This work was funded by the NERC under Grant GR3/8274. The 10-yr run of the GCM was supported by UGAMP. I am grateful to Dr. K. Haines for helpful comments and discussions. Thanks are also due to Dr. G. Branstator for his thorough and constructive review and to an anonymous reviewer for helpful comments.
Aart, E., and J. Korst, 1990: Simulated Annealing and Boltzmann Machine. John Wiley and Sons, 272 pp.
Anderson, J. L., 1992: Barotropic stationary states and persistent anomalies in the atmosphere. J. Atmos. Sci.,49, 1709–1722.
Barnston, A. G., and R. E. Livezey, 1987: Classification, seasonality, and persistence of low-frequency atmospheric circulation patterns. Mon. Wea. Rev.,115, 1083–1126.
Berry, F. A., E. Bollay, and N. R. Beers, 1973: Handbook of Meteorology. McGraw-Hill, 1068 pp.
Branstator, G., 1987: A striking example of the atmosphere’s leading travelling pattern. J. Atmos. Sci.,44, 2310–2323.
——, and J. D. Opsteegh, 1989: Free solutions of the barotropic vorticity equation. J. Atmos. Sci.,46, 1799–1814.
Charney, J. G., and J. G. Devore, 1979: Multiple flow equilibria in the atmosphere and blocking. J. Atmos. Sci.,36, 1205–1216.
Dole, R. M., 1986: Persistent anomalies of the extratropical Northern Hemisphere wintertime circulation: Structure. Mon. Wea. Rev.,114, 178–207.
——, and D. N. Gordon, 1983: Persistent anomalies of the extratropical Northern Hemisphere winter circulation: Geophysical distribution and regional persistent characteristics. Mon. Wea. Rev.,111, 1567–1586.
Duchon, C. E., 1979: Lanczos filtering in one and two dimensions. J. Appl. Meteor.,18, 1016–1022.
Everitt, B. S., and D. J. Hand, 1981: Finite Mixture Analysis. Chapmann and Hall, 143 pp.
Frederiksen, J. S., 1992: Towards a unified instability theory of large-scale atmospheric disturbances. Trends Atmos. Sci.,1, 239–261.
Haines, K., and J. Marshall, 1987: Eddy-forced coherent structures as a prototype of atmospheric blocking. Quart. J. Roy. Meteor. Soc.,113, 681–704.
——, and A. Hannachi, 1995: Weather regimes in the Pacific from a GCM. J. Atmos. Sci.,52, 2444–2462.
Haltiner, J. G., and R. T. Williams, 1980: Numerical Prediction and Dynamic Meteorology. John Wiley and Sons, 477 pp.
Hannachi, A., and B. Legras, 1995: Simulated annealing and weather regimes classification. Tellus,47A, 955–973.
Hansen, A. R., 1986: Observational characteristics of atmospheric planetary waves with bimodal amplitude distributions. Advances in Geophysics, Vol. 29, Academic Press, 101–133.
——, and A. Sutera, 1986: On the probability density distribution of large-scale atmospheric wave amplitude. J. Atmos. Sci.,43, 3250–3265.
Horel, J. D., 1981: A rotated principal component analysis of the interannual variability of the Northern Hemisphere 500 mb height field. Mon. Wea. Rev.,109, 2080–2092.
Hoskins, B. J., and D. J. Karoly, 1981: The steady linear response of a spherical atmosphere to thermal and orographic forcing. J. Atmos. Sci.,38, 1179–1196.
——, I. N. James, and G. H. White, 1983: The shape, propagation and mean-flow interaction of large-scale weather systems. J. Atmos. Sci.,40, 1595–1612.
Illari, L., 1984: A diagnostic study of the potential vorticity in a warm blocking anticyclone. J. Atmos. Sci.,41, 3518–3526.
Kimoto, M., M. Mukougawa, and S. Yoden, 1992: Medium-range forecast skill variation and blocking transition: A case study. Mon. Wea. Rev.,120, 1616–1627.
Legras, B., and M. Ghil, 1985: Persistent anomalies, blocking and variations in atmospheric predictability. J. Atmos. Sci.,42, 433–471.
Lichtenberg, A. J., and M. A. Lieberman, 1983: Regular and Stochastic Motion. Springer-Verlag, 499 pp.
Lorenz, E. N., 1963: Deterministic nonperiodic flow. J. Atmos. Sci.,20, 130–141.
——, 1965: A study of the predictability of a 28-variable atmospheric model. Tellus,17, 321–333.
Marshall, J. C., and F. Molteni, 1993: Toward a dynamical understanding of planetary-scale flow regimes. J. Atmos. Sci.,50, 1792–1818.
Michelangeli, P. A., R. Vautard, and B. Legras, 1995: Weather regimes: Recurrence and quasi-stationarity. J. Atmos. Sci.,52, 1237–1256.
Mo, K. C., and M. Ghil, 1987: Statistics and dynamics of persistent anomalies. J. Atmos. Sci.,44, 877–901.
——, and ——, 1988: Cluster analysis of multiple planetary flow regimes. J. Geophys. Res.,93, 927–952.
Molteni, F., S. Sutera, and N. Tronci, 1988: The EOFs of the geopotential eddies at 500 mb in winter and their probability density distributions. J. Atmos. Sci.,45, 3063–3080.
——, 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.
Mukougawa, H., 1987: Instability of topographically forced Rossby waves in a two layer model. J. Meteor. Soc. Japan,65, 13–25.
——, 1988: A dynamical model of “quasi-stationary” states in large-scale atmospheric motions. J. Atmos. Sci.,45, 2868–2888.
Namias, J., 1950: The index cycle and its role in the general circulation. J. Meteor.,7, 130–139.
——, 1964: Seasonal persistence and recurrence of European blocking during 1958–1960. Tellus,16, 94–407.
Neven, E. C., 1994: Baroclinic modons on a sphere. J. Atmos. Sci.,51, 1447–1464.
Nitsche, G., J. M. Wallace, and C. Kooperberg, 1994: Is there evidence of multiple equilibria in planetary wave amplitude statistics? J. Atmos. Sci.,51, 314–322.
Palmer, T. N., 1988: Medium and extended range predictability and stability of the Pacific/North American mode. Quart. J. Roy. Meteor. Soc.,114, 691–713.
——, and D. L. T. Anderson, 1994: The prospects for seasonal forecasting—A review paper. Quart. J. Roy. Meteor. Soc.,120, 755–793.
Rex, D., 1950: Blocking action in the middle troposphere and its effect upon regional climate. Tellus,2, 196–211.
Shutts, G. J., 1983: The propagation of eddies in diffluent jet streams: Eddy forcing of blocking flow fields. Quart. J. Roy. Meteor. Soc.,109, 737–761.
Silverman, B. W, 1986: Density Estimation for Statistics and Data Analysis. Chapman and Hall, 175 pp.
Simmons, A. J., J. M. Wallace, and G. W. Branstator, 1983: Barotropic wave propagation and instability, and atmospheric teleconnection patterns. J. Atmos. Sci.,40, 1363–1392.
Thuburn, J., 1991: Data sampling strategies for general circulation models. Quart. J. Roy. Meteor. Soc.,117, 385–397.
Tung, K. K., and A. J. Rosenthal, 1985: Theories of multiple equilibria—A critical reexamination. Part I: Barotropic models. J. Atmos. Sci.,42, 2804–2819.
Vautard, R., 1990: Multiple weather regimes over the North Atlantic: Analysis of precursors and successors. Mon. Wea. Rev.,118, 2056–2081.
——, and B. Legras, 1988: On the source of low frequency variability. Part II: Nonlinear equilibration of weather regimes. J. Atmos. Sci.,45, 2845–2867.
Wallace, J. M., and D. S. Gutzler, 1981: Teleconnections in the geopotential height field during the Northern Hemisphere winter. Mon. Wea. Rev.,109, 784–812.
Wiin-Nielsen, A., 1979: Steady states and stability properties of a low order barotropic system with forcing and dissipation. Tellus,31, 375–386.
Wolfe, J. H., 1970: Pattern clustering by multivariate mixture analysis. Multiv. Behav. Res.,5, 329–350.