Abstract:
Features and mechanisms of the probability changes of spring and summer extreme precipitation during super El Niño events are investigated using the 0.5°×0.5° resolution China daily precipitation data from the National Meteorological Information Center. Through analyzing the water vapor transport and vertical motion characteristics contributed by the super El Niño and its derived mode, the mechanism of super El Niño impacts on extreme precipitation over eastern China are discussed. The results show that during the decaying phase of the super El Niño event, the occurrence probability of spring extreme precipitation increases significantly over the whole eastern China, especially to the north of the Yangtze-Huai River Valley. In summer, the probability is almost doubled that in regular years over the Yangtze River Valley, whereas it decreases sharply over southern and northern China. Physical analysis indicates that in spring, the super El Niño itself and the combination mode (C-mode) derived from its nonlinear interaction with the tropical Pacific annual cycle both have significant impacts on the anomalous circulation background, i.e., the strong anti-cyclonic circulation anomaly over the northwestern Pacific leads to abundant moisture convergence and ascending motion over eastern China, which is conducive to the occurrence of the observed extreme precipitation. In the subsequent summer, the super El Niño event has disappeared, but the anomalous Northwest Pacific anti-cyclonic circulation associated with the C-mode still exists, and the favorable condition for extreme precipitation maintains over the Yangtze River Valley. Additionally, in spring and summer, daily meridional wind anomalies in the mid-upper troposphere over eastern China are exceptionally active during the super El Niño events, and the frequent meridional convergence of cold air from north and warm moisture from south could lead to enhanced convective events, which may also contribute to the increased occurrence of extreme precipitation.