Atmospheric teleconnections and flow regimes under future climate projections

This paper presents an analysis of the low-frequency variability of the midtropospheric atmospheric flow of the Northern Hemisphere during winter in terms of teleconnection patterns and atmospheric flow regimes. Teleconnection patterns have been determined by two different methods, correlation analysis and empirical orthogonal function analysis. Flow regimes have been determined by analysing the structure of a spherical probability density function in a low-dimensional state space spanned by the three leading empirical orthogonal functions. To assess the ability of state-of-the-art coupled atmosphere-ocean general circulation models (AOGCMs), multi-model simulations for present day conditions, performed for the 4th assessment report of the Intergovernmental Panel on Climate Change have been analysed. The comparison with observations reveals, that state-of-the-art AOGCMs are able to describe the low-frequency variability in terms of teleconnections and flow regimes realistically. The analyses of simulations for future climate scenarios reveal changes in the strengths of the centers of action. Concerning climate regimes, two new regimes appear and additionally, slight changes were found in the structure of some regimes.