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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-110
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-110
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Sep 2019

Submitted as: research article | 09 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Teleconnections and relationship between ENSO and SAM in reconstructions and models over the past millennium

Christoph Dätwyler1, Martin Grosjean1, Nathan J. Steiger2, and Raphael Neukom1 Christoph Dätwyler et al.
  • 1Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Bern, 3012, Switzerland
  • 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA

Abstract. The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Due to the temporally very limited instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability and its stability over time. Here, we use proxy-based reconstructions and climate model simulations to quantify changes in tropical-extratropical SH teleconnections as represented by the correlation between the ENSO and SAM indices. Reconstructions indicate mostly negative correlations back to around 1400 CE confirming the pattern seen in the instrumental record over the last few decades. An ensemble of last millennium simulations of the model CESM1 confirms this pattern with very stable ensemble mean correlations around −0.3. Individual forced simulations, the pre-industrial control run and the proxy-based reconstructions indicate intermittent periods of positive correlations and particularly strong negative correlations. The fluctuations of the ENSO-SAM correlations are not significantly related to solar nor volcanic forcing in both proxy and model data, indicating that they are driven by internal variability in the climate system.

Pseudoproxy experiments indicate that the currently available proxy records are able to reproduce the tropical-extratropical teleconnection patterns back to around 1600 CE. We analyse the spatial temperature and sea level pressure patterns during periods of positive and particularly strong negative teleconnections in the CESM model. Results indicate no consistent pattern during periods where the ENSO-SAM teleconnection changes its sign. However, periods of very strong negative SH teleconnections are associated with negative temperature anomalies across large fractions of the extra-tropical Pacific and a strengthening of the Aleutian Low.

Christoph Dätwyler et al.
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Christoph Dätwyler et al.
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Short summary
The El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM) are two important modes of climate variability, strongly influencing climate across the Tropics and Southern Hemisphere mid- to high-latitudes. This study sheds light on their relationship over the past millennium, combining evidence from paleoclimate proxy archives and climate models. We show that their indices were mostly negatively correlated with fluctuations likely driven by internal variability in the climate system.
The El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM) are two important modes...
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