Autumn Tropical Cyclone Slowdown in East Asia: A Link to Pacific Decadal Oscillation

Abstract

In the mid-1990s, a phase shift in the Pacific Decadal Oscillation (PDO) altered atmospheric circulation over the western North Pacific (WNP). This study explores the relationship between seasonal changes in environmental flow associated with PDO phase shift and the translation speed of tropical cyclones (TCs) over East Asia during the 41-year period from 1982 to 2022. In summer, despite a negative phase in the PDO, changes in westerly winds (25-45 °N, 120-150 °E) are relatively small, resulting in no significant trend in TC translation speed or steering flow over East Asia. In contrast, autumn shows a notable weakening of westerly winds, accompanied by significant decreases in both TC translation speed and steering flow. In particular, TCs between 25 °N and 35 °N experience a marked slowdown in the translation speed during negative PDO phases in autumn. Although a northward migration of autumn TCs during negative PDO phases is generally associated with faster translation speeds in the mid-latitude, the observed slowdown in autumn suggests that the weakening of westerly flow during negative PDO phases has a stronger influence on TC motion than the acceleration effect of increased TC latitude. These findings highlight a strong seasonal dependence in the relationship between the PDO and TC translation, with the PDO playing a critical role in slowing TC movement over East Asia during autumn.