Recent Enhanced Impact of the Regional Hadley Circulation Expansion over Western Pacific on Increasing Frequency of Landfalling Tropical Cyclone

Tropical cyclone (TC) is one of the most severe natural disasters in terms of human casualties and economic losses. Hadley circulation (HC), a dominant thermally driven meridional overturning circulation over tropics, has a prominent impact on TC activities. Previous study reveals that the expansion of boreal winter regional HC over western Pacific (WPHC) contributes to the increasing frequency of succeeding summer landfalling TC (LTC) in China. Here, we find that their relationship is nonstationary and experiences a marked interdecadal change around the mid-1990s, with the connection being weak before but significant after. The enhanced influence between them in recent decades is manifested by enhanced responses of summer sea surface temperature (SST), precipitation, and winds anomalies over tropical Pacific to the meridional movement of the preceding winter northern WPHC edge (WPHCE). Stronger climatological mean precipitation and trade winds strengthen the wind-evaporation-SST feedback over the subtropical North Pacific after the mid-1990s. As such, the winter WPHCE-related subtropical anomalous signals can more efficiently propagate to the deep tropics and then change the following summer LTC-favorable climate conditions over the tropical Pacific via positive air-sea interaction, thus leading to an enhanced impact of the WPHCE variation on LTC activity during recent decades. Besides, an increased standard deviation of the WPHCE variation after the mid-1990s may also partially contribute to this recent stronger WPHCE-LTC relationship. The results from this study emphasize the increasingly importance of the WPHC expansion for LTC activity over China, which calls for more attention to be paid to the WPHCE variation for LTC prediction.