青藏高原西侧绕流风系的变化及其与东亚夏季风和我国华北地区夏季降水的关系

从观测资料分析了青藏高原西侧绕流偏北风系的年际和年代际变化及其与东亚夏季风和华北地区夏季降水的关系。研究表明 ,前者对后者有很大影响 ,若夏季青藏高原西侧绕流的偏北风系强 ,则东亚夏季风偏南风分量强 ,且华北地区夏季降水可能偏多 ;相反 ,若夏季青藏高原西侧绕流的偏北风系弱 ,则东亚夏季风的偏南风分量弱 ,且华北地区夏季降水可能偏少。分析结果还表明 ,由于从 1 965年之后 (特别从 1 977年之后 ) ,高原西侧绕流的偏北风系减弱 ,可能导致了东亚夏季风的偏南风分量减弱 ,使得输向华北的水汽大大减弱 ,且引起华北地区降水减少 ,发生了持续严重干旱。

The Variability of the Wind System Circulating round the West Side of the Tibetan Plateau and Its Relation to the East Asian Summer Monsoon and Summer Rainfall in North China

The interannual and interdecadal variations of the northerly wind system circulating around the west side of the Tibetan Plateau and their relation to the East Asian summer monsoon and the summer rainfall in North China are analyzed from the observed data. The results show that there is a close relationship between the variations of the wind system circulating round the west side of the Tibetan Plateau and the interannual and interdecadal variations of the East Asian summer monsoon and summer rainfall in North China. If the northerly wind system circulating round the west side of the Tibetan Plateau is strong in summer, the southerly component of the East Asian summer monsoon is strong, and summer rainfall maybe above normal on North China. Oppositely, if the northerly wind system circulating round the west side of the Tibetan Plateau is weak, the southerly component of the East Asian summer monsoon is weak, and summer rainfall maybe below normal. The analyzed results also show that after 1965,especially from 1977,since northerly wind system circulating round the west side of the Tibetan Plateau weakened, the southerly component of the East Asian summer monsoon also weakened, and the water vapor transported into North China also weakened greatly. This caused the decrease of summer rainfall and the persistent and severe drought in this region.