中国北方夏半年最长连续无降水日数的变化特征

Variations in longest consecutive dry days in warm half year over Northern China

利用1951—2004年中国北方各气象台站夏半年逐日降水资料,建立最长连续无降水日数时间序列,采用经验模态分解(EMD)求出该序列的本征模态函数(IMF),分析原序列内在的多尺度振荡变化。用小波分析原序列的突变。结果表明,连续无降水日数的变化主要是由IMF1、IMF2和IMF3这3个本征模态构成,3—4a、8—10a尺度的振荡对整个变化起主要作用。近50年来,最长连续无降水日数呈线性增加趋势;显著增加的年份在1960年和1994年前后,与干旱现象的发生有紧密的联系。

Daily precipitation data in northern China are selected to construct the time series of the longest consecutive dry days in warm half year（April-September） in northern China.The empirical mode decomposition（EMD） method is used to obtain intrinsic mode functions（IMFs）,by which variations of the original series are analyzed on various time scales.By use of wavelet analysis and M-K method,sudden jump points of the series are detected.Results show that the drought variation was characterized by 3-4-year and 8-10-year oscillation patterns during the recent 50 years,and mainly composed of IMF1,IMF2 and IMF3.There was an increasing trend of the longest consecutive dry days in warm half year in the northern China.The longest consecutive dry days increased significantly in 1960 and 1994 in the northern China,which are close related with the occurrences of drought phenomena.