东北5月降水在21世纪初的年代际变化及可能成因

Decadal variation of rainfall in May over Northeast China since the early 21st century and possible causes

基于1961—2015年东北地区的台站降水观测资料及全球环流和海温再分析资料,利用统计分析、物理量诊断等方法,探讨了东北5月降水的年代际变化,及其与大气环流和海温外强迫的关系。研究发现,东北5月降水具有和东北盛夏降水明显不同的年代际变化特征,在20世纪80年代中期至90年代初处于年代际偏少阶段,而在21世纪初转变为年代际偏多阶段。东北5月降水在21世纪初的年代际变化主要由5月东北亚低压强弱的年代际变化造成,在21世纪初,东北亚低压相对于气候态明显偏强,有利于东北降水偏多;而在20世纪80年代初至90年代初,东北亚低压减弱为较浅的低槽,导致东北降水偏少。来自北大西洋的欧亚大陆位势高度异常波列引起东北亚上空的垂直运动异常,导致了东北亚低压的上述年代际变化。5月热带北大西洋海温异常很可能是激发上述波列进而造成东北亚低压和东北5月降水在21世纪初年代际变化的外强迫信号。

Based on monthly gauged rainfall data in Northeast China and the global atmospheric and oceanic reanalysis dataset for 1961-2015,the decadal changes of rainfall in May over Northeast China(NEC)as well as its relationship with atmospheric circulation and sea surface temperature were investigated using statistical and diagnostic methods.Different from that in late-summer,the rainfall in May over NEC depicted negative anomalies during 1984-1993 and positive anomalies during the early 21st century.The decadal changes of rainfall in May over NEC is mainly attributed to the decadal variation of Northern East Asian Low(NEAL)in May.During the early 21st century,the NEAL was much stronger than its climatology,resulting in surplus rainfall over NEC.Nevertheless,the NEAL was weakened into a shallow trough during 1984-1993,leading to deficient rainfall over NEC.A wave train in the geopotential height field over the Eurasia causes significant vertical motion over the Northern East Asia,which contributes to the above variation of the NEAL.The sea surface temperature anomalies over the tropical North Atlantic in May is the possible external forcing generating the above wave train,which gives rise to the corresponding decadal changes of rainfall over NEC.