资源环境科技发展态势分析平台

In this study, the leading empirical orthogonal function mode of the interannual variations of boreal spring (April-May) precipitation over China (SPC) is shown to shift from a mono-sign distribution during 1964-1985 (P1), with the largest loading over southern China, to a north-south dipole structure during 1986-2004 (P2), with the northern and southern poles centered over the Yangtze River and the Pearl River Delta, respectively. The results show that the El Nino-Southern Oscillation(ENSO)-related negative western tropical Pacific sea surface temperature anomalies persist longer from the previous winter into the following spring in P2 than in P1. The ENSO-related western tropical Pacific anticyclone in spring is stronger and extends farther northeastward after the mid-1980s. As a result, in P2, the moisture transport by anomalous southerly winds along the western flank of the western tropical Pacific anticyclone penetrates northward to central China, and moisture convergence and divergence are observed over the Yangtze River and southern China, respectively. The SPC-related North Atlantic sea surface temperature anomalies (NAST) are stronger after the mid-1980s than before the mid-1980s, and the NAST-related atmospheric wave train over the middle-latitude Eurasian continent is more pronounced in P2 than in P1. Furthermore, to the east of 90 degrees E, the downstream propagation pathway of the NAST-related wave train turns southeastward, which may be caused by the weakened intensity of the meridional gradient of the potential vorticity over this region. The pronounced wave train-related positive height anomalies over the western North Pacific favor a north-south dipole structure in the SPC variation in P2.