1961~2016年中国春季极端低温事件的时空特征分析

Spatial and Temporal Features of Spring Extreme Low Temperature Events in China during 1961–2016

利用1961~2016年中国529个台站逐日最低气温资料,研究了中国春季极端低温事件的时空变异特征。旋转经验正交分解结果显示,中国春季极端低温事件的频次在空间上可以分为5个区域,即东北—华北东部地区、江南地区、西北东部—华北西部地区、西南地区和新疆北部地区。小波分析表明,这5个区域春季极端低温事件的频次在年际尺度上呈现出2~4年的振荡周期,其中江南地区、西北东部—华北西部地区和新疆北部地区2~4年的振荡周期在整个研究时段都显著,但东北—华北东部地区和西南地区2~4年的显著周期分别出现在20世纪80年代之前和80年代到90年代中期。在长期变化上,这5个区域春季极端低温事件的频次总体均呈减少趋势,但突变年份具有明显差异。Mann-Kendall和滑动t检验结果表明,东北—华北东部地区春季极端低温事件频次的突变时间为1987/1988年、江南地区为1995/1996年、西北东部—华北西部地区为1990/1991年、西南地区为1987/1988年、新疆北部地区为1997/1998年。伴随着春季极端低温事件频次的降低,5个区域春季极端低温事件的强度在过去半个多世纪也呈现出显著的下降趋势。但近10年来,中国东部地区春季极端低温事件的频次和强度却有所增加,需要引起关注。

Based on daily minimum temperature data from 529 stations in China for the period 1961–2016,in this study,we investigated the spatio-temporal features of spring extreme low temperature(ELT)events.The results of our rotated empirical orthogonal function(REOF)analysis indicates that,with respect to the variability of the spring ELT events frequency,China can be divided into five regions,including Northeast China–eastern North China,the Jiangnan region,eastern Northwest China–western North China,Southwest China,and northern Xinjiang.The results of our Morlet wavelet analysis indicate that the spring ELT events frequencies over the five regions exhibit a 2–4-year quasi-periodicity.This 2–4-year quasi-periodicity is significant over the whole period for the Jiangnan region,eastern Northwest China–western North China,and northern Xinjiang;over the period prior to the early 1980 s for Northeast China–eastern North China;and over the period between early 1980 s and mid-1990 s for Southwest China.With respect to long-term variation,the spring ELT events frequencies over all five regions exhibit decreasing trends,although the years of their abrupt change differ.The results of our Mann–Kendall analysis and moving t-test suggest that the abrupt change in the spring ELT events frequency occurred in 1987/1988 for Northeast China–eastern North China,1995/1996 for the Jiangnan region,1990/1991 for eastern Northwest China–western North China,1987/1988 for Southwest China,and1997/1998 for northern Xinjiang.Along with the decreasing spring ELT events frequency,the spring ELT events intensities have weakened in the five regions in the past half century.However,in the past 10 years,the spring ELT events frequency and intensity over eastern China have increased,which merits concern.