Separation of Interannual and Interdecadal Variations of Rainfall in North China
华北汛期降水量变化中年代际和年际尺度的分离

The precipitations in North China in rainy seasons (July and August, or JA) show variation characteristics both on interannual and interdecadal scales. In this study, these two time scales are separated by: considering five-year running mean of JA precipitations as interdecadal variations, and considering the difference between JA precipitations and the interdecadal variations as interannual variations. After the separation, analyses are performed by use of NCAR/NCEP reanalysis data on respective atmospheric circulation anomalies associated with these two time scales. The great differences between these two kinds of asociations suggest the different physical mechanisms for interannual and interdecadal variations of JA rainfall in North China. The atmospheric circulation associations on interdecadal scale include the remarkable anomalies of the meridional velocity over the eastern part of China and geopotential heights over the Asian continent. The associations on the interannual scale by a routine composite method without the separation exhibit the mixed characteristics of two types of atmospheric circulation anomalies associated with the separated time scales. The atmospheric circulation associations on the interannual scale, after removing the interdecadal scale, include the anomalies of geopotential heights and zonal velocities over East Asia, indicating the poleward displacement of the upper-level jet during flood summers.