Winter ENSO teleconnections in a warmer climate
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Changes in the winter atmospheric response to sea surface temperature (SST) anomalies associated with the El Niño-Southern Oscillation (ENSO) in a warmer climate conditions are estimated from the two 20-member ensembles made by an atmospheric general circulation model of intermediate complexity. Warmer climate is simulated by a modification in the radiation parameterisation that corresponds to the doubled CO2 concentration, and SST forcing is represented by the same SST anomalies as in current climate (1855–2002) experiment superimposed on the climatological SST that was obtained from a complex atmosphere-ocean general circulation model forced with the doubled CO2. SST anomalies in the Niño3.4 region, categorised into five classes, enabled a composite analysis of changes in the Northern Hemisphere tropical/extratropical teleconnections. The main features of the tropical–extratropical teleconnections are maintained in both experiments; for example, irrespective of the sign of SST anomalies, the amplitude of the atmospheric response is positively correlated with the intensity of ENSO event and the El Niño impact is stronger than that of La Niña of the same intensity. The strongest extratropical signal in the warmer climate, particularly significant for strong warm events, is found over the Pacific/North American region; however, this extratropical teleconnections is reduced in a warmer climate relative to the current climate. Over the North Atlantic/European region, a detectable signal linked to ENSO is found; this model response is significantly strengthened in the experiment with the doubled CO2 concentration. Such an atmospheric response in a warmer climate is found to be associated with changes in the mean state followed as well as in the jet waveguiding effect and stationary wave activity.
KeywordsENSO Tropical-extratropical teleconnections Warmer climate
We thank to two reviewers and the editor J-C Duplessy for their valuable comments, suggestions and constructive criticism which greatly improved the original version of the manuscript. This work has been supported by the Ministry of Science, Educational and Sports of the Republic of Croatia (grants No. 119-1193086-1323 and 004-1193086-3035). Ivana Herceg Bulić also acknowledges support by the European Science Foundation (ESF) activity entitled Mediterranean Climate Variability and Predictability (MedCLIVAR). Fred Kucharski has been supported by the EU ENSEMBLES project 6th Framework Programme, contract GOCE-CT-2003-505539.
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