东亚夏季风推进过程的气候特征及其年代际变化

利用1951～2001年NECP的逐日再分析资料及中国东部366站1957～2000年逐日降水资料．提出东亚夏季风推进过程的定量指标．分析东亚夏季风推进过程的年代际变化。结果表明：标准降水指数为1．5的等值线较好反映了中国东部夏季雨带的南北移动．以及雨带推进过程中呈现的阶段性与突变性特征。东亚夏季风的推进过程具有显著年代际变化．与夏季风前沿位置有关的指标在20世纪60年代中期前后发生显著变化．与夏季风推进强度有关的指标则在70年代末出现突变。60年代中期前．南海夏季风的建立时间较迟，但北推较快．夏季风前沿到达华北地区时间较早，在华北地区维持时间长，夏季风的北界位置偏北．华北雨季、淮河梅雨明显。70年代末以后南海夏季风的建立时间较早．夏季风前沿附近南风强度明最偏弱．降水主要集中在长汀流域及其以南地区．华北雨季不明显。

Northerly Advancement Characteristics of the East Asian Summer Monsoon with Its Interdecadal Variations

In the context of 1951-2001 NCEP daily re-analyses and the 1957-2000 daily precipitation from 366 stations over eastern China,a quantitative index is proposed to study the interdecadal variation of the northerly advancement of East Asian Summer Monsoon(EASM).The results show that drawing the isoline of standardized rainfall index of 1.5 that is better indicative of the meridional shifting of the summer rainband in eastern China,and its phased and abrupt change in its northward march.The northerly march of EASM displays conspicuous interdecadal variations.The position indices of the EASM jump in the mid-1960s,however the jump of the intensity indices occurs in the end of the 1970s.Before the mid-1960s,the onset of the South China Sea monsoon is later,but the northward advance is quicker,the time of arrival in North China is earlier,which maintains a longer time in North China,its north edge lies north to the normal position,and thus the North China rainy season and Huaihe River Valley(HRV)Mei-yu are distinct.In recent 20 years,the onset is earlier,the intensity is obviously weaker,and therefore precipitation mainly concentrates in the Yangtze River Valley(YRV)and areas south of the Yangtze River,and the North China rainy season is not evident.