Journal article
Mechanisms of influence of the semi-annual oscillation on stratospheric sudden warmings
- Abstract:
- The influence of the Semi-Annual Oscillation (SAO) on the timing and evolution of major sudden stratospheric warmings (SSWs) is examined using the 2008/9 SSW as the primary case study. When the zonal winds in both the troposphere and the SAO region of the equatorial upper stratosphere / lower mesosphere are relaxed towards reanalysis fields in the UK Met Office Unified Model a remarkably accurate representation of the January 2009 SSW is achieved. The accurate timing of the SSW is determined by the SAO zonal wind relaxation. The westerly to easterly phase transition of the SAO in the lower mesosphere (0.1-0.5 hPa) is found to be a key factor for this influence. It defines an initial conical-shaped vortex that determines the upward propagation of wave activity and subsequent evolution of wave mean-flow interaction. Internal transient wave reflection in the subtropics and associated wave-induced acceleration of the mean-flow is found to be an important component, strengthening the vortex and thus delaying the onset of the SSW. The sensitivity of SSW timing to the equatorial westerly winds in the lower mesosphere is further explored in the context of all major SSWs during the 1979-2018 period. The timing of SSWs is found to be significantly correlated with the timing of the equinoctial westerly-to easterly phase transition at 0.3 hPa in early winter (r = 0.79). This relationship is discussed in the context of the more widely recognised influence of the quasi-biennial oscillation (QBO). These results suggest that accurate simulation of the timing of SAO phase transitions, as well as knowledge of the QBO phase, is likely to provide additional and extended Northern Hemisphere winter-time seasonal forecast skill.
- Publication status:
- Published
- Peer review status:
- Peer reviewed
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(Preview, Version of record, 8.4MB, Terms of use)
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- Publisher copy:
- 10.1002/qj.4256
Authors
- Publisher:
- Wiley
- Journal:
- Quarterly Journal of the Royal Meteorological Society More from this journal
- Volume:
- 148
- Issue:
- 774
- Pages:
- 1223-1241
- Publication date:
- 2022-05-13
- Acceptance date:
- 2022-02-13
- DOI:
- EISSN:
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1477-870X
- ISSN:
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0035-9009
- Language:
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English
- Keywords:
- Pubs id:
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1239702
- Local pid:
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pubs:1239702
- Deposit date:
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2022-02-14
Terms of use
- Copyright holder:
- Gray et al
- Copyright date:
- 2022
- Rights statement:
- © 2022 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
- Licence:
- CC Attribution (CC BY)
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