长江中下游夏季降水变化与亚洲夏季风系统的关系

Variation of Summer Precipitation and Its Connection with Asian Monsoon System in the Middle-lower Yangtze River Basin

以长江中下游流域实测降水数据和亚洲季风指数为基础,采用Mann-Kendall检验、线性相关和偏相关分析、小波分析等方法,揭示长江中下游夏季降水的时空变化特征及其与亚洲季风系统之间的相互关系和影响差异。结果表明,近50 a来长江中下游夏季降水量呈显著的增加趋势,其与亚洲主要夏季风指数之间均呈负的线性相关关系,且显著性影响范围东亚夏季风大于南海夏季风大于南亚夏季风。不同亚洲夏季风子系统间存在复杂的相互作用关系,尤其是东亚夏季风和南海夏季风之间的相互作用对长江中下游夏季降水产生了重要影响。长江中下游夏季降水量与亚洲主要夏季风指数存在2~4 a时间尺度上的显著相关性,且以反位相关系为主。此外,长江中下游夏季降水量与东亚夏季风的相干性最为突出,在小于8 a的时间尺度上,两者之间的相关性在近50 a来呈现减弱的趋势,特别是自20世纪80年代中后期以来。

The Asian monsoon system is the most typical and complex monsoon system on the earth, which plays a decisive role in the spatio-temporal distribution of summer precipitation in the central and eastern China. Based on the measured precipitation data across the middle-lower Yangtze River Basin, the current study investigated the spatio-temporal variation of summer precipitation in middle-lower Yangtze River Basin and its connection with main components of Asian summer monsoon system by using the methods of Mann-Kendall test, correlation and partial correlation analysis and wavelet analysis. Result demonstrates that the summer precipitation in the middle-lower Yangtze River Basin has increased significantly during the past 50 years, and shows a negative linear correlation with the main components of Asian summer monsoon indices. Specific significant influencing area shows the largest for East Asian summer monsoon, followed by South China Sea summer monsoon and South Asian summer monsoon. With reference to the linear correlation, the partial correlation coefficient between the summer precipitation of the middle-lower Yangtze River Basin and the main Asian monsoon indices decreased remarkably, and all the correlations were not significant. The three Asian monsoon subsystems show strong interactions which exert important influence on the local precipitation. Cross wavelet transform and wavelet coherence analysis revealed that summer precipitation in the middle-lower Yangtze River Basin and the main Asian summer monsoon indices shows multi-time scale oscillation period, which is dominant by anti-phase relationship. Wavelet analysis also indicates that significant coherence between summer precipitation and the Asian summer monsoon indices seems to be weakened in recent years since the middle 1980 s.