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| Titel |
Systematic attribution of observed southern hemispheric circulation trends to external forcing and internal variability |
| VerfasserIn |
C. L. E. Franzke, T. J. O'Kane, D. P. Monselesan, J. S. Risbey, I. Horenko |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2198-5634
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics Discussions ; 2, no. 2 ; Nr. 2, no. 2 (2015-04-30), S.675-707 |
| Datensatznummer |
250115160
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| Publikation (Nr.) |
 copernicus.org/npgd-2-675-2015.pdf |
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| Zusammenfassung |
| A critical question in the global warming debate concerns the causes
of the observed trends of the Southern Hemisphere (SH) atmospheric
circulation over recent decades. Secular trends have been identified
in the frequency of occurrence of circulation regimes, namely the
positive phase of the Southern Annular Mode (SAM) and the
hemispheric wave 3 pattern which is associated with
blocking. Previous studies into the causes of these secular trends
have either been purely model based, have not included observational
forcing data or have mixed external forcing with indices of internal
climate variability impeding a systematic and unbiased attribution
of the causes of the secular trends. Most model studies also focused
mainly on the austral summer season. However, the changes to the
storm tracks have occurred in all seasons and particularly in the
austral winter and early spring when mid-latitude blocking is most
active and stratospheric ozone should not a play a role. Here we
systematically attribute the secular trends over the recent decades
using a non-stationary clustering method applied to both reanalysis
and observational forcing data from all seasons. While most previous
studies emphasized the importance of stratospheric ozone depletion
in causing austral summer SH circulation trends, we show
observational evidence that anthropogenic greenhouse gas
concentrations have been the major driver of these secular trends in
the SAM and blocking when all seasons are considered. Our results
suggest that the recovery of the ozone hole might delay the signal
of global warming less strongly than previously thought and that
effects from all seasons are likely crucial in understanding the
causes of the secular trends. |
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