海河流域夏季降水与北半球环流异常的相关

Connection between Summer Precipitation over Haihe Basin and Northern Hemisphere Circulation Anomalies

使用1981—2013年6—8月的月平均海河流域站点降水资料以及NCEP/NCAR再分析资料,采用SVD方法分析了北半球高度场环流异常与海河流域夏季降水的关系。结果表明夏季海河流域的一致型降水异常主要受热带地区高度场异常的影响,而北半球中高纬的高度异常分布对海河流域东南部降水异常有重要作用。热带及中高纬地区的高度场异常与副热带西风急流和流域上空的水汽输送有一定的对应关系,急流强度和位置的变化以及水汽辐合异常造成海河流域降水异常,尤其中高纬高度异常的这种对应关系更加明显,并且两个地区的高度异常分布对应的海河流域异常水汽输送有不同来源。

Using the monthly precipitation data of stations over the Haihe basin and NCEP/NCAR reanalysis data,the large-scale relation between summer precipitation over the Haihe basin and Northern Hemisphere circulation anomalies from 1981 to 2013is examined.The singular value decomposition（SVD）analysis is applied to reveal the connection between two fields.Results show that the leading two SVDcoupled modes explain more than half of the squared covariance between those two fields.It is found that tropical 500-hPa height anomalies affect the precipitation anomalies of the whole basin,and the subtropical 500 height anomolies has significant effects on the summer precipitation anomalies over the southeast part of the basin.Tropical and sub-tropical circulation indices are then defined,according to the spatial patterns of the leading two SVD modes,to analyze possible mechanisms of the mentioned coupling connections.Composite analysis with respect to the above indices suggests that anomalous sub-tropical westerly jet and water vapor transports are associated with the anomalous indices.In weak tropical index years and especially strong sub-tropical index years,there can be seen a stronger and northward subtropical westerly jet,as well as significant anomalous water vapor flux convergence accumulation near the basin region.Especially,anomalous water vapor transports associated with the two anomalous indices are from different origins.