1076 / 2024-09-20 10:58:36

Extreme Rainfall over South China in 2024 April: Role of Indian Ocean

Eextreme rainfall,South China,Tropical Indian Ocean warming,IOD,ENSO,MJO,AAC

Session 60 - Indian Ocean Dynamics, Air-sea Interaction and Biogeochemical Cycles

Climate conditions over East Asia are significantly affected by the coupled ocean-atmosphere interaction in the tropical Indo-Pacific Ocean. In April 2024, East Asia, especially South China suffered extreme rainfall that broke the record since the 1980s, resulting in causalities and loss of socio-economics. Here, we find that the early Indo-western Pacific Capacitor (IPOC) effect and two Madden-Julian oscillation (MJO) events played crucial roles. Co-occurrence of El Niño and positive Indian Ocean Dipole events in 2023-24 led to strong sea surface temperature warming in the western tropical Indian Ocean via wind forcings and oceanic Rossby waves. Such warming induced persistent easterly wind and maintained the anomalous anti-cyclonic (AAC) winds over the western North Pacific. It activated the IPOC and enhanced northward water vapor transport via the South China Sea in April, earlier than the typical boreal summer. Moreover, two MJO events were observed during March 30-April 6 and April 19-30. The MJO propagating eastward caused the AAC-like winds in its Phase 2-3. Therefore, along with the IPOC, the MJO strengthened the water vapor transport towards South China, leading to extreme rainfall there. This study emphasizes the synergistic contributions of climate modes on different time scale to extreme weathers.