This study investigates the decadal change of East Asian climate from April to May, using the 10-day mean data of 560 meteorological stations in China and the ERA-40 re.analysis data during 1958-2000. Results show that the decadal drought in Southeastern China occurring in the late 19705 exists from mid-April to mid-May, mov-ing southward with time. This southward moving feature is consistent with the decadal cooling in the middle and up-per troposphere. Both of the anomalous subsidence and northerlies in the lower troposphere associated with the up-per cooling occur from mid-April to mid-May and move southward. The southward movement of the decadal drought implies that April precipitation in the Huanghe River-Huaihe River basin is an indicator of the amplitude of southern China precipitation in May. The drought tends to occur in the south of the upper cooling region, which suggests that the decrease of the latent heating in the drought region may in turn cool the upper troposphere. This is verified in a sensitive experiment with a regional model. This partly explains the persistence and southward movement of the cooling signal in the atmosphere in late spring.%利用1958～2000年旬平均中国560站地面观测资料和ERA-40再分析资料,分析了东亚气候在4～5月的年代际变化特征.发现发生在1970年代末的中国东南部干旱出现于4月中旬至5月中旬,干旱带随季节推进逐渐向南移动.这种南移特征与对流层中上层年代际变冷中心的移动是一致的,上层变冷中心所伴随的局地风场异常,即异常下沉运动和对流层低层北风异常,均显著存在于4月中旬至5月中旬,且逐渐南移.中国东南部年代际干旱带在4～5月的南移从一定程度上意味着4月黄淮流域降水异常对5月江南地区的降水多少具有一定的指示意义.由于干旱区位于上层变冷区的南侧,意味着该地区向上输送的潜热通量减少能够使对流层大气进一步冷却,这在一个变网格全球模式的敏感性试验中得到了验证,能够部分地解释大气中的冷信号为何持续存在和南移.
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