近百年长江中下游梅雨的年际及年代际振荡

利用一种小波变换和统计检验相结合进行气候突变检测的新方法, 分析了1885~2000年长江中下游梅雨强度序列多尺度层次的谱系结构, 并对各层次的突变点进行统计显著性检验; 利用小波能量密度研究了梅雨强度年际及年代际振荡随时间的演变及其方差贡献。结果表明:就大尺度而言, 近百年梅雨强度以1941年为界分成强、弱两种状态, 同时, 在不同时间尺度的层次上, 还存在多个突变点, 例如, 在梅雨较强的1885~1941年阶段中, 含有两个梅雨相对弱的时段, 在梅雨较弱的1942~2000年阶段中亦存在1991~2000年梅雨相对强的时段; 2~3年和6~7年振荡在长江中下游梅雨强度的年际变化中占有较大方差贡献, 其中1978~1987年和1996~2000年段2~3年振荡的方差贡献较大, 1920~1932年段6~7年振荡的方差贡献明显; 在长江中下游梅雨强度的年代际变化中, 23~24年和36~37年振荡的方差贡献在20世纪40年代以后比较突出。

INTERANNUAL AND INTERDECADAL OSCILLATIONS OF MEIYU OVER THE MIDDLE-LOWER REACHES OF THE CHANGJIANG RIVER FOR 1885-2000

A scheme is proposed for detecting multi-scale climate accidents by means of the combination of Morlet wavelet transform and statistical validation with which to examine multiscale spectrum structure of Meiyu intensities in the timeseries for 1885--2000 over middlelower reaches of the Changjiang River, and make significance tests of the abrupt change points at different scales. Also the time-dependent evolution and variance contribution of Meiyu intensity series are investigated using wavelet energy density technique. Results show that on a large-scale basis, 1941 can be viewed as the division between high and low intensities and multiple abrupt change points appears at diverse time scales, for instance, during the 1885--1941 for stronger rainfall stage two phases of relatively weak rainfall occur and in 1942--2000 weak rainfall stage the 1991--2000 relatively high rainfall occur; the 2--3 and 6--7 year oscillations have higher variance in interannual variation over the study basin, the 2--3 year oscillations have pronounced variance contribution in 1978--1987 and 1996--2000, so are the 6--7 year oscillations in 1920--1932; the 23--24 and 36--37 year oscillations have higher variance contribution after the 1940s on an interdecadal basis.