基于改进的EMD的运城市持续极端气温的初步分析

采用每日最高（最低）气温的历史同期序列的分位数作为该日的极端阈值,运用改进的经验模态分解（empirical mode decomposition,EMD）方法对山西省运城市1971—2005年每年发生的持续（3 d及3 d以上）极端气温频数进行了初步分析。结果表明,1971—2005年运城市每年的持续极端高温频数（frequency of sustained extreme-high temperature,FSEHT）和持续极端低温频数（frequen-cy of sustained extreme-lowtemperature,FSELT）序列均存在线性下降趋势;在0.05的水平下,运城市的FSEHT序列与该地区的年平均气温序列的线性相关性不显著,而该地区的FSELT序列与年平均气温序列的负线性相关关系是显著的;此外,这两个频数序列分别存在不同的周期振荡。从主要周期看,运城市的FSEHT和FSELT序列与厄尔尼诺现象的周期相一致。

Preliminary Analysis of Sustained Extreme Temperature Events in Yuncheng Using Improved EMD

In recent years, extreme weather events have caused the widespread concern of the Whole world,but sustained extreme temperature events have been seldom researched up to now.The extreme threshold of temperature is defined in this paper by the percentile value of time series of daily maximum or minimum temperature,and the annual frequency of sustained(greater than two successive days)ex-treme high(FSEHT)and low temperature(FSELT)events during 1971-2005 in Yuncheng are alia.1yzed with the improved Empirical Mode Decomposition(EMD)method presented by Deering.The re-suits show that during the 35 years,the FSEHT and FSELT series both exhibit a linear decreasing trend in Yuncheng;the negative linear correlation between the FSELT series and the annual mean temperature series is statistically significant at the 0.05 confidence level, while changes in FSEHT are almost not af-fected by the annual mean temperature. Besides there are also oscillations of different periods in the two frequency series;and in view of principle periods,the oscillations of the two series are consistent with those of El Nino events.