the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Dec 2023
Initial conditions control transport of volcanic volatiles, forcing and impacts
Abstract. Volcanic eruptions impact the climate and environment. The volcanic forcing is determined by eruption source parameters, including mass and composition of volcanic volatiles, eruption season, eruption latitude and injection altitude. Moreover, initial conditions of the climate system play an important role in shaping the volcanic response. However, our understanding of the combination of these factors, the distinctions between tropical and extratropical volcanic eruptions and the co–injection of sulfur and halogens remains limited. Here, we perform ensemble simulations of volcanic eruptions at 15° N and 64° N in January, injecting 17 Mt of SO2 together with HCl and HBr at 24 km altitude, considering different initial conditions of the El Niño–Southern Oscillation, Quasi–Biennial Oscillation, and polar vortex. Our findings reveal that initial conditions control the transport of volcanic volatiles from the rst month and modulate the subsequent latitudinal distribution of sulfate aerosols and halogens. This results in different volcanic forcing, surface temperature and ozone responses over the globe and Northern Hemisphere Extratropics (NHET) among the model ensemble members with different initial conditions. NH extratropical eruptions exhibit a larger NHET mean volcanic forcing, surface cooling and ozone depletion compared to tropical eruptions. However, tropical eruptions lead to more prolonged impacts compared to NH extratropical eruptions, both globally and in the NHET. The sensitivity of volcanic forcing to varying eruption source parameters and model dependency is discussed, emphasizing the need for future multi–model studies to consider the influence of initial conditions and eruption source parameters on volcanic forcing and subsequent impacts.
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RC1: 'Comment on egusphere-2023-2374', Anonymous Referee #1, 31 Dec 2023
There’s some interesting stuff in here, and I think with some revision this paper could be a useful contribution. I am recommending major revisions. I have a few big issues:
The first is that many of your descriptions are unclear, so you get conclusions that don’t obviously make sense. I’ve pointed out some detailed examples below.
The second is that your experiment is not well controlled. You don’t provide simulations of sulfur injection without halogens. You also don’t carefully control for different ENSO states. Perhaps this can be addressed through my first main point, in that it’s not entirely clear what questions you’re trying to answer.
Third, which may also be related to the first point, is about statistical significance. You do a good job of showing when the ensemble members are different from the control run. You do not differentiate the ensemble members from each other, which I think is the more interesting question and better aligned with what I interpreted as the purpose of your manuscript. This also leads to figures that are hard to interpret, as they contain a huge amount of information that obfuscates the intra-ensemble differences.
Some more detailed comments:
I think some more careful description in the first few pages is warranted. There are several points where you say that the initial conditions of the eruption are important, which is also known from the El Chichón and Pinatubo eruptions (the wind direction dictated where the aerosols went). But then you also talk about the season of the eruption, which matters more from a large-scale circulation perspective. I’d like you to be specific about what you mean by initial conditions and clarify the relevant timescales/processes.
This isn’t as controlled of an experiment as it could be, as you don’t provide simulations of sulfur injection without halogens. You mention that this could be important in lines 340-344. I realize doing new simulations could be a lot of work (although the simulations are short), so perhaps this could be solved by better caveating your study. And then your discussion of lines 346-347 (and perhaps all of Section 4.4) will need to be modified.
There isn’t much discussion of the phase of the QBO and tropical confinement in the Easterly phase.
Line 140: I suppose it depends on what you mean by “climate impact”. If one cares about tropical precipitation shifts or northern hemisphere winter warming, high latitude eruptions are known to have a greater impact than tropical eruptions.
Lines 146-148: So is the difference between the ensemble members due to wave breaking? It’s not obvious from reading this _how_ the ensemble members differ. I don’t see analysis supporting your statements.
Figure 2 is extraordinarily complicated, and it’s not obvious what the take-home message is just by looking at it. I wonder if this figure could go into supplemental material, and then another, simpler figure that highlights the main points can be in the main text.
Lines 172-174: Can you provide a brief summary of the findings of Fuglestvedt et al. (2023) for readers who haven’t studied that paper in detail?
Lines 204-205: Are these differences statistically significant?
Line 211: Well, sort of. The figures in Lacis stop at 1 micron. Above that you start to get pretty strong warming by the aerosols, which has an important effect on forcing. And the figures by Lacis refer to aerosol size, which is very different from effective radius.
Line 222: Citation to Kravitz and Robock (2011) seems appropriate here.
Lines 235-237: I find this part a bit unsatisfying, in that it does not represent a controlled experiment. Only H1 and H2 have strong positive ENSO states. Is that coincidence, or is there a reason that a strong positive ENSO would not lead to more poleward transport of sulfur? (Edit: you do address this somewhat in Section 4, but I think it’s still a bit lacking. Only two instances of positive ENSO states can’t cover the spread of initial conditions.)
Lines 249-250: Is this surprising? It seems as though mechanisms that transport one thing would transport other things.
Lines 262-264: This needs more clarification. Halogens from CFCs (what we typically think of when discussing stratospheric ozone) have a very long lifetime, so there shouldn’t be a lower burden due to removal. So what exactly are you injecting, and what are the removal processes and lifetimes? This will also aid Figure 4, in that you may not need to extend the panels out to 60 months to highlight differences between the ensemble members.
Figure 3: Are the ensemble members statistically significantly different from each other? It’s not obvious from this figure that the initial conditions of the eruption lead to climatically important differences.
Lines 283-287: Your results don’t make sense in the context of these lines. H6 involves the strongest poleward transport yet corresponds to a La Niña state with a strong polar vortex, which should serve as a transport barrier. The opposite is true for H1. Perhaps I’m unclear as to what you mean by poleward transport and how/where you’re measuring it?
From Figure S2, it looks like all of your simulations begin at approximately the same QBO state. So how exactly are you testing the influence of the QBO phase on your results?
Citation: https://doi.org/10.5194/egusphere-2023-2374-RC1 - AC1: 'Reply on RC2', Zhihong Zhuo, 15 Mar 2024
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RC2: 'Comment on egusphere-2023-2374', Anonymous Referee #2, 19 Jan 2024
This study uses CESM2 to look at the dependence of the evolution of volcanic aerosols, forcing, and impacts on surface temperature and ozone on the eruption latitude, season, atmospheric initial conditions, and presence of halogens.
This is an interesting study and could be a valuable addition to the literature, but I am suggesting major revisions as some of the statements (detailed below) are not well supported by the data. The authors need to be more quantitative when describing the difference between simulations.
Also, the figures contain a lot of information and I found it hard to follow at times. It might be clearer to reduce the amount of information to what is strictly necessary, but I recognise this is difficult.
Major comments:
Fig 1 : Too many lines and difficult to read. Is it possible to choose certain ensemble members?
Can you specify exactly what measure you used to classify from H1 to H6?
L.161/2 : “there is comparatively lower upward transport of SO2 compared to the other members” How do you deduce that? They look similar to me.
L.166-8 : Again, that does not seem terribly obvious to me.
Fig 2 : What latitudes is NHET defined over?
L.179 : Is the difference in e-folding times significantly different?
L.197-8: “the global–mean SO4–mass–weighted mean effective radius (Ref f , Fig. 2e) increases faster after tropical eruptions compared to NH extratropical eruptions for the first 6 months.” Again, I don’t really see a significant difference between the 2 ensembles in the first 6 months, so this claim is not supported by the data.
L.218-220 : “Both global–mean (Fig. 3a and 3c) and NHET–mean surface temperature (Fig. 3b and 3d) show a weaker but longer–lasting surface cooling after 220 tropical eruptions (Fig. 3a and 3b) compared to NH extratropical eruptions (Fig. 3c and 3d).” Again, I am a little concerned about whether the data supports that statement.
L.268-9 : Again you might want to be more quantitative here, because the blobs in figure 1 all look similar to me.]
L.316 be more quantitative, the differences are really quite small.
Minor comments:
L.48 : replace “next to” with “as well as”
L.72/76 : replace “co-injecting” with “which inject”?
L.121 : lasts -> lasting
L.224 The use of “interrupt” here is weird.
L.250 representative -> present
Fig S2 : make the vertical lines thicker. Also the difference between the initial states might be clearer if you did a line plot with the winds along the transects?
L.300-311 : Nice paragraph!
Fig 5 : Need to clarify that the first bar is Cly and the second bar is Bry, that confused me a bit.
Fig 6 : are panels e-h the same as figure 3 with added lines for S injections?
Citation: https://doi.org/10.5194/egusphere-2023-2374-RC2 - AC1: 'Reply on RC2', Zhihong Zhuo, 15 Mar 2024
Status: closed
-
RC1: 'Comment on egusphere-2023-2374', Anonymous Referee #1, 31 Dec 2023
There’s some interesting stuff in here, and I think with some revision this paper could be a useful contribution. I am recommending major revisions. I have a few big issues:
The first is that many of your descriptions are unclear, so you get conclusions that don’t obviously make sense. I’ve pointed out some detailed examples below.
The second is that your experiment is not well controlled. You don’t provide simulations of sulfur injection without halogens. You also don’t carefully control for different ENSO states. Perhaps this can be addressed through my first main point, in that it’s not entirely clear what questions you’re trying to answer.
Third, which may also be related to the first point, is about statistical significance. You do a good job of showing when the ensemble members are different from the control run. You do not differentiate the ensemble members from each other, which I think is the more interesting question and better aligned with what I interpreted as the purpose of your manuscript. This also leads to figures that are hard to interpret, as they contain a huge amount of information that obfuscates the intra-ensemble differences.
Some more detailed comments:
I think some more careful description in the first few pages is warranted. There are several points where you say that the initial conditions of the eruption are important, which is also known from the El Chichón and Pinatubo eruptions (the wind direction dictated where the aerosols went). But then you also talk about the season of the eruption, which matters more from a large-scale circulation perspective. I’d like you to be specific about what you mean by initial conditions and clarify the relevant timescales/processes.
This isn’t as controlled of an experiment as it could be, as you don’t provide simulations of sulfur injection without halogens. You mention that this could be important in lines 340-344. I realize doing new simulations could be a lot of work (although the simulations are short), so perhaps this could be solved by better caveating your study. And then your discussion of lines 346-347 (and perhaps all of Section 4.4) will need to be modified.
There isn’t much discussion of the phase of the QBO and tropical confinement in the Easterly phase.
Line 140: I suppose it depends on what you mean by “climate impact”. If one cares about tropical precipitation shifts or northern hemisphere winter warming, high latitude eruptions are known to have a greater impact than tropical eruptions.
Lines 146-148: So is the difference between the ensemble members due to wave breaking? It’s not obvious from reading this _how_ the ensemble members differ. I don’t see analysis supporting your statements.
Figure 2 is extraordinarily complicated, and it’s not obvious what the take-home message is just by looking at it. I wonder if this figure could go into supplemental material, and then another, simpler figure that highlights the main points can be in the main text.
Lines 172-174: Can you provide a brief summary of the findings of Fuglestvedt et al. (2023) for readers who haven’t studied that paper in detail?
Lines 204-205: Are these differences statistically significant?
Line 211: Well, sort of. The figures in Lacis stop at 1 micron. Above that you start to get pretty strong warming by the aerosols, which has an important effect on forcing. And the figures by Lacis refer to aerosol size, which is very different from effective radius.
Line 222: Citation to Kravitz and Robock (2011) seems appropriate here.
Lines 235-237: I find this part a bit unsatisfying, in that it does not represent a controlled experiment. Only H1 and H2 have strong positive ENSO states. Is that coincidence, or is there a reason that a strong positive ENSO would not lead to more poleward transport of sulfur? (Edit: you do address this somewhat in Section 4, but I think it’s still a bit lacking. Only two instances of positive ENSO states can’t cover the spread of initial conditions.)
Lines 249-250: Is this surprising? It seems as though mechanisms that transport one thing would transport other things.
Lines 262-264: This needs more clarification. Halogens from CFCs (what we typically think of when discussing stratospheric ozone) have a very long lifetime, so there shouldn’t be a lower burden due to removal. So what exactly are you injecting, and what are the removal processes and lifetimes? This will also aid Figure 4, in that you may not need to extend the panels out to 60 months to highlight differences between the ensemble members.
Figure 3: Are the ensemble members statistically significantly different from each other? It’s not obvious from this figure that the initial conditions of the eruption lead to climatically important differences.
Lines 283-287: Your results don’t make sense in the context of these lines. H6 involves the strongest poleward transport yet corresponds to a La Niña state with a strong polar vortex, which should serve as a transport barrier. The opposite is true for H1. Perhaps I’m unclear as to what you mean by poleward transport and how/where you’re measuring it?
From Figure S2, it looks like all of your simulations begin at approximately the same QBO state. So how exactly are you testing the influence of the QBO phase on your results?
Citation: https://doi.org/10.5194/egusphere-2023-2374-RC1 - AC1: 'Reply on RC2', Zhihong Zhuo, 15 Mar 2024
-
RC2: 'Comment on egusphere-2023-2374', Anonymous Referee #2, 19 Jan 2024
This study uses CESM2 to look at the dependence of the evolution of volcanic aerosols, forcing, and impacts on surface temperature and ozone on the eruption latitude, season, atmospheric initial conditions, and presence of halogens.
This is an interesting study and could be a valuable addition to the literature, but I am suggesting major revisions as some of the statements (detailed below) are not well supported by the data. The authors need to be more quantitative when describing the difference between simulations.
Also, the figures contain a lot of information and I found it hard to follow at times. It might be clearer to reduce the amount of information to what is strictly necessary, but I recognise this is difficult.
Major comments:
Fig 1 : Too many lines and difficult to read. Is it possible to choose certain ensemble members?
Can you specify exactly what measure you used to classify from H1 to H6?
L.161/2 : “there is comparatively lower upward transport of SO2 compared to the other members” How do you deduce that? They look similar to me.
L.166-8 : Again, that does not seem terribly obvious to me.
Fig 2 : What latitudes is NHET defined over?
L.179 : Is the difference in e-folding times significantly different?
L.197-8: “the global–mean SO4–mass–weighted mean effective radius (Ref f , Fig. 2e) increases faster after tropical eruptions compared to NH extratropical eruptions for the first 6 months.” Again, I don’t really see a significant difference between the 2 ensembles in the first 6 months, so this claim is not supported by the data.
L.218-220 : “Both global–mean (Fig. 3a and 3c) and NHET–mean surface temperature (Fig. 3b and 3d) show a weaker but longer–lasting surface cooling after 220 tropical eruptions (Fig. 3a and 3b) compared to NH extratropical eruptions (Fig. 3c and 3d).” Again, I am a little concerned about whether the data supports that statement.
L.268-9 : Again you might want to be more quantitative here, because the blobs in figure 1 all look similar to me.]
L.316 be more quantitative, the differences are really quite small.
Minor comments:
L.48 : replace “next to” with “as well as”
L.72/76 : replace “co-injecting” with “which inject”?
L.121 : lasts -> lasting
L.224 The use of “interrupt” here is weird.
L.250 representative -> present
Fig S2 : make the vertical lines thicker. Also the difference between the initial states might be clearer if you did a line plot with the winds along the transects?
L.300-311 : Nice paragraph!
Fig 5 : Need to clarify that the first bar is Cly and the second bar is Bry, that confused me a bit.
Fig 6 : are panels e-h the same as figure 3 with added lines for S injections?
Citation: https://doi.org/10.5194/egusphere-2023-2374-RC2 - AC1: 'Reply on RC2', Zhihong Zhuo, 15 Mar 2024
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