07 Nov 2022
07 Nov 2022
Status: this preprint is open for discussion.

On the magnitude and sensitivity of the QBO response to a tropical volcanic eruption

Flossie Brown1, Lauren Marshall2,a, Peter H. Haynes3, Rolando R. Garcia4, Thomas Birner5,6, and Anja Schmidt2,5,6 Flossie Brown et al.
  • 1College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
  • 2Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
  • 3Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK
  • 4National Center for Atmospheric Research, Boulder, USA
  • 5Faculty of Physics, Meteorological Institute, Ludwig-Maximilians-University Munich, Munich, Germany
  • 6Institute of Atmospheric Physics (IPA), German Aerospace Center (DLR), Oberpfaffenhofen, Germany
  • anow at: Department of Earth Sciences, Durham University, Durham, UK

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: open (until 21 Dec 2022)

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Flossie Brown et al.


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Short summary
Large-magnitude volcanic eruptions have the potential to alter large-scale circulation patterns, such as the quasi-biennial oscillation (QBO). The QBO is an oscillation of the tropical stratospheric zonal winds, between easterly and westerly. Using a climate model, we show that large-magnitude eruptions can delay the progression of the QBO, with a much longer delay when the shear is easterly than when it is westerly. Such delays may affect weather and transport of atmospheric gases.