Professor Pang-chi Hsu

School of Atmospheric Sciences, Nanjing University of Information Science & Technology

Abstarct:
In recent years, severe flood disasters have occurred in regions outside the core areas of Asian summer monsoon precipitation, such as the heavy rainfall events in Henan Province, China, in July 2021 and in Pakistan in August 2022. These events have attracted attention due to the substantial socio-economic losses and casualties they caused. Many studies have focused on the influences of seasonal anomalies and synoptic-scale systems. In this talk, I will show that the coupling of tropical and extratropical intraseasonal oscillations played a crucial role in these disaster events. While extratropical intraseasonal wave trains provided favorable circulation conditions, the intense moisture convergence induced by tropical intraseasonal oscillations (including the 30-90-day MJO and the 10-30-day quasi-biweekly oscillation) was more critical for the occurrence of heavy rainfall. Assessments of operational subseasonal-to-seasonal prediction products also confirm the importance of tropical intraseasonal oscillations. When the models accurately predict the phase and amplitude of tropical intraseasonal oscillations, the forecast bias for regional heavy rainfall is also reduced.