中文摘要：

通过对1960—2011年江淮地区夏季降水的研究发现其存在准两年周期振荡（TBO）,且此TBO存在着年代际变化,1960—1974年和2001—2011年期间TBO较弱,1975—2000年期间TBO较强。对此TBO及其年代际变化的机理进行分析发现：（1）此TBO与印度洋热含量的TBO有密切联系,前冬季印度洋热含量若为西正东负,其上空会出现两个反气旋性异常环流,到了夏季与西太平洋的异常反气旋合并,使得西太平洋反气旋加强,并出现一个类似东亚-太平洋（EAP）型遥相关波列,导致江淮地区夏季降水偏多,热含量也在海洋Rossby波和Kelvin波的作用下向东西方向移动,并在秋季使热含量发生反转,印度洋上空转为两个气旋性异常环流,在冬季加强,使得次年降水偏少,形成TBO;（2）TBO的年代际变化可能是由PDO的位相变化引起的,PDO暖（冷）位相,信风偏弱（强）,海气耦合偏弱（强）,降水受印度洋热含量（太平洋海温）影响较大,受ENSO影响较小（大）,TBO较强（弱）。

英文摘要：

The summertime precipitation in Yangtze-Huaihe Region is characterized by tropospheric biennial Os- cillation （TBO） according to an analysis of 1960--2011 rainfall, which also exhibits inter-decadal variations. The periods 1960--1974 and 2001--2011 witness weak TBO while the period 1975--2000 experiences strong TBO. The mechanism of this TBO and its inter-decadal variation are studied and the results are shown as follows ： （ 1 ） The TBO has close relations with the Indian Ocean heat content. If the heat content in the southern Indian Ocean in the preceding winter is positive in the west and negative in the east, there will be a pair of anomalous anticyclone circulation above. The anomalous west Pacific anticyclone combines with it in summer and sets off an East Asia-Pacific like wave train pattern which leads to more precipitation in the Yangtze-Huaihe region. Under the effect of the ocean Rossby wave and Kelvin wave, the ocean heat content moves west and east and reverses in autumn and the anticyclones change into cyclones and strengthen in winter, resulting in less precipitation in the consecutive summer and forming the TBO; （2） The inter-decadal variation of TBO may be caused by the phase change of the PDO, the warm （cold） phase is accompanied by the weak （strong） trade winds that weaken （strengthen） the coupled ocean-atmosphere interactions, all making the precipitation influenced more （less） by Indian Ocean heat content （ Pacific SSTs） and less （more） by ENSO, corresponding to a strong （weak） TBO phase.