Influences of Summer Northeastern Arctic Sea Ice on September Compound Heatwave and Drought Events in the South China

Compound heatwave and drought events (CHDEs) in South China (SC) have intensified in early autumn, yet their driving factor remains unclear. Based on reanalysis data and numerical experiments, this study investigates the potential influence of the summer northeastern Arctic Sea ice concentration (NEASIC) on the interannual variation of September CHDEs in the SC. Results demonstrate that positive NEASIC anomalies during summer trigger a quasi-barotropic Rossby wave train, originating over the Greenland Sea, arching across the North Atlantic and the Mediterranean–Caspian region, and extending into East Asia. This wave dynamically drives a northward-shifted and intensified East Asian subtropical jet and anomalous anticyclonic circulation over SC. The resulting subsidence induces moisture flux divergence, suppresses cloud cover, and enhances surface radiative forcing, explaining about 28.4% of the CHDEs variability per interquartile NEASIC increase. This mechanism enhances predictive frameworks for subtropical compound extremes, emphasizing the role of NEASIC in regional climate resilience strategies.