<p>Tropical cyclone (TC) genesis frequency over the western North Pacific (WNP) is reduced significantly since the late 1990s, coinciding with a Pacific decadal oscillation (PDO) phase change from positive to negative. In this study, the underlying mechanism for this reduction is investigated through analysis of asymmetric central Pacific (CP) El Ni&#241;o-Southern Oscillation (ENSO) properties induced by the negative PDO phase. Results suggest that the significant reduction is caused by asymmetric CP ENSO properties, in which the CP La Ni&#241;a is more frequent than the CP El Ni&#241;o during negative PDO phases; furthermore, stronger CP La Ni&#241;a occurs during a negative PDO phase than during a positive PDO phase. CP La Ni&#241;a (El Ni&#241;o) events generate an anticyclonic (cyclonic) Rossby wave response over the eastern WNP, leading to a significant decrease (increase) in eastern WNP TC genesis. Therefore, more frequent CP La Ni&#241;a events and the less frequent CP El Ni&#241;o events reduce the eastern WNP mean TC genesis frequency during a negative PDO phase. In addition, stronger CP La Ni&#241;a events during a negative PDO phase reinforce the reduction in eastern WNP TC genesis. The dependency of CP ENSO properties on the PDO phase is confirmed using a long-term climate model simulation, which supports our observational results.&#160;</p><p>Acknowledgements: This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT; No. 2019R1A2C1008549).</p>
Multi-model Projection of Global Warming Impact on Tropical Cyclone Genesis Frequency over the Western North Pacific