Tropical cyclone-related heatwave episodes in the Greater Bay Area, China: Synoptic patterns and urban-rural disparities

Tropical cyclone (TC) peripheral downdrafts and urbanization can promote extreme heatwave (HW) events in the Greater Bay Area (GBA), a highly urbanized coastal area in China. However, the roles of synoptic patterns and urbanization in the HW events remain unclear, particularly for the joint occurrences of the tropical cyclone and heatwave (TC-HW) extremes. Here, we identify three synoptic patterns closely related to TC-HW events, namely: the northeastern Taiwan TC pattern (P4), the southeastern Taiwan TC pattern (P6), and the eastern Taiwan-Philippine Sea TC pattern (P7), as these patterns could enhance HWs through strong downdrafts, strong solar radiation, and low humidity, thereby favoring the maintenance of TC-HW events. Among the three patterns, P6 is most conducive to the occurrence of TC-HW compound events in the GBA. Moreover, the urban-rural temperature disparities under the TC-HW events are unique than those on the days without TC-HW events, i.e., the daily maximum temperature at rural and suburban stations is higher than that at urban stations. This unique feature is the opposite of the urban heat island and is mainly attributed to the rural subsidence warming induced by the TCs and Foehn effects. These results indicate that the spatial distribution of HW in coastal area is substantially modulated by TCs, which is meaningful to understanding the features and underlying mechanism of compound TC-HW events and adapting to their impacts.