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

Abstract Previous studies reveal that the expansion of the boreal winter regional Hadley circulation over the western Pacific (WPHC) contributes to the increasing frequency of succeeding summer landfalling tropical cyclones (LTCs) 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 the 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 recently 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. Significance Statement 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 the tropics, has a prominent impact on TC activities. Particularly, it has been reported that the variation of the regional HC edge over the western Pacific (WPHCE) is an important predictor for seasonal forecasting of landfalling TC (LTC) activity in China. Stability in the relationship between WPHCE and LTC remains unclear, however. Here, we find that their relationship is nonstationary and appears a marked interdecadal enhancement around the mid-1990s. This strengthened impact on LTCs by the WPHCE is mainly attributed to an increase in the air–sea coupling strength over the subtropical North Pacific during recent decades, which can be confirmed by both the observations and the numerical model experiments. Therefore, the WPHCE variation plays an increasingly important role in LTC activity over China and becomes a more influential precursor for their predictability.