Cooling-Induced Suppression in Heat Extremes over the Yangtze River Basin

Extreme heat occurrences are primarily driven by abnormal heating of the atmosphere and land surface. Interestingly, throughout the lifecycle of extreme heat events, cooling-induced suppression processes frequently occur, including both the pre-event interruption of heat accumulation and the termination of extreme heat. This study analyzes the characteristics and mechanisms of these two cooling types using 68 extreme heat events in the Yangtze River Basin during a long period from 1979 to 2024. Results indicate that terminative cooling exhibits strong cooling rates, with 92% of these events exceeding the average daily cooling rate in summer. Interruptive cooling typically occurs 1–5 days before extreme heat’s onset, exhibiting relatively weaker cooling intensity than terminative cooling. A single moderate interruptive cooling event may delay extreme heat’s onset by approximately 2 days. Diagnostic analysis reveals that both cooling types are primarily driven by horizontal advection and diabatic processes, though these physical mechanisms exhibit a significant inverse relationship and alternately dominate across events. Advection-dominated cooling mainly results from anomalous easterly winds in the lower troposphere, while diabatic-dominated cooling is primarily caused by rainbelt movement into the study area due to strengthening of both the Western Pacific subtropical high and mid-latitude trough. Further analysis of large-scale circulation reveals that the occurrence and dominant physical process of terminative cooling are mainly influenced by a meridional wave train associated with convective anomalies extending from the western Pacific to South China, while interruptive cooling tends to be modulated by mid-latitude zonal wave trains.