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