Interannual variations in extreme wet spells and their potential causes in Southwest China

Abstract

Instead of passively receiving and transmitting air-sea interaction signals from the Pacific Ocean, the view that the Tropical Indian Ocean (TIO) significantly influences the climate of neighbouring continents is becoming increasingly accepted. Through the investigation of interannual variations in extreme wet spells (EWS) and their potential causes across three subregions of Southwest China (SWC), we have discerned the differing impacts of the Indian Ocean Basin mode (IOBM) and ENSO on the interannual variation of EWS in SWC. Specifically, 1) the positive phase of the IOBM favours anomalous diabatic cooling extending from northern India to the northeastern maritime continents, which induces anomalous anticyclonic circulation there and a negative phase of East Asia-Pacific teleconnection, resulting in more EWS in the west Sichuan Plateau; 2) the atmospheric heating anomaly over the maritime continents in the El Niño decaying summertime shows an anomalous diabatic cooling in the northeastern part and anomalous diabatic warming in the southwestern part, which corresponds to a more robust and westward extending western Pacific subtropical high and favours the occurrence of EWS in the Sichuan Basin; 3) to the interannual variation of EWS in the Yunnan-Guizhou Plateau, it is closely related to the anomalous cyclonic circulation covering South China, which is significantly associated with the anomalous diabatic cooling over the Arabian Sea-Bay of Bengal region. Our findings provide a comprehensive understanding of the interannual EWS variations in three subregions of SWC and their possible causes, thereby giving us more insights into the interannual prediction of regional climate.