Different impacts of El Ni?o and El Ni?o Modoki on China rainfall in the decaying phases

摘要

In this study, we investigate the different impacts of El Ni?o and El Ni?o Modoki on China rainfall in their decaying phases. During spring, in the decaying year of El Ni?o 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 Ni?o Modoki. In the subsequent summer season, the wet signal south of the Yangtze River associated with El Ni?o 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 Ni?o 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 Ni?o and El Ni?o Modoki events. For the case of El Ni?o, 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 Ni?o 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 Ni?a and extends more northwestward towards the inland region, compared to its El Ni?o counterpart. The anomalous moisture transport and sub-tropical high activity associated with this WNP anti-cyclone result in different summer rainfall anomalies in China.