北极涛动与北大西洋涛动的低频变化特征

LOW-FREQUENCY VARIABILITY OF AO AND NAO

本文主要利用小波分析方法研究北极涛动(AO)和北大西洋涛动(NAO)的低频变化和周期特征。结果表明:AO在1965年以前有准两年周期振荡,1975年后转为准8 a周期和准16 a周期;NAO也存在相似的周期转变,但其准8 a周期出现在60年代末到1976年前后,并且没有明显的准16 a周期;AO和NAO准8 a周期的交叉小波能谱在1975年前后达到极大值,这与北半球气候突变时间基本吻合。另外,AO和NAO模态的北大西洋中心在1975年后表现出不同程度的东移,AO中心移到地中海地区,且太平洋中心明显增强,使其纬向对称的环形模态较突变前更显著。

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.