The 500 hPa mean monthly height field in Eurasia during 1951~1992 is analysed by using principal component, power spectral, band-pass filter and complex principal component analysis. Features of interannual oscillation of the general circulation in Eurasia are investigated. The results show that there exist quasi-2.5 year and quasi-3.5 year oscillations in the 500 hPa mean monthly circulation in Eurasia, the main oscillation in the subtropical zone is quasi-3.5 year, and the quasi-2.5 year oscillation is prominent in the area of the middle and high latitudes. Furthermore, the complex principal component analysis indicates that the propagation directions for the two oscillations and their variations with time are different from each other, and that the features of quasi-3.5 year oscillation of the 500 hPa mean monthly circulation in Eurasia are closely associated with the E1 Nino phenomenon and the variation of SSTA in the equatorial eastern Pacific
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