Shifted relationship between the Pacific decadal oscillation and western North Pacific tropical cyclogenesis since the 1990s

The Pacific Decadal Oscillation (PDO) and Pacific Meridional Mode (PMM) are prominent climate modes in the North Pacific with well-established impacts on tropical cyclone (TC) genesis in the western North Pacific (WNP) basin. While previous research has primarily focused on the roles of the PDO and PMM in regulating TC genesis through the modification of large-scale environmental factors, this study investigates the evolving influence of the PDO on WNP TC genesis since the 1950s. Remarkably, our analysis reveals a shift in the PDO-TC genesis relationship, transitioning from a significant negative correlation to a significant positive correlation since the 1990s. This shift is attributed to variations in the specific large-scale factors through which the PDO affects TC genesis. Furthermore, this study suggests that these changes appear to be linked to the PMM strengthening on the interdecadal timescale in recent decades. The linkage of the PMM strengthening to the PDO-related atmospheric circulation is further confirmed by the results of a 500 year pre-industrial numerical experiment, suggesting that the PMM strengthening may result from natural internal variability. The results underscore the non-stationary relationship between PDO and WNP TC genesis, with the PMM intensity probably influencing their relationship.