Nonstationarity in Southern Hemisphere Climate Variability Associated with the Seasonal Breakdown of the Stratospheric Polar Vortex
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Author(s)
Byrne, Nicholas J.
Shepherd, Theodore G.
Woollings, Tim
Plumb, R. Alan
Date Issued
August 2017
Journal
Journal of Climate
Publisher
American Meteorological Society
Citation
Byrne, Nicholas J. et al. “Nonstationarity in Southern Hemisphere Climate Variability Associated with the Seasonal Breakdown of the Stratospheric Polar Vortex.” Journal of Climate 30, 18 (September 2017): 7125–7139 © 2017 American Meteorological Society
Version
Final published version
Abstract
Statistical models of climate generally regard climate variability as anomalies about a climatological seasonal cycle, which are treated as a stationary stochastic process plus a long-term seasonally dependent trend. However, the climate system has deterministic aspects apart from the climatological seasonal cycle and long-term trends, and the assumption of stationary statistics is only an approximation. The variability of the Southern Hemisphere zonal-mean circulation in the period encompassing late spring and summer is an important climate phenomenon and has been the subject of numerous studies. It is shown here, using reanalysis data, that this variability is rendered highly nonstationary by the organizing influence of the seasonal breakdown of the stratospheric polar vortex, which breaks time symmetry. It is argued that the zonal-mean tropospheric circulation variability during this period is best viewed as interannual variability in the transition between the springtime and summertime regimes induced by variability in the vortex breakdown. In particular, the apparent long-term poleward jet shift during the early-summer season can be more simply understood as a delay in the equatorward shift associated with this regime transition. The implications of such a perspective for various open questions are discussed. Keywords: Antarctic Oscillation; Stratosphere-troposphere coupling; Climate classification/regimes; Seasonal forecasting; Anomalies; Ozone
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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DOI of Published Version
https://doi.org/10.1175/JCLI-D-17-0097.1
