A systematic analysis of wave acthities and blocking in the Northern Hemisphere winter is performed with the daily 500 mb height fields for the 1956-1991 period and the monthly sea surface temperatures (SSTs) for the 1970-1991 period. The power spectra in the wavenumber-frequency domain are partitioned into westward propagating, eastward propagating and standing variances. Regional indices are used to classify the seasonal circulation into fou r categories of circulation patterns according to the dominant blocking activities or the season: Pacific blocking, Atlantic blocking, double blocking, and no blocking. The distinctions among categories of blocking are characterized in the standing, westward propagating and eastward propagating variances. The distinctions are also renected in the kinetic energy and nonlinear wave-wave interactions of the planetary-scale and the synoptic-scale waves.

A com)l-Ositc study of dominant circulation patterns is also presented in this study. The results show that the wave-wave interaction of the planetary- scale and the synoptic-scale waves plays a crucial role in the formation and maintenance of Pacific blocking, and that Atlantic blocking and double blocking might be forced and maintained by baroclinic processes.