Combined Influence of 10–30‐Day Tropical and Mid–High‐Latitude Intraseasonal Oscillations on the Rapid Increases of Humid Heatwaves in Southern China

Abstract As a typical hotspot of heatwaves, southern China experienced a marked shift from dry to humid heatwaves in the recent decade of 2013–2022. Significant 10–30‐day intraseasonal oscillation (ISO) in temperature and humidity is a major contributor to the humid heatwaves. Configuration of the 10–30‐day quasi‐barotropic wave train at mid–high latitudes with the dipolar pattern of tropical convection leads to the concurrence of strong moisture convergence and anomalous descents over southern China. The increased downward longwave radiation in association with moisture enhancement, shortwave radiation and adiabatic heating in association with descents bring about the persisting hot and humid conditions in humid heatwaves. Due to stronger barotropic energy conversion from mean flow to 10–30‐day circulation at mid–high latitudes, and stronger tropical convection activities in the recent decade, the occurrence of 10–30‐day circulation configuration induced humid heatwaves has increased by 13.3%, thus leading to the predominance of humid heatwaves.