Stimulating discussions with R. A. Pasmanter, as well as valuable comments from J. D. Opsteegh, F. Verhulst, and F. M. Selten, have helped in the investigation and preparation of this paper. Comments and criticisms by Michael Ghil and by three anonymous reviewers helped to improve the quality of the paper significantly. Financial support for this study came from the Netherlands Organization for Scientific Research (NWO).
Cheng, X., , and J. M. Wallace, 1993: Cluster analysis of the Northern Hemisphere wintertime 500-hPa height field: Spatial patterns. J. Atmos. Sci, 50 , 1205–1216.
Corti, S., , F. Molteni, , and T. N. Palmer, 1999: Signature of recent climate change in frequencies of natural atmospheric circulation regimes. Nature, 398 , 799–802.
Crommelin, D. T., 2003b: Regime transitions and heteroclinic connections in a barotropic atmosphere. J. Atmos. Sci, 60 , 229–246.
Hannachi, A., , and A. O'Neill, 2001: Atmospheric multiple equilibria and non-Gaussian behavior in model simulations. Quart. J. Roy. Meteor. Soc, 127 , 939–958.
Kimoto, M., , and M. Ghil, 1993a: Multiple flow regimes in the Northern Hemisphere winter. Part I: Methodology and hemispheric regimes. J. Atmos. Sci, 50 , 2625–2643.
Kimoto, M., , and M. Ghil, 1993b: Multiple flow regimes in the Northern Hemisphere winter. Part II: Sectorial regimes and preferred transitions. J. Atmos. Sci, 50 , 2645–2673.
Majda, A. J., , I. Timofeyev, , and E. Vanden-Eijnden, 1999: Models for stochastic climate prediction. Proc. Natl. Acad. Sci. USA, 96 , 14687–14691.
Majda, A. J., , I. Timofeyev, , and E. Vanden-Eijnden, 2003: Systematic strategies for stochastic mode reduction in climate. J. Atmos. Sci, 60 , 1705–1722.
Molteni, F., , S. Tibaldi, , and T. N. Palmer, 1990: Regimes in the wintertime circulation over northern extratropics. I: Observational evidence. Quart. J. Roy. Meteor. Soc, 116 , 31–67.
Monahan, A. H., , L. Pandolfo, , and J. C. Fyfe, 2001: The preferred structure of variability of the Northern Hemisphere atmospheric circulation. Geophys. Res. Lett, 28 , 1019–1022.
Nitsche, G., , and J. M. Wallace, 1994: Is there evidence of multiple equilibria in planetary wave amplitude statistics? J. Atmos. Sci, 51 , 314–322.
Pasmanter, R. A., , and A. Timmermann, 2003: Cyclic Markov chains with an application to an intermediate ENSO model. Nonlinear Proc. Geophys, 10 , 197–210.
Selten, F. M., , and G. Branstator, 2004: Preferred regime transition routes and evidence for an unstable periodic orbit in a baroclinic model. J. Atmos. Sci, 61 , 2267–2282.
Smyth, P., , K. Ide, , and M. Ghil, 1999: Multiple regimes in Northern Hemisphere height fields via mixture model clustering. J. Atmos. Sci, 56 , 3704–3723.
Stephenson, D. B., , A. Hannachi, , and A. O'Neill, 2004: On the existence of multiple climate regimes. Quart. J. Roy. Meteor. Soc, 130 , 583–605.
Wallace, J. M., , X. Cheng, , and D. Sun, 1991: Does low-frequency atmospheric variability exhibit regime-like behavior? Tellus, 43AB , 16–26.