On the magnitude and sensitivity of the QBO response to a tropical volcanic eruption
Abstract. Volcanic eruptions that inject sulphur dioxide into the stratosphere have the potential to alter large-scale circulation patterns, such as the quasi-biennial oscillation (QBO), which can affect weather and transport of chemical species. Here, we conduct simulations of tropical volcanic eruptions using the UM-UKCA aerosol-climate model with an explicit representation of the QBO. Eruptions emitting 60 Tg of SO2 (i.e., 1815 Mt. Tambora-magnitude) and 15 Tg of SO2 (i.e., 1991 Mt. Pinatubo-magnitude) were simulated at the equator initiated during two different QBO states. We show that tropical eruptions delay the progression of the QBO phases, with the magnitude of the delay dependent on the initial wind shear in the lower stratosphere and a much longer delay when the shear is easterly than when it is westerly. The QBO response in our model is driven by vertical advection of momentum by the stronger tropical upwelling caused by heating due to the increased volcanic sulfate aerosol loading. Direct aerosol-induced warming with subsequent thermal wind adjustment, as proposed by previous studies, is found to only play a secondary role. This interpretation of the response is supported by comparison with a simple dynamical model. The dependence of the magnitude of the response on the initial QBO state results from differences in the QBO secondary circulation. In the easterly shear zone of the QBO, the vertical component of the secondary circulation is upward and reinforces the anomalous upwelling driven by volcanic aerosol heating, whereas in the westerly shear zone the vertical component is downward and opposes the aerosol-induced upwelling. We also find a change to the latitudinal structure of the QBO, with the westerly phase of the QBO strengthening in the hemisphere with the lowest sulfate aerosol burden. Overall, our study suggests that tropical eruptions of Pinatubo-magnitude or larger could force changes to the progression of the QBO, with particularly disruptive outcomes for the QBO if the eruption occurs during the easterly QBO shear.
Flossie Brown et al.
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2022-1096', Daniele Visioni, 19 Dec 2022
- RC2: 'Comment on egusphere-2022-1096', Anonymous Referee #2, 15 Feb 2023
Flossie Brown et al.
Flossie Brown et al.
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Review of “On the magnitude and sensitivity of the QBO response to a tropical volcanic eruption” by Brown et al.
This study uses the UM-UKCA model to investigate the response of the QBO to tropical eruptions. They then try to give a mechanistic explanation through the use of a common 2D dynamical model, which is nicely described in Section 2.4.
The paper does a good job at framing the issue overall (clarity over their definition of the QBO phase and state is greatly appreciated!), although they could include in their initial discussion some more recent studies (some done with their same model) of Pinatubo, for instance. The paper is well written and the results are explained clearly. I have just a few suggestions for improvement here and there, mainly about contextualizing this work a bit better, but other than that, the paper is in a really good shape and will make a good contribution to the literature.
L 68: “Sulfate geoengineering is, in effect, equivalent to a sustained volcanic eruption, although somewhat different to a short-lived, explosive eruption” A bit of a convoluted phrase. “somewhat different” – how?
L 108: Also se Pitari et al. (2016) which discusses this exact issue in the context of the four main volcanic eruptions.
L 130: “Inacted”?
S2.2 Interested here as to why the authors don’t reference or compare their results with those from Dhomse et al. (2020)? It seems like the model is the same, maybe a slightly different version, however the amount of SO2 is different, and Dhomse found a better agreement for lower injections of SO2. Their simulations are also AMIP-style. This needs to be discussed (and perhaps, if the models’ versions are compatible, one could look at those already available simulations which are part of ISA-MIP and compare the QBO response…). In terms of the location of the injection (in altitude), the authors can also refer to the range explored in the ISA-MIP experiments (Quaglia et al., 2022) – at least acknowledging that different altitudes of injection produce different clouds with, potentially, different QBO effects.
L. 433 Stop is inside the parenthesis but should be outside.
Figure 9 and 10 are really, really hard to interpret due to the different contours. I would suggest duplicating the figure for T and for SO4 mass rather than try to cram everything in one panel.
Overall, a panel showing AOD (both global over time, or 30N-30S, and latitudinal) could be very useful to understand better how the QBO is affecting the aerosols.
L 578 (paragraph) I agree with the authors’ assessment that it is hard with a continuous perturbation to make similar attributions. However, I would stress here that “the preference for sulfate geoengineering to halt the QBO following e-QBO conditions” only refers to SG applied at the equator (see the cited Richter et al., 2017 and Kravitz et al., 2019), and not even in all climate models (see Niemier et al., 2020, but also Jones et al., 2022, Fig. 8)
L. 622 feedbacks “among” maybe “between” is better
L. 644 “aerosols are”
L. 672 (paragraph) In parts, this paragraph feels rather weak and just thrown out there to give a broader scope to the paper. I don’t have much doubt that this research is useful, mind you, I just feel like this could be better justified. “species such as ozone and stratospheric water vapour have different signals depending on the zonal wind shear and their distribution is important for climate change projections” sounds rather weak – if there was a volcanic eruption capable of modifying the QBO, the main effect on climate change projections wouldn’t be the distribution of ozone. We should know it, but the aerosols’ distribution (which is affected by the QBO more than WV) would affect the climate more. Similarly, ozone is influenced by many factors in case of a volcanic eruption (see Aquila et al., 2013). “despite an increased probability of a QBO disruption in a warmer future climate” I can see why you would say this and can think of a few references for it (like Aubrey et al., 2021) but you should 1) cite them and 2) contextualize this a bit better. Seems like a shame to conclude this paper this way, the authors should work on this a bit more.
Data availability – This won’t do, you need to make it public by ACP guidelines.
Aquila, V., Oman, L. D., Stolarski, R., Douglass, A. R., & Newman, P. A. (2013). The Response of Ozone and Nitrogen Dioxide to the Eruption of Mt. Pinatubo at Southern and Northern Midlatitudes, Journal of the Atmospheric Sciences, 70(3), 894-900. Retrieved Dec 19, 2022, from https://journals.ametsoc.org/view/journals/atsc/70/3/jas-d-12-0143.1.xml
Aubry, T.J., Staunton-Sykes, J., Marshall, L.R. et al. Climate change modulates the stratospheric volcanic sulfate aerosol lifecycle and radiative forcing from tropical eruptions. Nat Commun 12, 4708 (2021). https://doi.org/10.1038/s41467-021-24943-7
Dhomse, S. S., Mann, G. W., Antuña Marrero, J. C., Shallcross, S. E., Chipperfield, M. P., Carslaw, K. S., Marshall, L., Abraham, N. L., and Johnson, C. E.: Evaluating the simulated radiative forcings, aerosol properties, and stratospheric warmings from the 1963 Mt Agung, 1982 El Chichón, and 1991 Mt Pinatubo volcanic aerosol clouds, Atmos. Chem. Phys., 20, 13627–13654, https://doi.org/10.5194/acp-20-13627-2020, 2020.
Jones, A., Haywood, J. M., Scaife, A. A., Boucher, O., Henry, M., Kravitz, B., Lurton, T., Nabat, P., Niemeier, U., Séférian, R., Tilmes, S., and Visioni, D.: The impact of stratospheric aerosol intervention on the North Atlantic and Quasi-Biennial Oscillations in the Geoengineering Model Intercomparison Project (GeoMIP) G6sulfur experiment, Atmos. Chem. Phys., 22, 2999–3016, https://doi.org/10.5194/acp-22-2999-2022, 2022
Kravitz, B., MacMartin, D. G., Tilmes, S., Richter, J. H., Mills, M. J., Cheng, W., et al. (2019). Comparing surface and stratospheric impacts of geoengineering with different SO2 injection strategies. Journal of Geophysical Research: Atmospheres, 124, 7900– 7918. https://doi.org/10.1029/2019JD030329
Pitari, G.; Di Genova, G.; Mancini, E.; Visioni, D.; Gandolfi, I.; Cionni, I. Stratospheric Aerosols from Major Volcanic Eruptions: A Composition-Climate Model Study of the Aerosol Cloud Dispersal and e-folding Time. Atmosphere 2016, 7, 75. https://doi.org/10.3390/atmos7060075
Quaglia, I., Timmreck, C., Niemeier, U., Visioni, D., Pitari, G., Brühl, C., Dhomse, S., Franke, H., Laakso, A., Mann, G., Rozanov, E., and Sukhodolov, T.: Interactive Stratospheric Aerosol models response to different amount and altitude of SO2 injections during the 1991 Pinatubo eruption, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2022-514, in review, 2022.