Different impacts of El Nino and El Nino Modoki on China rainfall in the decaying phases

In this study, we investigate the different impacts of El Nino and El Nino Modoki on China rainfall in their decaying phases. During spring, in the decaying year of El Nino events, there are positive rainfall anomalies south of the Yangtze River, whereas no obvious rainfall signals are found in the same season for the decaying El Nino Modoki. In the subsequent summer season, the wet signal south of the Yangtze River associated with El Nino continues, while suppressed rainfall now appears in the northern Yangtze-Huaihe River region. In contrast, the rainfall is above normal in the region from the Huaihe River to the Yellow River, and below normal in southern China during the summer of the decaying El Nino Modoki events. The distinct China rainfall anomaly is mainly attributed to the difference between the evolution and location of the anomalous western North Pacific (WNP) anti-cyclone associated with El Nino and El Nino Modoki events. For the case of El Nino, the WNP anti-cyclone brings plentiful moisture to southern China; meanwhile it shifts the ridge of sub-tropical high westward in both spring and summer. These tend to induce positive rainfall anomalies in the southern Chinese region. In contrast, due to fast decaying of El Nino Modoki, the anomalous WNP anti-cyclone becomes weak so that there are no significant rainfall anomalies in China. In summer, however, the WNP anti-cyclone re-invigorates possibly associated with a subsequent developing La Nina and extends more northwestward towards the inland region, compared to its El Nino counterpart. The anomalous moisture transport and sub-tropical high activity associated with this WNP anti-cyclone result in different summer rainfall anomalies in China. Copyright (C) 2010 Royal Meteorological Society