Northern Hemisphere circulation regimes: observed, simulated and predicted
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Nonlinear principal component analysis provides evidence that the Northern Hemisphere extratropical atmosphere supports three distinct circulation regimes with an average residence time of about 7 days. The role of high- and low-frequency dynamics is studied and results indicate that they are both involved in the formation, maintenance and decay of the regimes. A global coupled climate model also supports three distinct circulation regimes with strikingly similar spatial structures, residence times and linked high- and low-frequency dynamics to those observed. The issue related to how long a data record is required to properly resolve the regime structures is addressed by exploiting the model output. Regime residence times and spatial structures are predicted to change over the next century given increasing concentrations of atmospheric greenhouse gases.
KeywordsTransient Eddy Regime Structure Synoptic Eddy Stabilization Simulation Nonlinear Principal Component Analysis
We would like to thank Steve Lambert, Oleg Saenko and two anonymous referees for their helpful comments on this manuscript. This work was supported by the Canadian CLIVAR Research Network. Q. Teng would also like to thank Greg Flato and Hisashi Nakamura for their help at the early stage of this work.
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