多窗谱分析方法及其在全球变暖研究中的应用

多窗谱分析方法是一种低方差、高分辨的谱分析方法 ,尤其适合于非线性气候系统中高噪声背景下弱信号、时频演变信号的诊断分析。文中简要地介绍了多窗谱分析方法的基本原理 ,并将其用于近 1 5 0 a来全球及南、北半球温度变化的研究。结果表明 :(1 )在温度呈线性变暖的背景趋势下 ,北半球、全球年平均温度还具有显著的 40～ 70 a的准周期低频振荡 ,它们与变暖过程中的波动性密切相关 ;(2 )年代际振荡信号在北半球温度序列中也相当明显 ,南半球则存在多种低于 5 a尺度的显著振荡周期 ,半球或全球 ENSO振荡分量、QBO周期信号的振幅都具有缓变包络的特性 ;(3 )与传统功率谱估计、最大熵谱估计结果的对比表明 ,多窗谱分析方法方法得到的谱估计分辨力高 ,稳定性强。

MULTI-TAPER METHOD OF SPECTRAL ANALYSIS AND APPLICATIONS IN GLOBAL WARMING STUDY

The Multi-Taper method (MTM) of spectral analysis provides a means for spectral estimation with a low variance and high resolution. It is particularly well-suited for the diagnosis analysis of weakly signals with a time-depended amplitude and frequency against a high-noise background. We briefly introduced basic outline of MTM and apply this approach to global, Northern and Southern Hemisphere mean surface temperature time series. Results are as follows. (1) There is an significant low-frequency =40-70 year timescale oscillation superimpose on a linear warming trend in global and Northern Hemisphere annual mean temperature time series, which appears mainly contribution to fluctuation of warming process. (2) Decadal signal is considerably significant in Northern Hemisphere annual mean temperature time series, while interannual quasiperiods signals (periods of 5 year shorter) are significant in Southern Hemisphere mean temperature series. Reconstructed ENSO band and quasibiennial components of above time series each exhibit modulation both amplitude and frequency. (3) Compared to the Black-Tukey method and Maximum entropy method, the spectral estimations based on MTM are of high resolution and strong stability.