Changes of the Subtropical Intraseasonal Oscillations and the associated Tropical Cyclones on the interdecadal time scales in East Asia

This study uses the regime shift index to detect the interdecadal shift of the summertime intraseasonal oscillation (ISO) in the East Asian monsoon region during July-September from 1979 to 2021. A regime shift index was found to specify three distinct epochs: 1979-1993, 1994-2004, and 2005-2021. The middle epoch yields a westward extension of the subtropical anticyclonic circulation and maximal intensity in the westerly phase of the northward-propagating ISO, and his is apparently different from other epochs. These circulation anomalies intensify southeasterly winds south of Japan, which block tropical cyclones (TCs) from east of this strong wind zone. The circulation anomalies therefore result in more contracented TC tracks between Taiwan and Japan as well as increased TC frequency and duration. The findings yield a concentration of TCs can lead to more rainfall in the westerly phase of the northward propagating ISO or the middle epoch. The present work shows that ISO variability itself, especially the connection between the subtropical anticyclone and ISO cyclonic anomalies, directly influence TC genesis, clustering, and intensity. The resulting changes in TC characteristics, particularly in frequency and intensity, could have significant implications for regional disaster preparedness and climate adaptation strategies. This highlights the critical need to consider the interdecadal ISO variability in long-term climate projections and TC prediction models, ensuring more accurate forecasts and informed decision-making in the face of evolving climate patterns. As we know that global warming is taking place, the present climate pattern change such as decadal variability of the ISO can also be part of the results of the climate change under global warming. This study could be a hint of representing changes in the future. In other words, the climate pattern change in the future might also undergo the decadal change as in the present study. These insights can be useful for improving TC rainfall prediction under changing climate patterns.