Distinctive local and large-scale processes associated with daytime, nighttime and compound heatwaves in China

Different heatwave types exert distinctive impacts on the socio-economic and ecosystems, but the potential mechanisms for different heatwave types remain poorly understood. In this study, we identify the hot spots of daytime, nighttime, and compound heatwaves over China during 1991-2022, and provide a systematic investigation of their distinctive atmospheric configurations. The results show that the daytime heatwave clusters in China are closely linked to the various teleconnection wave trains (i.e., Eurasian or Scandinavian patterns) with quasi-barotropic structures. The hot spots are typically located at the center or southern flank of the anticyclone in the troposphere, accompanied by anomalous descending motions and reduced cloud cover, thus providing dry-hot conditions for daytime heatwaves. In comparison, the nighttime heatwave clusters are modulated by the atmospheric circulations that exhibit more local features, and the hot spots are generally located between the anticyclone and the cyclone with anomalous ascending motions. This feature favors the convergence of water vapor and leads to more cloudy and moist conditions, which hinder upward emissions of longwave radiation at night. On the other hand, the hot spots of compound heatwave clusters are controlled by the anticyclone in the middle level while they are located between the anticyclone and the cyclone in the lower level, which can simultaneously cause adiabatic descending motions and enhanced water vapor, conducive to the continuation of high temperature from daytime to nighttime.