资源环境科技发展态势分析平台

Spring rainfall over southern China experiences both strong inter-annual variability and inter-decadal variability. Employing the monthly precipitation data from 1901 to 2010, this research examines the inter-decadal change of the leading pattern of spring rainfall over southern China. Based on the empirical orthogonal function (EOF) analysis, four distinctive precipitation periods (epochs) have been identified: 1901-1937, 1938-1958, 1959-1994 and 1995-2010. During the first and third epochs, the centre of the inter-annual variation of spring rainfall is located in the South China (SC) region. Low-latitude climate forcing plays an important role in the inter-annual variation of the spring rainfall anomaly over the SC region within these epochs. During typical eastern Pacific El Nino conditions, the western Pacific subtropical high (WPSH) is stronger, driving an abnormally warm, moist southeasterly air mass across the South China Sea and onto the SC region. In addition, an anomalous vertical circulation is forced with ascent over the warmer eastern Pacific, descent over the cooler western Pacific and ascent again over the SC region. During the second and fourth epochs, the maximum of the leading mode of the spring precipitation anomaly is located in the mid-lower reaches of the Yangtze River (MLRYR) region. Counter to the first and third epochs, the leading mode of the spring rainfall anomaly is mainly attributed to mid- and high-latitude forcing during the second epoch. In the wet years a negative Eurasian teleconnection (EU) wave train is observed with a positive anomaly in 500hPa geopotential height located over southern Japan. The WPSH is located further to the north, bringing more water vapour into the MLRYR region from the northwestern Pacific. During the fourth epoch, the EU wave train and WPSH are similar to those of the second epoch. Furthermore, a central Pacific El Nino pattern is evident in the wet years, suggesting a wider teleconnection.