日长亚季节变化的振幅调制与厄尔尼诺现象

利用Ｈｉｌｂｅｒｔ变换解算了１９６２年至１９９６年日长亚季节振荡的包络变化．结果显示，日长亚季节变化的振幅调制不仅具有一线性增长趋势，而且包含一个超前厄尔尼诺变化历程的年际变化．分别研究日长亚季节准５０天包络变化以及准１２０天包络变化后发现，这种超前性来自日长亚季节准５０天的振幅变化，这一结论与大气的研究结果一致．日长亚季节准１２０天的振幅变化在１９７２年附近发生了位相１８０°反转，因此日长亚季节准１２０天的振幅变化自１９７６年以来与厄尔尼诺的历程正好同步，１９７２年以前则截然相反．众所周知，日长变化在亚季尺度上具有显著的易变性，然而上述的非线性调制现象不仅表明了日长亚季节变化的内在规律性，而且证实了地球自转运动在不同时间尺度上存在极明显的非线性相互作用．同时也表明，日长变化作为全球风系变化的一个有价值的信息指标，将逐渐成为研究气候系统全球状态的有效手段之一．

CORRELATION OF INTRASEASONAL LENGTH OF DAY AMPLITUDE MODULATION WITH ENSO

The Hilbert transform is used to extract the amplitude modulation signals for the intraseasonal variation of Length of Day ranging from 1962 to 1996.The results reveal that the intraseasonal Length of Day amplitude modulation variation has not only a positive secular trend,but also an interannual variation which is ahead of the ENSO evolution.The amplitude modulations for the about 50 day oscillation and the about 120 day oscillation have been studied separately.This shows that the peaks of the approximately 50 day oscillation amplitude modulation always occur longer than one year before the appearance of each ENSO event and seem to be the precursor of the ENSO event,and this is the same with the atmospheric research results.They also indicate the dominant correspondence between the about 120 day oscillation amplitude modulation and ENSO events since 1976 and the absolutely negative correlation with ENSO before 1972 because of phase change of 180 degrees in the evolution of the about 120 day oscillation amplitude modulation time series at the beginning of the 1970's.