中国北方地区(33°～41°N,108°～115°E)过去500年夏季降水量的周期成分分析

摘要

利用连续小波分析和经验模态分解方法,对我国北方地区(33°～41°N,108°～115°E)1470 ～2002年每年夏季降水量指数的时间序列进行了周期成分分析,探索全球气候变暖下的该地区降水量的多尺度变化特征.小波分析表明,降水量指数的可能周期有2.57a,4.83a,10.65a,23.25a,48.56a,68.30a和105.90a的周期,在95％置信水平有统计意义的周期是2.57a和23.25a的周期.这些周期和自然因素导致的周期相联系,不仅包含了气候系统内部(平流层准2a振荡和厄尔尼诺/南方涛动)的非线性作用,还包含了气候系统外(主要是太阳活动)受强迫的周期变化,且二者在原始降水量中所在比重相当,共同反映了原始降水量的绝大部分变化.降水量不只是在百年尺度上受太阳活动的驱动,在数十年尺度上也受到太阳活动的影响.我国北方地区的夏季降水量指数和夏季温度指数同相位反相关,全球增温并没有明显地改变二者之间的反相关关系.近百年来全球变暖期间,夏季降水量出现明显的新特征:短周期成分(小于30a的周期)的振幅比以往要显著大,而长周期成分的振幅比以往要显著小,同时呈现降水量逐年减少的长期变化趋势.%The complex Morlet( dimensionless frequency ω0 = 6 ) wavelet transform and the empirical mode decomposition methods are used to analyze the periodical components of the yearly summer (June to August) precipitation indexes (PI)in the north-Central China(33° -41°N,108° - 115°E)in the years of 1470 to 2002,and then to investigate their multi-scale characteristics in the background of the global warming. The global wavelet power spectrum shows that the PI have possible periods of 2. 57 ,4. 83 ,10. 65 ,23. 25 ,48. 56,68. 30, and 105. 90 years, but only the two periods,2. 57 and 23.25 years are statistically significant at the 95% confidence level. It is inferred that these possible periods should be related to the natural factors of the climate change, including the non-linear forcing factors of both the inside and outside climate system,such as the 2-year QBO in the stratosphere,El Nino/Southern Oscillation (SO) , and the solar forcing. The solar forcing component in the PI is found equal in value to the components correlated with the inside-climate-system factors ( QBO, El Nifio and SO ) , and these two kinds of components can account for more than 90% of the PI. The climate changes at both the centennial scales and the decadal scales are found driven by solar activity. The precipitation index is reversely correlated with the temperature index in the north-Central China, and the global warming does not obviously affect such a correlation. The global warming in the recent century does not destine an increase of temperature in the north-Central China, showing different effects in different regions. The PI is found to show a special feature in the background of the global warming: the PI decomposition components of short-time periods ( less than 30 years) fluctuate obviously more violently in the recent century than before, but a completely inverse case occurs for those of long-time periods, meanwhile the PI trends to decrease in the recent century.