中国南方夏季低频雨型特征及其年代际变化研究

Characteristics and the inter-decadal variation of the low-frequency rainfall regimes over southern China in summer

为了揭示南方低频降水的季节内及年代际变化规律,利用1961—2011年夏季中国南方逐日降水资料和大气环流再分析资料,运用经验正交函数分解(EOF)与聚类分析相结合方法,将南方地区10 d以上的低频尺度降水划分为5个异常雨型。分析表明,各雨型具有较好的持续性,与同期的环流场有很好的对应关系,彼此间水汽异常输送特征有明显差别。通过对雨型的统计特征进行分析,指出不同于以往的季节平均雨型,低频雨型可在季节内交替出现,反映了大尺度异常降水的低频演变特征。进一步研究发现,近50年来各低频雨型的多项统计特征存在显著的年代际变化:20世纪80 90年代各多雨型均相继出现峰值,进入21世纪偏旱型的各项统计特征存在明显上升趋势,而大部分低频多雨型出现次数减少,这可能预示着中国南方地区正在进入一个季节内尺度降水减少的阶段。

Using the daily precipitation dataset covering southern China and the NCEP/NCAR daily reanalysis data for the period 1961 -2011,the intraˉseasonal and interˉdecadal variations of the lowˉfrequency rainfall regimes over southern China in summer are investigated.Five rainfall regimes （RRs）generated from the 10 day lowˉpass filtered data are identified by applying the empirical orthogonal function and cluster analysis method.The results show that RRs match well with the largeˉscale circuˉ lation and significant difference exists in characteristics of water vapor transport.It is more important that the new RRs can deˉ scribe intraˉseasonal dynamic characteristics of largeˉscale rainfall anomalies,which is the most significant difference between the new RRs and the conventional season average rainfall patterns.Moreover,a significant interˉdecadal variation is observed in statistical characters in the last five decades：peak values of the regimes appear in succession from 1980s to 1990s;in the 21 century,the statistics of the rainless regime shows a significant increasing trend,while most lowˉfrequency regimes are less seen .It indicates that southern China is entering a period of the decrease of intraseasonal precipitation.