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集合经验模态分解(EEMD)是一种适用于非线性、非平稳序列的信号分析方法, 将EEMD 应用于气候要素时间序列, 可提取可靠真实的气候变化信号, 同时, EEMD可以得到气候变化的固有时间尺度.本文使用EEMD方法, 从气候时间序列中提取气候信号中各个尺度的变化, 对渭河流域过去50年来的秋季降水进行多尺度分析,结果显示, 对于20世纪70年代末80年代初的全球气候突变, 渭河流域的秋季降水也有很好的响应, 而且大尺度上的响应要早于中小尺度, 其中在大尺度上主要表现为波动形式, 即降水距平正负位相持续期的变化, 从持续正位相到正负位相周期性交替出现; 而在中小尺度上主要是振幅大小, 即降水距平正负位相量级的变化, 量级从相对较大变为相对较小再逐渐增大.Recently, ensemble empirical mode decomposition (EEMD) method has been developed for non-linear and non-stationary signal analysis. The method can work on nature signals (non-linear and nonstationary signals) and reduce the speckle noise. With the EEMD method, the signal is decomposed into several intrinsic mode functions (IMFs) and the frequencies of IMFs are arranged in decrease order (high to low) after the EEMD processing. The scaling mode of the EEMD method is similar to wavelet transform, but the signal resolutions in different frequency domains do not decrease by down-sampling. There are a large population and a developed economy in Weihe watershed, the disasters of droughts and floods caused by the autumn precipitation (here is precipitation in September and October) less or more than normal cause great loss and serious influence. In this paper, we propose the EEMD method to decompose the autumn precipitation series in the Weihe river basin during last 50 years into several IMFs, then extract the information including in the precipitation series and get the characteristics of multi-scales. The result shows that it is well response to the autumn precipitation series in the Weihe river basin and to the abrupt climate change in late 1970s and early 1980s of last century. The response appears earlier for high time scales than for low time scales In addition, the expression of the response for high time scales is the form of variability, but it is the amplitude of variability for low time scales.
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Keywords:
- ensemble empirical mode decomposition/
- multi-scale analysis/
- autumn precipitation/
- Weihe river basin
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