the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Nov 2025
Multi-model assessment of impacts of the 2022 Hunga eruption on stratospheric ozone and its chemical and dynamical drivers
Abstract. The 2022 Hunga eruption injected unprecedented quantities of water vapor into the stratosphere, alongside modest amounts of aerosol precursors. There remain uncertainties regarding the extent to which it influenced the stratospheric ozone layer. We address this using a multi-model ensemble of chemistry-climate model simulations, assessing the impacts of Hunga-induced perturbations in both water vapor and aerosol by combining free-running and specified-dynamics experiments. The results confirm that the Hunga eruption contributed to the anomalously low ozone abundances observed in the southern mid-latitudes in 2022. The simulations also indicate enhanced ozone depletion inside the Antarctic polar vortex, albeit with significant differences in magnitude and persistence across the models. Our results indicate that the chemical contribution was as important as the dynamical contribution in determining the overall ozone response to the Hunga eruption in the southern extra-tropics, with anomalous chemical (chlorine, bromine and nitrogen) processing on aerosol surfaces under conditions of water-induced stratospheric cooling together with dynamical contributions from altered circulation and ozone transport. Finally, while Hunga may continue to exert a smaller influence on ozone as the anomalous water vapor and aerosol is removed from the atmosphere, natural dynamical variability will likely hinder detection of any such influences, with the most robust Hunga signal expected in the upper stratosphere. Our study confirms the eruption’s role in modulating stratospheric ozone levels in the short term, but also highlights the associated uncertainties and the presence of large natural variability, all of which makes confident attribution of the Hunga impacts an ongoing challenge.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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Status: open (until 14 Jan 2026)
- RC1: 'Comment on egusphere-2025-4609', Anonymous Referee #1, 27 Dec 2025 reply
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- 1
This manuscript analyzes data from multi-model ensemble simulations using 5 chemistry-climate models, to assess the impacts of the 2022 Hunga eruption on the ozone layer, which injected unprecedented amount of water vapor and modest amounts of aerosol precursors. This is a result from an international collaboration activity, the Hunga Tonga–Hunga Ha’apai Volcano Impact Model Observation Comparison (HTHH-MOC) project, and the simulation protocol is explained by Zhu et al. (Geosci. Model Dev., https://doi.org/10.5194/gmd-18-5487-2025, 2025).
In the manuscript, the changes in ozone, aerosols, water vapor, NO2, ClOx, BrOx, temperature, and zonal wind, with respect to the control simulations without any injection, are analyzed and discussed in detail. The interpretation of the simulation results seems to me mostly very reasonable. I think that the manuscript can be accepted for publication in Atmospheric Chemistry and Physics after considering the following few points.
Figure 1(a) (and Figure S1(a)): Why does the GEOSCCM panel not have any dotted region?
Lines 197-201: It is not clear whether the negative tropospheric ozone anomalies are due to the negative lower stratospheric ozone anomalies or due to reduced amount of stratosphere-to-troposphere transport. Please clarify in the text.
Regarding the paragraph starting from Line 189: I feel that the cause-result relationship described here for temperature and zonal wind anomalies is not very clear to me. Is the following understanding of mine correct? If so, could you rewrite the text more clearly?
The main causes for the temperature anomalies are composition changes (that affect radiative heating/cooling distribution) and meridional circulation changes probably due mainly to natural variability. The zonal wind anomalies are primarily the immediate response (on monthly time scales) to the temperature anomalies through the thermal wind relationship, as it is a very strong constraint. Of course, changes in the zonal wind distribution would influence the meridional circulation through changes in the Rossby wave propagation, and changes in the meridional circulation would change the ozone distribution and thus influence temperature through radiative process; but these two may be considered as secondary.
(The main point here is that zonal wind anomalies could be just a reflection of the temperature anomalies through the thermal wind relationship.)
Section 3.4. Its title is “Radiative impacts . . .”, but do the authors actually mean “Temperature impacts on ozone photochemistry”? This is because at Lines 345-347, the authors write about temperature dependence in the ozone chemistry. This might seem rather picky, but I think that the temperature anomalies here are probably due to both the radiative cooling due to increased water vapor and the changes in the meridional circulation (i.e. ascent anomalies), the latter of which is probably mainly due to natural variability. Note that ascent anomalies would result in both (1) adiabatic cooling and (2) less lower stratospheric ozone that leads to less solar heating on ozone there. If so, “Temperature impacts” rather than “Radiative impacts” would be more appropriate.
Lines 386-387: Could you clarify the causes of the cooling anomalies? More longwave cooling due to increased water vapor is one cause, but ascent anomalies (if they exist) lead to adiabatic cooling and less ozone and less solar heating on ozone.
Line 395: It would be nice that the authors clarify a little bit more what are the dynamical processes here. They could be meridional circulation, zonal wind, transport (in particular, of ozone). Or, radiative processes are also included in this term implicitly?