Characteristics of surface energy balance and atmospheric circulation during hot-and-polluted episodes and their synergistic relationships with urban heat islands over the Pearl River Delta region

Abstract. This study analyzed the nature, mechanisms and drivers for hot-and-polluted episodes (HPEs) in Pearl River Delta, China. Numerical model simulations were conducted summer autumn of 2009–2011. A total eight HPEs identified, mainly occurring August September. K-means clustering was applied to group into three clusters based on their characteristics mechanisms. We found driven by weak subsidence convection induced approaching tropical cyclones (TC-HPE) two controlled calm (stagnant) conditions (ST-HPE) with low wind speed lower atmosphere, whereas remaining combination (hybrid) both aforementioned systems (HY-HPE). positive synergistic effect between HPE urban heat island (UHI; ∼ 1.1 ∘C increase) observed TC-HPE ST-HPE, no discernible HY-HPE. Total aerosol radiative forcing (TARF) caused a reduction temperature (0.5–1.0 ∘C) ST-HPE but an increase (0.5