We wish to acknowledge useful discussions with Drs. Paul Dirmeyer, Ben Kirtman, and Edwin Schneider. In addition, the comments of the anonymous referees were helpful. This work was supported by National Science Foundation Grant ATM 93-01228.
Benzi, R., P. Malguzzi, A. Speranza, and A. Sutera, 1986a: The statistical properties of the general atmospheric circulation: Observational evidence and a minimal theory of bimodality. Quart. J. Roy. Meteor. Soc.,112, 661–674.
——, A. Speranza, and A. Sutera, 1986b: A miminmum baroclinic model for the statistical properties of low-frequency variability. J. Atmos. Sci.,43, 2962–2967.
Blackmon, M. L., and G. H. White, 1982: Zonal wavenumber characteristics of Northern Hemisphere transient eddies. J. Atmos. Sci.,39, 1985–1998.
Bloom. S. C., L. L. Takacs, A. M. daSilva, and D. Ledvina, 1996: Data assimilation using incremental analysis updates. Mon. Wea. Rev.,124, 1256–1271.
Boer, G. J., and T. G. Shepherd, 1983: Large-scale two-dimensional turbulence in the atmosphere. J. Atmos. Sci.,40, 164–184.
Boyle, J. S., 1993: Sensitivity of dynamical quantities to horizontal resolution for a climate simulation using the ECMWF (cycle 33) model. J. Climate,6, 796–815.
Branstator, G., 1992: The maintenance of low-frequency atmospheric anomalies. J. Atmos. Sci.,49, 1924–1945.
Charney, J. G., and J. G. deVore, 1979: Multiple flow equilibria in the atmosphere and blocking. J. Atmos. Sci.,36, 1205–1216.
——, and D. M. Straus, 1980: Form-drag instability, multiple equilibria and propagating planetary waves in baroclinic, orographically forced, planetary wave systems. J. Atmos. Sci.,37, 1157–1176.
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.
Colucci, S. J., 1985: Explosive cyclogenesis and large-scale circulation changes: Implications for atmospheric blocking. J. Atmos. Sci.,42, 2701–2717.
——, 1987: Comparative diagnosis of blocking versus nonblocking planetary-scale changes during synoptic-scale cyclogenesis. J. Atmos. Sci.,44, 124–139.
Daley, R., 1991: Atmospheric Data Analysis. Cambridge University Press, 457 pp.
Davies, H. C., and R. E. Turner, 1977: Updating prediction models by dynamical relaxation: An examination of the technique. Quart. J. Roy. Meteor. Soc.,103, 225–245.
de Weaver, E., and S. Nigam, 1997: Dynamics of zonal-mean flow assimilation and implications for winter circulation anomalies. J. Atmos. Sci.,54, 1758–1775.
Dole, R. M., and N. D. Gordon, 1983: Persistent anomalies of the extratropical Northern Hemisphere wintertime circulation: Geographical distribution and regional persistence characteristics. Mon. Wea. Rev.,111, 1567–1586.
Egger, J., and H.-D. Schilling, 1983: On the theory of the long-term variability of the atmosphere. J. Atmos. Sci.,40, 1073–1085.
Ferranti, L., T. N. Palmer, F. Molteni, and E. Klinker, 1990: Tropical-extratropical interaction associated with the 30–60 day oscillation and its impact on medium and extended range prediction. J. Atmos. Sci.,47, 2177–2199.
Frederiksen, J. S., 1982: A unified three-dimensional instability theory of the onset of blocking and cyclogenesis. J. Atmos. Sci.,39, 969–987.
Haines, K., and J. Marshall, 1987: Eddy-forced coherent structures as a prototype of atmospheric blocking. Quart. J. Roy. Meteor. Soc.,113, 681–704.
Hansen, A. R., and A. Sutera, 1986: On the probability density distribution of planetary-scale atmospheric wave amplitude. J. Atmos. Sci.,43, 3250–3265.
Held, I. M., S. W. Lyons, and S. Nigam, 1989: Transients and the extratropical response to El Niño. J. Atmos. Sci.,46, 163–174.
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.
Hurrell, J. W., 1995: Transient eddy forcing of the rotational flow during northern winter. J. Atmos. Sci.,52, 2286–2301.
Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-year/reanalysis project. Bull. Amer. Meteor. Soc.,77, 437–472.
Kimoto, M., and M. Ghil, 1993: Multiple flow regimes in the Northern Hemisphere winter. Part I: Methodology and hemispheric regimes. J. Atmos. Sci.,50, 2625–2643.
Krishnamurthi, T. N., H. S. Bedi, W. Heckley, and K. Ingles, 1988: Reduction of the spinup time for evaporation and precipitation in a spectral model. Mon. Wea. Rev.,116, 907–920.
Kung, E. C., and W. E. Baker, 1986: Spectral energetics of the observed and simulated Northern Hemisphere general circulation during blocking episodes. J. Atmos. Sci.,43, 2792–2812.
Kushnir, Y., and J. M. Wallace, 1989: Interaction of low- and high-frequency transients in a forecast experiment with a general circulation model. J. Atmos. Sci.,46, 1411–1418.
Lau, N.-C., 1988: Variability of the observed midlatitude storm tracks in relation to low-frequency changes in the circulation pattern. J. Atmos. Sci.,45, 2718–2743.
Legras, B., and M. Ghil, 1985: Persistent anomalies, blocking and variations in atmospheric predictability. J. Atmos. Sci.,42, 433–471.
Macpherson, B., 1991: Dynamic initialization by repeated insertion of data. Quart. J. Roy. Meteor. Soc.117, 965–991.
Miyakoda, K., J. Sirutis, and J. Ploshay, 1986: One-month forecast experiments—Without anomaly boundary forcings. Mon. Wea. Rev.,114, 2363–2401.
Molteni, F., and S. Tibaldi, 1990: Regimes in the wintertime circulation over northern extratropics. II: Consequences for dynamical predictability. Quart. J. Roy. Meteor. Soc.,116, 1263–1288.
——, and T. N. Palmer, 1991: A real-time scheme for the prediction of forecast skill. Mon. Wea. Rev.,119, 1088–1097.
——, S. Tibaldi, and T. N. Palmer, 1990: Regimes in the wintertime circulation over northern extratropics. I: Observational evidence. Quart. J. Roy. Meteor. Soc.,116, 31–68.
Nakamura, H., and J. M. Wallace, 1991: Skewness of low-frequency fluctuations in the tropospheric circulation during Northern Hemisphere winter. J. Atmos. Sci.,48, 1441–1448.
——, and ——, 1993: Synoptic behavior of baroclinic eddies during blocking onset. Mon. Wea. Rev.,121, 1892–1903.
O’Lenic, E., and R. Livezey, 1989: Relationships between low-frequency anomalies and systematic errors in medium- and extended-range forecasts. Mon. Wea. Rev.,117, 1262–1280.
Palmer, T. N., 1988: Medium and extended range predictability and the stability of the Pacific/North American Mode. Quart. J. Roy. Meteor. Soc.,114, 691–713.
——, C̆. Branković, F. Molteni, and S. Tibaldi, 1990: Extended-range predictions with ECMWF models: Interannual variability in operational model integrations. Quart. J. Roy. Meteor. Soc.,116, 799–834.
Rambaldi, S., and K. C. Mo, 1984: Forced stationary solutions in a barotropic channel: Multiple equilibria and the theory of nonlinear resonance. J. Atmos. Sci.,41, 3135–3146.
Reinhold, B. B., and R. J. Pierrehumbert, 1982: Dynamics of weather regimes: Quasi-stationary waves and blocking. Mon. Wea. Rev.,110, 1105–1145.
——, and S. Yang, 1993: The role of transients in weather regimes and transitions. J. Atmos. Sci.,50, 1173–1180.
Simmons, A. J., and B. J. Hoskins, 1978: The life cycles of some nonlinear baroclinic waves. J. Atmos. Sci.,35, 414–442.
——, J. M. Wallace, and G. W. Branstator, 1983: Barotropic wave propagation and instability, and atmospheric teleconnection patterns. J. Atmos. Sci.,40, 1363–1391.
Straus. D. M., and J. Shukla, 1981: Space-time spectral structure of a GLAS general circulation model and a comparison with observations. J. Atmos. Sci.,38, 902–917.
Tanaka, H. L., 1991: A numerical simulation of amplification of low-frequency planetary waves and blocking formations by the upscale energy cascade. Mon. Wea. Rev.,119, 2919–2935.
Tibaldi, S., and F. Molteni, 1990: On the operational predictability of blocking. Tellus,42A, 343–365.
Tracton M. S., 1990: Predictability and its relationship to scale interaction processes in blocking. Mon. Wea. Rev.,118, 1666–1695.
——, K. Mo, W. Chen, E. Kalnay, R. Kistler, and G. White, 1989: Dynamical extended range forecasting (DERF) at the National Meteorological Center. Mon. Wea. Rev.,117, 1604–1635.
Vautard, R., and B. Legras, 1988: On the source of mid-latitude 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.
Xue, Y., M. J. Fennessy, and P. J. Sellers, 1996: Impact of vegetation properties on U.S. summer weather prediction. J. Geophys. Res.,101D, 7419–7430.