北半球环状模周期变化和突变研究

利用NOAA提供的1871-2008年月平均海平面气压场、雪盖、海冰等再分析资料、NASA提供的地表温度场资料、太平洋年代际振荡(PDO)指数,采用小波分析、带通滤波和凝聚谱分析等方法,研究了北半球环状模(NAM)周期变化及其影响因子.研究结果表明NAM在20世纪60年代前后发生了显著的年代际尺度周期突变,NAM在1895-1955年存在显著的准35年周期振荡,而在1971-2008年则主要以准15年周期振荡为主.NAM年代际尺度周期突变与外强迫源振荡周期变化有关,但突变前后与NAM周期振荡密切相关的外强迫因子并不尽相同.在1960年代之前,PDO、ATM、北美雪盖以及南极海冰涛动等外源强迫因子与NAM在准35年尺度上关系密切;而在1960年之后,NAM准15年振荡则与ATM和欧洲雪盖、南极海冰涛动等因素有关.

Research on the northern annular mode cycle variation and mutation

Using the NOAA monthly reanalysis sea level pressure, surface temperature, snow cover and sea ice data from 1871 to 2008, and the Pacific decadal oscillation (PDO) index from 1900 to 2008, the northern annular mode (NAM) index cycle variation and mutation were studied with wavelet analysis method, band pass filter method and coherence wavelet analysis method. The results indicated that the decadal cycle of the northern annular mode index has mutated at 1960s. NAM presents significant quasi-periodic oscillation of 35-years in 1895-1955, and 15-years in 1971-2008. The decadal cycle mutation of NAM was owing to the oscillation cycle variation of the external forcing, and the external forcing factors before and after the mutation of NAM periodic oscillations were not exactly the same. Before the 1960s, the external forcing, such as PDO, ATM, North America snow cover and the Antarctic sea-ice oscillation(ASIO) contributed greatly to the NAM quasi-35-years-periodic oscillation. However, the main factors for NAM quasi-15-years-periodic oscillation after 1960s were ATM, the European snow cover, and ASIO.