc)
17) L51-52: "Clarisse et al. (2014) showed that IASI can provide SO2 data with vertical resolution down to ∼2 km,", this sounds a bit overestimated for infrared observations at the nadir, please check
18) L58: "column" --> "total vertical column"
19) L65: "implemented" --> the Authors mean "used as input"? See also L83
20) L73-76: I honestly did not understand the difference between second and third data sets. Please clarify.
21) L79-81: this three-lines introduction can be suppressed as it is redundant
22) L86: SO2 (AIRS) and aerosol (CALIOP) vertical profiles do not "have the same height profile" but the Authors assume this is the case, which implies the fact that the Authors assume that the SO2 and aerosol plumes are collocated. This has to be stated and the chemical/microphysical implications of this assumption should also be briefly mentioned.
23) L124: "M16 is a single column (1D) emission dataset with a vertical resolution of 1 km." How can a "single column emission dataset" have a "vertical resolution of 1 km" <-- this means that the emissions are not based on a single column but on different vertical layers (at 1 km resolution).
24) L125: why M16's and S21-1D emissions are released at a different time interval (15-16/6) than S21-3D (19/6)? If it is now known that Sarychev emissions were mainly on 19/6, why making simulations of the "wrong" days?
25) L125-126: how SO2 is released during the 6-hours period? Is it a constant emission rate? Is there a peak at some time? Why only 12:00 to 18:00 for the two days and not before/after? This sound as an unphysical way of “erupting” for a volcano and should be fixed.
26) L130-131: how SO2 is released here as well (cfr previous comment)? Same for the third dataset (L133-135)
27) L132-133: this is very puzzling. Do the Authors mixed-up the vertical and horizontal definition of "single column"? What's the actual meaning of "1D" here?
28) L151-152: using CALIOP data as a comparison data set is not completely satisfactory in terms of independence with the simulations, as one the simulation was partially initialised with CALIOP information (S21-3D)
29) Fig. 1 caption: In panel b, this is a daily average or at a specific hour? In panels c and d are also for S21-3D simulation? Please mention this in the caption.
Citation: https://doi.org/10.5194/egusphere-2024-1448-RC2 - AC3: 'Reply on RC2', Johan Friberg, 12 Sep 2024
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Data for: High-resolution stratospheric volcanic SO2 injections in WACCM Emma Axebrink, Johan Friberg, and Moa K. Sporre https://doi.org/10.5281/zenodo.11192344
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