Hotspots of summer heatwaves in East Asia and their associated radiative and dynamical forcing

Abstract The recent heatwave events and their repercussions on ecosystems and society underscore the necessity for an in-depth understanding of the mechanism responsible for heatwave formation. Utilizing spectral clustering method to classify the daily heatwave circulation over East Asia (EA) from 1979 to 2022, this study identifies three distinct heatwave hotspots in eastern China (P1; 22%), Mongolia (P2; 47%), and northwestern EA (P3; 31%), each of which has its own unique upper-level trough and ridge structures. The formation of heatwave hotspots is associated with the tropospheric anticyclonic anomalies, which are characterized by the westward extension and enhancement of the Western Pacific Subtropical High (P1), a strong ridge over Mongolia (P2), and anomalous anticyclones over northwestern and northeast EA (P3). These anomalous anticyclones lead to decreased cloud cover and atmospheric descent, influenced by specific quasi-barotropic teleconnection wave patterns in the mid-latitudes. The quantitative attribution results from the climate feedback response analysis indicate that the cloud, water vapor, and atmospheric dynamics constitute significant heat-generating mechanisms. Cloud changes provide the largest positive contribution (P1: 7.8 K, P2: 1.6 K, and P3: 1.9 K) to the formation of all three types of heatwaves through the shortwave radiation effect. Changes in atmospheric dynamics result in temperature increases of 2.7 K, 0.5 K, and 0.9 K in P1, P2, and P3, respectively. Atmospheric dynamics of P1 are primarily attributed to adiabatic warming, while both adiabatic and horizontal advection positively influence P2 and P3. Moreover, surface processes generally have compensatory cooling effects on the overall temperature anomalies associated with heatwaves. The findings of this study yield valuable insights into the underlying mechanisms of extreme heat events in EA, offering scientific support for disaster prevention and mitigation.