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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-56
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-56
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  10 Nov 2020

10 Nov 2020

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This preprint is currently under review for the journal WCD.

Origins of Multi-decadal Variability in Sudden Stratospheric Warmings

Oscar Dimdore-Miles1, Lesley Gray1,2, and Scott Osprey1,2 Oscar Dimdore-Miles et al.
  • 1Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, OX1 3PU, UK
  • 2National Centre for Atmospheric Science, Oxford, OX1 3PU

Abstract. Sudden Stratospheric Warmings (SSWs) are major disruptions of the Northern Hemisphere (NH) stratospheric polar vortex and occur on average approximately 6 times per decade in observation based records. However, within these records, intervals of significantly higher and lower SSW rates are observed suggesting the possibility of low frequency variations in event occurrence. A better understanding of factors that influence this decadal variability may help to improve predictability of NH mid-latitude surface climate, through stratosphere-troposphere coupling. In this work, multi-decadal variability of SSW events is examined in a 1000-yr pre-industrial simulation of a coupled Atmosphere-Ocean-Land-Sea ice model. Using a wavelet spectral decomposition method, we show that hiatus events (intervals of a decade or more with no SSWs) and consecutive SSW events (extended intervals with at least one SSW in each year) vary on multi-decadal timescales of period between 60 and 90 years. Signals on these timescales are present for approximately 450 years of the simulation. We investigate the possible source of these long-term signals and find that the direct impact of variability in tropical sea surface temperatures, as well as the associated Aleutian Low, can account for only a small portion of the SSW variability. Instead, the major influence on long-term SSW variability is associated with long-term variability in amplitude of the stratospheric quasi biennial oscillation (QBO). The QBO influence is consistent with the well known Holton-Tan relationship, with SSW hiatus intervals associated with extended periods of particularly strong, deep QBO westerly phases. The results support recent studies that have highlighted the role of vertical coherence in the QBO when considering coupling between the QBO, the polar vortex and tropospheric circulation.

Oscar Dimdore-Miles et al.

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Oscar Dimdore-Miles et al.

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Latest update: 03 Dec 2020
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Short summary
Observations of the stratosphere span roughly half a century preventing analysis of multi-decadal variability in circulation using these data. Instead, we rely on long simulations of climate models. Here, we use a model to examine variations in northern polar stratospheric winds and find they vary with a period of around 90 years. We show that this is possibly due to variations in the size of winds over the equator. This result may improve understanding of equator-polar stratospheric coupling.
Observations of the stratosphere span roughly half a century preventing analysis of...
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