The authors are grateful to past and present associates on three continents for interesting exchanges on low-frequency atmospheric variability. The NCEP–NCAR reanalysis data are provided through the NOAA Climate Diagnostics Center (http://www.edc.noaa.gov). Extensive and persistent comments by Klaus M. Weickmann and two anonymous referees have greatly improved the presentation of our results. Our work was supported by NASA Grant NAG5-9294 (FL), DOE Grant DE-FG03-01ER63260 (AWR), and NSF Grant ATM-0082131 (MG). This is publication 5837 of UCLA's Institute of Geophysics and Planetary Physics.
Barnston, A. G., and R. E. Livezey, 1987: Classification, seasonality and persistence of low-frequency atmospheric circulation patterns. Mon. Wea. Rev, 115 , 1083–1126.
Cheng, X., and J. M. Wallace, 1993: Cluster analysis of the Northern Hemisphere wintertime 500-hPa height field: Spatial patterns. J. Atmos. Sci, 50 , 2674–2696.
Dickey, J. O., M. Ghil, and S. L. Marcus, 1991: Extratropical aspects of the 40–50 day oscillation in length-of-day and atmospheric angular momentum. J. Geophys. Res, 96 , 22643–22658.
Dole, R. M., and N. M. Gordon, 1983: Persistent anomalies of the extratropical Northern Hemisphere wintertime circulation: Geographical distribution and regional persistence characteristics. Mon. Wea. Rev, 111 , 1567–1586.
Dole, R. M., and R. X. Black, 1990: Life cycles of persistent anomalies. Part II: The development of persistent negative height anomalies over the North Pacific Ocean. Mon. Wea. Rev, 118 , 824–846.
Ghil, M., 1987: Dynamics, statistics and predictability of planetary flow regimes. Irreversible Phenomena and Dynamical Systems Analysis in the Geosciences, C. Nicolis and G. Nicolis, Eds., D. Reidel, 241–283.
Ghil, M., and K-C. Mo, 1991: Intraseasonal oscillations in the global atmosphere. Part I: Northern Hemisphere and tropics. J. Atmos. Sci, 48 , 752–779.
Ghil, M., and A. W. Robertson, 2002: Waves vs. particles in the atmosphere's phase space: A pathway to long-range forecasting? Proc. Natl. Acad. Sci, 99 , (Suppl. 1),. 2493–2500.
Ghil, M., M. Kimoto, and J. D. Neelin, 1991a: Nonlinear dynamics and predictability in the atmospheric sciences. Rev. Geophys, 29 , (Suppl.),. 46–55.
Ghil, M., S. L. Marcus, J. O. Dickey, and C. L. Keppenne, 1991b: AAM the Movie. NTSC Videocassette AVC-91-063, Caltech/NASA Jet Propulsion Laboratory, Pasadena, CA.
Hurrell, J. W., 1995: Decadal trends in the North Atlantic Oscillation regional temperatures and precipitation. Science, 269 , 676–679.
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.
Koo, S., A. W. Robertson, and M. Ghil, 2002: Multiple regimes and low-frequency oscillations in the Southern Hemisphere's zonal-mean flow. J. Geophys. Res.,107, 4596, doi:10.1029/ 2001JD001353.
Kushnir, Y., 1987: Retrograding wintertime low-frequency disturbances over the North Pacific Ocean. J. Atmos. Sci, 44 , 2727–2742.
Lott, F., A. W. Robertson, and M. Ghil, 2004: Mountain torques and Northern Hemisphere low-frequency variability. Part I: Hemispheric aspects. J. Atmos. Sci, 61 , 1259–1271.
Marcus, S. L., M. Ghil, and J. O. Dickey, 1996: The extratropical 40-day oscillation in the UCLA general circulation model. Part II: Spatial structure. J. Atmos. Sci, 53 , 1993–2014.
Molteni, F., S. Tibaldi, and T. Palmer, 1990: Regimes in the wintertime circulation over northern extratropics. Part I: Observational evidence. J. Atmos. Sci, 47 , 31–67.
Penland, C., M. Ghil, and K. M. Weickmann, 1991: Adaptive filtering and maximum entropy spectra with application to changes in atmospheric angular momentum. J. Geophys. Res, 96 , 22659–22671.
Plaut, G., and R. Vautard, 1994: Spells of low-frequency oscillations and weather regimes in the Northern Hemisphere. J. Atmos. Sci, 51 , 210–236.
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.
Van Loon, H., and J. C. Rogers, 1978: The seesaw in winter temperature between Greenland and northern Europe. Part I: General description. Mon. Wea. Rev, 106 , 296–310.
Vautard, R., K. C. Mo, and M. Ghil, 1990: Statistical significance test for transition matrices of atmospheric Markov chains. J. Atmos. Sci, 47 , 1926–1931.
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.
Weickmann, K. M., W. A. Robinson, and C. Penland, 2000: Stochastic and oscillatory forcing of global atmospheric angular momentum. J. Geophys. Res, 105 (D12) 15543–15557.