Reduced Spring Extratropical Cyclone Activity Over the East Asian Subtropical Region has Suppressed Regional Precipitation From 1979 to 2023

Abstract Based on the European Centre for Medium‐Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) six‐hourly reanalysis data set and objective identification and tracking methods for extratropical cyclones (ECs), this study analyzes the characteristics of ECs over the East Asian subtropical region (110°–140°E, 25°–35°N) encompassing eastern China to the south of Japan in spring during 1979–2023. It further explores the linkage between the long‐term trends of ECs and concurrent precipitation. The results indicate that both the genesis frequency of ECs and the precipitation within the study domain have exhibited significant decreasing trends. A high positive correlation was found between the East Asian subtropical extratropical cyclone index and East Asian subtropical precipitation index, with a coefficient of 0.64. Further analysis reveals that nonuniform near‐surface warming across East Asia has suppressed the genesis of ECs over the subtropical region. The decline in ECs affects precipitation through dynamic and moisture‐related pathways: Dynamically, the transient eddies associated with reduced ECs contribute to weakened upper‐level divergence, particularly over southeastern China, and suppressed mid‐level vertical ascent in the East Asian subtropical region. Regarding moisture, the weakened low‐level cyclonic circulation reduces moisture transport from the South China Sea, leading to decreased low‐level moisture convergence within the study region. These factors collectively inhibit precipitation in the East Asian subtropical region in spring. This study provides a new perspective for understanding the mechanisms driving the observed decline in East Asian subtropical spring precipitation under global warming.