the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Apr 2025
Comparing Multi-Model Ensemble Simulations with Observations and Decadal Projections of Upper Atmospheric Variations Following the Hunga Eruption
Abstract. The Hunga Tonga-Hunga Haʻapai Model-Observation Comparison (HTHH-MOC) project aims to comprehensively investigate the evolution of volcanic water vapor and sulfur emissions and their subsequent atmospheric impacts and underlying response mechanisms using state-of-the art global climate models. This study evaluates multi-model ensemble simulations participating in the HTHH-MOC free-run experiment with climate projections for 10 years (2022–2032). Model results are evaluated against satellite observations to assess their ability to reproduce the observed evolution of stratospheric water vapor, aerosols, temperature, and ozone from 2022 to 2024. The participating models accurately capture the observed distribution patterns and associated upper atmospheric responses, providing confidence for their future projections. Model simulations suggest that the Hunga eruption-induced stratospheric water vapor anomaly lasts 4–7 years, with a water vapor e-folding time of 31–43 months. This prolonged water vapor perturbation leads to significant local cooling, resulting in significant ozone loss in the upper stratosphere and lower mesosphere for 7–10 years. Comparisons between simulations with both SO2 and H2O emissions and those with H2O-only emissions indicate that the pronounced dipole response with upper-stratospheric cooling and lower-stratospheric warming is driven by the combined effects of SO2 and H2O injections. These results highlight the prolonged atmospheric impacts of the Hunga eruption and the potential critical role of stratospheric water vapor in modulating long-term atmospheric chemistry and dynamics.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2025-1505', Christopher Smith, 01 Jul 2025
This paper introduces a multi-model study (can we call it a MIP?) of the stratospheric projections following the Hunga Tonga-Hunga Ha’apai (HTHH) eruption. Its utility arises from including both the water vapour and the aerosol components of the HTHH injection and using models that resolve ozone loss, therefore allowing (potentially - see comment below on radiative forcing) for the net climate impact of this eruption to be evaluated. It confirms that the water vapour perturbation is longer-lived than the stratospheric aerosol perturbation, potentially leading to a slight surface warming as a consequence (not evaluated). The model results are compared to the MLS data for water vapour and ozone and GloSSAC for stratospheric aerosol, showing good correspondence.
With the end of life of the MLS instrument and uncertainty around a suitable replacement platform, this MIP might be the best source of information available to estimate and project forward the evolution of the HTHH water vapour plume at a very critical time during a gap in the satellite observations. Therefore I fully support this initiative.
Please if possible could you analyse the effective radiative forcing from these results? It would simply be the global mean TOA net radiation change from 2022 and subsequent years compared to the no-HTHH runs in each model in the fixed SST runs. Splitting out the all-forcing and H2O-only forcing runs where models performed the latter would also be really useful. This help add to the discussion on whether HTHH is a net warming or net cooling climate influence.
Line 42: How does the “anomaly” duration differ from the e-folding duration? The anomaly perhaps being the period of time for which a non-zero increase in stratospheric water vapour is detectable?
Line 44: “local” cooling: in the sense of ULTS, rather than the surface? Please be explicit. (since this paper will be interesting to readers who are not upper atmosphere focused, like myself).
Line 127: there’s probably good reasons, but why limit to the 2012-21 climatology from MLS when data goes back to 2004?
Lines 135-138: I understand from reading the Randel et al (2024) reference why the temperature from MLS was detrended. It kind of makes sense, though not described how it was done, that QBO and ENSO are removed from the record since free-running models will generate their own variability patterns that will unlikely sync with that of the real world. Was the solar forcing (i.e. from CMIP6) an input forcing to the models? I presume not, since this has been taken out of the MLS data. And how did you account for the fact that the solar cycle isn't a monotonic trend?
Section 3.3: could you rename to “Global mean stratospheric air temperature evolution” or similar to reduce ambiguity – just because it’s not what I would define as global mean temperature, which commonly relates to the surface or near-surface air temperature. (similar comment to line 44). Similarly I recommend deleting “global mean” in line 362 and in figure 4.
Line 417: “et la” to “et al”
Data availability: please give more information on how to obtain the data from JASMIN: I ask as somebody who is interested in the results.
Citation: https://doi.org/10.5194/egusphere-2025-1505-RC1 -
AC1: 'Reply on RC1 and RC2', Zhihong Zhuo, 14 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1505/egusphere-2025-1505-AC1-supplement.pdf
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AC1: 'Reply on RC1 and RC2', Zhihong Zhuo, 14 Aug 2025
-
RC2: 'Comment on egusphere-2025-1505', Anonymous Referee #2, 05 Jul 2025
Zhuo et al. (2025) evaluates multi-model ensemble simulations of the Hunga volcanic eruption's atmospheric impacts by comparing model results with satellite observations from 2022-2024, finding good agreement in stratospheric water vapor, aerosols, temperature, and ozone patterns. In general, I find the paper interesting, however lack of in-depth evaluation expeically on the ozone chemistry. Besides, the discussion on the upward motion of SWV to the mesophere can be improved.
Line 325-224: “Beyond this phase, the upward transport of H2O into the mesosphere above 1 hPa becomes the dominant mechanism for the removal of stratospheric water vapor (SWV).”
Maybe this statement and relevant discussions are correct but could be misleading.- This sentence discussed the fate of a tiny amount of HTHH water vapor (<1% of total water). The majority of HTHH water fells down to the troposphere in the mid and high latitudes. Please add one sentence to avoid confusion.
- Still, from Figure 3, the water mixing ratio is similar between 1 and 0.1 hPa, which means the mass is one order of magnitude larger at 1 hPa. How we can tell it is the dominant mechanism for the removal of SWV at 1 hPa? A concentration map can be helpful.
The interpretation of lower-level warming could be strengthened by overlaying aerosol fields on Figure 4. If the warming is indeed caused by aerosol descent, this should be evident in the aerosol spatial distribution patterns. Furthermore, this hypothesis could be tested by examining SO2-only simulations from 2022, where such warming should be absent due to lack of aerosol formation. Including these additional analyses would help validate the proposed mechanism for the temperature response.
Lines 415-420: The analysis of ozone chemistry (Figure 5) remains largely qualitative. While the authors attribute the simulated ozone changes - depletion in the lower mesosphere and enhancement in the middle stratosphere - to both UV radiation and various chemical pathways, the paper lacks quantitative calculations to support these mechanisms. Including detailed photochemical reaction rates, radiative transfer calculations, or chemical box model simulations would strengthen their arguments about the relative importance of different processes controlling ozone distribution changes.
Line 94, Please more specific, what aspects of short or long-term evolution of HTHH are unclear from previous studies, and why previous studies only provided “limited” findings as you stated in Line 75.
Figure 1 caption says OMPS data is used. Both datasets were used in the GSFC2D model.
Line 229: How does the secondary sAOD peak between 30-60S form?
Line 292: could you please explain why one model injects 750 Tg WV, which is about 5 times of other models?
Line 311: Does the model simulate reduced ice cloud formation in MIROC-CHASER-Fs?
Line 319: Could you please elaborate the quantities that determine the lifetime (or e-folding time) of water and key differences between Zhou 2024 and present study?
Citation: https://doi.org/10.5194/egusphere-2025-1505-RC2 -
AC1: 'Reply on RC1 and RC2', Zhihong Zhuo, 14 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1505/egusphere-2025-1505-AC1-supplement.pdf
Status: closed
-
RC1: 'Comment on egusphere-2025-1505', Christopher Smith, 01 Jul 2025
This paper introduces a multi-model study (can we call it a MIP?) of the stratospheric projections following the Hunga Tonga-Hunga Ha’apai (HTHH) eruption. Its utility arises from including both the water vapour and the aerosol components of the HTHH injection and using models that resolve ozone loss, therefore allowing (potentially - see comment below on radiative forcing) for the net climate impact of this eruption to be evaluated. It confirms that the water vapour perturbation is longer-lived than the stratospheric aerosol perturbation, potentially leading to a slight surface warming as a consequence (not evaluated). The model results are compared to the MLS data for water vapour and ozone and GloSSAC for stratospheric aerosol, showing good correspondence.
With the end of life of the MLS instrument and uncertainty around a suitable replacement platform, this MIP might be the best source of information available to estimate and project forward the evolution of the HTHH water vapour plume at a very critical time during a gap in the satellite observations. Therefore I fully support this initiative.
Please if possible could you analyse the effective radiative forcing from these results? It would simply be the global mean TOA net radiation change from 2022 and subsequent years compared to the no-HTHH runs in each model in the fixed SST runs. Splitting out the all-forcing and H2O-only forcing runs where models performed the latter would also be really useful. This help add to the discussion on whether HTHH is a net warming or net cooling climate influence.
Line 42: How does the “anomaly” duration differ from the e-folding duration? The anomaly perhaps being the period of time for which a non-zero increase in stratospheric water vapour is detectable?
Line 44: “local” cooling: in the sense of ULTS, rather than the surface? Please be explicit. (since this paper will be interesting to readers who are not upper atmosphere focused, like myself).
Line 127: there’s probably good reasons, but why limit to the 2012-21 climatology from MLS when data goes back to 2004?
Lines 135-138: I understand from reading the Randel et al (2024) reference why the temperature from MLS was detrended. It kind of makes sense, though not described how it was done, that QBO and ENSO are removed from the record since free-running models will generate their own variability patterns that will unlikely sync with that of the real world. Was the solar forcing (i.e. from CMIP6) an input forcing to the models? I presume not, since this has been taken out of the MLS data. And how did you account for the fact that the solar cycle isn't a monotonic trend?
Section 3.3: could you rename to “Global mean stratospheric air temperature evolution” or similar to reduce ambiguity – just because it’s not what I would define as global mean temperature, which commonly relates to the surface or near-surface air temperature. (similar comment to line 44). Similarly I recommend deleting “global mean” in line 362 and in figure 4.
Line 417: “et la” to “et al”
Data availability: please give more information on how to obtain the data from JASMIN: I ask as somebody who is interested in the results.
Citation: https://doi.org/10.5194/egusphere-2025-1505-RC1 -
AC1: 'Reply on RC1 and RC2', Zhihong Zhuo, 14 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1505/egusphere-2025-1505-AC1-supplement.pdf
-
AC1: 'Reply on RC1 and RC2', Zhihong Zhuo, 14 Aug 2025
-
RC2: 'Comment on egusphere-2025-1505', Anonymous Referee #2, 05 Jul 2025
Zhuo et al. (2025) evaluates multi-model ensemble simulations of the Hunga volcanic eruption's atmospheric impacts by comparing model results with satellite observations from 2022-2024, finding good agreement in stratospheric water vapor, aerosols, temperature, and ozone patterns. In general, I find the paper interesting, however lack of in-depth evaluation expeically on the ozone chemistry. Besides, the discussion on the upward motion of SWV to the mesophere can be improved.
Line 325-224: “Beyond this phase, the upward transport of H2O into the mesosphere above 1 hPa becomes the dominant mechanism for the removal of stratospheric water vapor (SWV).”
Maybe this statement and relevant discussions are correct but could be misleading.- This sentence discussed the fate of a tiny amount of HTHH water vapor (<1% of total water). The majority of HTHH water fells down to the troposphere in the mid and high latitudes. Please add one sentence to avoid confusion.
- Still, from Figure 3, the water mixing ratio is similar between 1 and 0.1 hPa, which means the mass is one order of magnitude larger at 1 hPa. How we can tell it is the dominant mechanism for the removal of SWV at 1 hPa? A concentration map can be helpful.
The interpretation of lower-level warming could be strengthened by overlaying aerosol fields on Figure 4. If the warming is indeed caused by aerosol descent, this should be evident in the aerosol spatial distribution patterns. Furthermore, this hypothesis could be tested by examining SO2-only simulations from 2022, where such warming should be absent due to lack of aerosol formation. Including these additional analyses would help validate the proposed mechanism for the temperature response.
Lines 415-420: The analysis of ozone chemistry (Figure 5) remains largely qualitative. While the authors attribute the simulated ozone changes - depletion in the lower mesosphere and enhancement in the middle stratosphere - to both UV radiation and various chemical pathways, the paper lacks quantitative calculations to support these mechanisms. Including detailed photochemical reaction rates, radiative transfer calculations, or chemical box model simulations would strengthen their arguments about the relative importance of different processes controlling ozone distribution changes.
Line 94, Please more specific, what aspects of short or long-term evolution of HTHH are unclear from previous studies, and why previous studies only provided “limited” findings as you stated in Line 75.
Figure 1 caption says OMPS data is used. Both datasets were used in the GSFC2D model.
Line 229: How does the secondary sAOD peak between 30-60S form?
Line 292: could you please explain why one model injects 750 Tg WV, which is about 5 times of other models?
Line 311: Does the model simulate reduced ice cloud formation in MIROC-CHASER-Fs?
Line 319: Could you please elaborate the quantities that determine the lifetime (or e-folding time) of water and key differences between Zhou 2024 and present study?
Citation: https://doi.org/10.5194/egusphere-2025-1505-RC2 -
AC1: 'Reply on RC1 and RC2', Zhihong Zhuo, 14 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1505/egusphere-2025-1505-AC1-supplement.pdf
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