The wavelet analysis method was applied to investigate the low-frequency variability and period features of AO and NAO.The results indicate that AO is dominated by quasi-biennial period prior to 1965 while it shifts to more low-frequency periods of quasi-8yr and quasi-16yr post-1975.The shift is similar for NAO,but with the quasi-8yr period appearing earlier between the late-1960s to mid-1970s and the quasi-16yr period unrecognizable.The cross-wavelet power spectrum of AO and NAO exhibits the quasi-8yr period maximum about 1975,which is coincident with the time of Northern Hemisphere climate change.In addition,the North Atlantic active center of AO and NAO modes both shift eastward about 1975,though that of AO is more notable.The AO active center shifts from North Atlantic to Mediterranean Sea after 1975,which,together with its strengthened Pacific center,endows AO the more prominent annular configuration.
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胡躍文,楊小怡.北極濤動(dòng)與北大西洋濤動(dòng)的低頻變化特征.氣象科學(xué),2007,(3):316-322 Hu Yuewen, Yang Xiaoyi. LOW-FREQUENCY VARIABILITY OF AO AND NAO. Journal of the Meteorological Sciences,2007,(3):316-322