Impacts of Central Pacific El Nino on Southern China Spring Precipitation Controlled by its Longitudinal Position

摘要

Here we investigate the response of boreal spring precipitation over southern China (SPSC) to central Pacific (CP) El Nino based on observational datasets. While there is enhanced precipitation over southern China during the decaying boreal spring of eastern Pacific (EP) El Nino events, so far no clear precipitation response has been detected during the same decaying stage for CP El Nino composites. Here we show that around half of the CP El Nino events coincide with enhanced SPSC (wet CP El Nino), while the other half are accompanied by reduced SPSC (dry CP El Nino). These two types of CP El Nino events bear dramatically different evolution features in their respective tropical sea surface temperature anomaly (SSTA) patterns. Wet CP El Nino events are characterized by an SSTA longitudinal position confined to the tropical central-eastern Pacific. In contrast, dry CP El Nino events exhibit a clear westward propagation of SSTAs during their evolution, with maximum SSTAs located to the west of the date line after their mature phase. These different longitudinal positions of positive SSTAs during their decaying phase result in distinct meridional structures of the tropical Pacific convection anomalies as well as the ENSO combination mode (C-mode) response. An anomalous low-level anticyclone is evident over the western North Pacific during wet CP El Nino events during their decaying phase, while an anomalous cyclonic circulation is found for dry CP El Nino events. We emphasize that the impacts of CP El Nino on the SPSC depend crucially on the simultaneous zonal location of warm SSTAs in the tropical Pacific.