The Hadley Centre is acknowledged for providing the HadAM1 simulations. Particular thanks go to S. Brown for his help in getting the HadAM1 data and D. Rowell for his comments on the text. Discussions with M. R. Allen and R. Sutton are very much appreciated. I am also grateful to G. Branstator for stimulating discussions and comments on the paper and also for hosting me during a visist to NCAR and would like to thank two anonynmous reviewers for their constructive reviews that improved the manuscript. This work was supported by U.K. Universities Global Atmospheric Modelling Project (UGAMP).
Allen, M. R., and L. A. Smith, 1997: Optimal filtering in singular spectrum analysis. Phys. Lett. A,234, 419–428.
Anderson, B. O., and J. B. Moore, 1979: Optimal Filtering. Prentice Hall, 357 pp.
Blackmon, M. L., J. E. Giesler, and E. J. Pitcher, 1983: A general circulation study of January climate anomaly patterns associated with interannual variation of equatorial Pacific SSTs. J. Atmos. Sci.,40, 1410–1425.
Branstator, G., 1985: Analysis of general circulation model sea-surface temperature anomaly simulations using a linear model. Part I: Forced solutions. J. Atmos. Sci.,42, 2225–2241.
Burgers, G., and D. B. Stephenson, 1999: The ‘normality’ of El Niño. Geophys. Res. Lett.,26, 1027–1030.
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.
Davies, J. R., D. P. Rowell, and C. K. Folland, 1997: North Atlantic and European seasonal predictability using an ensemble of multi-decadal AGCM simulations. Int. J. Climatol.,17, 1263–1284.
Everitt, B. S., and D. J. Hand, 1981: Finite Mixture Distributions. Chapmann and Hall, 143 pp.
Gershunov, A., and T. P. Barnett, 1998: ENSO influence on intraseasonal extreme rainfall and temperature frequencies in the contiguous United States: Observations and model results. J. Climate,11, 1575–1586.
Haines, K., and A. Hannachi, 1995: Weather regimes in the Pacific from a GCM. J. Atmos. Sci.,52, 2444–2462.
Hannachi, A., 1997: Low-frequency variability in a GCM: Three-dimensional flow regimes and their dynamics. J. Climate,10, 1357–1379.
——, 2000: Probabilistic-based approach to optimal filtering. Phys. Rev. E,61, 3610–3619.
——, and M. R. Allen, 2001: Identifying signals from intermittent low-frequency behaving systems. Tellus, in press.
Hasselmann, K., 1993: Optimal fingerprints for the detection of time-dependent climate change. J. Climate,6, 1957–1969.
Hoerling, M. P., A. Kumar, and M. Zhong, 1997: El Niño, La Niña, and the nonlinearity of their teleconnections. J. Climate,10, 1769–1786.
——, ——, and T. Xu, 2001: Robustness of the nonlinear climate response to ENSO’s extreme phases. J. Climate,14, 1277–1293.
Holton, J. R., 1992: An Introduction to Dynamic Meteorology. Academic Press, 511 pp.
Horel, J. D., and J. M. Wallace, 1981: Planetary-scale atmospheric phenomena associated with the Southern Oscillation. Mon. Wea. Rev.,109, 813–829.
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.
——, and T. Ambrizzi, 1993: Rossby wave propagation on a realistic longitudinally varying flow. J. Atmos. Sci.,50, 1661–1671.
Hurrell, J. W., 1995: Decadal trends in the North Atlantic Oscillation:Regional temperatures and precipitation. Science,269, 676–679.
Kendall, M., and J. K. Ord, 1990: Time Series. Edward Arnold, 296 pp.
Killworth, P. D., and M. E. McIntyre, 1985: Do Rossby-wave critical layers absorb, reflect, or over-reflect. J. Fluid Mech.,161, 449–492.
Klein, S. A., B. S. Soden, and N.-C. Lau, 1999: Remote sea surface temperature variations during ENSO: Evidence for a tropical atmospheric bridge. J. Climate,12, 917–932.
Kushnir, Y., and I. M. Held, 1996: Equilibrium atmospheric response to North Atlantic SST anomalies. J. Climate,9, 1208–1220.
Lau, N.-C., and M. J. Nath, 1994: A modeling study of the relative roles of tropical and extratropical SST anomalies in the variability of the global atmosphere–ocean system. J. Climate,7, 1184–1207.
——, and ——, 1996: The role of the atmospheric bridge in linking tropical Pacific ENSO events to extratropical SST anomalies. J. Climate,9, 2036–2057.
Livezey, R. E., A. Leetmaa, M. Mautani, H. Rui, N. Ji, and A. Kumar, 1997: Teleconnective response of the Pacific–North American region atmosphere to large central equatorial Pacific SST anomalies. J. Climate,10, 1787–1820.
Lorenz, E. N., 1963: Deterministic nonperiodic flow. J. Atmos. Sci.,20, 130–141.
North, G. R., T. L. Bell, R. F. Cahalan, and F. G. Moeng, 1982: Sampling errors in the estimation of the empirical orthogonal functions. Mon. Wea. Rev.,110, 699–706.
Palmer, T. N., 1999: A nonlinear dynamical perspective on climate prediction. J. Climate,12, 575–591.
——, and Z. Sun, 1985: A modelling and observational study of the relationship between sea surface temperature in the north west Atlantic and the atmospheric general circulation. Quart. J. Roy. Meteor. Soc.,111, 947–975.
Parker, D. E., C. K. Folland, A. Bevan, M. N. Ward, M. Jackson, and F. Maskell, 1995: Marine surface data for analysis of climate fluctuations on interannual to century timescales. Natural Climate Variability on Decadal to Century Timescales, D. G. Martinson et al., Eds., National Academy Press, 241–250.
Phillips, T. J., 1994: A summary documentation of the AMIP models. PCMDI Rep. 18, University of California, 343 pp. [Available from Lawrence Livermore National Laboratory, University of California, Livermore, CA 94550.].
Renshaw, A. C., D. P. Rowell, and C. K. Folland, 1998: Wintertime low-frequency weather variability in the North Pacific–American sector 1949–93. J. Climate,11, 1073–1093.
Rowell, D. P., 1998: Assessing potential seasonal predictability with an ensemble of multidecadal GCM simulations. J. Climate,11, 109–120.
Saravanan, R., 1998: Atmospheric low-frequency variability and its relationship to midlatitude SST variability: Studies using the NCAR climate system model. J. Climate,11, 1386–1404.
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.
Thacker, W. C., 1996: Climatic fingerprints, patterns and indices. J. Climate,9, 2259–2261.
Thompson, D. W. J., and J. M. Wallace, 1998: The Arctic Oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett.,25, 1297–1300.
Trenberth, K. E., and J. W. Hurrell, 1994: Decadal atmospheric-ocean variations in the Pacific. Climate Dyn.,9, 303–309.
——, G. W. Branstator, D. Karoly, A. Kumar, N.-C. Lau, and C. Ropelewski, 1998: Progress during TOGA in understanding and modeling global teleconnections associated with tropical sea surface temperatures. J. Geophys. Res.,103, 14 291–14 324.
Venzke, S., M. R. Allen, R. T. Sutton, and D. P. Rowell, 1999: The atmospheric response over the North Atlantic to decadal changes in sea surface temperature. J. Climate,12, 2562–2584.
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.
Webster, P. J., and H.-R. Chang, 1988: Equatorial energy accumulation and emanation regions: Impacts of a zonally varying basic state. J. Atmos. Sci.,45, 803–829.