华北夏季降水异常的变化及其与大气环流的联系

利用中国160站1951-2005年的逐月降水资料，以华北17站夏季降水异常为研究对象，在对其时空变化特征进行分析的基础上，探讨了影响其异常的同期因子——该地区上空大尺度环流异常特征.研究结果表明，华北夏季降水在55a里总的趋势是减少的，该地区干旱化的趋势明显，华北夏季降水存在准3a、准6a、准8a的年际周期和17～19a的年代际振荡周期。在华北夏季降水异常的年份，其降水通常与江南和华南的呈现反位相。在低层850hPa，当贝加尔湖地区的东北气流、中南半岛的西南气流及青藏高原北侧的偏西气流较常年偏强时，华北夏季降水较常年偏多；中层500hPa，副热带高压较常年偏弱、偏北、偏西，冷空气偏强，低纬热带季风活跃，南方水汽也供应充沛，从而华北多雨.

Spatial/Temporal Variations of Summer Precipitation Anomalies in North China and Their Relations to Atmospheric Circulation

Based on the monthly rainfall data at 160 stations in China during 1951--2005, the spatialtemporal variations of summer rainfall anomaly at 17 stations in North China are studied, and the atmospheric circulation factors influencing the rainfall anomaly over North China are discussed. Results show that the total summer rainfall tendency of North China decreases significantly during 1951--2005 with the interannual variations of quasi-three, quasi-six, quasi-eight years and the interdecadal variation of 17--19 years. The summer rainfall in North China is usually opposite to the rainfall in Southern Yangtze River and South China in phase. The summer rainfall in North China is more than the normal when the northeast wind in the Baikal region,the southwest air current over Indo-China Peninsula and westard air current at the north side of Tibetan Plateau are stronger than the normal at 850 hPa,meanwhile the subtropical high is weaker and lies northward and westward of it normal position, and the cold air stronger,and summer monsoon more active with abundant vapor at 500 hPa.